set up of 901 R & P

[0687]

I'm in the process of going thru the transaxle and have replaced several bearings as well as seals, synchros, dogs, etc. and now am ready to re-assemble. Problem is I dont have (nor have access to) the R & P dummy carrier (P 258) used to set the R&P axial spacing. The factory manual seems pretty straightforward - time consuming but straight forward...and mentions after using the dummy carrier "It is not required to check the gear contact pattern again" which sort of implies the contact pattern can be used instead of the dummy carrier.

anybody out there who's done a lot of these care to comment on setting the spacing using layout dye to check contact pattern, then getting the backlash set per shop manual?

help from experienced trnxle folks appreciated.

thx

Chip

[Scott Clarke]

Chip-
If you want the best answer, Grady Clay is your man. If you post your question on the Pelican board you will likely get a response. Having said that, if all of the spacers are the same as they were before the rebuild, and the bearings are all that you have changed, and all of the spacers are in their same positions, you are probably OK as is. Have you checked the backlash? If the backlash is OK, then you likely needn't worry.

The alternative is to check the pinion depth. Without the dummy carrier, this is hard to do. You could send the gearbox to a shop that had the tool to have the pinion depth checked, and then adjust the backlash to spec.
-Scott

[Eric911S]

Hello: You should check the pinion depth everytime you change the bearings or go into the gearbox. I sweep the pinion everytime and check backlash. I made my own tools to do this (it helps if you are a Tool and Die maker). Porsche sent out some 968 gearboxs with the ring and pinion setup wrong and they were noisey. I have fixed these as well. Now saying all that if the gearbox was in good shape before with no noise you may get away with it. The blueing will tell you some things but does not tell you all. Hope this helps. Thanks Eric

[Grady Clay]

Chip,

If you are replacing “several” bearings, I would go for all six. The marginal additional cost isn’t that great.

You will probably find the differential bearing pre-load way below spec with the old bearings and still not in spec (bearing torque or backlash) with a new pair. That is your starting point. It isn’t difficult to make the tools necessary for setting the running torque and backlash. A Pelican search will show them.

There should be someone local to your parts that has P258 and the other little accessories. Once you have the pinion depth set correctly, you can then set the backlash to what is indicated on the ring gear.

I am not very skilled investigating the contact pattern. That said, I’m increasingly leaning to adding that technique whenever setting a R&P (particularly a used one).

My recent procedure is:
Remove the differential and measure the undisturbed pinion depth.
Reinstall the differential, remove the nose piece (keeping the seal at the shim gaskets) and measure the backlash.
Clean the gears and investigate contact pattern.
Remove the pinion and axle flange seals and measure the differential bearing running torque.
Install six (eight on 915) new bearings, setting the differential bearing preload.
Measure/set the pinion depth.
Reinstall differential and measure/set the backlash.
Investigate the contact pattern.

The serious question comes if/when the contact pattern has changed (particularly for the worse).

As you can see, this is very time intensive.

There are three issues here (some times they are mutually exclusive): First is insuring the R&P is set to the original numbers (done for quiet running).
Next is having the R&P running as it was before the bearing change ( to minimize the “disturbance” to previous running wear patterns.
Third is improving the running contact, possibly to extend the R&P life (also possibly with increased noise).

It is easy to rebuild a transmission with all new parts. It is not so easy to rebuild one trying to extend the life of 40-year-old good used parts. One reason you find many pros (with all the tools) shying away from this is it may take several iterations (of the entire rebuild process) to find the best compromise. The Forums can help with this.



BTW, I am collecting marginally rebuildable transmissions (901/911/915) in order to document some of these issues. Please let me know if you have something sitting around – nothing really good. I may even pay some money. Even 4-speed and Sportomatics will help. Eventually I hope to brow-beat Wayne Dempsey into authoring a really good and comprehensive Porsche Transmission Book. I’ll provide the 901/911/914 and 915 chapters. If this stuff doesn’t get written down, in another generation or two the information will be lost. Porsche doesn’t have it any longer.

Best,
Grady
email is best:
gradyclayathotmaildotcom.

[kenikh]

Eventually I hope to brow-beat Wayne Dempsey into authoring a really good and comprehensive Porsche Transmission Book.

PLEASE DO!

[Grady Clay]

Kenik,

Wayne started this thread 4/16/05:
http://forums.pelicanparts.com/showt...hreadid=216727
”101 MORE Projects for your Porsche 911...”

Starting about page 5 of 9 is serious transmission book discussion.
Here is from page 6:
http://forums.pelicanparts.com/newre...postid=1884674
We refined an outline for a transmission book. There is a LOT of support.

You have to realize that Wayne has three newborn-to-toddlers at home, a business to run (he bought out his partner), a forum to monitor, a lot of events to attend and somehow have a “real life”. He posted that he is somewhat “burned out” authoring books – for then.

I see it up to us to collect the technical info and more transmissions. At some point there will be enough info for him to easily self-publish a very comprehensive book. I think even PAG/PCNA would help.

Wayne notes that it would be difficult to find a publisher for this subject. I think this is an ideal candidate for a publish/print-on-demand kind of book. What if it were multi-volume covering 519, 644, 741, 904/901/906/911/914, 908/915, 950, 964 and many more? Each having a body of experts to update.

Best,
Grady

[0687]

Hi all, and esp Grady:

Thanks!!

Grady - I have replaced all bearings - the backlash "seemed" large when taking the diff out - but I didn't measure it - also didn't measure the preload torque. Symptoms were howl (almost) on overrun in 4th and 5th - couldn't hear it in 3rd probably because of engine revs.

When I bought the car, one of the things I didn't do was check or change the trans lube - not good. It didnt leak a drop, but about a year after I bought it I heard a noises, checked, and it was low. Clean and not burned smelly, but low. Went back with a mix of Mobil 1 and Kendall syn lube cuz thats what I had, with a tablespoon of MoS2 powder. Noise slowly got worse - lifted the car up and listened to it in gear running, couldnt hear jack. Replaced both rear wheel bearings - the driver side was TRASHED. Some noise went away, then slowly got worse on over-run (months). I take 400mile road trips about every other month and got worried about being stranded. On dis-assembly, I was amazed at the good condition of all bearings and gears. The diff side brgs looked a little grey with some metal pickup (?) as did the pinion shaft roller, but everything else looked great - all caged needles, needle cylinders and the input and pinion shaft surfaces are mirrors. Even the ball thrust on nose of input shaft was good enough for me to put all them up labeled and oiled for some future job.

Just to be sure, I took the R & P to a local guy who does only 911 work, and has for years - very good reputation. He said the R&P looked good, as did the bearings. He didn't believe the bearing pickup would be noisy nor did I. So I was happy with that. Quandary is where the hell is the noise coming from? Don't wanna put it back and have it worse!

Also would like to spend the 4-6oo set up on go fast parts, and I have the time to do it myself. So my plan now is to re-read your email and references and maybe send you a pm w questions. Any further thoughts after reading my diatribe are welcome, and thanks again!

Chip