Strange Transmission noises

[cmonref]

Have run up against my first transmission problem in over well over 200,000 miles of 912/911 ownership. Please help me identify possible causes and fixes. I've never been into a transmission but I retire in two weeks and there's always a first time ...

1980 911SC, original transmission, 211,000 miles, new 1st/2nd syncros and bearings 61,000 miles ago. Clutch cable replaced about 4,000 miles ago. Removed and reinstalled engine/transmission 3,000 ago (58,000 since "rebuild") for a Megasquirt installation. Changed/refilled transmission oil while out. Did not replace pilot or throwout bearings. Clutch/flywheel fine.

3,000 miles since reinstallation and things have been fine. Until last weekend when first strange noises were noticed. A little diagnosis surfaces these observations:

o Engine running, sitting still, clutch in, stir the shifter and no noises or in transit between gears.

o Driving down the road, noise when pushing forward out of 2nd gear and into 3rd gear. Not synchro noise -- much higher pitch. Noise stops when in 2d or other gear -- noise present when shifter is moving.

o Same noise out of 3rd gear, stops at the shift gate and does not occur going into either 4th or 5th from there. Into 2nd the noise recurs.

o Synchro noise going into 1st is new. At a stop, goes in without grinding. No synchro noise in any other gear.

o No strange noises when fully in gear, on or off power.

Checked clutch adjustment -- right on 1 mm. No fluid leaks anywhere on transmission. I did not check the fluid level since the rear was way up in the air and I don't think it gives a good reading of fluid level in that attitude.

The only source that comes to mind is a transmission component sliding on a rotating shaft and producing noise when actually sliding. If this is the case, are the 2nd and 3rd gears on the same shaft ? -- the noise occurs coming out of 2d enroute to 3rd.

Any help welcome. I'm guessing any fix will involve removing the transmission, but I would like to know a little better what the problem might be before I do the drop.

Brian

[Peter Zimmermann]

This will answer a lot of your questions:

Welcome to Red Line Porsche Wiki - Porsche Wiki

Scroll left side of page, click on "915" under "Page tags" and you'll be at my 915 repair Tutorial.

Loose gears (gear w/synchro ring), are: 1/2 on P/S, and 3/4 are on M/S. Your problem might be a loose fork on the bottom plate (the one held on with 3x 6mm nuts). Of course, that's just a guess, but a relatively easy place to start.

[cmonref]

Glad you answered! After I posted, I read your tutorial (downloaded a while back) --nd now my eyes are spinning and I can hardly type. My wife just announced dinner time, so I'll look into your answer in a little while. Great tutorial -- thanks for all the time it took you to put that together!

Brian

[Bob Kontak]

Originally Posted by Peter Zimmermann

Your problem might be a loose fork on the bottom plate (the one held on with 3x 6mm nuts). Of course, that's just a guess, but a relatively easy place to start.

+1

Check that v shaped block fastened to that plate. Not sure if you have to drain the all the fluid to do this.

My 81 915 was making buzz saw noises going into (3rd and a wee bit into 4th) gear and I found the V block was loose after I pulled the trans. Given the work to drop everything I had it rebuilt anyways. It did not make noises coming out of gear or across the transition to the next gear.

Mayo Performance said it was probably not the reason for the noise but I am not sure that was the case given the threads I have read.

[cmonref]

Thanks, guys. I'll pull that plate in the morning and check the fork. Near as I can tell, that is about the only thing that does not require a drop.

Brian

[pete3799]

You'll want to drain all the oil out before you pull the cover off.
Keep in mind you may need a new gasket to re-install it.
You can make one out of some gasket paper if need be.
Don't think that this is where your noise is coming from though.
Mine was extremely loose but made no noise.

[buckhunter101]

Brian, I have the same noise going into third any luck with the inspection?

[strudelwagon]

Peter,
Thanks for the link to your 915 rebuild site. I constantly amazed by the amount of great detailed info on this site and others. My next project will likely be a 3.0-3.2 with a 915 and I was searching for a good tutorial.
Awesome!
Cheers
SW

[Josh D]

The same scenario can occur if the shift pivot fork is tight, but the pinion shaft is walking allowing 4th gear to make contact with the fork. When you pull the fork, check for a wear pattern on the outside of a tang where it shouldn't be. If this is the case, you'll have to deal with a probable bad 4 point bearing and bearing tension plate. Hopefully it's just a loose fork.

[cmonref]

Report to the field of removing the transmission outer plate and shift pivot fork. Executive Summary: Not Good …

Here’s a picture of the plate with the fork. When I removed it, I could not wiggle it by hand. Thought at the time that this was good, but read on …



1. The two removed nuts were loose and one had a broken lock washer (see upper left.)

2. Both nut-less studs had backed out of the plate. Note on the far stud that the unthreaded portion is above the fork. I removed both with my fingers.

3. The third nut was later removed with only a little more torque than my fingers could apply. The stud was in full depth.

4. The near fork tine shows 3/16” tall (axially along the tine) that is .020” deep (perpendicular to the tine). When viewed from the end of the tine looking along the tine, the scoring has a “V” pattern with a distinct “peak” between two planes.

5. The near fork tine shows bluing from heating consistent with scoring.

6. There is a similar scoring on the other tine but it is quite shallow and less than 20% of the area of the scoring in the picture above. The tine shows less heating evidence than the other tine does.

7. Inside the transmission, the smaller gear on the forward side (in the direction of driving) has a scoring on the teeth that seems to match the scoring on the tine in the picture. I could not get a good view of it but I could definitely feel a “shoulder” on the gear tooth when I felt along the tooth edge with a dental pick.

8. Inside the transmission, the piece that is between the tines of the fork has (guessing here) maybe .020” play fore and aft.

9. Not in the picture is the drain plug which held a collection of fuzz plus one iron solid that appears to be a gear tooth tip. It was about 1/8” in what I think was the radial direction on the tooth.

So, yes there were multiple problems with the fork, but other problems point to removal and dealing with more serious problems inside the transmission. The scoring on the side of the tine was just as JoshD described so there are likely problems inside the transmission.

Anybody have other observations the might help in the next steps?

Brian

[Josh D]

Using a long screwdriver, try to move the output shaft for and aft for play. Also, a pic of the chunk will let us see if it is a dogtooth or something else.
BTW, I'm going through this right now as well. I have a thread going "found my noise" with some worthwhile pics.

[cmonref]

Nice thread, Josh. Good luck on reassembly and hitting the road again. Interesting similarities: I lived in Cave Creek north of Phoenix and went to college in Tucson. Guards Red 1980 911SC WITH a sunroof and a Carerra tail. Small world.

I'll do the screwdriver test after breakfast. Regretably, I'm thinkin' that any movement would suggest a drop and teardown.

Brian

After breakfast: Could not feel any motion on the pinion shaft in either direction. Tried to orient the chunk for a picture but could not hold it in a position that made it look like something recognizable.

[cmonref]

bump.

[buckhunter101]

Brian,
Sorry to hear about the outcome of the inspection.
I will be pulling the motor and trans next week for a leaking rear main seal and will take a look at my fork also. That tutorial was great thanks Peter.

[Josh D]

Brian,

At this point it wouldn't be unreasonable to repair the shift fork pivot, reinstall, refill, and see if problem is is solved. If problem still exists, or other problems surface, then the box will have to come out for disassembly and inspection.
Is it possible the chunk found could be from a previous repair? I found three teeth on my drain plug, but when I disassembled mine, I had no broken off teeth whatsoever. I had receipts showing the box had been repaired before under previous ownership.

[yelcab1]

If you find one big metal nugget on the magnet then there is more you cannot see. Continue driving is bad.

[Peter Zimmermann]

Brian, I agree with Josh. There are times when noises make no sense, and this is one that might fit that category. Repair the plate/fork, put it back together, fill the trans and drive it.

You reported a recent trans oil change, so I doubt that your "chunk" was left behind by a previous repair. Before you put back the lower plate/fork, try to turn the gear shafts while watching the dog teeth to see if you can find a "missing" tooth. Did you find the missing piece of lock washer?

Don't worry about the "blue" areas on the fork tines - that's normal. It is definitely possible that your trans has another issue, but I always like to start with the easy stuff!

[buckhunter101]

Brian,

Could that "chunk" be the missing piece of lock washer as Pete stated? Will report back next week on my inspection as i feel that this is a must do while the trans is out. Just did fluid change last winter with no suprises but still have squeaking noise going into third.

[cmonref]

Pete Z: Somehow I missed the last three posts, including yours -- I missed your thought to turn the gears and check for broken teeth. Darn -- opportunity missed!

I reinstalled the plate today and filled the transmission -- then drove it. No unusual noises at all -- the higher-pitched noise between neutral and 3rd is gone. Before I installed it, I filed off the ground place on the tine (see pic above) and installed the 6mm studs with blue loctite.

I'm guessin' that the loose 6mm nuts allowed the fork to rotate in the forward direction until the tines rubbed against the gear. By reinstalling them and tightening down the nuts, that motion was prohibited and the rubbing averted.

Thanks, Pete, Josh, and others. I will keep an eys on the transmission for any other problems that may still exist.

Brian