Why does my SC want to pop out of 1st gear?

[oregonmon]

Hey all,
So my 79 SC has some of the common shifting quirks of the 915 that I've heard others talking about. Have to be completely stopped to get in 1st, a little clunky into 2nd. I just can't power shift the thing, I know.
But a few times, first time was at autocross at the start, when I try an aggressive launch, the car shutters and the gear lever popped out of 1st. Took it to my a shop and the guy said the shift coupler was loose so he tightened up, which I could feel. As a separate project I asked him to check the tranny mounts. He said the 2 in the back were worn and allowing some play. He replaced them, which I did notice a difference as well.
Because of all the tranny symptoms above, I thought it maybe time for a rebuild of maybe the 1st and 2nd gears but after him doing the adjustments, he thought it was pretty good. I got the car back and although the tightened coupler and mounts tightened things up a bit, it didn't fix the shuttering.
Your guys thoughts.

[enzo1]

clutch?

[oregonmon]

Crap. Forgot to mention that clutch assembly was done about 5000 miles ago.

[oneblueyedog]

1.Clutch cable adjustment. (common shudder symptom but not gear jumping)
2.Shifter adjustment if he took the shift coupling off. (not a shudder symptom though)
3.Grease on the clutch from spline shaft too greasy, or oil seal leaks. (stinky shudder)
4. Flywheel not true to new disk and pressure plate (true it up if within tolerance)

Hope it helps

[enzo1]

"it didn't fix the shuttering", two different problems ? Did it do it right after the clutch assembly, then guessing, #4 from above poster or cable adjustment

[oregonmon]

It did not do it right after the clutch job. Are these symptoms that there might be something wrong internally with the transmission?

[Porsche_monkey]

When my 915 popped out of second the dog teeth and synchro's needed replacing.

[911pcars]

Lift the shift lever boot out of the way so you can see the position of the shift lever in neutral. It should be exactly halfway between the stops.

If the shift bushings haven't been replaced for awhile, I'd try that next.

Shuddering is usually caused by grease or lube on the clutch facings (leak from input shaft seal, excessive lube applied to the TO bearing shaft, leaking rear main seal).

Also check the motor and transmission mounts; make sure they're okay..

Sherwood

[Peter Zimmermann]

Originally Posted by oregonmon

Hey all,
So my 79 SC has some of the common shifting quirks of the 915 that I've heard others talking about. Have to be completely stopped to get in 1st, a little clunky into 2nd.
But a few times, first time was at autocross at the start, when I try an aggressive launch, the car shutters and the gear lever popped out of 1st.

1. Drain the trans oil and see how many dog teeth are on the drain plug magnet.

2. Your need to be stopped to engage 1st is a classic 915 synchro problem. As a synchro wears out the friction ring deteriorates, which leads to grinding, which leads to broken dog teeth, which leads to a non-synchro type of shift quality.

3. Clunky into 2nd is also a fairly good indicator that the 2nd gear synchro is also near its end.

4. Shutter (I assume that you are talking about clutch chatter) can be many things; clutch cable, clutch adjustment, a failed main shaft seal that has allowed trans oil to contaminate the clutch disc...even driver technique. Aggressive autox starts are not something that the 911 takes kindly to.

5. Popping out of 1st can be, and usually is, caused by #1 & 2 above. It can also be a miss-adjustment of the shifter/coupler which prevents complete engagement of 1st, but given your other symptoms, I doubt it.

[911Rich]

Sounds like synchros but, besides the usual bushing/coupling/alignment issues, whenever I see 915 shift problems, I first check the shift alignment fork as they love to come loose, there is a recent thread on here I replied to describing the entire issue.

Shifting issues driving me Crazy! Few ?'s...

[oregonmon]

Thanks guys for reading and posting.
Regarding some things that have or have not been done. I belive the mechanic replaced the rear main seal when he did the clutch. Also, bushings have been replaced as well. I guess there still could be a leak to the clutch though. I guess I will check with the mechanic to see what areas he tried adjusting.

[oregonmon]

Could this be motor mounts? Mech replaced the two mounts toward the rear, but not the front.

[Porsche_monkey]

Read what Peter Zimmermann wrote. I suspect he is correct. The trouble is inside, not outside the tranny.

[Paulporsche]

When it happened to my trans it was dog teeth.

[sc_rufctr]

I would have thought that "popping out of gear" would be a symptoms of worn synchro rings and the internal friction surfaces of the "sliders".

If you think about it these two items keep the dog gear "teeth" meshed with the teeth on the "sliders".
But it would depend on when the "popping out" occurs.

If it happens on over run, after removing your foot from the accelerator then I would suspect worn synchros and sliders only...

But if it happens on acceleration then I would suggest in addition to worn synchros and sliders the dog gear teeth are worn or broken as well.

[DonNewton]

Why does the car pop out of first? It doesn't like you.

[oregonmon]

Originally Posted by sc_rufctr

I would have thought that "popping out of gear" would be a symptoms of worn synchro rings and the internal friction surfaces of the "sliders".

If you think about it these two items keep the dog gear "teeth" meshed with the teeth on the "sliders".
But it would depend on when the "popping out" occurs.

If it happens on over run, after removing your foot from the accelerator then I would suspect worn synchros and sliders only...

But if it happens on acceleration then I would suggest in addition to worn synchros and sliders the dog gear teeth are worn or broken as well.

No, the tranny and shift lever starts to shutter if I release the clutch too quickly than a couple of times it popped out right when I release the clutch. I'm really starting to second guess the mounts.
I really don't have the tranny knowledge but if these were worn couldn't it allow the tranny/engine to move therefore it popping out of gear.

[sc_rufctr]

Originally Posted by oregonmon

but if these were worn couldn't it allow the tranny/engine to move therefore it popping out of gear.

In theory this is possible but the natural/natural play in your shift linkage bushings should prevent this happening... (lots of assumptions here)

What I suspect is happening is that your trans, clutch, shift linkage and engine mounts are all worn to a point that combined together are causing you to pop out of gear.

If you fix one thing it, like replace the engine mounts it may improve things but the rest of your issues may "catchup" eventually.

I guess the logical thing to do is check and replace as required anything on the outside of the trans that could be causing this.
This list isn't long... Engine mounts, clutch check and adjustment, shift rod coupler, bush at base of shifter and finally a proper adjustment of your shifter.

If it still pops... The only thing relatively easy to check is the shift fork in the base of the trans. (although I doubt this would cause popping out of gear)

If it still pops after all after all this then the problem must be with the internals of the gearbox...

I was never completely happy with the shift of my gearbox. I worked through the list until I got to the shift fork check but my gearbox never popped out of gear.

My thread is here .... Turned out to be a bit more complex...lol... 915 Shift fork check with an unexpected outcome

I'm re assembling this troubled trans at the moment. Long story but I have to source a second hand trans with a known history as a replacement.