Where to go from here...or how to approach this? (915 trans)

[BGCarrera32]

Hello all

As my 3.2 to 3.4 engine rebuild is nearing completion, I wanted to run through my 915 box. It's from my '84 Carrera, but the transmission has a storied history, not all of which is bad.
Somewhere prior to my purchasing the car 10 years ago, the box had been rebuilt. Evidenced by the gray spray paint all over the outside of the housing...derp...the front housing bell, center section, and several matching gears inside having been marked with 5-'85 indicating they were clearly not from the '84.

The box shifted very mediocre years ago when I bought the car, but felt really stiff going into 1 and 2. I opened it up back in 2004 (15k miles ago) and replaced the 1-4 synchro rings and brake bands, and gave it a fluid change. That in itself was a noticeable improvement in shifting smoothness, but I always felt that it could be better. My car is 90% street, 10% DE male crisis mobile.

Going through the box this time, I want to solve the following:

1) Smooth as possible shifts into 1 and 2
2) Under hard full throttle acceleration, the shift lever felt to "fly" out of 2 on the way across to 3rd. Perhaps this could be chased to a coupler adjustment and trans mounts, which will become Wevo blues this time around (would like an opinion on this too.)
3) Evaluate everything- gears, sliders, dog teeth
4) Removal of the evil rebuilder's spray paint

The conundrum is throwing money at everything and refreshing it all, which sorta seems unnecessary. From machine and bicycle bearings I've looked at over the years, the bearings in here look very, very good. And again, no idea what sort of mileage is on them, but probably far less that average. The center carrier bearings are tight in the housing, no issues there. If I purchase all the tools to press gears on and off, the $ adds up quick. It almost feels as if I should hand over the gear stacks to an expert, and go from there. Can you see anything from the pics below, and how would you approach this in the most cost effective and reasonable manner?

Please discuss! Better pics and more complete ones are here:

More images and more details here:
https://picasaweb.google.com/bgale911/9 ... 9cXUloaBfw

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[Steve]

Hi,

Perchance, did you measure & replace the operating sleeves, spiders and energizers (stop & anchor blocks) when you rebuilt it?

While its a complex issue and too much for a long posting, there are serious issues now with 915 parts. Many of these aren't made by the original vendors and tolerances vary widely which cause shifting problems. Even when everything is brand new, all parts are now closely inspected & measured for proper fitment and in some cases, some "massage" work is necessary for good shift quality.

Honestly, I'd need to see everything for myself to determine why you are having issues, however I can tell you that old, worn rubber engine mounts allow everything to bind in a high-torque, full throttle shift and the Wevo or factory sport mounts will really help.

[BGCarrera32]

Steve:

Thanks for chiming in. The last time the box was opened up, when I went through it, I did not measure any of the components you speak of or replace those. Would it be correct to assume that the only place for reliable part measurements would be a factory manual?

Thanks again,
Brian

[Steve]

Hi Brian,

The factory manuals assumed that new part dimensions would be the same so there is nothing in there about that. We've relied on long-term experience to know when something will cause a shifting problem when all assembled.

In some cases such as race boxes, we purposefully set clearances a tad looser so they shift nicer right after rebuild, at the expense of long-term longevity. For street transmissions, we'll try to set things up tighter so that the transmission lasts longer at the expense of some initial stiffness until things are run in a little bit.

I'm sorry to say that there is now a bit of "Kentucky Windage" in this process that's necessary to accommodate a lack of strict QC in the manufacturing process.