901 Tranny - Something Slipped

jtmarran · 03-28-2004, 01:53 PM

Took the car out for a drive yesterday. I got out of my neighborhood and upon shifting into second, my car started making a rubbing or slight grinding noise from the transmission. The shifter also had a vibration in it, the frequency of which seemed to match the speed of the car. The noise got worse with the speed of the car, not the RPM’s, and remained in all four gears. I decided to start troubleshooting. I took the tires off and drive shafts out of the car and started it on jack stands. With the car in gear and clutch engaged, the sound was still apparent. If I disengaged the transmission from the engine, the transmission would grind to a halt. OK, obvious problem in the transmission. Dropped the engine and proceeded to start dismantling the tranny. The only things that I’ve found so far are the speedo gear at the front of the pinion shaft was only on hand tight and there seem to be two gears that are rubbing against each other. I’ve attached two pictures showing these. Not having ever rebuilt a transmission, I’m not quite sure if what I’m looking at could have caused this problem. Every thing else in the transmission looks brand new. Opinions and advice is appreciated!

Thanks!
Joe

Grady Clay · 03-28-2004, 02:35 PM

Joe,

I assume this is a ’71 911 (magnesium case) transmission, Type 911/??.

First, help me identify some stuff in your two images.

What is around the pinch bolts for the shift forks? Is that an artifact of the image?

In the upper-left of the first image there appears to be a metal part between the R-1 and 2-3 shift rails. What is that? Is it loose to float on the R-1 and 2-3 shift rails?

Why did you arrow indicate the 3,4,5 gear mesh? Are those some failed parts? I can’t tell from the image.

Just to the right of the 4th gear mesh (toward 5th) and apparently away from the camera, there is something I don’t recognize. Is that an artifact or is the gear cluster sitting on something?

What did you find on the magnetic drain plug? Any extra parts in the bottom of the transmission, including the differential area?

Are the shafts secure on the intermediate plate bearings? The input shaft intermediate plate bearing is always suspect. Occasionally the pinion shaft intermediate plate ball bearing fails also.

Do all the gears have all their teeth?

I see some dents in the pinion gear. How does it look overall? What does the ring gear look like?

Have you inspected the differential gears?

Are the sliding sleeves free to shift into all gears? In your illustration, you are in reverse. Does the shifting work OK with it as presented? Do the syncros, sliding sleeves, and engagement dogs all appear to be OK (all the same)?

Please post more images.

Best,
Grady

jtmarran · 03-28-2004, 04:26 PM

Grady,

Thanks for the quick reply! This is the transmission out of my ’71 911T. It’s a four speed.

There’s some dirt and grime around the shift fork pinch bolts. Nothing that I would think is out of the ordinary. It does seem to reflect in the images I posted earlier.

I took another picture of the shift rails (see below). The metal object, I think is how the case showed up because of the angle of the shot.

I put arrows at each of these gears because it seems that there is some interference between the gears up against the sides of the small teeth when I turn the shafts. The arrow all the way on the right is to show the amount of overhang at that gear, seems excessive to me, as if the entire pinion shaft has shifted aft (right in this shot).

I think that part might be the shift fork wrapping around?

The magnetic plug obviously hadn’t been pulled in millennia. There were a lot of fines attached to it, but nothing that I would be worried about. No parts or chunks in the bottom of the tranny or differential case (although I fully expected to find something like that).

The shafts seem to be secure, I can not move them axially, but I’m suspecting that the pinion shaft has moved aft.

All the gears have all their teeth and there is hardly any wear.

Overall, the pinion gear, differential, and ring gears look well. I’ve included a shot of the differential. I could find nothing wrong here.

I can get the transmission into each of the gears. Everything in the synchros, sliding sleeves, and dogs appear to be OK, although 4th (5th) seems to be a little tough getting into.

Thanks for the help Grady! And I think I hit each of your questions.

Regards,
Joe