Anybody running 3.73 gears w no overdrive?

[ssommerfield]

Just moved back to Montana from coastal TX and brought the bronc with me. Currently running a 33 in. mud terrain. Problem being is my truck is non-overdrive (C-6), 5.8 with 3.08 gearing. Wasn't an issue on the flat lands of TX but in the mountains not doing so hot, especially with a boat. Not my daily driver but still sees a lot of miles. Does anyone have this set up? and what is the mileage trade off. I'm trying to go low enough to compensate for tires but not so low as to run up the RPM's through the roof at highway speeds. As long as I can keep it in the 11 mpg range I'm happy. Thanks.

[Kingfish999]

33" tires with 3.08? i think ull be quite happy with 3.73 gears. 3.55 is the most common for our trucks. the little extra will jsut help with the slightly bigger tires. ull probably save alot of gas on accelerating less ahrd anyways

[TheUnforgiven]

[reptillikus]

everything assumes 33's



3.08, 65mph = 2154rpm
3.55, 65mph = 2482rpm
3.73, 65mph = 2608rpm
4.10, 65mph = 2867rpm



What will work best for you? Do you really need that extra 126 rpm the 3.73s offer over 3.55s? I only bring it up because 3.55s & 4.10s are factory ratios so you can get them at a junkyard cheap, whereas youre going to have to buy all new on the 3.73s. That turns into a lot of gas!

[riccnick]

Keep the gears and swap in a zf-5 = Best of both worlds. Great MPG on the Highway, and enough get up and go in the mountains. Just a suggestion, probably more expensive and complicated than most want to do, but I plan on doing it in the spring to my truck.

[TheUnforgiven]

a transmission isn't going to help him with his lack of final gearing and oversize tires. he needs to start at the gears before he does anything else.

[87Roughneck]

I have 3.55:1 gears with 35" tires and a 300cid 6, and no overdrive. Okay from the line, good at speed, but a dog between 40mph and 55mph.

4.10:1 gears would put me back almost exactly to the final ratio of the original tires with the 3.55:1, but I don't know if I want to go to that much trouble. If I was going up a hill alot, or pulling a boat, though, it would already have happened.

[riccnick]

Originally Posted by TheUnforgiven

a transmission isn't going to help him with his lack of final gearing and oversize tires. he needs to start at the gears before he does anything else.

Sure it will man, he'll have two extra gears to choose from. He'll be back wondering how to get his MPG up after he switches to lower gears. His real problem will be no OD after the gear swap.

Edit: Ohhhhhh, 35's not 33's....
Yeah, maybe start with 3.55's...

[TheUnforgiven]

Originally Posted by riccnick

Sure it will man, he'll have two extra gears to choose from. He'll be back wondering how to get his MPG up after he switches to lower gears. His real problem will be no OD after the gear swap.

Edit: Ohhhhhh, 35's not 33's....
Yeah, maybe start with 3.55's...

the OP said 33's in his post. sure he'll have 2 extra gears but the granny is only good for getting going, and the OD is only good on the highway IF the final drive ratio is low enough to permit the use of the OD. which in this case it isn't. so that leaves him with a lot of work, for almost zero gain. there is also a big gap in i think 2-3 on the zf so that is also working against it's case.

the zf would not fix the problem, only kind of treat the symptom. fixing the problem is changing the gears. however reptilikus made a great point by saying go with 4.10's because they are cheap and plentiful.

also, if anything, his mileage will go UP with the change of gears because the engine won't be straining so much. the current set up is also very hard on the transmission, as the trans has to take the heat (literally) to get this rig moving. the big tires and lack of gearing is like pulling a boat ALL the time. lowering the gears will give the engine back that leverage, and make it easier to pull the truck.

[87Roughneck]

Originally Posted by riccnick

Edit: Ohhhhhh, 35's not 33's....
Yeah, maybe start with 3.55's...

The OP said he has 33's. I have 35's.

[riccnick]

Originally Posted by TheUnforgiven

the OP said 33's in his post. sure he'll have 2 extra gears but the granny is only good for getting going, and the OD is only good on the highway IF the final drive ratio is low enough to permit the use of the OD. which in this case it isn't. so that leaves him with a lot of work, for almost zero gain. there is also a big gap in i think 2-3 on the zf so that is also working against it's case.

the zf would not fix the problem, only kind of treat the symptom. fixing the problem is changing the gears. however reptilikus made a great point by saying go with 4.10's because they are cheap and plentiful.

also, if anything, his mileage will go UP with the change of gears because the engine won't be straining so much. the current set up is also very hard on the transmission, as the trans has to take the heat (literally) to get this rig moving. the big tires and lack of gearing is like pulling a boat ALL the time. lowering the gears will give the engine back that leverage, and make it easier to pull the truck.

Originally Posted by 87Roughneck

The OP said he has 33's. I have 35's.

Still learning how to read I guess.... I'll get it one of these days...

Anyway, OP did mention MPG and the Non OD right from the get-go. It's his call, and his budget. Gears will definitely help, but I'm not sure will solve the problem. Just my point of view. Not saying I'm right or anyone else is wrong.

[Kingfish999]

i have 4.10 and 33" tires. i have OD but i love it. i would say 3.55 or 3.73 would be great for you but 3.55 would be easy and cheap to replace both axles with JY axles. much cheaper and easier than regearing

[ssommerfield]

Ok... All good info, would definitely consider 3.55 if it would be enough of an increase over 3.08. I do believe that due to the mountainous area I am living in now the truck is working harder than it should. That being said I am concerned about the MPG. Running flat land in TX I worked hard to get a consistant 11 MPG. With the increased strain on the motor in the hills I am down to single digits. My concern is to not go so low as to offset the efficiency gained by re-gearing.

[TheUnforgiven]

3.55's will help you. however you have everything working against you, hills, a lift, and 33's. drop the lift and you'll see an improvement right there.

[Kingfish999]

cost of regearing is expensive. usually around $1-2k per axle. not to mention its not something a DIY can really do themselfs. junkyards are full of 8.8 axles and i swear 80% must be 3.55 and they will usually cost from 50-300$ at a junkyard. for the front you can either swap out the front diff or you can install the whole driver side beam. depends really if you wanted to replace other stuck and you find one with the same breaks. it shouldnt cost half the price as the rear axle. as you can see it would be alot cheaper and earier to swap than regear.

how fast do you usually go? my area is pretty much 55mph or less. if ur doing 75 alot you might perfer the 3.55 but if ur area is slower then you might perfer 3.73 if your area is really that hilly and slow, you might even want 4.10

[ssommerfield]

There is no "interstate" in my area so definitely not hitting the 75 MPH mark. However, it is Montana with a lot of open space and I do like to get at least 65 on the highway so I'm not a traffic hazard. Also, the tire is 33 but only 10.50 wide, so maybe I should be looking at 3.55

[TheUnforgiven]

3.55 would be your best bet, as 33's are only 2 inches over stock height=not a huge difference.

[Alvin in AZ]

Originally Posted by ssommerfield

...like to get at least 65 on the highway so I'm not a traffic hazard.
...tire is 33 but only 10.50 wide, so maybe I should be looking at 3.55

I like the ratio you picked out first the best, but yeah, try out the 3.55 for
cheap? :)

Got 3.55 with ~31.5" tires on the Bronco and 3.50 with the same diameter
tires on the pickup ('75 F150 360FE+T18) and that 3.50 gearing is real good
everywhere except the freeway where it seems a little low geared but ok...
it'll pick 'em up and put 'em down when I need it to. 65mph is good with the
Bronco or pickup in 4th. That's why I say I think you'd be happy with 3.73.

---------------------

What's your elevation there now? You're used to sea level performance and
you can kiss that goodbye. ;) I live at ~3600' and don't have to go far in
any direction to hit 2500' to 5000'.

There's a formula for how much horsepower you lose per foot of elevation.
...it ain't pretty! ;)

Alvin in AZ

[777_bronco]

hey guys, i know its a really old post but i am planning on doing some regearing to my 89. it has 3.08s, C6, 351w and 32s for the moment. want to get 33x10.50 or 12.50 later and am in the process of collecting all the parts for it. i have found a 8.8 with 3.55s from a 96 bronco and from what i read above, it seems it would be easier to swap in the axle instead of regearing. correct? also found a dana44 ttb from a 95 bronco with 3.56s, now heres were i am confused. those gears should work fine together, right? and from what i understand it is easier and cheaper to just swap the third members. oh and i do around 50/50 highway and offroad.

[Bronco83]

I have a C6 with 4.10s and 32's on the highway the rpms are a little higher then I would prefer, but in town they're great.