Ok, folks, I've been doing some research with regards to gearing since spring is hopefully just around the corner and I might finally get something done with the Bronco.

In my quest for information I discovered something rather intriguing and perhaps others already know this and I'm just now catching up. (I rode the short bus). I will be swapping from an E4OD to an M5OD. (Don't beat me up about going to a ZF I know, I know). The OD gearing in the E4OD is 0.71:1 which would kill my passing and climbing power if I went from OEM size tires to 33's dropping rpm's by nearly 200 with 3.55:1 axle gearing. However, and here's the intriguing part, in doing the arithmetic I discovered that with the taller OD ratio of 0.80:1 in fifth gear of the M5OD, I could swap to 33's and only gain about 35 rpm and KEEP the 3.55:1 axle gearing! I know the math doesn't lie but my question is, "What am I missing?" or "Am I missing anything that would make this a bad idea"? "What do I do with a perfectly good set of 4.11 gears for the Bronco"?

Better yet, I am looking at this as a good thing since the more I think about it, the more I think I would rather run 35's. Going to 35's and doing the tranny AND gear swap puts me about 185-190 rpm higher than stock. This I could live with since more rpm on the bottom won't bother me at all for torque development. I welcome questions, comments, concerns etc.

 

grey,
The M5OD is a very week tranny. ive seen this tranny fail behind a 300-6 after being rebuilt 2 different times and the truck was used for in town driving an occasionally towing a contractor trailer. you will sacrifice a great deal of realiability if you go this route.

now what your missing regarding the gearing is also the weight of the tires and what it takes to turn that weight. my bronco weights 6200-6500lbs and with the E4OD,5.8, 35" bfgMT's and 4.88's i am running 2000-2200rpms at 65. in town driving my rpm rarely exceed 2000rpms. i still maintain 12mpg in town.
so whats wrong with the e4od? is it needing rebuilt or are you just tired of driving an auto?

 

My experience with the E4OD? Well let's see, I've replaced TWO in two Bronco's at approximately the same mileage. The one that I have right now is the reman from Greystreak and it's getting goofy now too. One of my best friends has replaced TWO in the same 97 7.3 Superduty. Far too temperamental for my tastes and because it was so poorly designed from the get go. (Transmission guys will tell you that if you have an 89-90 model that needs rebuilding, you can't even re-use the casing because Ford had to redesign so much of it after the initial release) The remanufacturing costs are so ridiculously high by comparison to ANY other automatic that I'll take the need to replace a clutch every once in a while in place of the headaches the E4OD presents on a very predictable basis. The E4OD can be a doorstop or a stage weight in my opinion and serve as well as it does after a few years of driving it around.

I have a freebie M5 and if it fails I will hunt down a ZF or 435 before I put another E4OD anywhere near my Bronco!

 

Thats funny. My stepson has built many mud trucks with lots of motor and lots of tire and he says the E40D is the preferd trans because of strenth. My current Bronco has one and its in need of rebuild. I havent heard about not useing the caseing. I'm going to have to do some research. I use to have the AOD and rebuilt it once in 300,000 miles. Everybody says it's junk. I guess its just luck.

In any case, if your going to have slightly more rpms than stock, (at the engine) I think you will be happy. With a 302, I dont think you afford to have any decrease in engine rpms. (unless its really built up)

I'm not fermilluar with that tranny, but it must have a really low first when running stock tires.

In any case

 

Personally, I rather have the ZF for the heavier duty tranny that it is but I also like shifting gears over slush boxes of any kind. I think gearing would be your best bet, and with the numerically lower overdrive you could use numerically higher gearing yet than the M5OD.

 

grey the problem with the m5od isnt with the loosing a clutch. its with the internals going boom while going down the road especially with insufficent gearing and larger tires

now the 89-92 e4od's were junk it wasnt till 93 that ford figured this out and some still had problems but if you dont have a good tranny guy that knows the e4od you might as well do it yourself and hope for the best. i agree its very very expensive but its a proven tranny if built properly. it sucks that we dont have more options so i feel your pain.

 

I suppose I will have a closer look into the ZF before I do the swap. Even so, the ZF overdrive gearing is still up at 0.76:1 by comparison to the E4OD's 0.71:1. But the math is a bit more favorable with rpm's climbing only about 100-110 over stock if I go for 4.11's and 35's. I appreciate the input, guys. I always told myself that if I went for a ZF I was gonna find a stronger t-case to follow it around so maybe I'm just gonna go for broke.

 

IMO all 302 trucks should have been equipped with minimum 3.73 gears from the factory, that motor makes better power further up the tach so it should be geared appropriately. If you want the same old just enough power to get around performance then 4.10's will do, but why settle for that when you could have better, go 4.56 or 4.88, it won't hurt milage anything worth talking about, your transmission will last longer, and the truck will perform better as you open up the motor with some performance goodies.