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RARE!!! OEM 10.25 ring and pinion 3.08 gear set

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Ford F834

RARE!!! OEM 10.25 ring and pinion 3.08 gear set

Administrator

This is a closed group, but I can pass a message on to Brian if anyone is interested. You sure don’t see these every day. I’d seriously consider this if I was running a D44 front axle, but the tallest gear that fits a D60 is a 3.31.

SHORT BED 4-DOOR DIESEL: 1986 F350 4x4 under construction-- 7.3 IDIT ZF5+GVOD

STRAIGHT SIX 4X4: 1981 F150 2wd to 4x4-- 300 I6 close ratio diesel T19, hydroboost brakes, Saginaw steering

BIG F: 1995 F-Superduty under construction— converting to 6.9L IDI diesel ZF5+DNE2

Gary Lewis

Re: RARE!!! OEM 10.25 ring and pinion 3.08 gear set

Administrator

3.08's would work with my T19's 1:1 4th, but I don't think I'd want them with the soon-to-be ZF5.

Let's see, 3.55's give me 2500 at 65 MPH with the T19, so 3.08's would give me 2168 at 65 MPH. But, I'll have 1900 at 65 MPH in 5th with the 3.55's, and 1650 with the 3.08's. That's a bit low for an F250, but might be nice with an F150 w/a 300 six.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

Dyn Blin

Re: RARE!!! OEM 10.25 ring and pinion 3.08 gear set

In reply to this post by Ford F834

Hmm, That would take the RPM's even further down (2200?) for the interstate runs on my NP435.

Sonoma County,CA
1982 F150 Flareside XLS
NP435 4x4
351W Motorcraft 2150

Gary Lewis

Re: RARE!!! OEM 10.25 ring and pinion 3.08 gear set

Administrator

Dyn - Your truck probably has a 9" - unless you've swapped a 10.25 in. But, you can get equivalent gears for a 9" easily, and probably less expensive than these since the 9" is so common.

Gary, AKA "Gary fellow": Profile

Dyn Blin

Re: RARE!!! OEM 10.25 ring and pinion 3.08 gear set

Thanks for the Clarity, Gary. Yes, I have the original 9. I got excited for another RPM reduction.

At some point I should likely start looking for a 5 speed to swap if I continue to make these longer trips that I never originally intended on taking when I got the truck.

Sonoma County,CA
1982 F150 Flareside XLS
NP435 4x4
351W Motorcraft 2150

Gary Lewis

Re: RARE!!! OEM 10.25 ring and pinion 3.08 gear set

Administrator

Given that yours is a 4x4 it'll cost 2x to change the diff's. So a 5 speed might be a better choice, as you said. Most have a wider range of ratios.

Gary, AKA "Gary fellow": Profile

Ford F834

Re: RARE!!! OEM 10.25 ring and pinion 3.08 gear set

Administrator

In reply to this post by Gary Lewis

There was a guy on the diesel board running a 3.08 Sterling 10.25 and he also had overdrive. E4OD .71 x 3.08 = 2.19 final drive. He was getting 25 mpg out of his 6.9 IDI, but I think he was a bit over-geared and he might have gotten even better mileage with 3.55’s. I think 3.08 and a (close ratio) ZF would be a great combo for the IDI, but is at the upper edge of what would work well. I can’t speak to whether the 460 would like it but I’m guessing not so much.

Dyn, I have 3.00 gears in my F150. It feels pretty decent without overdrive, but I am running tall skinny tires and the close ratio diesel transmission that shifts like a true 4 speed (not granny geared 1st). Without the taller tires I think that final ratio might not be quite enough without overdrive, and with a NP435 I think the 2nd gear starts would be pretty rough. I would lean towards a 5 speed as Gary suggested. I like my combination a lot, but not everyone wants to run those wheels and tires, or track down a diesel T19.

Rembrant

Re: RARE!!! OEM 10.25 ring and pinion 3.08 gear set

Ford F834 wrote

I think 3.08 and a (close ratio) ZF would be a great combo for the IDI, but is at the upper edge of what would work well.

I'm running an M5OD 5spd and have a 3.08 (8.8) rear diff, and I'm quite happy with it, but it is knocking on the door of being geared too tall (In the 1988-1996 era, Ford did build 5spd trucks with 3.08 rear diffs, so it's not like it's a custom combination, but it IS tall). I really like it, but I specifically wanted the truck to be geared like that. The 3.08 rear diff was originally behind a 3-on-the-tree with a 1:1 final drive. It is tolerable with my "short" tires...I believe mine are only about 27". My truck is also only 3400 lbs, and has a little extra power, which helps it move along at lower RPM's.

I think a 5spd and 3.08 gears would be really nice behind a 300/6 in a 2wd truck. I would think it would be too tall a combo in a 4x4 truck, one because of the extra weight, but with the usual taller tires on 4x4 trucks, 5th gear would be super tall. Unless of course you specifically wanted the taller gearing for highway use...then by all means, it would definitely be the way to go.

I did see a few guys on Facebook bashing 5spd swaps as useless (and just extra gears to shift), but one of them did later say that he was running a 300/6, with 31" tires, and a total weight of 4800 lbs.

I'm all for 5spd swaps and tall gears, but I think with them tire size selection becomes even more important to keep everything functional.

1994 F150 4x2 Flareside. 5.0 w/MAF, 4R70W, stock.
1984 F150 4X2 Flareside. Mild 302 w/ 5spd. Sold.
1980 F150 4X4 Flareside. 300i6 w/ 5spd. Sold in 2021.
1980 F100 4X2 Flareside. 351w/2bbl w/NP435. Sold in 1995

Ford F834

Re: RARE!!! OEM 10.25 ring and pinion 3.08 gear set

Administrator

Good observations, but I will add that the M5OD has a 5th gear ratio of only .80 so it’s not a very tall overdrive. The math on your gear spread is actually very similar to my set up except I don’t have overdrive, and I’m running taller tires.

I was assuming .76 overdrive ratio (ZF) and 235/85R16 tires which were stock on our 8 lug trucks. (Final ratio of 2.34) When I say it is at the edge of what will work for the IDI, I am basing this off of Justin Anderson’s experience with double overdrive on his rig (ZF + DNE2). He started to see rising exhaust gas temperatures, sluggishness, and no mpg improvement over straight 5th gear without the extra overdrive. So he was past the point of diminishing returns on gearing. That was at an equivalent of ~2.23 final ratio considering both overdrives and his 35” tires. Maybe if he was driving very very fast it would have been beneficial? His truck sits at ~7,000 lbs curb weight, so it is a different world than a 2wd half ton.

Rembrant

Re: RARE!!! OEM 10.25 ring and pinion 3.08 gear set

Ford F834 wrote

Good observations, but I will add that the M5OD has a 5th gear ratio of only .80 so it’s not a very tall overdrive. The math on your gear spread is actually very similar to my set up except I don’t have overdrive, and I’m running taller tires.

Yes, I forgot about the ZF having a little taller 5th gear. I guess the ZF has a lower low, and a higher high, right? I think the M5OD 5spd is a great trans for a light little half ton truck...but it has a bit of a bad reputation for being weak from what I read. Still, I've read lots of reports of guys putting hundreds of thousands of miles on them, trouble free, and Ford did sell a zillion of 'em. Beating on it in an offroad application...it likely doesn't stand up, and certainly not when compared to the ZF5.

I guess the problem with gearing is that people have different needs, tastes, and requirements. All too often, people forget the impact tire OD has on overall gearing.

Lots of guys would hate my truck geared the way it is, but I like it the way it just fine. Maybe something like a 3.25 diff would be an even better balance, but I was in a situation where I wanted to have my cake and eat it too! I wanted decent low end gearing, but I didn't want the thing to be screaming on the highway either. I HATED that 3spd. I've had an NP435 before, and I would take that all day long over the 3-on-the-tree 3spd.

Again, like I said above, I think the only reason I'm getting away with my set-up is the small tires. If I suddenly switched to 31" tires, I think the truck would be geared way too tall.

Gary Lewis

Re: RARE!!! OEM 10.25 ring and pinion 3.08 gear set

Administrator

I agree with what you'se guys are saying. And, saying it another way, you have to start with the end in mind. If you have a light truck, like to cruise, and don't tow "heavy" then the M5OD might be a good choice. It shifts better than the bigger transmissions, and has a more usable gear ratio spread - for those conditions.

On the other hand, if you are going to tow much, or need the creeper gear for off-roading or starting a load, the heavier transmission like the ZF is a better choice. But, you get fewer useful gears for daily driving and you get the big truck "feel" in shifting - meaning you shouldn't expect to speed shift.

Gary, AKA "Gary fellow": Profile

Gary Lewis

Re: RARE!!! OEM 10.25 ring and pinion 3.08 gear set

Administrator

I just had an interesting idea - a spreadsheet that allows you to find the engine RPM at a given vehicle speed given a bunch of variables, like tire diameter, axle ratio, transfer case ratios, and transmission ratios. And, it would have the transmission ratios already loaded.

I know there are lots of calculators "out there", but I don't remember seeing one that already has the gear ratios loaded in for the transmissions we use in these trucks.

It would be a way to let you see what a given setup would do.

So, maybe at the top would be the various inputs, like tire diameter, test MPH, axle ratio, and transfer case. Then below would be a column for each transmission showing the RPM in each gear, including when in 4Low.

What! There is! Driveline/Calculators.

Gary, AKA "Gary fellow": Profile