915 Questions

[motogman]

I am contemplating replacing the syncro rings in my 915 trans. Car is 81 with 68k miles.

I don't know if this perception is correct, but my understanding is that a big part of the set up challenge in a trans-axle rebuild is getting the ring and pinion set up correctly. If just doing the syncros, can you leave well enough alone with the ring and pinion and be OK?

Is lack of synchronization in the 915 due to the wear of the friction material on the steel syncor rings? If so, then when in the trans replacing the syncor rings (to refresh the friction material on the steel rings) what are the other - really should do items?

Is this minimal rebuild approach going to end up with additional problems shortly down the road that one might regret?

I am not sure where to head yet, a trans oil change is the first step, but I am interested in the informed opinion found here.

[plumb4u2]

i am no expert but i do know that my tranny didnt shift that well until i learned how to properly adjust my shift coupler.

before you go through all this trouble are you sure all your bushings are in good shape and coupler adjusted as it should be?

[motogman]

Well.... No. I am not sure.

Others... can you tell me more?

[plumb4u2]

do you have Waynes book 101 projects? this is a great tool to have and describes everything you need to know

You can also go to the tech info section at top of this page to get instructions

[Bob Kontak]

Good idea to check.

plumb4u2 provides sound advice.

Suggest reading this: Swepco Transmission Fluid Question

The dis-assembly and re-assembly of a 915 transmission by a very competent technician - one who repairs Porsche transmissions for a living - is $750-ish labor if you drop it off on their doorstep. Parts extra, of course. The parts are pretty standard as to price. $750 is not a lot of money - like maybe a rebuilt warm-up regulator. Just data that you should consider before ripping into it.

So for my 915 I had Mayo Performance do the work. Below are a few pics.

First pic shows open and cleaned case against a wall full of tools I have never seen before.

Second pic shows some kind of special socket and fixture that Harbor Freight Tools does not sell.

Third pic shows a shift fork jig that you will need.

Fourth pic shows complete.

Last is in my garage where I put it back together.

Several problems from previous work were identified and corrected.

[Eagledriver]

You are right about not having to reset the pinion depth if you don't change the pinion shaft or number of shims. The syncro rings wear the most, but you also need to evaluate the sliders (rings with dog teeth that mesh with the dog teeth on the gears). An experienced eye or comparison with other parts is the only way to evaluate them. The dog teeth on the sliders and gears need to be fairly sharp and not rounded or buggered up. Since most of the cost is the assembly and disassembly you might send the shafts and sliders to a shop for evaluation. Other potential problems are the bearings and bearing races. The races tend to loosen up in their bores and spin. If the races are moving around you'll need to do something to fix the case or change cases.

-Andy

[bullethole]

Phil (or Pete not sure) Zimmerman (I'm sure of the last name) on this board has an excellent write up of re-building a 915. I knew after reading it that I would personally NEVER attempt a rebuild myself, but you may be more adventursome than I am (I'll rebuild a motor, but i'll leave the 915 to a pro).

I was having major problems with my 915 shifting from 2nd to 3rd (hargett precision shifter). So much so that I lunched the 1st gear syncro (new) on a newly rebuild. I ended up buying a 2nd trans and when I had the same problem, I knew it was not the trans. Ended up figuring out that if I moved the shift lever about 2mm further to the right on the upshift that i never had the problem again (retrained my muscle memory). So I have to adjust the linkage such that the 3/4 plane moves the shaft a little more to the right... Check your linkage, you'll be amazed at what it can do to change the characteristics of the gearbox.

[Peter Zimmermann]

Originally Posted by motogman

I am contemplating replacing the syncro rings in my 915 trans. Car is 81 with 68k miles.

I don't know if this perception is correct, but my understanding is that a big part of the set up challenge in a trans-axle rebuild is getting the ring and pinion set up correctly. If just doing the syncros, can you leave well enough alone with the ring and pinion and be OK?

Is lack of synchronization in the 915 due to the wear of the friction material on the steel syncor rings? If so, then when in the trans replacing the syncor rings (to refresh the friction material on the steel rings) what are the other - really should do items?

Is this minimal rebuild approach going to end up with additional problems shortly down the road that one might regret?

I am not sure where to head yet, a trans oil change is the first step, but I am interested in the informed opinion found here.

Here you go...

Welcome to Red Line Porsche Wiki - Porsche Wiki

Scroll left side of page, click on "915" under "Page tags" and enjoy the Tutorial. Hopefully it will answer 99% of your questions!

[motogman]

Thanks all. Thanks Peter.

I will do some more reading, some more research and likely ask some more questions.

The shifting is not a huge problem for me but after having driven another SC recently, I now realize how tough my car is to shift.

[ivangene]

I have followed "some" of this and didnt read it all....

BUT

there are huge gains from a properly adjusted and re-freshed shift linkage system including under the shift housing, top of the shift tower, coupler and all the bushing and connections - ALL of these parts are dirt cheap too and can be replaced with very little "know how"

another great place to look is inside your trans...that is it running for oil? I had a profound change when I switched to the Kendall NS-MP oil,,, and many say Swepco 201 is the stuff... but you can see what's in there and change it out for a chance to make things better too

[al lkosmal]

+1 for Ed's and bullethole's advice. At least from a prioritization standpoint. Before you tear it down............hit the basics. New juice, new bushings and a linkage adjustment may improve the situation dramatically..............if not, dig in. Lots of guidance for the tranny rebuild from Peter and others................or open your wallet and take it to one of the masters. Typically not a huge hit.

Regards,
al

[ivangene]

OHHHH

I forgot to add...

adjust that clutch - WOW!!! I was amazed how much that even changed things....