hacker-pschorr

Some of you may remember Todd's twin turbo project:

https://rennlist.com/forums/928-foru...deo-added.html

www.erik27.com/todd


I was at his shop last night and he was working on radiusing and polishing the ring and pinion from his turbo car.
He has spent most of the winter going through the transmission with a fine tooth comb. He has more than a few 928 transmission completely apart studying every aspect of the unit.
I cannot comment on the changes he's implementing to the transmission, he did say I could share his work on the R&P, so here it is.

He has NOT broken a 928 transmission or ring an pinion (yet).
This work is his attempt to prevent failure from putting well over 1,000hp through the drive-train (he also installed higher output turbo's over the winter and has a higher output set waiting in the wings for when he gets those dialed in.....)

Little background for those of you who do not know Todd.
He spends day job as an industrial machinist specializing in metallurgy, he is the "go to" guy for anything out of the ordinary.
As he explained to me, some of the machines in our area he regularly services (paper mill related mostly have very large ring and pinions that he repairs as they fail.

As Todd was taking these apart for repair, he started to polish up and smooth out the gears. As he expected, the service life greatly increased.

So he figured, why not apply that same logic to the 928 ring and pinion before he finds the limit of the stock one.
Todd is funny that way, he would rather not "push it until it breaks, then make it better" if he knows an improvement can be made on day 1.


He has over 40 hours into these two gears alone when I took the photos and he wasn't 100% done with them yet.

The first photo demonstrates how he's doing the polishing. Just a piece of sandpaper tapped over a piece of fat vacuum line.









Comparison to a stock pinion gear:





Comparison to a stock ring gear:

GregBBRD

Wow. Manual labor intensive! Since the pinion never hits the edges of the ring gear (unless there is a ding) and the ring gear never hits the edges of the pinion (unless there is a ding), all of that radius work is somewhat moot....but it sure is pretty! (Is it still winter there?)

Ring and pinion wear was a really extreme problem in the 964 and 993 RSR transmissions....especially when equipped with the smaller pinion that was required for closed course road racing (8 tooth, very small "helmet".)

We had to do special things to these, for them to "live" for tracks that had very bumpy surfaces (the 12 hours of Sebring was a bitch on ring and pinions, axles, and suspensions.)

Careful break-in (ran them extensively on the dyno under light load before getting to the track) and never, never changing the wear pattern, once the ring and pinion were broken in (never, ever, re-shim) were key, for us. We also had to run a special gear oil to further protect the ring and pinion, at Sebring....which worked really well on the gears, but the Borg Warner syncros and the friction discs in the limited slip hated the stuff...the drivers had to live with the gearbox "crunching" into every gear and a bit of limited slip shudder. (Redline Shockproof)

Luckily, the pinion gear in the automatic 928 transmission is very robust and should be able to hold much more power than the "toy pinion" we had in the RSR transmissions. Perhaps also worth noting is that I've never seen a broken or worn out ring and pinion in any automatic transmission....which speak volumes about the quality of the pieces.

Shane

Very cool!

I've stoned a few ring and pinions in my day. Never polished them to this level though.

jeff spahn

Thank you for reminding me of how little I know. I will now go eat some mush with the rest of the dummies.

slate blue

Thanks for posting, that is a lot of work and I completely agree with fixing or changing something before it breaks. The one advantage I became aware of regarding the automatic ring and pinion is, unlike the manual it can run heavy gear oil where in the manual it is a compromise.

After seeing that car run down the quarter mile I am one, in awe, two very happy with my decision to use the automatic's differential and PSD. While I can confess to not having the idea to "tidy up" the ring and pinion I can see it is a very good idea. I was actually going to buy a new ring and pinion have it cyroed and then get it REM finished. However while I still may do that, the fact that the stresses should be now lower in that ring and pinion mean that it would start with an advantage.

I was actually this week designing my crankshafts, how that relates is, while the ring and pinion don't make contact on the edges, this may well be a stress riser, crankshafts often break in the radius where the journals meet the cranks web. Nothing runs there either but it is a high stress point. The Nascar crank I have runs a radius of approx 4 mm. Which is big when compared to the factory crank. The factory crank gets its strength from the fact it is made from a good steel and is very beefy.

When you get into smaller parts like our ring and pinion and start putting more than Nascar power through them they better not have any high stress areas. Remember all the drag racers use a Ford 9" or bigger, ours is no where near that size. Well done!

IcemanG17

I remember asking Mark Anderson how many used ring-pinion sets he sells......I recall the answer as NEVER..... Granted 1000hp will stress things far beyond anything Porsche intended. It appears the strongest parts of 928 driveline are the ring-pinon and CV joints (930 part).

The automatic in general is quite strong. Not flawless, since nothing is, but much stronger than the 5 speed. I would say the 5 speeds are by far the weakest link. Then the torque tube. Most of it is age related.

The automatic in my old estate has at least 7 full lemons events on it. Plus sprint racing I did on slicks. Lets call that 120 hours on track. Not too bad really

Leon Speed

What's with the cut on top of each teeth? Mark for the original contact points?

Jerry Feather

Yeh, I wonder about that too. Looks like it is on both the ring and the pinion. It doesn't look like it is compromising anything -- it is just there. But I wonder why?

SeanR

I was guessing that it helped keep the flow of gear oil on all contact surfaces. Putting the grooves there isn't going to cause any weakness. I may be wrong but that seems like a smart idea.

Rob Edwards

I think they're part of the manufacturing process, or at least that was Erkka's thought the last time these notches came up.

Here's a new 5th gear layshaft gear:

robot808

Todd is building a monster. If he knows how to improve on a part, why wouldn't he?