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Rebuild 4 Speed And Installing Lsd


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Hey folks. I wanted to ask a question to see what path to take next for my 2002.

Is rebuilding the 4 speed and installing a LSD stupid? I have looked into a 5 speed conversion but don't think the extra cost is going to warrant that, especially given that I plan to just use this car for rallycross and occasional fun runs. So, then I figured I'd just rebuild what I have and install the LSD (I want this real bad).

I found in this document that "The 3.64 limited slip is nice for 4 speed 

2002’s and the 3.9 is preferred for 5 speed cars."

What else is involved in mating a 3.64 and 4 speed gearbox?

Thanks for your input guys.
Edited by Marshizzle
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Hey folks. I wanted to ask a question to see what path to take next for my 2002.

Is rebuilding the 4 speed and installing a LSD stupid? I have looked into a 5 speed conversion but don't think the extra cost is going to warrant that, especially given that I plan to just use this car for rallycross and occasional fun runs. So, then I figured I'd just rebuild what I have and install the LSD (I want this real bad).

I found in this document that "The 3.64 limited slip is nice for 4 speed 

2002’s and the 3.9 is preferred for 5 speed cars."

What else is involved in mating a 3.64 and 4 speed gearbox?

Thanks for your input guys.

 

you want better accel for fun and rallycross?  put a 3.91 in it.   

3.64 is only "better for 4spd" because 4spd has no overdrive.  other than that it is all negative.

 

are you rebuilding a 4spd yourself?  the 5spd conversion is probably cheaper if you are paying someone to rebuild.

 

what else involved in mating 3.64 to 4spd?  nothing.  any of the diffs bolt to the end of the driveshaft regardless of transmission.

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If you think 5-speeds are expensive, wait until you try to find a 3.64 LSD. As I understand, they are quite a bit more rare than the 3.91 LSDs. The 3.91 will give you a bit more jump off the line compared to the 3.64, which might be important if you're rally crossing. The other nice thing about sticking with the 4 speeds is that you can keep picking them up for peanuts if you grenade one. 

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I like my 3.91 LSD paired with the E21 5 speed.  Not too buzzy on the highway.  Good acceleration.  Car had better response during the last Autocross session in NC (than the previous one in MD with my old open 3.64).

 

The 69 will retain a stock 4-speed and 3.64 diff (the one removed from the tii).   I too would like to have a 3.64 LSD eventually.

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you want better accel for fun and rallycross?  put a 3.91 in it.   

3.64 is only "better for 4spd" because 4spd has no overdrive.  other than that it is all negative.

 

are you rebuilding a 4spd yourself?  the 5spd conversion is probably cheaper if you are paying someone to rebuild.

 

what else involved in mating 3.64 to 4spd?  nothing.  any of the diffs bolt to the end of the driveshaft regardless of transmission.

 

Alright, so I'll be on the lookout for a 3.91.

 

I was thinking of rebuilding the 4 speed myself (although I've never done it I have very competent friends who have), but maybe I should just get a good 4 speed and change the seals? I'm not looking to sink a lot of money into this car right now, but it needs a refresh before I rallycross it more than I already have.

 

Great to hear about the mating. I was worried that I'd need a new driveshaft and all kinds of custom work.

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The 3.64:1 is the stock ratio for a 68-75 2002.  The 3.9:1 came in the 76 2002.  I have been running a 3.64.1 with Lsd behind a 4 speed in my 72 TII for the last 36 years with no problems.    G

To clarify, the U.S. 49-state versions of the '76 cars came with a 3.90:1 open differential having a 39/10 ring/pinion combo. The 3.91 LSD from the e21 cars are 3.91:1 having a 43/11 ring/pinion combo.

Having spent years with a 4-speed, 3.90 car, it's great up to, say, 70 mph. Above that, it's busy! If my use ever changed back from weekend drives to interstate cruising, I'd probably move to a 3.64 diff before a 5-speed: the former is a largely a plug-and-play swap, the latter modification is more nuanced (as the '02 was not originally fitted with an O/D 5-speed) and requires massaging the driveline tunnel (which I object to on my un-molested example).

Steve

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Find a working 4-speed and put new seals in it (if it even needs them), the parts to rebuild (if anything needs replacing) are incredibly expensive, especially since a moderately well cared for getrag will run forever, you can pick up used ones for $50-$75, trying to rebuild one will cost you as much as converting to a 5-speed.

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