Has anyone ever changed the differential ratio (ring and pinion gears) in a PSD automatic transmission? I'm considering such a change and would like to communicate with anyone who has done this. Send me a PM, e-mail, or respond to this if you would.
Thanks,

Gary Knox

 

5sp or automatic, factory ring and pinion gear pair or custom parts?

 

Looks like you have an auto from the avitar.

What is the goal for the ring and pinion change?

mk

 

I asked about this a while back and for a 5-speed it would require a lot of work because the rear pinion is 5th gear, or is on the same shaft as 5th or something like that. I believe on an auto all you would need to do is change the rear pinion gear, possibly not even requiring a transmission removal?

Dan
'91 928GT S/C 475hp/460lb.ft

 

The automatic the pinion gear is bolted to the trans output shaft....the large bearing that locates it is the same. So it appears that it "should" bolt right in. The advantage being the 2:20 ring and pinion lowers the RPM per mile ups the potential top speed....

 

All 4sp pinions work in all 4sp gearboxes AFAIK. Ring needs to be for later style diff. IIRR first 4sp automatics still used old style diff. Also ring and pinion needs to be pair meant to be together.

 

Garity at Motorsport SLC did mine. Swapped the ring and pinion from an 88 into my 90.

 

The question was did the PSD box ( computer controlled limited slip ) accept the earlier ring and pinion..... it seem that it does !

 

FWIW to remove a differential from a Auto box the rear Xmember has to either be lowered or better yet removed so the lower edge of the diff housing will clear the top Xmember. Trans box can stay in the car however it must be supported.
For a 5 speed the trans/axle must be removed that also includes either dropping or removing the Xmemeber

 

Why wouldn't it. If change could cause problems they could only come at speeds where revs run out at top with original diff. Up to that point PSD behaves exact same as it doesn't have any connection to engine management AFAIK.

 

Erkka, et al,
The GTS is an automatic, and I would get ring/pinion gears from an '87 or '88 automatic. Looking to reduce engine RPM's, for the great "touring" driving of the early S4's, with the added torque/HP of the GTS. In my opinion, for my driving, (real OLD dude)this would provide the best of both worlds!!!
Thanks for this and any other info anyone has. Haven't pulled the trigger yet, but am giving it serious consideration.

George, Garrity, and Mrmerlin - any further info you can give on the process would REALLY be appreciated. THANKS.

Cheers, as well as a Merry Christmas and Happy New Year to all.

Gary Knox
West Chester, PA

 

ah, interesting. Talk to Shocki, he's also planning on doing this on his 1992 GTS. If it solves the humming of the differential in his GTS, I will try the same I think. Both our GTS have the same issue: humming soudn at part load at 50-60 km/h
So replacing R&P is thought as a solution, not particularly to change the ratio.

 

I hand delivered his ring and pinion 2 weeks ago

 

Hi Mark,
so it can't be long before results come in

 

Swap isn't hard at all if one is familiar on how to set up diff bearing preload etc. Only real down side is that all other gears are messed up too unless entire gearbox is changed. Both automatic and 5sp 2:20:1 diff use totally different gear ratios on all other gears too to correct taller diffs effect on each lower gear. In reality 4sp automatic has 1st, 2nd, 3rd and 5th and 5sp has 1st, 2nd, 3rd, 4th and 6th. They are basically ideal for both acceleration in smaller gears and long legged cruising speed no matter what Kibort says.

By replacing just ring and pinion end result is in automatic boxes case gearbox which has in effect 2rd, 3rd, 4th and 5th but is totally missing 1st gear. I think in the end very few people are willing to trade 1st to 5th even though 5th would be nice to have in automatic. I would at least try out first by modifying stock box in a way that it always starts with second and never changes down if that is somehow easily doable. This would allow simple test for few weeks to see what its really like to live with bad sides of such setup where no matter how deep pedal is pressed box will not change down to 1st.

I bet swaping in entire '87-88 US model automatic box except PSD diff would be better solution. Such swap is basically same job as swaping ring and pinion only to GTS box and I would expect end result to be much better.