[kaefer]

Bad news guys - I think the 3rd gear synchro may have died in my 911 yesterday. It seems odd to me how it happened too. I was just cruising on the highway and downshifted into third and when I did it felt very weird - like the synchro literally was falling off 3rd gear during the shift. I took it easy for the rest of the drive but the problem does seem like it's only affecting 3rd gear.

Last night I checked the shifter, shift coupler, and all external linkage and didn't see anything out of place. Today I'm going to try and drain the swepco and pull the inspection plate hoping I find a loose shift fork. I'll also be looking for loose bits of broken synchro.

I find it odd that seemingly at a random time the synchro just broke. I wasn't pushing it or anything.

Ugh. I've never done any transmission work. I'm already starting to think of the "while you are in there" stuff. Luckily it's already a late 915 trans with factory LSD and I like the gear ratios so I think any parts that will be replaced would just be maintenance items.

I'm not looking forward to having to drop the engine and trans for a trans rebuild. Oh well. I guess it's a good excuse to add some sound insulation on the rear firewall and more heat insulation around the muffler.

[kaefer]

More info:

I've owned this 915 trans for a few years and have put maybe 20k street miles on it (12k miles with a 3.2 and 8k with a 3.6 engine). One of the first things I noticed about this trans was that it is sometimes difficult to shift out of 3rd and into 4th. Sometimes it's "sticky" pulling out of 3rd. Shifting into 3rd has been no problem (until yesterday).

I change the Swepco at least annually (about 5k miles). A few times I have seen 1 or 2 pieces/teeth/chunks like in the pic below.

Time for some pics. I changed the swepco last year and the car has gone maybe 3-5k street miles since then. Also fyi I've been running Swepco 212 (not the usual 201).

Here's the magnetic fill plug. Lots of fuzz but nothing too out of the ordinary:




Here's the drain plug. This one unfortunately has some chunks in it:




The shift fork attached to the inspection plate seems fine. The fork is firmly attached to the plate - no movement. However I did find some small teeth/chunks that came out with the inspection plate.

[Vicegrip]

Dog teeth. Drop time. History of 3rd geat issues? save the time spent, pull the motor and trans get a new dog tooth ring and anything else needed and get backon the road.

I roasted 3rd gear on the #7 car. All it took to do this to a bone stock 915 was a 3.6L 993 motor and 600 or so WOT to red line pulls out of corners....

[kaefer]

Ok will do. I'll start planning the drop.

It still seems weird how this just happened in normal driving. I don't even think there was a substantial load on the trans when it happened. I was just shifting into 3rd to shift into 3rd.

Thinking back on things I guess I may have been exercising 3rd getting on the highway... Still, I don't powershift the trans or anything.

I guess it was just it's time to let go.

[Vicegrip]

could be. One goes and the shock load builds and moves to the next tooth in line it gives and on and on. the dog tooth ring can be removed from 3rd gear. They make a tool for pulling the dog ring but it is not needed if you use care. Slit it edge to center with a dremmel cut off wheel and the pop it open with a cold chisel. New ring has to be carefuly cleaned and presssed on tight. any gap between the dog ring and the gear wil cause issues.

[Dr K]

To my memory, the shift fork from the inspection plate looks worn/rounded. Sure, that's not your problem, but just one other issue.

[Lupin..the..3rd]

Originally Posted by kaefer

Here's the magnetic fill plug. Lots of fuzz but nothing too out of the ordinary:

Woah, nice porcupine! I would say that this much metal fuzz is definitely out of the ordinary.

[kaefer]

Yesterday I dropped the engine and trans in preparation for the trans rebuild. This time I decided to do things a little different and make use of my lift vs. doing the drop on the floor. This method turned out to be very easy and I did the drop solo in record time.

Now that the easy part is done I need to figure out what I'm going to do with the trans. Since the trans is paired to my 3.6 I'll either go with a stockish rebuild with reinforcements as necessary or go all out with close ratio 2nd, 3rd, 4th, and 5th gears and required reinforcements.

[kaefer]

Originally Posted by Lupin..the..3rd

Woah, nice porcupine! I would say that this much metal fuzz is definitely out of the ordinary.

Yes. It's officially time for a rebuild.