Mongo

Years ago I put a thread up on thoughts of swapping ring and pinions out, but the thread was inconclusive and closed.

Looking through the archives, I have seen both Shocki and Speedtoys have done some ring and pinion work on their cars. However, Schocki's pictures have disappeared into the netherrealm of Photobucket never to be seen again.

Rather than doing a massive transmission/drivetrain swap to a 4L60E from a C5 Corvette for shorter gears, what about just dropping a matched 2.75 (or is it 2.73) ring and pinion from a pre-1983 928 into the S4's differential?

I have read that shimming is required to compensate for the lash of the change, and that automatic transmission ring and pinions are not as difficult to service as much as a manual car.

I would like to hear from the great minds on the board about this as I really want shorter gearing in a car I use more for cruising on the weekends than commuting.

I'm no transmission expert by far, and I'm sure I will be taking the transmission to a Mercedes expert given its origin when that time comes to do the swap.

However, I do know that the shafts for the 2.73 pinion and 2.20 are a little different in OD, 2.73 being 92mm and the 2.20 at 100mm. What I don't know is what are the other specs, dimensions, and how both R&Ps compare.The difference in diameter worries me and could be detrimental to this project, or even makes it impossible to do entirely without dropping serious amounts of money.

I have located the following table below from the archives to assist in obtaining additional information. What else would be involved besides shimming?



Thanks!

Mongo

Aside from the fact it would probably be more practical to find a G28/16 (or A28.16) and dropping it in, I just want to know if the R&P swap can be done.

GregBBRD

The chart you have posted is for manual transmissions. Your thread title says '87 auto, so there would not be any useful data, in that chart.

The pinions from the 3 speed automatics do not transfer into the 4 speed automatic transmission cases...completely different design.

You choices are to use the ring and pinion from a Euro 4 speed (2.36) or the ring and pinion from a Swiss option Euro transmission (2.54.)

Swapping requires set-up of the internal end play of the transmission, pinion set-up, differential preload and differential backlash. These operations will be completely foreign to any Mercedes transmission expert, as these operations were not required on any Mercedes version (separate differential) and are frequently messed up by these transmission rebuilders.

Mongo

Yikes. In the end an A28.16 swap is the better way to go and cheaper too. Thanks for the reply and info.

mark kibort

one doesnt get the other.

the gears are all different internal, so you end up with near the same with a super 1st gear and then just a lower ratio 5th.

the real question is what do you want to achieve. can you articulate?

Mongo

I was looking for a little bit more acceleration by playing with the final drive. And I don't have a fifth gear as I have an auto. I will wait around for a nice 2.54 gearbox to pop up.

mark kibort

I know you have heard it before, but the acceleration will shift around the speed ranges you will target. It's not for all speed ranges. we raced the auto in lemons. it was pretty optimal any lower gearing would have hurt the area that we needed the most amount of acceleration. the gear spacing really was the problem and that doesnt change with the rear end change alone

PorKen

A shift kit helps. On my '86.5 auto I went with an 'extra-firm' K1 spring which makes it rev higher before shifting 2-3, helping to fill the 2-3 ratio gap. (The other two I rolled 'normal-firm'.)

Install pics - https://rennlist.com/forums/928-foru...l#post11536836

GregBBRD

I have a factory new Swiss Euro, in inventory, with limited slip. Complete from the bell housing all the way to the oil pan. Even has the wring loom. It is the 1985 version....so it has the higher stall converter, also! Turns US cars into virtual rockets, in comparison to the stock US transmissions. (I don't know what Kibort said....but I'm betting it is about gear ratios and we've heard his ridiculous theory a dozen times before....so you can ignore him, regardless.)

$5K exchange, if your transmission has a limited slip. $500 more if your core doesn't have a limited slip.

You will not find a used Swiss transmission with limited slip and rebuild it for anywhere near that....

Glen McCartney

I can attest to that, I installed one in my '85, totally different car!

mark kibort

Greg, if you don't understand what i was talking about, it can be discussed here.

https://rennlist.com/forums/928-foru...l#post12768029

Mongo

$5k is pretty steep and I would go the route of a 6-speed C5 T56 conversion, or heck even do the first 4L60E (C5 Corvette Automatic) paddleshift 928 on this board for that money.

I think the 2.54 swap of an A28.16 from an '89 car would be more practical.

dr bob

Andy--

How much do you think you'll have in a R&P swap for a 2.54, installed? How far down the road is the trans in your car now?

The offer Greg made is golden for you, as you get the ratios you want, the higher stall-speed converter, all new. Vs the 100k+ box in your car. old seals and pistons, worn clutches and bands, torque converter bearings etc. $5k may be more than you initially had in mind, but it's far from "steep". Search a little on 928 transmissions rebuilt by M-B experts. My memory does not include a lot of happy experiences. Glen M will share his experiences, and how the GB deal turned out to be better than several attempts at a local rebuild.

Mongo

My transmission is still good *knocks on wood* and should give me another 40-50k as long as I keep religiously maintaining the fluid in it. The shorter gears would be more of a novelty. There are too many projects that take priority over a transaxle swap at the moment and I am trying to pace myself. If I had the cash available, I would be sending GB a paypal right now rather than typing this

mark kibort

do a comparison of the 2.75 on a 2.2 US auto and the gears naturally of a 2.54 auto. you will be surprised of the overlap and the net effects. However, it would be nice to have that super first in the 4 speed.