Transmission Clinic

[davep]

I just attended a clinic put on by Dr Evil this past weekend. I must say that it was very enjoyable and useful. I fully rebuilt one transmission that had a lot of crud in it. It need parts that I got from a second box which had first gear torn off the mainshaft. There were ample parts available from Mike (Dr Evil), or from a few other guys. One other fellow (the host) had about 5 transmissions to go through, and another local went through about 6 of the 30 he had available. I have 8 more that I did not bring. A third box I opened up looked almost mint, so I didn't waste time to tear it down; later I'll do the seals. I wound up with several good spare parts, and started my collection of alternate gear sets.

Oh yeah, I learned much more about what gears can be used where. Gears for third should not be used for fourth or fifth and vice versa in a 5 speed box; that is, flipping the gears is not good for the bearings in boxes used for serious power. So an O3 and an O4 are not the same, and the same goes for M3 & M4; numerically they are the same, but are cut in reverse to each other.

Things can be a bit different in the 4 speed and sporto boxes. So I'm studying hard and researching the nuances. I'll be able to make many additions and changes to the Wiki.

[gms]

Sounds great Dave.
I met Mike (Dr. Evil) last year, he is a great resource and nice guy

[davep]

I wen through my pile of transmissions and have a 905/13 box to go along with a 902/01 box I acquired on the weekend. Both 4 speeds. The 902/01 has an A first gear on the mainshaft like our second gear, so basically it is like a 5-speed without first gear. Other than that it looks identical. Anyway, the gears from these boxes give me an HB 2nd or 3rd, and O, Q or X for 4th & 5th gear in addition to the stock gears.

[Richard Casto]

Dave,

It sounds like you had a good time. I haven't posted much about this (laying low), but I am working on taking over for Mike once he is off to his residency program in June. I spent some time with him up in Hershey recently rebuilding some boxes I brought with me. Will be doing this again in the near future so that I can absorb as much of his knowledge as I can. I will have everything up and running and ready to hit the ground running when he is ready to pass the torch.

What I have found so far is that the transmissions are relatively easy to work on, but being able to decide "is this part worn enough that it needs to be replaced" is that hard part. First gear slider wear is an example of that. I also plan on eventually getting the proper tools to be able to set pinion depth, ring backlash, etc. My goal is to eventually work on that and be able to do diff flips (such as on 915 transmissions) as well as match up R&P to new cases. At the clinic I am sure everything you all did ensured that you kept the pinion, diff and case all matched together so that you don't have to worry about various shim adjustments.

Richard

[dug]

At the Jerry Woods transmission class, he said that he doesn't bother with the fancy pinion depth tool. He showed us how to determine the shim stack by using "gear paint". It was this sticky yellow stuff that you painted onto the ring gear. Then you run the pinion through it and see what the contact pattern shows you. Ideally, it should be centered on the gear. That's it. Nothing all that complicated about it. No rare, expensive factory tool.

cheers,
dug

[Richard Casto]

While the Porsche manuals says that they have matched up the ring and pinion for optimal “wear and noise” characteristics, I think it really is all about proper contact patch. I think that most people use the gear marking compound (special colored paste with yellow being a common color) to look at the actual contact patch.

I suspect that the marking compound method is the best (if not the most cost effective) method, but I would like to eventually get a pinion depth tool as I am curious as to how the two methods compare. Even then, the pinion depth method requires you to use measurements provided by Porsche. So if for some reason you believe those are incorrect, etc. your only option is the marking compound.

The originals pinion depth tools are hard to come by and some have made reproductions using old diff housings. They usually sale quickly when one is available and still go for a few thousand dollars if it’s a complete and working kit.

[davep]

Do a search on Pelican for P258 and VW385 or just 258 & 385 for some threads on the diff tools. Tony is supposed to be making some from old diffs for about $500.

[Richard Casto]

I know exactly what thread you are talking about (Tony Proasi's repro). :) I have it on my bookmark list and saw that you had posted on it today to get an update. It will be interesting to see what he says.

[dug]

I'm going to the Dr Evil trans class in Sonoma with Randy on Dec 5th and 6th. Can't wait to get my six boxes rebuilt. I have two original six boxes, plus a third 914-6 nose cover that I might put on a 4 cylinder tail shifter.

I will keep the #'s matching box with stock ratios of A-GA-O-V-ZA.

The second six box I am going to make A-GA-M-T-Y by swapping the O and ZA gears. I haven't found a T 4th yet, but I found an S for cheap, so I might go with that. I'd love to find a B first too, but they are $$$.

The four cylinder box I want to build into A-F-KA-Q-V a really short box just to experiment. KA is ZD flipped. V is 4th moved to 5th. Just need to find a Q.

I definitely want to get an LSD for one of them eventually, but first I will decide which ratios are my favorite. After driving my Spec Miata with the clutch type mazdacomp LSD, I am 100% convinced this is some of the best money you can spend on your car. The stability under braking and the ability to brake while turning in was amazing.

cheers,
dug

[Robby]

The Sonoma clinic has turned into quite a shindig. I am glad I asked Mark to host and got Mike to do it. I just wanted to put MSX gears in mine. I have decided since to leave my 5th gear stock as I do street drive it to events within 125 miles.

[Eric_Shea]

You'll have almost the exact tranny I have. M-S-ZA

Yours should be a M-S-ZD for the 4?

[davep]

I know that you can flip the gears, but I'm leery of doing so myself. When you flip them, the gears are running backwards, and that puts a lot of thrust in the opposite direction for which the design was made. That may be okay for a street car, but for a track car it would probably cause a lot more wear on the bearings. I believe that Grady is not in favour of flipping.

When choosing a gear, you need to be careful of the position. From M through R there are third gear position sets, and fourth gear position sets; M3 & M4 ... R3 & R4.

BTW, has anyone got access to a 904 parts catalog that gives the part #'s for the gearsets? In the 914/6 GT parts manual, they list the part #'s for N4 & P4 but they actually seem to be providing individual gear numbers rather than a number for the pair (very interesting since I've never seen it done that way before).

Since I found an O4 gearset I'm thinking of making a very short box with O as fifth gear.

[Robby]

You'll have almost the exact tranny I have. M-S-ZA

Yours should be a M-S-ZD for the 4?

Yup! Thanks to you. I had planned an MSX but the more I thought about it, 4K RPM at highway speed did not seem appealing. You mentioned that stockish 5th and I figured when the heck am I going to get into 5th on the track? Certainly not an autocross. But on the way??? Sure...