[silver70]

Well, life is getting busier and going in an unanticipated, but positive, direction. My interest for vehicle builds has taken a back seat to life and getting older, in general, and I'm trying to get all my sh*t boxes buttoned up before I get to the point where they're neglected entirely. That concrete ain't gettin' any softer on the back and transmissions ain't gettin' any lighter. I've got, perpetually, more and more going on and it seems to be the natural progression of things. I had a fairly organized plan of how I was going to present all this material and the format I was going to use. Also, I had a vision of what the BKO was going to be. That's all become relatively impractical and gone out the window now. Lol. So, I'll just take anyone who's interested along on the sporadic play of how things have materialized and some tech/fab/industry tidbits along the way.

Because of my background in motorsports, throughout the years, I've gotten many questions, from many people, about how things are done. There is no single proper way to do something. PERIOD. Many different methods are utilized by different professionals to achieve a desired result. So, the information I'm presenting has been the result of working hand-in-hand with some of these professionals and taking their application techniques down to the "home garage" level. If you can take something away from this build thread to apply to your own work: make it yours, make it work for you, your budget, and your situation. That being said, this is how this particular build progressed. Let's hit it...

This is how my BKO started its life with me. I saw it sitting on a used car lot that I passed by every day to work. It hadn't moved in over a year. I decided to stop by one day and check it out. It was an '88 XLT, 5.0L, AOD, 3.55 open diff, top-hat hubs, quad shock option, swing-away tire carrier and 187,000 miles. It had a sticker price of $2,995. This was in August of 2014. When I popped the hood and crawled underneath the chassis everything was completely original with factory parts. Nothing had been modified. Hell, the shocks were still factory. Even the dash was in good shape, under the cover. I had to have this unicorn. It was a little mom-and-pop car lot and the owners agreed to a "layaway" payment plan with no interest. They kept the vehicle until I paid it off. Win.
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Now, during this time, I was building an engine for a customer I had done some work for in the past. The motor was as roller block 5.0L out of a '92 T-bird. It was going to go in a '66 Bronco he had recently acquired. He wanted a mild build, initially, just to have something to take the BKO out and about. Something in the 250-300 HP range and erring towards a practical TQ curve. He wanted to show the truck off more than wheel it, so aesthetics were a priority on the build. This is what we came up with based on the budget constraint he specified:

• 5.0L roller block with stock rotating assembly/bottom-end, bored .020" over, maintaining serpentine belt accessory drive.
• Explorer 5.0L camshaft.
• GT40P (4-bar) cylinder heads, re-man'd with Viton valve seals.
• Weiand Street Fighter dual-plane intake manifold.
• Holley Truck Avenger 670 cfm carburetor.
• Holley 110 GPH fuel pump.
• HEI-style distributor.
• 8mm MSD plug wires (customized cut-to-length).
• Flow Kooler water pump.
• Full-length headers (brand to be determined based on engine bay fitment).
• ARP fasteners/studs used throughout.
• Color scheme: New Ford Gray/black accents.

I had a different thought about what to run for carburetor sizing, but he opted for the 670 "in case" he wanted to build the motor into a stroker at a later date. This outline was a pretty straightforward build, relatively inexpensive, and would get him in the power-band he wanted. This guy usually goes pretty big with his builds, but this one seemed kinda "low-buck" given his prior requests. No custom cam grinds, no CNC'd heads, no port work, no gasket-matching, no lightening/balancing of the rotating assembly, no forged bottom end componentry, etc. Hell, not even roller rockers or one-piece pushrods. This led me to believe it was just a temporary motor and he had bigger plans in the works for down-the-road. That's fine. Easy build. Here's how it went down, starting at a local machine shop I've been going to for almost 20 years (which is where some of my industry "education" comes from):

The above 4 pics are of the bare block after it comes out of the hot-tank cleaning and bead blasting. It's been inspected, via magnafluxing, for cracks/damage and all threaded holes are chased.

This is the block being fixtured in the boring machine. The block's cylinder walls will develop a wear pattern from the piston traveling up-and-down, over millions of cycles, during the engine's service life. If you were to cut the cylinder in half, longitudinally, and view it straight on, it would look like this: ( ). We need to "true-up" the cylinder walls to "re-set" the wear pattern to zero. I didn't want to overbore the the cylinders too much, as I wanted the customer to get as many rebuilds as possible out of this block. Therefore, we only went with a .020" overbore because that's the minimum it took to "clean up" the cylinder walls to this: I I. So, we had this: ( ) and we want this: I I.

Here are the heads being fixtured for a rebuild. They've gone through the same hot-tank, blast, and mag process as the block. They've also been "decked/milled" to true up their mating surface to the block. You can do further machining processes to modify the heads, but we'll get into that later on in this build where we get our hands on some GT40 (3-bar) heads.

Here's everything complete and ready-to-go. The rods have been sized, and everything has been cleaned/inspected. Master overhaul kit came in, too. Let's get this stuff back to the garage and get started.

Ta-da! It's on the stand, it's got a neighbor to keep it company, and all the parts made it back safe. I opted to have to machine shop use their rod heater to install the piston wrist pins. I have the ability to do this work myself, but I wanted the shop's warranty for the customer.

Stay tuned... lot's more ready-to-go and coming, but I'm out of posting time for the moment. Just got called into work.

 

[silver70]

Okay, since I seem to be able to only attach 10 pictures per post, I guess I'll have to start a new post to continue. Let's get back to it...

Here is where I start to coat the block with engine enamel. The color is "New Ford Gray" and I'm using a special application technique that I'll cover, in detail, later on when we get to those GT40 heads I mentioned earlier. The customer wanted to show off the cast aluminum components in their natural color, so I taped off all the gasket mating surfaces and am painting everything separately, as opposed to assembling the entire block and coating the whole thing at once.

Now, I've verified the piston ring gaps and have knocked the pistons into their bores. Wiping the cylinder walls with WD-40 on a paper towel helps prevent pre-mature galling of the cross-hatch hone by the rings and makes install a bit easier. I always use plain paper towels when dealing with engine internals because any small fibers left behind will either disintegrate in oil or burn up during the combustion process if it's left in the cylinder.

As a note, prior to assembling the engine it's wise to blow every orifice out with compressed air as leftover particulates from the machining process could have been missed by the shop and get trapped in oil/water passages. These small particulates can later make their way into bearings and do damage.

This is a shot of the rotating assembly after turning the engine upside-down. All factory rod and cap bolts were replaced with ARP fasteners. They have a much higher tensile strength than factory hardware and will help prevent bolt stretch so we can maintain our bearing clearances longer. We want to do what we can to ensure a long service life. All bearings get coated with Lucas assembly lube prior to install as well. It has a long tack duration, so we don't have to worry about a dry startup. Finally, the rear main cap should get a thin coat of anaerobic sealant on the sides (not underneath) of the cap-to-block mating surfaces. This will help prevent rear main leaks in the future.

Next up is the double-roller timing chain and fuel pump eccentric. I asked the customer if he wanted to replace the cam sprocket bolt with an ARP as well, but he declined.

Now it's time for the oil pump. It has a unique 4WD pickup for the rear sump oil pan, so one of the ARP cap bolts will have to be replaced with an ARP stud to accommodate the pickup's support arm. The cap needed to be completely removed and bearing clearance re-verified for this change. One cannot simply replace the bolt.

 

[silver70]

Some of these pictures are a bit out-of-sequence because I failed to document the process while I was actually doing the work and the customer went back-and-forth on a couple things he wanted. The timing cover/water pump fasteners, for example need to be torqued in a specific sequence and I wanted to get it done before the sealant had a chance to start flashing, so I didn't get pictures of that. That being said...

The timing cover bolts are a special-made set, by ARP, for Late Model Restoration, which is a Mustang parts company. The studs that come in the kit are the proper length for serpentine belt front dress/bracketry. The oil pan and balancer also got ARP hardware. The timing cover install uses a special process I was taught years ago by the machine shop where I had all the work done. Permatex's "The Right Stuff" black is what was used for all RTV on this build. The machine shop buys the stuff, in bulk, in caulking gun tubes for their use, but you can pick up small applicator cans at any parts store. A thin film of RTV is smeared, with a nitrile-gloved finger, around the front crank seal's metal body and it's tapped into the bore in the timing cover with a soft-face dead-blow hammer, using a wood block as a backer, so you don't crack/chip the cover. The "leak-proof" timing cover and water pump install is as follows:

1.) Using a nitrile-gloved finger, smear RTV on the block's timing cover mating face in a thin film.
2.) Using bolts to help with the hole alignment, stick the timing cover gasket to the block.
3.) Smear a thin film of RTV on the front of gasket you just stuck to the block leaving the bolts in place to keep the gasket from shifting while you do this. This film of RTV will be used to seal the BACK of the timing cover on in a minute.
4.) Smear a thin film of RTV on the FRONT of the timing cover and stick the water pump gasket in place using bolts to help with the alignment. The back of the cover is clean, so you can set it on a clean surface to help with this.
5.) Smear a thin film of RTV on the front of the water pump gasket you just stuck to the timing cover, making sure to avoid getting any RTV too close to the pump passageway openings.
6.) Using the bolts that go all the way through the pump and timing cover to screw into the block, as guides, set the water pump into place on top of the gasket that's stuck to the timing cover. This is all done on a table surface so you can stack one thing on top of the other.
7.) Remove the gasket alignment bolts from the block that were used in step #2 and take the entire pump/cover/block bolt assembly off the table and use those block bolts to affix the assembly to the gasket that's already stuck to the block. Verify which bolts go into water passages and coat those threads with thread sealant. Install all fasteners and torque to spec in proper sequence.

Now every component has a film of RTV in between. The RTV sets up (flashes) fairly quickly, so you should plan to move though this process quickly. Plan it out ahead of time and make sure you know what you're going to do and the steps you're taking.

Moving forward, there are several areas of engine builds in which I refuse to compromise on quality. One of those areas is preventative measures. Solving a problem before it becomes a problem. The most common leaks on an engine occur from the oil pan, the valve covers, and the rear main seal. The gaskets for these need to be quality. Therefore, I use Fel-Pro's Perma Dry gasket for the oil pans I install. It is re-useable, single-piece silicone rubber construction, and has integrated crush limiters. The crush limiters not only help with install of the pan for even torquing, but in the future when motor mounts need to be replaced in the vehicle, where do guys usually place the jack to lift the motor up? That's right... the oil pan. This action hyper-compresses the gasket and then allows for the potential for leaks when the pressure of the jack is released. Crush limiters help avoid that situation. These gaskets get installed DRY. NO RTV except for smearing a little on the joint of the timing chain cover-to-block interface before putting the gasket on.

Some straight 30W (or even better is a very thin film of axle grease) is smeared on the inner lip of the front cover seal lips just before the balancer is installed. The rotational friction of the engine start-up can smoke a front seal very quickly, if it's not lubricated, and you'll have leaks or a noisy squeal.

 

[silver70]

Picking up where we left off...

The customer wanted the GT-40P heads to be painted a "cast aluminum" color, at first. After deciding that it was too "wanna-be" he changed his mind and requested they be painted the New Ford Gray color like the rest of the block. This way, all the cast iron components share the same color. Personally, I agree with him, as the paint looked like something we used to do back-in-the-day, when we were really young, to try to impress people with the look of high-dollar aluminum heads on our junk yard spin boxes. Everyone who's a serious hobbyist will know it's just painted and anyone who doesn't know isn't someone we were trying to impress anyways. Lol. In this pic you can see the 4 vertical "bars" on the front/rear face of the heads very clearly. This is what people are referencing when they talk about "4-bar heads." Standard GT-40 heads from the Cobra/Lightning models (with the functional thermactor passages that work with our old emissions system) have 3 bars in this location. There is some debate about overlap of installation platforms on which you can find either head, but the "bar" count is a quick indicator of what you've got when you're out scouring junkyards.

These GT-40P heads are from a '98 Explorer 5.0. They have smaller combustion chambers than the GT-40 heads and the exhaust runners have slightly better profiling. Getting the exhaust out of the cylinder efficiently is one key to making HP on the 5.0L platform. I've built engines with 1.6 ratio rockers on the intake side and 1.7 on the exhaust for some customers for this very purpose. Ford addressed this design flaw (assuming a large credit due to the newly-available flow projection modeling software in the mid-'90's) and that's one reason they revised the runner design on the GT-40P heads. Combined with a slightly smaller exhaust valve, the exhaust flow speed is increased which helps with cylinder scavenging on larger LSA (lobe separation angle) production cams. This helps maintain streetability and idle vacuum. In addition, the spark plug ports are rotated to angle the plug electrode, towards the center of the combustion chamber more, in an effort to improve combustion efficiency. This, however, can cause issues with exhaust manifolds and headers where the mounting flanges and tubes are designed to work with standard plug boot angles. This is why Explorers have those crazy-looking exhaust manifolds. Standard GT-40 heads do not have this issue. Moving on...

Here is a side-view of the gt-40P heads. You can also see the "GTP" cast near the lower head bolt hole. Regular GT-40 heads simply have "GT" cast here. This is another identifier of which head you're looking at. Given this view of the valve springs, now is a good time to talk about some of the limitations of stock "P" heads. If you'll notice the thick rotators on the top of the exhaust valves (the ones in line with the exhaust ports), you can see how much more vertical area they take up under the retainer. These are so thick, in fact, and due to their assembly, they significantly limit spring travel. Hot Rod Magazine gets the credit for the numbers they've assigned to the predicament in this excerpt:

"The GT40P incorporates a rotator into the exhaust valve retainer, which, through a series of ball bearings, allows the valve to rotate slightly each time it opens. This helps prevent exhaust valve seat erosion. The valve rotators are thicker than standard valvespring locators and retainers, though, and require a spring with a shorter installed height on the exhaust valve. The installed height is the distance from the valvespring seat in the head to the underside of the retainer. On these heads, the installed height of the intake valvespring is around 1.780 inch, but the exhaust is less at roughly 1.600 (the installed heights can vary by 0.050 inch or more). Because of this discrepancy, the exhaust valve's valve-lock groove must be shorter to allow sufficient room above the retainer for the guided rockers. This reduces the actual distance between the bottom of the retainer and the top of the valve guide and seal, so this combination can't accommodate any kind of performance cam with more than 0.450 inch of lift."

If you look at the intake vs. exhaust valve spring installed heights, there's almost 3/16" difference between them. Yikes. Good thing we're just running the stock Explorer cam in this motor.

Here are the same heads, but re-shot in New Ford Gray. Much better, IMO.

Aaannnddd here they are installed in their respective positions on the block. I have gotten in a habit, over the years, of coating all lower head bolt threads in liquid thread sealant. Some are near water passages in the block and can corrode over time. There is an entire dissertation on the years that blocks were cast with bolts in these locations, but whatever the year, it will hurt absolutely nothing to do this on all lower head bolts for SBF engines. Best to form good habits and cover your bases. I would rather "do more than I need to" instead of finding I "did less than I should have."

Here's a good shot of the spider hold-down and dog bones, which retain the roller lifters in their bores. The tops of the tappet bosses are machined flat so that the dog bones sit perfectly flat on top of them. This is one way to tell if you have a roller block or not. A non-roller block will have the tops of the tappet bosses "as cast" with no machining/milling done.

Next up is the install of the intake manifold. It's a Weiand Street Warrior dual plane. If you look closely, you can see where I use silicone (Permatex Right Stuff, black) at the front and rear of the intake-to-block, on the "China wall", instead of the cork gaskets that come in the gasket kit. No decent machinist/builder will use the cork gaskets unless specifically directed by the customer. They are a, repeated, point of failure and leaks. Pro Tip: if using the silicone, wait for it to cure and trim any excess "squeeze/extrusion" away with a razor blade for a detailed look. Don't try to wipe it while it's still uncured. It will only make a mess. Personally, I don't trim the extrusion unless the customer requests. I believe the more material you leave intact, the more reinforced the joint/seal is. I just try to keep a fairly even bead application the entire length and don't use an excess amount.

Bolts near water passages get their threads coated in liquid thread sealant, just like the head bolts mentioned earlier.

We're getting close to buttoning up this motor pretty soon. There's a plot twist, with a surprise ending, coming in the near future. Then we can get on to the other parts of this build, which are loosely based on a "standard" event sequence for builds. Again, some are done out-of-sequence just because of how much back-and-forth I've gone through on this truck. Almost everything will get covered, though. As mentioned, though, most vehicle builds have a "typical" progression in order-of-attention:

1.) Engine. This comes first so you don't scratch a new paint job installing the motor or get grease all over your new interior. The engine also sets the pace for exhaust and drivetrain mods, that may need to happen, based on how the engine sits in the bay.

2.) Drivetrain. This is where transmission, driveline, and axle modifications come into play. In part, because of the same reasons for not scratching paint moving around heavy/cumbersome objects.

3.) Suspension/wheels/tires. Once the vehicle is at its "curb weight", with the entire drivetrain in place, you can determine desired ride height and get the vehicle moveable to roll in and out of the paint booth.

4.) Interior. This comes next because, again, you don't want your paint scratched by climbing in-and-out of the vehicle while trying to wrestle seats, dash components, package trays, etc. into place. Also, sometimes holes need to be drilled in fire walls to route wiring. If you've already painted the engine bay on a show car, now you have to worry about masking off the drill site.

5.) Body/paint. This is what everyone sees when you pull up. This is what the sun gleams off of when you're cruising. This what gets inspected as someone walks right next to your vehicle at a show.

The paint was the hardest decision in this build because I wanted a nice paint job, but, at the same time, this is gonna be a trail rig. It's going to get wheeled. I came up with, what I believe to be, a decent compromise and we'll see what everyone thinks. More to come!

 

[silver70]

Re-firing the continuation...

Carb goes on next. It's a Holley 670 Truck Avenger, IIRC. Pretty standard fare for wheeling purposes and the customer wanted to go a little larger, on the carb size, than I would normally recommend for this engine displacement and parts combo. Again, I think he planned to go through the engine at a later time and maybe build a stroker or something. I like Holley carbs because they're easy to rebuild/tune and very common. Personally, I run Barry Grant carbs, which are based on a Holley platform. However, for street vehicles that are just going to be "drivers", or when the owner of the vehicle isn't too keen on mechanical upkeep, I'll recommend an Edelbrock.

Valve covers are next. The customer opted for some Ford Racing cast aluminum "tall" covers in a black, powder-coated crinkle finish . We didn't run roller rockers on this build, but I think we were leaving room for later improvement. Once again, I insist on PermaDry gaskets, just like we did for the oil pan. In the past, when a customer absolutely wants to go cheap and run the cork gaskets on stamped steel valve covers, I will silicone the gaskets to the valve covers and install them, dry, onto the rail on the heads. This allows the gaskets to deform with the stamped steel covers (as this frequently happens with careless maintenance procedures) and keeps them attached to the covers, if/when they are removed, so the gaskets don't get damaged or lost. When a customer wants to replace the gaskets, they can simply use a drill, die grinder, or bench grinder to wire-wheel the gasket and silicone off the stamped covers without risking damage to the cylinder heads or getting debris in the valvetrain.

Next up we have a HEI-style distributor with vacuum advance. No fancy timing curve tuning on an MSD Pro Billet available here. Kinda boring, but not every build gets knocked out-of-the-park with a huge budget. Old school meets new school in a practical and simple application. And yes... the dizzy has a steel gear for the roller cam (I know someone will wonder about that). The customer also decided he wanted a phenolic "swirl torque" carb spacer to try to keep engine heat from sinking to the carb too much, based on a suggestion I made. No problem, but I'm going to install studs. Nobody likes doing routine maintenance, while dinking around with bolts, on a set-up like that.

Finally! She's ready to drop in. I sourced the air cleaner the customer wanted and took the sandwich plates to my powder coater and had him match the texture and color on the valve covers. Plus, some MSD 8mm cut-to-length plug wires got installed and a valve cover breather that doubles as a filler cap. I left the air cleaner stud a little long because I know what it's like to break down, somewhere out-of-town, and the nearest parts store only has a limited selection of air cleaner sizes. And the only one with the right diameter is the wrong height.

This build didn't take that long and was pretty simple. The total cost to build this particular engine, as it exists in the above pic, was $2,662.45. That includes my discounted cost for the machine work and retail pricing for the aftermarket parts. However, this amount does not include my labor charge for assembly and I received the original long block for "free" as a result of a very long drive to pick it up. I also received special pricing on the master rebuild kit due to my relationship with the machine shop. If a "typical" consumer were to pay retail for everything in this build, this would probably end up as a ~$4,500.00 engine.

With the full-length headers the customer was going to install, this motor would probably kick out around 260-280 HP/310-325 TQ with a good low-mid power band, rolling on smoothly to a declination start at ~5k RPM with a ~5,800 RPM redline, where the cam would just fall flat on its face and you'd get some valve float. A set of roller rockers and a ~.500 lift cam (with better valvesprings on the "P" heads, of course) and you'd probably be right around 300-315 HP/320-340 TQ with a 6,200-6,400 RPM redline. However, this is all based on proper tuning.

Well, that's it for this version of the engine. More to come later on, after another project or two.

Wait... what was that? "This" version of the engine?!

Yup. That's right. The customer decided, after the build, that he was going to go for broke and stuff a 460 into that little Bronco and make a "mini monster truck." I asked him what he wanted to do with the 302 I just built him and that he already paid for all the parts for. The only thing that hadn't been settled was my assembly fee, to be paid on delivery and customer inspection, as usual. He asked me if I would be willing to keep the engine as my assembly fee. My fee is nowhere near what the engine cost and this dude has more money than God (owns a construction contracting company), so I readily agreed with minimal guilt. Looks like this thing's going EFI and will still end up in a BKO, after all. 🙂

In the meantime, though, I'd just bought new 33" MT tires for the BKO after gouging a hole in my AT's (that only had 10k miles on them 😑). Well... can't have new tires and stock suspension. That just won't do. But, if I'm going with heavier tires and tearing into the suspension, won't I want better gears? Maybe some fresh axles and a carbon fiber Trac-Lok?

.....and this is where "proper build sequence" just fell the f*** apart.

More to come!

 

[silver70]

So, now comes the part where I've just inherited a new engine for my BKO and I'm staring down the barrel of a suspension rebuild. Okay... let's come up with a plan-of-action for this developing, though unanticipated, vehicle build. Now, for some boring reading, with no pics, for a while...

First, what am I going to use this BKO for, exactly? I don't do any serious wheeling where I need ridiculous suspension travel or monster tires. I don't rock crawl or bomb down desert trails at 90 mph. I, mostly, just use the BKO for adventuring, hunting, and moderate wheeling for fun. I suppose "overlanding" would be a solid comparison of the type of wheeling I use the BKO for.

Okay, now that I have my "purpose/use" defined, I need to explore how far into the rabbit hole I want to go with the build to achieve my scope of purpose.

First, I probably shouldn't go crazy with power mods. I need a practical vehicle that doesn't push itself to the brink of failure and is reliable. I need a vehicle that I can source parts for, no matter where I am. I should be able to find parts, to keep the BKO running, in any junkyard, in any town I happen to find myself in. This means that I should limit myself to factory parts. The BKO shares drivetrain components with many vehicles: F-series trucks, Mustangs, Explorers, Cougars, Thunderbirds, Crown Vics, Mountaineers, other Broncos... I shouldn't change any of that. All those vehicles are readily found in any junkyard and parts for those vehicles are commonly stocked at parts stores all over the nation. Okay, that settles it. I'm going to leave the drivetrain stock. But, stock is boring. Well... performance stock isn't completely boring. Hmmm... what was the Ford SVO/SVT team working on right around the production time of my BKO? The Lightning and the Cobra. The Lightning is based on an F-series platform (so is my BKO) and the Cobra shares drivetrain componentry with my BKO (5.0L engine, 8.8 rear). Sweet! Let's take some cues from those vehicles in this build. I can bump power levels with production parts. Just... really good production parts. Nothing crazy, but still a modest improvement.

Second, I need to overcome trail obstacles. Let's address suspension and tires. To start, there are limits to everything. I'm not doing KOH or Baja. So, I thought of the most difficult obstacles I've run into while exploring in the places I typically go. I could use a 4" lift, but I don't need one. Most overland vehicles run stock suspension, or maybe a 2" lift. Driving skill, coupled with traction, will get you through most average things you run into on the trail. Leveling coils will work well, I think. I don't need to bolt or weld on any drop brackets and can still use my factory pitman arm (remember, we're maintaining those factory parts). Also, I can already run 33's on stock suspension and not have to worry about breaking axles and what not. They're larger than stock, but not taxing on the drivetrain. I can even swap in a Saginaw pump (factory part) to deal with the slightly added steering load. 33" MT's are still pretty heavy, though. I'm going to want some axle gears to help turn those things. Hmmm... I kinda want 4.56 gears and everyone on FSB tells me do it and not look back. @BikerPepe` made really good points in that thread I started, too. He sold those gears hard and he loves the ones he has in his own BKO. Damn... Ford didn't make production 4.56's, though, and that's kinda the "theme" of this build: "Factory Parts." Plus, I still need to take the BKO on the freeway, at 70+ mph, to get to some of my destinations for wheeling/hunting. Those 4.56 will be great for wheeling, but I need all the help I can get for fuel economy at freeway speeds. Okay... let's compromise:

What is the purpose of the new gears? Well, I want better gears to overcome the heavier tires and get some TQ multiplication going on to maximize the limited power I'm making from my mild engine build. Ford didn't offer production 4.56 gears for the 8.8 diff. The best production gear offered for the 8.8, and readily available, is 4.10. Not a 4.56 ratio, but close. Conversely, I need to maintain a decent cruise RPM for fuel economy. So, how can I make up that little bit of extra gear reduction that I really want and @BikerPepe` worked so hard to sell me on, and still keep my low-rpm highway capability? Interestingly enough, Ford does offer a solution that moves us away from the axle and into the AOD transmission in my BKO. This "solution" is part of the old "wide ratio" planetary gear-set that Ford developed to put in the 4R70W transmission that was going behind the new 4.6L motor they were developing in the early '90's. The new 4.6L didn't have the displacement to provide the low-end TQ needed to get heavier vehicles moving, so Ford decided to improve the gears in the trans to help overcome this. For comparison, here's the breakdown:

AOD trans gear ratios:
1st- 2.40:1
2nd- 1.47:1
3rd- 1.00:1
4th/OD- 0.67:1
Reverse- 2.00:1

4R70W trans gear ratios:
1st- 2.84:1
2nd- 1.55:1
3rd- 1.00:1
4th/OD- 0.70:1
Reverse- 2.32:1

The awesome news: the gear sets and upgraded parts in the 4R70W are a direct fit in the AOD! The Hell, you say. It's true. The 4R70W is based on the AOD platform. At one point, in the past, Ford actually used to market this entire "guts assembly" as their "wide ratio upgrade kit" and offered it in their performance catalog under the AOD trans section. Now, let's run the numbers for 1st and 2nd gear, where the BKO will need the most help getting those larger tires turning, taking off from a stop, and getting up to road speed. This compares the two trans gearings vs. the two axle ratios I'm considering:

AOD 2.40 first gear x 4.56 rear axle gears = 10.94 over-all drive ratio
4R70W 2.84 first gear x 4.10 rear axle gears = 11.64 over-all drive ratio (better)

AOD 1.47 second gear x 4.56 rear axle gears = 6.70 over-all drive ratio (better)
4R70W 1.55 second gear x 4.10 rear axle gears = 6.36 over-all drive ratio

These numbers are damn close to being a very happy compromise. I get better 1st gear performance, but 2nd gear suffers a little. That's okay, 1st gear is where I need the absolute most TQ anyways. Additionally... remember the "freeway speed" conundrum? This is where the wide ratio upgrade really shines:

AOD 0.67 fourth gear x 4.56 rear axle gears = 3.06 over-all drive ratio
4R70W 0.70 fourth gear x 4.10 rear axle gears = 2.87 over-all drive ratio (better)

Now let's toss those 33" tires into the mix, compare it to the factory specs, and see what it does to our engine RPM at 75 mph for highway cruising:

Factory BKO:
0.67 OD ratio + 3.55 axle gears + 29" tires = 2,067 RPM

Factory trans/4.56 axle gears/ larger tires:
0.67 OD ratio + 4.56 axle gears + 33" tires = 2,333 RPM

Happy Compromise:
0.70 OD ratio + 4.10 axle gears + 33" tires = 2,192 RPM

So, what does this all mean? Well, with 4.10 production axle gears (that I can find in any junkyard in the nation), the 4R70W transmission gear swap, and 33" tires I will have more low-end TQ multiplication than with 4.56 gears, and near-factory engine RPM at highway speeds despite the numerical increase in axle gearing. Increased low-end TQ with factory highway cruising: best of both worlds.

..... and this is how I decided which gears to run.

If you've made it this far, I have underestimated your interest in my build thread and you have my appreciation. More to come...

 

[BikerPepe`]

If you've made it this far, I have underestimated your interest in my build thread and you have my appreciation. More to come...

Well ya did tag me a few times.
I like your thinking and my experience jives right up there with your estimated speed/RPM w/4.56 & 33's.
I ran the 4.10/AOD combo on the old '89 "Stoned Bronco" and it was a noticeable improvement over the factory 3.55 but I had a standard AOD and 35's before the gears, so the improvement wasn't just expected, it was nearly necessary. You're a sharp guy, so I can only assume your AOD tinkering will be adequate.
Should be interesting to hear what more experienced, educated minds might think.

 

[silver70]

Well ya did tag me a few times.
I like your thinking and my experience jives right up there with your estimated speed/RPM w/4.56 & 33's.
I ran the 4.10/AOD combo on the old '89 "Stoned Bronco" and it was a noticeable improvement over the factory 3.55 but I had a standard AOD and 35's before the gears, so the improvement wasn't just expected, it was nearly necessary. You're a sharp guy, so I can only assume your AOD tinkering will be adequate.
Should be interesting to hear what more experienced, educated minds might think.

To be honest, I was like, "Crap. I hope folks don't think I'm just trying to rope them into my build thread with all the mentions I have planned." However, I did want to mention the people that contributed to this build, in one way or another. Without you guys, this build wouldn't have been possible and I might have lost interest a long time ago. Really, this forum played a huge role in keeping me going on the BKO. You guys are awesome. 👍

 

[BikerPepe`]

It's a mutual thing bud. I'm beyond certain I wouldn't be the Bronco lovin' nut or even 1/2 as competent at keeping it on the road and trails without my FSB family.

 

[silver70]

Okay, back to it for a lil:

Now that I have my gears figured out, I need to decide how to build the axles. I want to run "performance" versions of stock/factory parts, so a D60 won't be in the plans. The 8.8 will be fine for my application. I know I won't be running any tires larger than 35's, so I don't really need super HD axles. I won't be jumping the BKO or doing anything crazy that will require trussing for the housing. I know I don't want to have a hard time finding parts for the thing, no matter where I end up in my travels. This will be an "overland" type build, so street manners are as important as trail capability. And given my goal of factory parts, no mechanical or air lockers for the axles. These are my "don'ts/won'ts."

I do want to run some pretty heavy 33" M/T's and I like to know that the axles will hold up under some stress, so upgraded axles are reasonable. I know the pumpkin-to-tube joints can be a point of failure under accidental overloads, so while I don't need trussing, I do want to weld the tubes. I have had to do trail repairs on vehicles, in the past, and know I want a crush sleeve eliminator for the 8.8 so I don't have to dink with pre-load should I need to make axle repairs in the field. While a locker might not be in the plans, the factory Trac-Lok is kinda weak for my application. However, Ford offers some carbon fiber clutch packs that were used in their 03-04 Cobra and GT500 Mustang. Those will help the Trac-Lok live a little longer and hold a little tighter with those heavy tires. Finally, since I want to know I can make JY parts work, no matter where I am, let's source a good rear axle candidate from the JY, right out of the gate (and save a couple bucks to boot).

So, my donor for the the rear axle was a 1992 F-150. The 4.10 gears and Trac-Lok unit came from a 1998 Explorer. I didn't get as many pics as I wanted, but let's start with these:

I hadn't "walked the cup" with my TIG welder for quite a while (and you can tell from my results... 😕) and decided that's the weave I wanted to use for welding the tubes to the center section. Once the axle had been cleaned and prepped, and after the factory rosette/plug welds had been inspected to ensure they hadn't cracked and allowed the tubes to possibly shift out of alignment, I used a high-tensile filler rod called Tensileweld and made by Washington Alloy. It's designed for use in repairing tool and die steels and is great for welding cast because the weld is very malleable/ductile. It's a tough weld that is extremely crack resistant. When using this particular filler rod, it's not necessary to pre-heat or cool-control the joint, even though it is recommended. I have used this filler many, many times on numerous axle repairs and it's never failed me.

I decided to re-weld the mounting flanges for the brake backing plates while I was at it. I figured I may want to do a disc brake conversion in the future and wanted a better weld than the factory offered for more security. You can see one small void, in the second pic, that I ended up catching and fixing.

Setting up JY/used gears can be tricky. However, they are easy to come by and offer a good value if you know what to look for when you're inspecting them. After running for so long in the donor vehicle, the used gears develop a wear pattern. This pattern is specific to the shims used and the casing they came out of. It's especially tricky if you're pulling the gears out of one vehicle and re-setting them in a casing from another vehicle. Manufacturing and assembly line variances will usually be significant and no two sets will ever be set up exactly the same. In this case, the Explorer's gears were in excellent condition and I liked the wear pattern I saw when I pulled them at the JY. I kinda rolled the dice on my personal set-up though. Ideally, you want to try to match the original set-up as much as possible to avoid a possible noisy running condition, or, gear whine. However, I like my pinion to track on the lower 1/3 of the ring gear teeth on the drive side. This comes from my background in drag racing. As extreme TQ is applied to the pinion gear, by the driveshaft, the pinion gear tries to "climb" up the ring gear, towards the heel, and can shear teeth under severe load. This same concept applies to high-TQ application when wheeling. For example, when you're loaded up on the converter trying to crawl your way over an obstacle. The deflection present between the ring and pinion act much the same as when launching off the line in the 1/4 mile. Plus, setting up the pinion on the ring's lower 1/3 puts the drive force of the pinion closer to the centerline of the axles for better force transfer.

You will seldom get a "centered" contact patch from used gears as they've already developed their wear pattern. Therefore, it's always a time consuming process to get the set-up where I want it and have it run quiet. I, probably, used 3 dozen shim combinations before I finally settled on the contact pattern you see above. ZERO noise and I got the performance I wanted.

Here is the housing with fresh ceramic Ford semi-gloss black paint, SOLID nodular iron diff cover with LubeLocker gasket, 4.10 factory gears with a Yukon crush sleeve eliminator, factory carbon fiber Trac-Lok unit, new Timken bearings and races, new seals, welded tubes/flanges, and upgraded axles (not in the pic). Wish I could've gotten more pics, but there's more to come when we tear into the front end for a rebuild and suspension upgrade.

 

[jfourdyce]

I think 4.10 is the way to go if you are planning any highway driving in you truck. I went 4.56 with a C6 and 35s, and highway speed requires ridiculous RPMs. 3500 to 3700 rpms to get 75 mph. If I had it to do over, 4.10 would have been my choice.

 

[BikerPepe`]

Good, educational info Silver... as always.