915 jumps out of 1st

[IMSA GTU #55]

My 83 SC is jumping out of first. I have read some posts, and I have checked the linkage, etc- all ok. What actually would cause it to jump out of gear?

[mnewport]

Mine does the same. Same car, btw.

[oregonmon]

Possibly bad trans/engine mounts. Start with the small stuff first. Mounts seemed to help mine.

[dentist90]

Assuming you are properly in 1st gear (no issues with coupler misadjustment) there are two things that 'lock' the tranny in gear: one is the shift sleeve (slider) snapping over the synchro ring, the other is a spring loaded detent on the shifter shafts that helps lock in the selected gear and locks out other gears.

As far as I know, the detents aren't a common wear item, so it is most likely worn synchronizer ring/sleeve teeth. If your transmission also crunches when you try to engage 1st while still rolling it is most certain your 1st gear synchronizing components are warning you.

[john walker's workshop]

check your drainplug magnet for little broken teeth.

[Bmxrams80sc]

What does a brand new tooth look like? Opened up mine today and on a few of the rings, the teeth are full size only half way up one tooth then the rest of the tooth is about 2mm thinner

[IMSA GTU #55]

OK, I found several teeth on the drain plug this morning, so I spent the rest of the day pulling the engine/trans. My plan is to open it up, replace the broken parts and put it back in. I was having trouble getting in 2nd before it started jumping out of 1st. I know exactly when I broke 1st- I was really beating on it at the time because of some jackass in traffic. I should have known better.

[dentist90]

Originally Posted by john walker's workshop

check your drainplug magnet for little broken teeth.

Originally Posted by IMSA GTU #55

OK, I found several teeth on the drain plug this morning...

JW has spoken. Again.

John - have you given any thought to diagnosing Porsche problems as a career?

[James Brown]

Skool of hard knocks my friend, John has sean 100's of these things. Oh and yes, he is the Dean!!
Hey IMSA GTU #55, what is the engine hoist connected to?

[IMSA GTU #55]

James- It's a pain jacking the car so high to get the engine out(jack stands don't go that high), so I remove my fiberglass bumper, lower the engine/trans, then lift the rear of the car with the hoist, and roll the engine out. I hook the chain hooks to the factory tie downs on both sides. I had this out in a couple hours by my self, no sweat.

[James Brown]

cool, nice job. are you rebuilding the trans. yourself?

[IMSA GTU #55]

Yeah, I'm going to give it a try. It looks pretty straight forward. I'm pretty handy when it comes to cars

[Joe V]

Hey IMSA,

Where in Tampa are you? I'm in Brandon, so if I can be of assistance, let me know.
Did my first tranny last year and, with the help of JW and this board, she's been great since. Even put a 2 day DE at Sebring on her with not a whimper.

I've got the shaft nut tool if you need to borrow it.

Anything to help out a fellow Tampon.

[IMSA GTU #55]

Hey Joe!

My car hobby shop is near the RJ stadium. Thanks for the assistance offer, I might need it. Sounds like yours turned out good.

Karl

[AlfonsoR]

Pete Zimmerman is putting together some kind of tutorial on rebuilding a 915. Not sure if he's mentioned it here or on Rennlist.

Also, Siene has instructions on blueprinting 915 shift linkage: Seine Systems > Blue Printing the 915 Shift Housing

[john walker's workshop]

you can rebuild the 1st/2nd syncro assembly without even removing the trans from the engine. both out of the car of course. end cover off, 5th and reverse items off, leave the fork clamped to the shaft and slide it off with the shift sleeve, remove guide fork plate off the center housing and then remove center housing, exposing the gears and shafts. carefully remove the roller bearings, mark where the 1st/2nd fork sits so you can duplicate that (leave it's shaft alone), and the rest is obvious. there's a detent in the end of the center housing that needs to be all the way down against the spring before installing the housing.

[IMSA GTU #55]

John,

Good idea. I got the engine/trans on the bench and tore it most of the way down after work. I took the center housing off, and sure enough 1st/2nd is completely shot.

[Hugh R]

That is how I pulled the engine in mine with an engine hoist. I owned the hoist, so why buy RV jackstands and an RV jack?

[James Brown]

Does sound like a slick idea, I have the 1/2 ton stands, they don't go that high. And I have a engine hoist from the "old days". Might put it to work!

[AlfonsoR]

IMSA, I'm impressed at how quickly you go after it!! Good job.