ARGHHHH! 3rd gear synchro may have died

PcarPhil · 09:11 AM

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.

Stay tuned... Advice or suggestions are greatly appreciated!

Autoban · Autoban's Garage

Quote:

Originally Posted by Kaefer

downshifted into third and when I did it felt very weird - like the synchro literally was falling off 3rd gear during the shift.

Well, it sucks when these things happen totally out of the blue. What do you mean with it felt weird? I don't know how it feels when a synchro goes out. How does it feel like?

midnight911 · midnight911's Garage

I just had my 915 rebuilt. Dropped the engine and tranny myself. Surprisingly pleasant experience than I expected. Fairly quick. If you decide to do it yourself let me know I have a good checklist to make the work even easier. Good luck.

PcarPhil · 05-18-2012, 08:39 AM

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.

Autoban · Autoban's Garage

Reading your thread and looking at the pictures I'm getting concerned about my transmission. I bought my '86 Cab with 3.2L in January and have put about 4K miles on it. When I purchased it the shifting was bad with a lot of sticking and grinding. I replaced all the bushings (including the coupler) on the shift linkage and made several adjustments to the coupler. Now all the gears shift fine except sometimes 2nd. It feels like I'm hitting a wall (especially downshifting). I hold the shifter against the "wall" firmly and with some pressure and then the gear will slip in. However, this is not always and more when the car is cold.
From your experience, could I be heading down the same pass as you? I now have Swepco in it and are about to order Kendall to see if it makes a difference and to look at the plugs to see if there is metal. I will follow your thread to see what you find.

Good luck!

PcarPhil · 05-18-2012, 09:23 AM

Autoban,

Don't read into this issue to far - every trans is different! Actually my problem sounds almost the exact opposite of yours. I've never experienced shifting issues shifting into 3rd, but the wall you describe is what I sometimes experience shifting out of 3rd into 4th.

Elombard · 05-18-2012, 09:41 AM

Yah a few years ago I was driving along not aggresively and not paying close attantion and I shifted into third and let the clutch out....it was not quite all the way into third or the clutch was not quite all the way in (I forget) and a big grind. From then on it complained going into 3rd I must have shaved the synchro right off with that one miss. Baought a re built slightly used tranny that came up rather than a rebuild.

I think you should build it your self - you have the skills in spades and it will increase your knowledge.

My current trans fights me going into second- I think it is getting tired. I want to rebuild with short gears and a LSD here in a few years.

Autoban · Autoban's Garage

Quote:

Originally Posted by Kaefer

Autoban,

Don't read into this issue to far - every trans is different! Actually my problem sounds almost the exact opposite of yours. I've never experienced shifting issues shifting into 3rd, but the wall you describe is what I sometimes experience shifting out of 3rd into 4th.

Scott:

What does the shift fork do? Sorry, I don't know much about transmission.

Juergen

Matt Monson · 05-18-2012, 11:22 AM

Those pictures look like chunks of dog teeth, not synchro parts...

callard · 05-18-2012, 04:58 PM

+1 on dog teeth.

PcarPhil · 05-19-2012, 03:53 AM

Dog teeth. Ok, got it.

(remember I have zero experience with transmissions)

I'll be dropping the engine and trans hopefully within a week. In the mean time I guess I'll start researching my options of who/where/how to fix this trans properly in hopes that it stays reliable in front of my 3.6 engine.

Autoban · Autoban's Garage

Scott, I'm not sure where in VA you are. Another Pelican member recommended to me a guy at Summit Point raceway for 915 transmission work. I don't know the guy and have not talked to him yet. Summit Point raceway is just East of Winchester, VA. I'll be glad to PM you his phone number.

Juergen

Geary · 05:27 AM

Quote:

Originally Posted by Kaefer

... One of the first things I noticed .. it is sometimes difficult to shift out of 3rd ... Sometimes it's "sticky" pulling out of 3rd.

This "sticky" feeling is actually the shift sleeve "tugging" on the synchro ring, which in turn exerts excessive outward pressure on the circlip. (This circlip retains the balkring and blocks in the engagement teeth of the gear.) When this circlip pops out of its groove (not that uncommon), synchronizing action is lost on this gear (and the blocks can fly free). Park it and drop the trans before the R&P and/or gears are ruined by free-floating blocks. (Well, you had to anyhow, because of the broken engagement teeth.)

There are updated (stronger) circlips for the 915 synchro assembly, but the trick deal is to install 930 engagement teeth, synchro, and associated bits on 3rd & 4th gears. The 930 "internal" circlip can't pop off like the "external" 915 one. (A "must" mod for track use.)

Back to the "sticky" feeling .. something is going on to cause incomplete clutch disengagement. This must be corrected, or you could have a repeat.

PcarPhil · 05-21-2012, 04:08 AM

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.

PcarPhil · 05-21-2012, 04:13 AM

Quote:

Originally Posted by Geary

Back to the "sticky" feeling .. something is going on to cause incomplete clutch disengagement. This must be corrected, or you could have a repeat.

Geary,

Thank you for your input. 3rd gear has been occasionally sticky the entire time I've owned it. I'm pretty sure a bad shift on track before my ownership is the original cause of the problem.

I'm not stressing the situation as I knew I would have to eventually rebuild this trans due to the 3rd gear. Now is the time!

Tippy · 05-21-2012, 05:33 AM

I have shattered a synchro on American iron and it felt really weird too.

It felt like a gaping hole as the slider wasn't engaging with anything - which it wasn't.

I broke the ring in 3 pieces.

Peter Zimmermann · 05-21-2012, 06:41 AM

Here's what you need...

Welcome to Red Line Porsche Wiki - Porsche Wiki

Scroll the left side of the page, click on "915" under page tags, and you will be taken to my 9-part 915 repair Tutorial.

PcarPhil · 05-21-2012, 08:23 AM

Peter,

I did read your 915 tutorial. I'm thinking for this project I'm going to have a pro with 915 experience handle the rebuild.

Matt Monson · 05-21-2012, 08:52 AM

Scott,
Here's where to take your 915 gearbox in Virginia for a proper service and upgrades:
Lüfteknic - Porsche Parts, Service, Sales, Restoration, Motorsport in Richmond, VA

Regards,

Matt Monson
Guard Transmission llc

PcarPhil · 05-21-2012, 09:22 AM

Matt,

Thanks I am familiar with them. I'm also seeing what other options I have.

I'm checking with Gary up in CT and may be contacting you as well.

Thanks for the info,