915 Transmission sudden grinding entering gear

[tdipower]

I have a 1975 911 with a 2,7l and a 915 transmission. The clutch was worn out, so a project to change this started. With the engine out, and a first gear that had a bit trouble with sync, the gearbox was sent for a rebuild. The inside was after what I got feedback on good, but the sync ring on the first was ready for a change.

After a long rebuild and renewal of the engine bay, the car is now finally rebuild. Have only been driving 5-10 miles doing tuning and adjusting to my Weber’s. The engine has been acting up with poor acceleration, but the transmission has been working perfectly.

Today I had the time to run the engine warm to adjust the Weber’s, and made the engine finally run smooth. But when I then was going to take the car for a test drive, I was getting a grinding noise when trying to reverse. Also the same with trying the other gears. Adjusted the clutch so it it release earlier, but this made no change to entering gear.

With the engine off the gear lever moves in and out as it should. Started the car with the gear lever in reverse and the clutch in. The car started and did not move. Drove a little mile, and all gears is working great. The change is good and smooth. No sounds. Stopped to turn back home. When I tried to put the car into first, I got a grinding noise again. Same with reverse. After rolling back half a meter I was able to smooth it into first and got going. Again smooth shifts all way home. Parked the car, and tried to get it into reverse. Grinding again. Turned off the engine and went for dinner….

Have tried to adjust the transmission shift rod, but the shift is good as long as the engine isn’t running. But adjusting this today, I feel that there is some kind of grinding when moving the shift rod from side to side. When I originally adjusted this it felt butter smooth. But this might be a feeling.

Have been reading a lot of forum posts and webpages, and is still not sure what this could be. Is there anyone out there that have a good idea to what this could be?

[r_towle]

Re-adjust your clutch. The cable stretches

[mood]

Try waiting a few seconds before selecting first gear after pressings the clutch. Maybe the friction disc became sticky from oil contamination, possibly from overlubing the input shaft splines.

[yelcab1]

take out ALL the free play in the clutch mechanism. A 48 years old car no longer have the required clearance for the proper free play and clutch travel.

Then, you still have to drive it until the clutch wears in from its brand new profile.

[tdipower]

I have adjusted the clutch wire, and felt no difference other than the grip-point when I got it going. It was loose adjusted earlier. Is it possible to overtighten it as well? As this is an arm with only the wire, and seems to be produced only in 75-76, all manuals is different then my clutch arm.

Now the car was cold, and it was only a little touch when putting it in reverse. In first gear it went in fine… Will have to try it some more then I guess.

[tdipower]

Originally Posted by yelcab1

take out ALL the free play in the clutch mechanism. A 48 years old car no longer have the required clearance for the proper free play and clutch travel.

Then, you still have to drive it until the clutch wears in from its brand new profile.

So you think that it could be from using a new clutch? It is an upgraded Sachs clutch with 4 springs. The one I exchanged was a “normal” clutch with 6 smaller springs.

[RobFrost]

Sounds like the clutch isn't disengaging fully. You can confirm this if it goes away when you match engine speed to the gears.

Sent from my SM-G988B using Tapatalk

[winders]

Originally Posted by RobFrost

Sounds like the clutch isn't disengaging fully. You can confirm this if it goes away when you match engine speed to the gears.

Sent from my SM-G988B using Tapatalk

You mean double clutching? Matching speeds by blipping the throttle does nothing help synchros...

[r_towle]

If it’s hard to get into 1st and reverse, you may have a clutch that is not releasing or something funky inside the trans.

Mine does not alway go into 1st or reverse, but I move the cat with a different gear and then things line up.

Rivh

[yelcab1]

If the clutch disc is too thick (because it is out of spec, or different than stock which is what upgrading is) the pressure plate has to travel longer in order to release it fully. That does not happen until the extra thickness is worn off a little. I don't put in anything other than a stock clutch, otherwise there is no warranty.

[tdipower]

Today everything is fine again... Will try to run the car a bit warm again and see if that changes anything.

[Matt Monson]

What are you using for oil?

[porschedude996]

Any noises when trying to put into gear?

[Mixed76]

If your nose bearing is binding that can also cause the input shaft to rotate with the flywheel

Sent from my Pixel 7 using Tapatalk

[Tyson Schmidt]

Like mentioned, a tight pilot bearing could be making the input shaft want to spin flywheel speed.

I've also seen some new clutch discs that were over thickness, making the release travel further than the original mechanisms can handle.

3rd thing is if the disc center got bent during installation, from letting the trans hang off center with the input shaft partly engaged.

[porschedude996]

I’m thinking as described above that the problem could be an axial misalignment. Chocking the shaft on the rear input shaft and the pilot bearing worn would bring the shaft out of proper coaxial alignment. Thus the disc would be forced to bind on the spline of the input shaft and splined hole of clutch disc.

[Dpmulvan]

A 75 915 with only a bad 1st gear synchro ring? Curious who rebuilt your box and how many miles on it? Prior rebuild? What was the cost for rebuild?