KenRudd

I am considering swapping my 2.20 R&P set out for a 2.73 R&P in my '86

The 2.73 R&P set appears to be part #928.302.911.55 based on G28/10 specs.
Is that part the only difference between the G28/10 ( Euro) and the G28/11 (US/Canada) transmission?

A used G28/10 #928.302.911.55 set is hard to come by in the US, and new is prohibitively expensive. Can we confirm which earlier or later versions are compatible? That would broaden my used parts pool:
G28/05 #928.302.911.26 (80-82) ( reliable source says this will likely work)
G28/07 #928.302.911.27 (83-84 Euro)
G28/55 #928.302.911.64 (88-91)
G28/57 #928.302.911.68 (92-95)

I've read the WSM procedure on Ring and Pinion Replacement, so I am aware that it is not a simple bolt in process. I'll take it to a pro for the actual swap, but does anybody have any experience with this and any useful information?

I have read Schocki's related thread. Unfortunately, all the picture links are now dead.

GlenL

I'll let you judge the usefulness...

Check a PET to look at pictures. The pinion gear is not replaceable as its own component. It is a single piece that includes the transmission main shaft. This means replacing the pinion gear requires a complete rebuild of the transmission. Or a near complete one.

I recently swapped trannys on one of my Euro S cars from a 2.73 to a 2.2 final drive. The difference is really noticeable. You might think it mean shifting 2.73/2.2 later (and it does) but the final drive really moves those points down. Now I want to cruise on the highway in third and grab second to pass. There are other gears involved in going from a G28.05 to a G28.11 but the change was remarkable.

Ya know... Since these transmissions are very different I'd be skeptical that the swap is doable. If you want a more sporty transmission, maybe find a G28.05 and and swap it in. It's a direct swap except for one tranny mount. See this post and thread: http://reutterwerk.com/forums/showpo...&postcount=112

KenRudd

Glen-

I appreciate the input. Yep, I can see what a PITA the R&P replacement is. I read the WSM on it and it made my skin crawl. It will be farmed out. The current status is that I have an LSD that I will be installing anyhow, the transmission is already out, and some of the R&P alignment work will need to be done anyhow, so if I want to swap, now is the time. I don't really want to go with a G28.05, as that uses the Porsche Syncho instead of the Borg Warner.

If it turns out to be too much of a hassle, I will keep the 2.20, and I may go back if I hate it, but now seems like the time to try.

GregBBRD

The immediate, obvious differences make this job "not user friendly". By the time you are done rounding up all the pieces required and paying for the machine work to accomplish this task, a G28/10 ring and pinion is going to look like a relative bargain.

The G28/05 transmissions have a non synchro reverse gear which is engaged by moving the idler gear. Reverse gear is splined and fits on splines on the pinion shaft. It has the retaining nut for the "gear stack" just behind the pinion bearing (the pinion shaft is threaded near the pinion bearing for this nut.) There's a circlip at the 5th gear end to retain the remainder of the gear stack.

The G28/11 transmission has a synchronized reverse gear which is engaged by a slider on the pinion shaft. Reverse gear, on the pinion shaft, is not splined, but runs on a needle bearing, because of this different design. The idler gear, for reverse, is in constant mesh. The entire gear stack is retained by a large nut near 5th gear (so the pinion shaft is threaded for this nut at the 5th gear end, not by the pinion.)

In short, the pinion shafts are not a similar design and the entire way 5th gear "functions" is completely different.

Anything is possible....and someone claimed that they had accomplished this task. (Sterling?)

Every time I've looked at the practicality of doing this conversion, I've ended up shaking my head and asking, "Is this going to be worth all the work to accomplish this task...when you can buy the correct part?"

Probably not.

Have you thought about finding a complete used G28/10 in Europe and having it shipped over?

mark kibort

i have to ask...... why?
Glen says the differneces are noticible, but it depends on the speeds you usually travel at and when you "pass a car" do you always pass from 40-50mph or do you pass from 55 to 66, or do you pass from 65 to 75mph...... depending on that answer the 2.2 might be best, OR the 2.75 might be best.

NOW, (glen read this please) if you are only changing the ring and pinion, you change NOTHING, except for getting a super LOW 1st gear.... the rest of the gears actually are almost the same, except for 5th , which would be much higher reving for the freeway speeds , and a closer ratio to 4th. aside from those two differnces, there is really no reason to swap out the rear end

the difference of 5th is 24% vs the 2.73. this means all gears are shifted 24% lower, and since the gear spacing for the 2.2 is already near 25% per shift, what did you acomplish?? nothing!!!!!!!
(excpect an unusally low 1st gear and a higher reving 5th)

so, in the end, there is NO logical reason for doing such a change, unless you are Glen and you like being at 4000rpm at 60mph in 2nd vs being 4000rpm at 60mph in 3rd.... (as a rough example) both cars are at 60mph and running 4000rpm.... does it really matter what the numerical gear name is??

hacker-pschorr

Jim Page and Twin Turbo Todd installed a 2.75 R&P from a 78/79 gearbox into an 87 S4 transmission.

So yes as Greg said anything is possible, it was far from a "bolt in" upgrade. I've talked to Todd about making another one for my 79, but he's far too busy at the moment.

Jim wanted to maximize the user of 5th gare (1:1 ratio) at Road America. With the 2:20 box he almost never used 5th.

Mongo

Although not related but why has no one attacked the ring and pinion market for 928s? I remember I wanted the 3.09 gears that came out years ago only for them to have completely disappeared. Why not aftermarket options for all cars looking to go to a 2.54, 2.73 and even 3.09?

GlenL

NOOOOOOOOOO!!!!!! MAKE HIM STOPPPPPPPP!!!!!!

GlenL

Because there's really no market for them.

Schocki

Here are some pictures.....

GregBBRD

Yes, if it was an automatic, the change is much easier.

The manual transmission is much more difficult.

GregBBRD

Thank you. Todd is who I had heard had done this. And when Todd says it was "tough"....that's a mouthful!

GregBBRD

I find first gear to be very "tall" and personally really enjoy the "shorter" Euro transmissions.....especially with engines that develop less torque at the lower rpms. Plus, anywhere in the higher rpm range in fifth gear is virtually unobtainable on any American highway (or almost any American racetrack.)

When I developed my latest set of headers for the 2 valve engines, my first set went on a true '85 Euro. With the combination of getting almost the same rear wheel horsepower than the car came from the factory with at the flywheel, plus some extra low end torque, plus the increased "breathing" at the higher rpms, and the shorter European transmission, I found that vehicle to be one of the most fun 928s I've ever driven.

Actually, that single "experience" with that Euro has completely made me rethink my engine configurations.

I agree it is probably a waste, when the low rpm torque is radically improved (like with a stroker).

I think that about 99.9% of the 928 population would enjoy a shorter ring and pinion.

KenRudd

I'm trying to parse out exactly what you are suggesting:
1. The "non-G28/10" ring and pinion ( Like a g28/05 )is not worth the effort, or;
2. Even a G28/10 Ring and Pinion is not worth the effort to put into a G28/11, or;
3. A G28/10 Ring and Pinion will work.
4. The only real choice is a whole G28/10 assembly.


I _think_ you mean #2

KenRudd

And to sort of answer Kiborts question "why": My current launch out of turns sucks with my existing open diff, so I am putting in an LSD. And since I already deep into it, changing the ratio may make sense.
Clearly, the Euro G28/10 2.73 is very drivable, and since the following are low priorities in this car
-Fuel Economy
-Highway noise
-Emission standards

I'm trying to find out how much time/hassle it would add to the LSD swap to also go with a shorter rear end.

If its not worth it, I'll stick with the 2.20