Rebuilt Transmission Issues

[jluetjen]

I just rebuilt the 901 transaxle in my 911 -- new 904 mainshaft, new gears, synchros, bearings, etc. Everything went together well. On the bench everything shifted great and was clean. No hang-ups.

I put everything back in the case. Before installing the access-plate/fork that anchors the selector, I confirmed that all of the gears are in neutral. The selector rotates freely between the forks.

I put the transaxle in the car. In neutral, I can manually spin both axles forwards and backwards together. I can find all of the gears. When in gear, I can't turn the axles together.

I start the car with gearbox in neutral and the clutch in as usual, and the engine fires right up. As soon as I start to release the clutch, I can hear the engine loading up and the wheels start to slowly spin forward.

I know that I did something wrong, but where should I start looking once I get the gearbox out of the car (again!)? Has anyone ever run into a similar issue?

My guesses are...
1) Make sure that the shafts are tight to the intermediate plate
2) Check the clearances on each side of the selector forks
3) ????

What do you think? Suggestions?

[gsxrken]

I can’t help with your issue but notice you’re in Westford, which is a few minutes ride from Kevin Gross in Stow. When you have it back out, it might be worth a ride over to have him look it over and point out what is amiss. Good luck

On Edit: my reading comprehension here was terrible. I thought you were on the ground and letting the clutch out. As the other guys suggested, you may be fine. Have you tried driving it?

[yelcab1]

It is very common for the car when jacked up with the wheels off the ground, it is common to have the wheels slowly spin with the gear in N.

[Matt Monson]

Originally Posted by yelcab1

It is very common for the car when jacked up with the wheels off the ground, it is common to have the wheels slowly spin with the gear in N.

^this. My first thought is,”what happens if you pull the e-brake? “

[MBEngineering]

HI jluetjen

when you assembled the shafts and gear into the bearing plate, both shafts FULLY turned? and when in gear they still FULLY turned.

what size shim gaskets did you fit to set the pinion depth when you fitted the gear set back in the diff/main case,? and did the input-shaft still turn when in gear with the box now fully assembled, there is a posibility that the pinion is to far in mesh with the crown wheel, just a thought

[kevingross]

Originally Posted by gsxrken

I can’t help with your issue but notice you’re in Westford, which is a few minutes ride from Kevin Gross in Stow. When you have it back out, it might be worth a ride over to have him look it over and point out what is amiss. Good luck

On Edit: my reading comprehension here was terrible. I thought you were on the ground and letting the clutch out. As the other guys suggested, you may be fine. Have you tried driving it?

Would be happy to help. Indeed we are close by.

[jluetjen]

Originally Posted by MBEngineering

HI jluetjen

when you assembled the shafts and gear into the bearing plate, both shafts FULLY turned? and when in gear they still FULLY turned.

what size shim gaskets did you fit to set the pinion depth when you fitted the gear set back in the diff/main case,? and did the input-shaft still turn when in gear with the box now fully assembled, there is a posibility that the pinion is to far in mesh with the crown wheel, just a thought

Thank-you. I've got the shim stack information at home and I'll post later. I'll check the pinion once I get under the car again.

[jluetjen]

Originally Posted by MBEngineering

HI jluetjen

when you assembled the shafts and gear into the bearing plate, both shafts FULLY turned? and when in gear they still FULLY turned.

what size shim gaskets did you fit to set the pinion depth when you fitted the gear set back in the diff/main case,? and did the input-shaft still turn when in gear with the box now fully assembled, there is a posibility that the pinion is to far in mesh with the crown wheel, just a thought

I think that you may have called it Mike. I took the transaxle apart while monitoring the effort required to turn the mainshaft.

• Complete Transaxle: Mainshaft is really stiff
• Remove the end cover and the intermediate reverse gears -- mainshaft is still bound up.
• Pulled the intermediate plate -- mainshaft freed up
• Reinstalled the intermediate plate assembly and removed diff cover -- somewhat less bound
• Removed the diff, and the mainshaft freed up.
• Reinstalled the diff and the diff cover, and the mainshaft got stiff again. That looks pretty conclusive.

I had not checked the diff clearance when I rebuilt the transaxle this year. I had rebuilt it last year with gears that I had collected along the way, and discovered that gears 3, 4 and 5 were really noisy. In 2nd gear (integral with the mainshaft), the car was fine. So I drove it down to the village in 2nd gear to get the car's annual inspection sticker, and drove the car home again -- in 2nd gear.

So much for buying used gears! I pitched the lot of them and bought some new gears, and rebuilt the two gear shafts again this year. I didn't recheck the diff again since it hadn't been a problem. But since I did reset the pinion-shaft shim stack, I should never have assumed.

Oh well. Lesson learned and shared here. Kevin, I may give you a call tomorrow.

More updates to come!

[jluetjen]

Now... (As Paul Harvey used to say...) the rest of the story.

I took my transaxle down to Kevin at Catellus Engineering, and even though it was prime rebuild season, he fit me in soon after Christmas. He sent me a bunch of in-process pictures showing me what he found and it was all done by the end of February for what I would consider a very reasonable price for a Porsche specialist.

Kevin gently shared that the problem I had was because I had inadvertantly put one of the shims from the mainshaft onto the pinion shaft. (whomp-whomp ) But while he was in there, he went through the box to make sure that everything else was set-up correctly, and also replaced some pieces (like the rocker-arm for the throttle) which I hadn't replaced, but should have. He even got the shifter seal installed so that the transaxle is no longer leaking very aromatic gear lube all of the exhausts. Something that I was never able to do. My wife is so happy that the garage no longer has that "stinky 911 smell".

I finished putting the drivetrain back into the car (again) last weekend, and I got the car successfully through inspection on Saturday. Kevin was even nice enough to take a ride with me this evening to sooth my "what is that sound?" jitters. I've never driven a 911 with a virtually new 901 transaxle. Everything seems great and I have to get used to the new synchros breaking in for a few miles. So I guess I just need to get back in the car and keep driving it.

[kevingross]

John, thank you for the ride. I believe you should post a picture of your very pretty car here!

[A930Rocket]

Nothing like a smooth, shifting transmission.

[Matt Monson]

Kevin is very good at what he does. Congrats.