While the tranny's out...

ohecht · 10:14 AM

I have my 915 transmission out of the car for some clutch work, and I am curious if it makes sense to try to repair the one small problem the transmission has.

This is my first 911 and 915, so I am not even sure if there is a real problem. I seems that the 1st gear synchro is weak. I can only go to first when the car is totally stationary, or when going from reverse to first and hitting second with the clutch in as the car is slowly rolling backwards. Any forward movement makes going into first painful and noisy for the transmission.

It gets annoying only when red lights turn green and I need to either stop short and risk getting rear-ended to get into first, or stay in second and bog the engine.

Is this something that is worth fixing? I would only consider it if it was one of the first parts I would get to in tearing down the transmission. I don't think I have the tools, patience, or space to pull everything apart and get it back together right.

Thanks,

Olivier

SC-targa · 12-03-2003, 05:09 AM

You really should rebuild it while you've got it out. It'll just tear more things up if you don't. Unfortunately, 5th and rev are the first things you get to when you open it up. First gear is at the other end of the gear stack and you have to take the whole tranny apart.

Regards,

Jerry Kroeger

ohecht · 12-03-2003, 05:32 AM

Do you really think it is worth a total rebuild just for the first gear issue? I have always looked closely for any synchro fragments during annual oil changes through the access plate, and found none.

Do "normal" 915s shift smoothly into first when the car is moving? (this is the oldest manual transmission I have ever owned)

Thanks,

Olivier

RoninLB · 12-03-2003, 05:42 AM

I always stop a reverse roll before shifting into 1st.
I always whack going twords 2nd before 1st.
I double clutch when tranny is cold.
I double clutch, and blip the gas in netural, when in a slight roll before 1st.

IMO, 915s suck. I drove a non syncro fire truck a long time ago that was more fun than my 915.......Ron

12-03-2003, 06:05 AM

Quote:

I always whack going twords 2nd before 1st.

Won't that grow hair on your shifting palm?

red-beard · red-beard's Garage

Rebuild it....

RoninLB · 12-03-2003, 06:41 AM

Quote:

Originally posted by red-beard
Rebuild it....

Jim Sims did an excellent couple of posts on rebuilding DIY.
I think he said a minimum of $700 in parts for a good simple rebuild.... Ron

john walker's workshop · 12-03-2003, 07:19 AM

i often do just a first gear repair. it's pretty easy, and doesn't require a complete teardown. the end cover comes off, then the 5th and reverse items are removed. the center housing comes off next, after removing the square shift guide plate. the gear stacks are now visible. pull off the bearings on the end of the shafts. 1st gear can be slipped off the pinion shaft at this point, to replace the syncro, and maybe the syncro teeth if they're worn. in addition, it's a good idea to replace the shift sleeve, because they wear out from scrubbing on the syncro ring. to get the sleeve off, mark the position of the shift fork on it's shaft, remove the lock bolt, and tap the fork off the shaft. be sure to point the shift sleeve's assymetrical side toward 1st gear on reassembly. there is one detent that has to be paid attention to. it's in the center housing on the 5th/reverse end. it has to be all the way inward, as the center housing is installed over the gear stacks. failure to do this can/will result in getting stuck in 2 gears at once. on reassembling the 5th/reverse setup, be sure that when in neutral, that the reverse idler teeth don't touch the teeth on the 5th/rev shift sleeve, or you will have a strange clatter. this can be avoided by not removing the lock bolt on the 5th/rev shift fork, so the fork position is not changed. the fork, shaft, and shift sleeve are removed together, after popping the main shift rod up and away from the 5th/rev shift sleeve to make room to remove the fork, shaft and sleeve as a unit.

ohecht · 12-03-2003, 08:27 AM

Thanks, John. I may give all of that a try if I can muster up the courage. Which of the special tools are necessary for that level of rebuild?

Do my symptoms sound like the first gear syncro and/or syncro teeth?

Olivier

dtfastbear · 12-03-2003, 11:51 AM

If first gear is the only issue you've got with the tranny, there are probably a LOT of miles left on the tranny before you truly NEED a rebuild. My first gear synchro was "shot" when I bought the car, and I put another 35,000 miles (about half of those on the track) on the tranny before I truly needed to rebuild.

If you can drop the engine and get the tranny off yourself, you don't gain all that much by doing this all now. However, if you have to factor in $500-700 for someone else to drop/lift the engine, then it might be worth it to do it now.

Just my two cents,

Dean

CHILI · CHILI's Garage

I love the title of the thread! Famous last words.

I replaced all 5 syncros (both from PP of course) about a year and half ago. I thought I lost 5th gear, but I guess it was just the linkage. Never figured that one out. Anyway, I can't believe all of the crap in there! Man, it's just 5 gears and looks more complex than a motor!

BTW, a buddy who races in POC helped me do it. I just took the case and clogs home to run through a parts cleaner bin. He did it all by memory. I couldn't beleive it. He looked up one torque setting and was right anyway. I want to be him when I grow up! hehehe

ohecht · 12-03-2003, 12:27 PM

"Famous last words" is the story of my mechanical life. I am always doing "while I am in there" things that either snowball or cause damage, but I can't resist the challenge and learning opportunity.

Dean, I am in the same boat, the car was this way when I got it 30,000 miles ago, and it is a minor complaint at best. I have never had any other problem with the tranmission, it runs all day without getting over 125 degrees and shifts great.

Dropping the motor and transmission took all of 6 hours working alone and for the first time, and I will be smarter about how I route and where I put the connectors in my aftermarket wiring in the future!

The hardest part was grinding off the engine-to-trans nut on the lower non-starter side that was totally seized without hurting the stud. That thing is tough to reach and I even had to grind off the washer to separate everything!

I am highly tempted to try and follow John's instructions, but I think the potential for damage and further expense is too high right now. I'd rather learn on a transmission that is already blown anyway or at least undriveable, so I can't make things worse so easily.

We'll see if I can resist peeking inside...

Olivier

john walker's workshop · 12-03-2003, 01:30 PM

it's not that hard.

ohecht · 12-03-2003, 02:24 PM

You're tempting me again...I will look at the Bentley manual again to see if I can risk it.

Would I need the special tools for separating (dog?) teeth, shifting gears, etc.?

Randy Webb · 12-03-2003, 04:13 PM

You can also spray a sound barrier on the tunnel above the tranny -- someone told me that (Ron?). I did it but don't have the engine back in yet so can't tell you how it sounds.

john walker's workshop · 04:59 PM

if the 1st teeth are chewed, the special tool makes removal easy, but i've done them in the past with a hammer and chisel sharpened to a knife edge. you work the teeth out enough so a crowfoot prybar can be inserted underneath to finish the removal. (facemask and gloves recommended to protect from possible metal chips). the new one should be pressed on. you really don't need any other special tools to do 1st only. just mark the 1/2 fork position on the shaft, and remove the 5th/rev fork and shaft together without loosening the bolt. a 1 1/16" socket for the mainshaft nut, a 1 7/16" socket for the pinion nut, a pin punch, 13mm socket and 13mm wrench, and even the shaft bearings generally come off pretty easily without a puller, just light tapping under the inner race. don't forget, it's just a partial teardown for 1st only.

12-03-2003, 05:11 PM

John knows...............

ohecht · 12-03-2003, 09:16 PM

I trust John's advice, just not my own track record for things like this. The Bentley instructions are pretty intimidating and it is hard to see how to get to first gear quickly following their directions. It is the little tricks like leaving certain bolts in place to save alignments, etc. that really help doing things like this when the whole thing is not being rebuilt.

Olivier

ohecht · 12-03-2003, 09:17 PM

Randy, I don't understand the sound barrier reference.

Olivier

84toy · 12-03-2003, 09:39 PM

I just overhauled my transmission. I replaced all the synchros, 4 dog teeth and 2 shift sleeves. 5th gear was OK I also replace my clutch cable and helper spring. With everything new, it drops into first at any speed without a problem and shifts very smoothly. I put about $800 total parts in the tranny. If you have never done a tranny, it might scare the hell out of you. If you have done other tranny work, it's no big deal.