901 Trans, freshen for the track....

[Tspringer]

It looks like I am going to need to drop the engine again and replace the transmission. Though it gave no symptoms of any problem before being removed for engine bay detailing and such.... apparently the sitting around has ruined the pinion shaft bearings and/or other bearings. See details here:

Grinding Noise under power ? Yikes!


I have a spare 901 trans. It received a "Joe Cogbill" rebuild from PAP several years ago and has been sitting since. For those not familiar with this type of rebuild, it refers to how Joe rebuilds things: new parts only where absolutly required. He prefers to rummage around the junkyard and use whatever semi-decent looking parts he can come up with. Basically, I would never install this trans without it being inspected and repaired by someone else I trust.

I am sure the gears and syncro rings are good because I demanded new parts be used. I was present as he "rebuilt" the unit. He took a quick look at the bearings and pronounced them "fine". Well.... I want new bearings and any other parts that could cause yet another engine drop.

So, what all should I have done to this 901 before I go to install it? All new bearings, gaskets and oil seals are a given (Joe also pronounced the old oil seals as "fine"), but is there anything else I should do? The car will see autocross and track duty... so I want it to be strong and RIGHT.

I want to have it all fresh and ready so I can just drop the engine, remove the old trans., bolt this new one on and re-install the entire unit. I am hoping for a 5-6 hour turn around with a friends help..... a good Saturday project.

[Jim Sims]

If you replace all the "gears", bearings, seals plus the other parts that usually are replaced: synchro hubs, operating sleeves, brake bands, etc. with new parts you will have replaced most of the transmission and probably spent $3000 or more on parts. Is this what you mean? Most rebuilds do not involve replacing gears. I recommend you familiarize yourself with the 901 tranmission and it's weaknesses like the intermediate plate and bearings and the weak first gear due to it's position cantilevered out on the end of a shaft. Cheers, Jim

[Tspringer]

No, Im not really looking to replace all the gears. Thats why I said "Im sure the gears and syncros are good".

I am wanting to have all the bearings, oil seals, gaskets and throwout bearing replaced at a minimum.

"familiarize myself with the 901 transmission".... thats really what this post was aimed at. I am aware of the weak first gear due to its position, but what can done to address this? Also what can be done at a reasonable costs to improve the intermediate plate?

Anyhow, thanks for the input..... and what other suggestions do folks have?

[Grady Clay]

Terry,

I assume you have an aluminum case 901 transmission. Do you have the Factory workshop manual and parts manual? Other? What is your access to P-tools for 901? A 901 transmission is very easy to tinker with properly.

I would first disassemble your 901 out of the car, primarily for diagnostic purposes. You want to find a problem. If you can’t find a problem then it must be elsewhere or a real gremlin.

My vote would be the input shaft ball bearing at the intermediate plate. You said it is starting to be noisy when the car is stopped at idle and in neutral. In that case the input shaft is turning on it’s bearings but the pinion shaft is stationary.

This bearing is a common failure point. I don’t think it could be just from setting unless the entire transmission got rusty internally.

If it is the input shaft ball bearing, it will be obvious. The inner races (usually) will show the most damage. I have never seen the outer race show damage and not the inner race. Replace both the input shaft ball bearing and the pinion ball bearing. Inspect carefully the roller bearings.

It may turn out that with only two bearings and the seals and gaskets you are back on the road. Of course “while you are there” inspect everything else.

How long and where has your spare 901 trans been stored? Has it been sitting outside on top of the wood pile, assembly dry? Has it been inside, lubed and turned over periodically? Good ol’ Georgia humidity can play havoc with nice Porsche parts that just sit.

If you feel you need to use your spare, at a minimum I would pull the gear cluster and inspect.

Good luck.

Best,
Grady

[Tspringer]

Hey Grady,

Honestly... transmissions are a total mystery to me. I have rebuilt Jaguar engines, restored from the ground up Jaguars, Triumphs, Healeys and MGs plus messed around a ton with Porsche and Ferraris.... but on none of them have I ever done any transmission work. I know what a transmission does, but the how is a baffling mystery!

The spare I have has new dog teeth and syncros plus the gears are all new or in excellent shape... of this I am sure. IT was stored indoors, but with minimal lube other than that used during assembly. I am going to have all the bearings replaced and the oil seals..... it should be good to go at that point.

As for what is wrong exactly with the one in the car.... well we will see after I have it out. At that point I will tear it open (slowly) and begin figuring out what all those parts actually do! Thanks for the tips..... more to follow!

[Grady Clay]

Terry,

Don’t be intimidated by a transmission, they are easy.

Send me your e-mail address and I’ll send you some 901 trans info.

Best,
Grady
gradyclay@hotmail.com

[jpnovak]

Grady, I will be rebuilding my 901 shortly. Most likely syncros need replacing and hopefully not all dog teeth/sliders. Can you send me some info too? I am still in the information gathering stage. I have the factory manuals and read Red-Beards website. Is there any other info I need?


you must remove spaces

[Grady Clay]

Terry, I got your e-mail and will send you stuff.

Jamie, send me your e-mail address also. BTW, red-beard’s 914 info is at: http://home.san.rr.com/pb914/rebuild/


Is there anyone else who wants to do a 901/911/914 transmission at the same time? (For that matter, 904 and 906 are also the same.)

Digital cameras are really worthwhile for having the many experts on this Forum to diagnose condition.

It would be best to keep the discussion on this Forum so all can benefit. We can e-mail bigger image files if necessary.

Best,
Grady

[Randy Webb]

I don't need to do my 911 trans now (I hope) but will later. Can you send me stuff at xrw@att.net ??

And keep as much info as possible here so we can all get it? Thx!

[jpnovak]

Thanks Grady, HMM I typed my email address above the last line. strange.

jnovak@appliednanotech.net