What gears

[20003.8stang]

Hey I'm doing a m112 build on my 2000 3.8. Automatic. I bought a 8.8" Axel and I am going to rebuild it and put new gears in it. With the build I'm doing and the automatic what gears do you think I should go with? I was thinking 3.73, 3.90, or maybe 4.10 but 4.10 may be too much in my opinion.

 

[Echonan]

Someone else with more experience with the autos should probably chime in but it's my understanding you don't want to go with too short of a gear especially with that type of boosted setup because you'll run out of gear too quickly. I've heard some people say 4.10 is too short for that kind of blower.

 

[20003.8stang]

I've heard other people say that to so would a 3.73 or 3.90 work better? Also what brand or gears should I go with? Are the ford racing ones on American muscle good?

 

[Jesse01V6]

I would agree that anything more than 3.73's with a blower is not a great idea. Unless its a race car and you have the rpm's figured out that you would go through the traps at.

 

[20003.8stang]

It's a daily in the summer so I will probably go with 3.73s! The 8.8 has 3.27 I believe. So is are the ford racing gears good?

Thank you guys!

 

[20003.8stang]

What would be a 28 inch tall tire like a 275/50 17?

And I heard if you go to a 3.73 or higher you have to grind down the cross pin or replace it with one ment for a 3.73. Should I grind or replace it and how do I grind it or where do I find a replacement one

 

[Phil II]

No! Do not grind the cross pin! Who told you that bs?

The cross pin in your differential may very difficult to remove if the carrier was subjected to a lot abuse without adequate lubrication. At that point its better to use a different carrier and pin. Maybe, maybe a machine shop could make it right.

Ford Racing gears are the best quality, as they are made to oem spec. American Muscle is only a retail distributor. Search by the part number, shop wisely.

Fwiw, I am using a stock 3.27 gear set and prefer how much more useful each gear is. I'm also driving a 5 speed, so it's apples and oranges.

Use the tremec gear ratio calculator and check the tire height as listed by the manufacturer.

 

[20003.8stang]

It was on another forum.

 

[BRN2RUN]

I've used Ford Racing 3.73's and 4.10's (currently have the 4.10's in the car), and the 4.10's feel much stronger off the line, and the highway revs aren't much higher than the 3.73's in my auto. That's for an N/A build--to put it in perspective, on my T-Bird with lots of modifications and lots of blower overdrive (15+ psi), 3.27's (auto), I don't think I'd go much higher than that, because you're going to have some severe traction problems with the low end torque in the M112.

 

[Jesse01V6]

Why do you want a 28 in. tall tire? That is nearly 2.5 inches taller than the factory height tire. That will make your 3.73's seem more like the stock 3.27's...... Whats the point?

Oh and BTW.... its easy to convert metric tire sizes to inches and find the height......

Example.... for 245/45/17

245mm multiplied by .45 gives you your side wall height of 110.25mm

110.25mm divided by 25.4 (25.4mm in every inch) is 4.34 in.

4.34 multiplied by 2 (top side wall and bottom sidewall) is 8.68 in.

8.68 plus 17in. (wheel diameter) 25.68 in total tire height for a 245/45/17

 

[20003.8stang]

I was only going to do the 28" if I went with 3.90s and it proved to be to much. Thank you guys for all your information! This is the first time I've used this site and it was very helpful! I'll be ordering the ford racing 3.73 soon along with 8.8 rebuild kit And lsd rebuild. I'm sure I'll have more questions as the build goes on!

 

[Jesse01V6]

^^^ if you do that, make sure you use the 28 spline specific 'S' spring, not the 31 spline one that comes with it...... unless you have a 31 spline diff and axles.

 

[20003.8stang]

You mean carbon discs for the limited slip?

 

[20003.8stang]

So you mean reuse my s spring from my 8.8

 

[Jesse01V6]

Or buy a new one from Ford, they're cheap.

 

[Joel Maxwell]

If you're throwing an m112 on there, you may just keep the 3.27s. You'll be chriping the tires hard with a jmod on the transmission alone with that blower. 3.55s are the highest I'd personally go.