So GET THIS trying to find a Rear 7.5 axle with a 3.08 ratio!!

[OilPatch197]

Junkyard had nothing close, NAPA said I would have to get it from Ford($$$!) and AutoZone can get a USED set for $500!!!!!!!

WTF! So it looks like I'm just going to have to use the gears I have, and get the backlash and contact pattern correct.

BUMMER.

So a couple of questions, I understand the crush washer, but what if I need to adjust my ring side to side? How do I do that on a 7.5? What do I shim, and more importantly, where do I get the shims?

 

[mongoose289]

check on car-part.com there is a few on there

 

[MAKG]

3.08s aren't that hard to find in a junkyard, though why you would want such a thing is beyond me.

Randy's (differentials.com) has a nice writeup on how to set up rears, but I really don't suggest going there unless you're very anal about details.

 

[OilPatch197]

though why you would want such a thing is beyond me.

because I want to save gas by keeping things OEM, right now I got a 4.XX in it, and it's turning extra rpms and gulping the gas.

If I post pictures of the condition of the gears, can you guys tell me if they really need replaced?

Again I got water into this axle, ruined the bearings, so I replaced all the bearings only and I am thinking that maybe I don't have enough preload on the pinion....but I'll tear it apart and give ya some pictures of the damage, and then you can tell me if I can still use them, does that sound good?

 

[MAKG]

You're overdoing it. If this is a 2.9L, it is going to EAT gas below 2000 RPM, and drive like a limp d**k.

It just ain't so that lower RPMs are always lower fuel. In particular, modern drivetrains sometimes push that too far.

 

[Dishtowel]

I think going from 4.xx ratio down to 3.08 would be incredibly foolish, you would be sacrificing overdrive, and no longer comfortably running in your powerband. Try a nice 3.73, unbelievably easy to find.

 

[Sevensecondsuv]

4.xx is probably a little much. But 3.08 is too low for anything but a 2wd 4.0. You'd probably be best off with 3.55 or 3.73 depending on engine and tire size.

My 4.0 went from 16 mpg to 19 mpg when I swapped from 3.27 to 3.73, and that was with 31" tires.

When it was naturally aspirated, my 2.3 went from 23 mpg to 27 mpg with a swap from 3.08 to 3.73. Plus it was actually capable of pushing the truck with 3.73s, which was something it sucked at with the 3.08s.

And 3.08 7.5s are worth nothing. I tried to sell mine for 50 bucks when I took it out. After a month and no interest I just scrapped it.

 

[Mac]

You're overdoing it. If this is a 2.9L, it is going to EAT gas below 2000 RPM, and drive like a limp d**k.

It just ain't so that lower RPMs are always lower fuel. In particular, modern drivetrains sometimes push that too far.

You go too high a gear and you may never see fifth gear. If I had a 3.08, I'd give it to you. Had a 4 banger with the 3.45 and it had a hard time in a little wind, up a slight hill on the interstate.
Dave

 

[Sunk]

There is a reason your truck came from the factory that way. I'd try to keep close to what it was.

 

[triumphrider-1]

+1 to what MAKG says, 3.08 will not improve the gas mileage. I had 3.55s in my old 1990 and usually got around 25mpg.

 

[OilPatch197]

No, no, if you read the other threads, it origianlly had the 3.08, I stuck a 4.xx in there because of the concern that the original axle assembly would fail, I had a spare so I stuck it in to keep it going while I fix the original axle.. It got 19-21 mpg with the original axle, and that is good for a 2.8 with a C-3 auto. With the 4.xx axle I'm getting hardly 11mpg. So I want to fix the 3.08!

 

[85_Ranger4x4]

If you have a C-3 = no overdrive, so you have to play by the rules of yesteryear where you make up your lack of transmission gears with high differential gearing.

 

[Mac]

Sorry but the only info we were going on is the info in this thread. Still think you might get better by going with a lower gear.
Dave

 

[Aragorn]

i've a got a 7.5 with 3.45s in my backyard if you want it. only 50k some miles on it. i'm in florida

 

[Hahnsb2]

Find some 3.45, I think 3.08 is too high even without OD.