I have a decision to make. Here's the situation I have now. I'm building a cup car and I have 2 trans with me. One trans is out of a 924S I believe and I bought it from someone in Cali and it's like in excellent shape. It looks brand new. It drives very nice too and it's has a short 5th but the only problem is, it is a open diff.

Now, I have another trans and this one is from a 1985.5 944 with regular long 5th but it has a LSD in it. The trans came with the car I just bought and not 100% sure of it condition. From the outside, it looks rough as it seems like it's wet outside and perhaps leaking???

So to do the swap of diff from the lsd one to the open diff trans will cost 8 hours from a local Porsche shop I just talked to and they want $800 for the job. That's a bit too expensive I want to do now and I'm not even 100% sure the actual condition of the LSD.

Can anyone here recommend me on what to do? Just install the short 5th trans and call it good or continue to use the long 5th LSD trans? Does the 5th ratio make that much of a difference in lap time on most tracks? I would really like to use the short 5th gear trans as it's in excellent condition but it has a open diff.

Thank you for looking...

I did all my DE's and first couple of races with an open diff long 5th! Short 5th is desirable and LSD is valuable as well especially in the rain. Upgrade as your budget allows and don't fret over the small stuff. Tranny swaps are not that difficult. The most time to be gained and biggest performance upgrade is in the SEAT! Time on the track regardless of your transmission will benefit you the most. That $800 dollar price tag is that a re-build as well? If so that's a deal. It won't take 8 hours to do the swap. Short 5th, LSD transmissions were on the market for over a grand so keep that in perspective.

If it were me, I'd choose a short 5th over the LSD. There's a significant drop off the torque curve with the long 5th and we need all the torque we can get!

Steve

Thank you for the reply. I think I will just swap over the good short 5th trans and just enjoy it. I will look for a lsd and short 5th trans later on down the road.

Answer is simple. Swap the 5th gears which can be done in less then two hours without taking tranny out, and use the tranny that now has the lsd and short fifth.

swap 5th just make sure when the rear caps off nobody shifts the trans. coming from experience its a long and tedious process to get it to ever shift again. i have also installed an lsd into an open diff tranny and honestly it wasnt bad at all but i think its easier to install the 5th.

Both the trans is out of the car so I'm about to do the 5th gear swap and perhaps do all the seals again. Is there any special procedure on replacing the seal where you open to get to the diff? Can I just open it up and just replace the seal and close it back up?

the rear plug gets destroyed remoing it to swap the gear. all the seals to my knowledge are just normal seal replacements nothing special