The trouble with Second

PandA · 01-14-2019, 04:02 AM

1986 911 915 3.2 all stock.
Most of us agree that second gear usually gets abused pretty badly. Punch it in first, slam into second, hit the brakes as you are out of speed limit.

Not that I am not guilty of that but, all of a sudden I seem to be having a rough time of getting second gear to cooperate. Down shift into second seems to have better luck, sometimes. Adjusted the shifter connector multiple times, same result.

Whole transmission was rebuilt 50k ago.
Wevo gate shift kit, 5k ago along with a Rauch Spiegel shift rod connector. (not the sold bushings, they still float a little bit.)

A video of the problem in action:
https://youtu.be/rgRzIZCxNqs

Any thoughts? Any suggestions?

Thanks!

Andrew

Matt Monson · 01-14-2019, 06:42 AM

Did you use R&S synchro? They aren’t hard enough and wear quickly. Could be worn out again.

PandA · 01-14-2019, 09:29 AM

Great question. I used what ever worldpac was selling ~8 years ago.
Do we like the Rauch Spiegel gears and brake bands (synchronizes?) Or are we better off with genuine?

Matt Monson · 01-14-2019, 04:13 PM

It's a mixed answer and you will need to do some analysis on teardown. 8 years ago there were two problems with the R&S stuff. There was the synchro hardness, and then there was the dog teeth backcut. If you replaced the dogteeth it's pretty cut and dry.

When R&S made their replacement teeth they just copied Porsche replacement teeth. The problem is that Porsche doesn't backcut their teeth either. Because of the curvature of the synchro, the dog needs to be backcut 9 degrees to let it sit in there properly. Won't matter if the teeth you used were R&S or Porsche, they will be wrong.

If you put a new synchro into the dog and measure it, it will be too tight (below spec) and won't shift well to start with. When it wears in, shifting gets good for a while, and then it goes away quickly.

If you didn't replace the teeth, it's probably just the synchro issue and get a new OE synchro and you're fine.

If you did replace the teeth and want to get rid of the defective ones, the current production of R&S teeth is now backcut. Porsche's still aren't. For 915 always replace dogteeth with good used or R&S new.

Worldpac sells a ton of R&S. They didn't mark it back then, but it would be marked now. I believe they also carry German OEM. If they don't Pelican does and SSF is a wholesaler who does.

Gordo2 · Gordo2's Garage

Quote:

Originally Posted by PandA

...Whole transmission was rebuilt 50k ago...

What's a realistic expectation for rebuilt milage before wear becomes noticeable?

Of course in part it depends how the vehicle is driven / shifted, but I personally won't be surprised if my trans gets rougher at ~ 50k due to the the way I drive it (I built it, therefore I will shift it how I want...).

Just a thought - but I wouldn't be surprised if you are starting to feel synchro component wear.

Gordo

PandA · 01-15-2019, 01:12 PM

Would that also explain why I usually have the spin the trans to get it into first? Or should I be looking for something else when I tear into it?

Thanks!

Andrew

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by PandA

Would that also explain why I usually have the spin the trans to get it into first? Or should I be looking for something else when I tear into it?

Tom Petrushka from Mayo Performance sent me these 1st gear pics in 2009 when he rebuilt my 915.

I did not have the back cut dog teeth (I don't think) and suffer some balking going into third occasionally.

Down shifting to first while moving is a breeze though on the small handful of times I have done it. I just don't as a rule as it's clear what the outcome will be. Before rebuild, forget it.

Best Matt actually answers your question.

30westrob · 30westrob's Garage

Can someone explain what is done in dog teeth backcut. Are the dog teeth machined prior to install on the gear, and can you tell if it has been done with the dog teeth on the gear.
Thanks. Rob