Rebuilt tranny...um...sort of works?

[Wrecked944]

Well, I got the newly rebuilt 915 transmission back in the car and hooked up everything last night. This morning I filled her up with oil and fired up. Reverse and first gear were engaged with no problems. However, as I rolled down the road, the underside of the car began making a chattering noise. It was not rhythmic - it seemed almost random and unrelated to my speed or tach. It only happens when the car is in motion and is unaffected by engaging or disengaging the clutch. I shifted through the first three gears and found that the chattering stopped abruptly when I shifted into third gear. Once in third gear, the car is quiet, smooth and happy. Shift out of third gear and she starts chattering again. I tried shifting into fourth gear, but the tranny grinded HORRIBLY whenever I went anywhere near fourth gear. This was not just balking or a little crunching...this was an awful grinding. I also noticed that second gear occassionally exhibits this godawful grinding...but with some TLC, it can be coaxed into gear without incident. Unable to use fourth gear, I never made it to fifth gear.

Any ideas? Is this stuff relatively normal after a rebuild? I am cruising here at Cluefactor Zero, Captain.



Thanks,

[island911]

if it's mounted correctly there should be no problems.

[Wrecked944]

What could have gone wrong with the mounting? The two motor mounts and two tranny mounts are attached. What are some of the typical ways of screwing this up? Maybe I twisted something or misaligned something?

I defintely had a little trouble getting the engine and tranny mounts lined up. It seemed either the engine mounts would line up or the tranny mounts...not both at once. So I basically lined up the engine and attached the mounting bolts. Then I just manhandled the tranny until the bolts lined up. It didn't require a great deal of effort to finally get it together. With engine and tranny bolted together, should the mouting bolts line up easily or does it normally require a bit (not a lot) of adjusting?

And if it is any help, I went out to do some more testing and found that fifth gear engages with no problems. Fourth is still unavailable and second still needs lots of TLC. Oddly, I often find that first gear engages poorly - as though first gear was very tall or I had accidentally started in third (which I checked and is not the case). Maybe this chattering is the clutch? Perhaps it is not fully engaging and slipping? The car seems to have very little power in any gear. I did a search on clutch chatter but could not tell if it is something which happens all the time or only of the clutch is engaged in certain gears.

I am at a loss. Heck, at this point, I'll even try popping a different tape in the tape deck to see if that helps.

Thanks,

[Dan Owens]

There isn't quite enough info to go on here. Does it make the noise while it's sitting still with the engine running, In gear or out? I guess I'll break the bad news to you. By the sounds of what you describe this may have nothing to do with the motor mounts. It could be that you don't have the shift shaft and coupler aligned correctly so it's not mating up to the gears. Does it shift into all the gears with the engine off? Have you re-checked the clutch adjustment? You may also want to check your CV joints and make sure that's isn't where the chattering is coming from. Last but not least there could be something amiss inside the trans.

[Early_S_Man]

Janus,

This doesn't sound good! Did you 'bench check' shifting into all gears ... before you put the transaxle back in the car?

[Jim Sims]

From your description it appears something is amiss on the main or input shaft. Probably the 4th gear synchro assembly is "messed up". The grinding you hear/feel when you try to go into 4th is the teeth of 3rd/4th operating sleeve and 4th gear dogteeth hitting each other (as they go past each other at different speeds) because they're not synchronized. I would stop trying to put it into 4th gear as you're likely damaging the teeth. The fact that the random chattering goes away in 3rd also points to a problem in this area. Did you trial shift the transmission "on the bench" after assembly? How did it shift; did it go into all gears readily? This is a start, but won't check whether the synchro works in dynamic operation. I would remove the transmission and inspect the main shaft for proper assembly (all parts in the proper order and orientation?) and check the 3rd/4th shift fork/operating sleeve position. Did you you use a shift rod template to set it? Good luck. Jim

[Wrecked944]

Wow, thanks for all the replies. I'll try to provide as much info as I can. The chattering only happens when the car is in motion. I bench tested shifting into all gears before closing up the case - checking to make sure all the synchro teeth mated. I also used the special jig during assembly. I also tested shifting into all gears before starting up the car and had no problems. I just crawled under the car and saw that my clutch linkage is out of adjustment (new clutch cable). I am hoping this will solve the power problems due to slippage. But as for the chattering and the grinding? Still not much of a clue. Standing still with the engine off she shifts into all gears no problem. Weird. I'm also not assuming these problems are all related. For instance, maybe the chattering isn't the tranny? Maybe it is the CV joints and I torqued them down wrong? I defintely broke a bolt on the sway bar mount during re-installation but it doesn't seem to be moving around much.

I'm just spilling data at this point. Not sure what is relevent and what is not.

[Early_S_Man]

Janus,

The 'bench testing' of shifting Jim and I were asking about isn't done until the transaxle is completely finished and ready to go in the car ... it is done from the shift rod where the coupler normally connects, typically with a 'T-handle' ...

I doubt that you can depend on CV-joints to be the culprit ... the trans needs to come out, again!

You may want to do one final test with the tail end up on jack stands ... run engine, and go through the gears with engine at idle, but don't force it into any gears that resist or make noise while attempting to get it into gear.

[Jim Sims]

There is a chance your clutch isn't releasing fully and allowing the synchro's to work. Try adjusting the clutch; ensure you have the right amount of free-play. Jim

[Jim Sims]

Free-play should be 15 to 20 mm at the pedal. Another question: did you put a small amount of grease on the main shaft splines where they pass through the clutch disk and also on the tip that engages into the pilot bearing in the end of the crankshaft? Jim

[Wrecked944]

Oh...My...God...I am such an idiot. Were he alive today, Herr Porsche would confiscate my car on the grounds that dumkoffs should not be allowed to drive his vehicles. This is really unbelievably dumb...it is hard to even type the words because I am so unbelievably embarrased...but here goes...

Not realizing that moving the shift lever to the left turns the shift linkage to the RIGHT, I had set the shift linkage adustment way too far to the right. So the gears were all shifted to the left. What this means is that when I said the car seemed like it was in third when it was in first, it really WAS in third (no wonder it had no power). When I thought I was in third, I was really in fifth. And when I was trying to shift into fourth, well...I was actually trying to shift into reverse at speed. And when I thought I was shifing into fifth, I really was in fifth except I was pushing the lever way to far to the right to do it. I am so glad I caught that mistake before completely destroying my transmission...

Anyway, if my Pelican membership doesn't get revoked for that bonehead move, I can happily report that re-adjusting the shift linkage fixed most of the problems. I also re-adjusted the clutch linkage. So now the car shifts smoothly through all five gears. No whining or whirring or grinding. And yes, the new 7:31 ratio seems to give it a big boost on the butt dyno (now that I am actually using the proper gears). So for the first time since April, the car is once again a five speed. Hurrah !!



However, the chattering sound remains. It seems to have no effect on performance, so part of me thinks I should just buy ear plugs. But all kidding aside, it only happens when the car is in motion, seems unaffected by engaging or releasing the clutch, seems to go away when I am in fifth gear (not third gear as previously reported), seems unaffected by my speed...it isn't rythmic...almost random...I am, of course, very suspicious of everything I touched...fifth gear slider and reverse idler arm seem likely suspects (hmmm...)...CV joints (maybe poorly torqued bolts, dirt, bearings "messed up" somehow)...sway bar mount...heck maybe I left a wrench inside the tranny before I closed it up...

Very weird.

[john walker's workshop]

if the 5th/reverse operating sleeve is adjusted too close to the reverse idler, their teeth will constantly rattle against each other.
is there any backlash noise on and off throttle, or heavy whining on acceleration in all gears? just wondering about the 7:31 R+P swap, and if you got the clearance right between them.

[Wrecked944]

JW - You are absolutely correct. I continued testing and driving and discovered I can totally stop the chatter by nudging the shifter slightly towards fifth gear and make the chatter louder by nudging slightly towards reverse. So I will just drop the engine/tranny again, pop off the front cover and re-adjust the fifth/reverse slider. No worries. Easy as pie.



And as for the 7:31 swap, I find that driving in fifth gear (to eliminate the chatter) produces a totally quiet ride. No whirring. No grinding. No humming. Nothing. Fast, slow, throttle, brake. It is totally smooth and better than ever.

And I should emphasize that the ring/pinion swap was accomplished using only a brief paragraph written by you in response to a question I posed about setting pinion depth. No other documentation was required.

So John Walker, for the record, you are a genius.

Thanks,

[hpv@west.net]

Originally posted by JanusCole
Well, I got the newly rebuilt 915 transmission back in the car and hooked up everything last night. This morning I filled her up with oil and fired up. Reverse and first gear were engaged with no problems. However, as I rolled down the road, the underside of the car began making a chattering noise. It was not rhythmic - it seemed almost random and unrelated to my speed or tach. It only happens when the car is in motion and is unaffected by engaging or disengaging the clutch. I shifted through the first three gears and found that the chattering stopped abruptly when I shifted into third gear. Once in third gear, the car is quiet, smooth and happy. Shift out of third gear and she starts chattering again. I tried shifting into fourth gear, but the tranny grinded HORRIBLY whenever I went anywhere near fourth gear. This was not just balking or a little crunching...this was an awful grinding. I also noticed that second gear occassionally exhibits this godawful grinding...but with some TLC, it can be coaxed into gear without incident. Unable to use fourth gear, I never made it to fifth gear.

Any ideas? Is this stuff relatively normal after a rebuild? I am cruising here at Cluefactor Zero, Captain.

Check your shift coupler behind the seats,the plastic breaks up and you can't find gears. $50.00 Henry

Thanks,