Transmission Broke. Ring gear?

[Jay Laifman]

My 902 5 speed transmission on my 1967 912 broke this weekend.

I was driving along, minding my own business, rolling up to a red light. The light turned green. I slipped the car into 1st, and started driving away - all smoothly, all like I normally do. Then I start hearing a gear grinding type noise and lose connection to the wheels - like it popped 1/2 way out of gear, but still bumping on the gear teeth. I pulled over and find that I can put it in gear, slowly release the clutch, start getting a tiny bit of forward motion, then the grinding and slipping starts. It does this in all 5 gears and reverse. There is no grinding when the gear is any gear and the clutch is in, or the car is rolling in neutral.

I did jack up the car and rotate the wheel holding the axel to see if the CV joint crumbled. Seemed to have zero play.

The clutch seems to be working fine - and if it had an issue, I'd think it would just be slipping rather than causing gear grinding.

The shifter still goes precisely into all gears, with no extra play. The shift linkage it still solidly attached where I marked it when I lined it up and attached it 2 years ago.

I posted this on the 912 list too, but no one had experienced this before. The best explanation I've received is that it is probably something wrong with the ring gear.

I'm curious if anyone else has had this specific thing happen before?

At this point, I have no choice but to pull the tranny out and have my mechanic or someone else rebuild it. Just wondering in advance if anyone has thoughts.

Jay

[M_deJong]

I think it is more likely a problem at the clutch end than the ring gear. Ring gear would be noisy when coasting too. Perhaps the input shaft splines or clutch hub have stripped. Should be obvious with the gearbox out.

[mike curnow]

No matter what the problem is you need to pull the engine. Its fairly fast to pull the engine on a 912 but you must support the trans when you do it. Its probably simpler to pull the engine and trans. Pull engine is approx 1 1/4 hr. , pull engine and trans 2 hr. If its a clutch problem you need to pull the engine, if a trans problem you need to pull both. If you need a ring and pinion I have both, they need to be a matched set.

[Jay Laifman]

Thanks guys. Yes, I'm pulling the engine this weekend. It is a relatively new clutch, disk and TOB - 2 years old and 15,000 miles (yeah, I've really been enjoying this SWB car). I've pulled this engine before, my 356 engine a few times, and VW engines in the past - all with a floor jack and a large piece of wood. But, I finally broke down and bought the Harbor Freight ATV/motorcycle lift to make my life easier. I think there were two reasons I got it: it is on sale for $99 and I just replaced the sump pan studs and don't want any risk of damaging them! (even with the cap nuts I have on them).

I would love it to be the clutch. Really. But, since I can press in the clutch pedal, get full disengagement, get the shift lever to feel like it puts the gear fully in gear, I'm thinking that letting out the clutch would not cause grinding no matter what is wrong with the clutch - unless the grinding noise is the clutch itself somehow. Hmm.

[Jay Laifman]

Ugh. Pulled the engine. The ATV jack was wonderful. Took the tranny to my mechanic today and he took it apart. Nothing obviously wrong other than a few worn synchros. Now we don't know what it is.

My mechanic says that since the obvious isn't the cause, we'll have to look at the bizarre unlikely things.

The CV joints all have nice rubber, and are full of grease. There is no sign of a broken carrier or anything else. He suggested maybe the splines inside are worn out, which he said doesn't make sense and is very unlikely - but still, since it is not the tranny, worth looking at. He said the only way to test that would be to take them fully apart.

We threw around the idea that the center of the clutch disc separated. But, it's a 2 year old clutch, and as far as I can see, firmly in there, with no broken pieces anywhere.

I'm starting the doubt what I saw when I inspected the shifter coupler. It appeared to be in the exact same location that I put it in 2 years ago (based on the whiteout and blue marker I used). And it didn't appear to budge as I shifted through the gears. But, now it is disconnected.

No other obvious or not-obvious causes.

[davep]

Did you pull ONE (and one only) output flange? If it has the tit on the end of the bolt, then you have to be very careful to either replace one at a time, or do the upgrade.
http://forums.pelicanparts.com/porsc...ferential.html

[Jay Laifman]

We pulled the entire tranny apart. Thanks for the reference to the bolt and the simplified differential. I don't know anything about it. I forwarded it to my mechanic - but it probably only succeeded in upsetting him!

Just looked at the clutch. I didn't unbolt it from the engine. But nothing looks remotely loose or amiss. I guess if everything else is a deadend, I'll bother to unbolt it.

[mike curnow]

Three off the wall possibles. The crank broke and the engine still runs but you hear the crank pieces grinding against each other. The flywheel is loose on the crank, disk problem, or the splines in the disk have broken.

[Mr9146]

I'd say the pressure plate blew up.

[Jay Laifman]

I will say that the effect was as if the splines in the disk have broken - no issue when idling, starts slipping once connected to the back force of the wheels, makes a grinding noise. But, unfortunately the splines on both the first motion shaft and the disk appear fine. That leads to a possible other scenario, which is the pressure plate/disk blew up. I'd think I'd see something amiss without having to take off the clutch to see. The engine is right on the ground to do it, easily enough. I just don't have a tool to line up the clutch disk when putting it back on. So, I'm going to hold off before unbolting.

Thanks for the great creative ideas. Rest assured, I will circle back once the answer is finally determined.