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Old 12-21-2003, 05:24 PM   #1
BurntOrange
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400/AOD/NP205 into an '81-'86

First time poster here seeking some technical info and advice to help with my search for a Bronco. I want to buy a worn early eighties Bronco to build as a hunting/tow/mild off-roader. I currently have a junk '79 F-250 4x4 that I'd like to use for drivetrain parts. It has a 351M/C6/NP205 with leaf-sprung hi-pinion D44 front and Dana 60 rear with 4.10 gears.

I've done quite a bit of research and think I've narrowed the years I'm looking for down to '81 through '86. I understand 1980 frames were a bit peculiar and can cause some issues when lifting, etc. due to them being inconsistent with other model years. I know '81 and partial '82 Broncos used the 351M and '86 got the AOD tranny.

Anyway, what I think I'd like to end up with is an '81-'86 with a 400/AOD/NP205 setup and a leaf sprung SAS using my D44, and naturally the D60 in the rear running 35" or 36" rubber. I would accomplish the 400-to-AOD by either using an adapter plate (Art Carr or other) or by building a 400 FMX block (SBF pattern) I am trying to buy cheap. I will spend the bucks for a built AOD that can handle the 400's hp and torque because I want the overdrive for long hauls. I will take this rig on five to ten 1400 mile hunting trips to my buddy's ranch in South TX every year in addition to other miles but it won't be my daily driver.

Whew, so all that being said here's what I'm needing some help on. I obviously want to look for a truck with an automatic, but, would a 302 be better than a 351W or 300six for ease of the 400 swap? That is, if I don't find an '81 or '82 already with a 351M. I had heard that the 351M/400 engine mounts would bolt up to the towers used with the 302. Thoughts on this?

And, I understand the AOD is only about a 1/2" difference from the C6 so all the crossmember stuff shouldn't be too bad right?

Any year-specific stuff that would be important in considering the leaf-sprung solid axle swap up front? Is an '86 better than say an '81 for some obscure TTB or front crossmember reason?

I am set on the choice of a 400 powerplant and automatic OD so please don't come right back at me with "use a 460/C6 dude" or "just build a sweet 351W/E40D setup man". I'm just trying to figure out the best starting platform to accomplish the specific goal as I start my search for a cheap (less than $1500) rig. Thanks for any comments...

-BurntOrange
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Old 12-21-2003, 09:01 PM   #2
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Biggest problem is the 400 uses the BBF trans bolt pattern, not the SBF that the 300/302/351 uses. If you can find an O/D trans from a BBF, then you'd be fine, otherwise "use a 460/C6 dude" or "just build a sweet 351W/E40D setup man".
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Old 12-21-2003, 09:10 PM   #3
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you'd be fine with a C6. i have one in my daily driver, and they stronger than an AOD too.

the very early 80's broncos have the gay swiss cheese frames with the huge holes in the end. if you were doing a leaf sprung swap, i can't imagine how you would realistically do it safely. if i were you, i'd look for an 88-89 bronco with an EFI 351 and a C6. then do your leaf sprung SAS/D60 rear. you can build the 351 as a stroker to boot and get plenty of power out of it.
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Old 12-21-2003, 10:36 PM   #4
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Quote:
Originally Posted by davids78bronco
Biggest problem is the 400 uses the BBF trans bolt pattern, not the SBF that the 300/302/351 uses. If you can find an O/D trans from a BBF, then you'd be fine, otherwise "use a 460/C6 dude" or "just build a sweet 351W/E40D setup man".
As my post stated there are two ways to mate up the 400 & AOD. First, use a SBF to BBF engine plate adapter. Check out the following writeup on swapping an AOD behind the 351M/400 in a '78-'79 Bronco.

http://www.ford-trucks.com/articles/feb2002/index.php

Second, I could use the rare 400 FMX block which has the SBF bolt pattern. I have a lead on one of these for $85.

Only overdrive option other than an AOD here is E40D which is expensive (more than an AOD for a built tranny) and would require a Baumann Engineering transmission controller or something similar.

So, like my post said, I am looking at the 400/AOD combo.
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Old 12-21-2003, 10:52 PM   #5
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Quote:
Originally Posted by Andy351
you'd be fine with a C6. i have one in my daily driver, and they stronger than an AOD too.

the very early 80's broncos have the gay swiss cheese frames with the huge holes in the end. if you were doing a leaf sprung swap, i can't imagine how you would realistically do it safely. if i were you, i'd look for an 88-89 bronco with an EFI 351 and a C6. then do your leaf sprung SAS/D60 rear. you can build the 351 as a stroker to boot and get plenty of power out of it.
Thanks for the reply. Yes, a C6 is stronger than an AOD in stock form but an AOD can be built incredibly strong. The reason I want the AOD here is for the .67 fourth gear. This means with my 4.10 axles and 35" tires I could turn something very reasonable like 2000 RPM at highway cruising speeds. If I used my C6 I'd be turning 3000 RPM. I've done all the calculations - the AOD does pay for itself when you consider the fuel savings.

I already have many parts for the 351M/400 and plan to use this engine. I love the torque it produces and want to run a simple carb setup. That's why my original post said I wasn't even considering a Windsor or anything else. Not sure how else to say it!

Your swiss cheese frame comment is the kind of thing I need to know. Is there really something inherently weak about the frames on early 80's trucks? Are they boxes or not boxed? Do people commonly have to reinforce the frame rails with steel plates or something? Are they prone to cracking near the steering box like on early K5 Blazers? What frame improvements were made during the life of the Bronco - did the '87 body style change also include frame improvements of some kind??

Thanks,
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Old 12-21-2003, 11:09 PM   #6
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seems you have it all fingered out then... I'd build the FMX, just because it's not near as common as cheating with an adapter plate
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Old 12-21-2003, 11:23 PM   #7
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Yup, the 400 FMX would be cool. I'm trying to confirm if it's a crack-prone Michigan casting or a good Cleveland casting before laying down the cash.

So does anyone have experience with swapping the 351M/400 in or out of an '80-'86? I'm really curious to know what is involved with the engine mount situation. Do I have to source these towers from an '80-'82 that came with a 351M? I haven't found them for sale from JBG or LMC. Will the 351M/400 mounts bolt up to the 302 towers??

Thanks,
-BurntOrange
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Old 12-21-2003, 11:40 PM   #8
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AFAIK, the 80-82 (not sure on the year that they stopped this) had the swiss cheese frames; they are called that because there are large (like 2" or bigger if my memory serves me) holes drilled in the frame rail ends. they were to make it "lighter and more fuel efficient." also, the only place i know of where the frame was boxed was right around the engine crossmember and where the steering box attaches. i think that the 83-91 have the better frames because the 80-82 are the swiss cheese and the 92+ have the crumple zones.
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Old 12-22-2003, 12:07 AM   #9
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great info. I'll keep an eye out for the swiss cheese frame holes you're talking about and search around some more on the SAS forum to see if there's anything else on this.

This got me thinking and I just found my Standard Catalog of 4x4s book. It has info on every model year domestic 4x4. It doesn't really specifically talk about frame differences from year to year, but it does have a Chassis Features section for each Bronco year. Here's what it has:

(1980-1985) Separate body and frame, box-section welded frame. 3.95 in. section modulus
(1986) Separate body and frame, single channel, 5 cross members, welded frame. 3.66 in. section modulus. Maximum side rail section: 6.95 x 2.12 x 0.170 in.
(1987-1989) Separate body and frame, single channel, 5 cross members, welded frame, 36,000 psi steel. 4.27 in. section modulus. Maximum side rail section: 7.01 x 2.12 x 0.202 in.
(1990-1992) same as 87-89 but also notes low carbon steel
(1993-1996) Separate body and frame, single channel, 5 cross members, welded frame, 3.66 in. section modulus. Maximum side rail section: 6.95 x 2.12 x 0.170 in. low carbon steel

-BurntOrange
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Old 12-22-2003, 01:44 AM   #10
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Quote:
Originally Posted by BurntOrange
Yup, the 400 FMX would be cool. I'm trying to confirm if it's a crack-prone Michigan casting or a good Cleveland casting before laying down the cash.
351M/400 blocks cast at Michigan Casting Center before March 1977 had casting problems, resulting in cracking of the water jacket inside the lifter gallery. Blocks with date codes of 7C01 or later should be OK.


Quote:
So does anyone have experience with swapping the 351M/400 in or out of an '80-'86? I'm really curious to know what is involved with the engine mount situation. Do I have to source these towers from an '80-'82 that came with a 351M? I haven't found them for sale from JBG or LMC. Will the 351M/400 mounts bolt up to the 302 towers??

Thanks,
-BurntOrange
Take the frame perches from the F250. If you can't, I have a pair from my Bronco that I'd be willing to sell you. Frame perches and motor mounts - package deal
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Old 12-22-2003, 10:14 AM   #11
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I'd look into using a C6/205 with an aftermarket US Gear OD box that replaces the existing t-case adapter or Gear Vendors box that replaces the tail housing on the t-case.

http://www.usgear.com/dual_range.htm

http://www.gearvendors.com/

You can buy them used here and there.
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