I have a question about matching ring and pinion gears. It is my understanding that the ring and pinion are each etched with the same numbers from the factory that indicate they match. What is the meaning of these numbers, exactly, apart from their aforementioned usage? How are they derived? Are they arbitrary (except that they match) or are they directly related to measurements of the two units? I want to know how close the numbers have to be in order to consider the gears "close enough" for use in the same trans. I have a pinion gear with the number 215 on it. I also have a ring gear that has 195 on it. So, is it the case that these units are more compatible than units with 215 and 800? Just wondering. I have everything needed to put together a nice little trans if I can use these two parts together with impunity.

Thanks!!!!

My understanding of the ring/pinion gearset is that when the two gears were cut, they were not matched.

In the finishing process of the ring and pinion gears, they were run together as a set and therefore "broken in" together as a set. They were "run in" at a known pinion depth and I believe were "run in" both forward and backward.

The numbers may or may not have something to do with the pinion depth as it was "run in". (I am unsure of this on 901/914 transmissions)

One of the reasons that they should remain pared together as a set is that the "run in" process (one of the most critical periods of a gears' life) created a wear pattern unique to the "pair". This is similar to running in a camshaft and lifters. Once broken in together, they should not be swapped around or the "set" broken up.

I believe that there are some other reasons that the ring & pinion should be kept as a set, and am looking forward to reading other people's take on the topic...


just my $0.02

Hi
When I did my trans I noticed the numbers didn't match. I just figured it was a pinion depth measurement, from the factory. I think there is only one member that still has the OEM tool, (that I know of), maybe he will chime in. When I had my....um...diff incident...I asked around (pre-www) and was told the the R&P are run in with a liquid cutting compound and cannot be swapped, this is the rule of thumb for any R&P. I was in a pinch and did what I had to do, and it whined like a cheap whore...

I gonna watch this thred, good question
and of course



Later

Who would that be?

It's not me. I borrowed one from work to do mine, and after that experience, I'm never doing it again. Core trannies with good R&P's are too easy to find.

I agree with the others... don't run an unmatched set. Don't mess with replacing it with a matched set either. Start with a core trans and use the case, intermediate plate, diff, diff cover, ring and pinion (and shims on the pinion). Make sure to measure the gasket between the intermediate plate and case when you take it apart. This way you have no pinion measurements to mess with. Your tranny will be done in half the time, cost less, go faster, smell better- you get the idea.

Thanks for the input. As I typically always consider monetary cost above labor I was hopefully curious about making these units work for me. Alas, someday I will learn that cold hard cash and labor, which equates to time, are actually the same thing. (Of course, there is always the matter of how efficiently one can be transformed into another, but that's a rant we've all heard . Anyway, I think I already knew what you kind folks are telling me... it won't work given the factory run in and years of wear, so I better look for a core trans. I may just do just that. As stated, thanks for the input.

Hey

Sorry for the late reply. I remember a thred awhile back, a member bought a OEM pinion depth tool off Ebay....I think its the Capt'n, but I could be wrong...

I would still like to know what the numbers mean cores are getting harder to find in my neck of the woods, I figure we either find a easy "swap" options, or better yet, have Alpha biuld us a tool...

Watcha think ?

Later

There is a person in CO that has the tool. It is a $20K tool supposedly. I remmember one for sale on ebay a long time ago and it was large $$$.

As for the ring and pinion, what they said Also, make sure you take note of the intermediate plate thickness and the gasket thickness that goes between it and the case. The differentials are actually shimmed as well. Its just easiest and best to get a core and start there.

There are two numbers. A "mating number" and a "deviation number" (on the pinion) The numbers should match between the ring and pinion and I would never mix numbers as it would surely be noisy.

The deviation number (how much out of spec) is the amount of shim required to properly align the gear mesh. It's done on a machine at the factory. My understanding is that they run the pinion in and out and find the "sweet spot" where the noise is the least and mark them accordingly.

Ah hah. So that's what the other number is on the pinion. I was trying to figure that one out. The deviation number... So if a person carelessly lost the shim (gasket) thickness on a core tranny and could interpret this deviation number properly, in theory that person could determine how much shim should be between the intermediate plate and case. All this assumes the core tranny has the factory installed R&P. Wish I'd known that about 7 years ago on my first 914 project when I was less well informed. Live and learn, I guess.

As for this project, I am considering a suby conversion and am now thinking through the suby fwd (2wd) trans as an option, since I now realize I can certainly not use the tranny I have. Anyway, I've got a list of pros and cons going that is favoring the pros side at the moment. No adaptor, optimal gearing. I have a cable shifter and hydraulic clutch in the works already, so no fear there. Suby motors are short, so I could move the whole drivetrain forward and avoid cutting a whole in my rear bumper to fit the big ass of the suby trans in the car. Still some more research needed before commitment, though.

Thanks for the input.