915 1st gear synchro

SP2 · 10-16-2006, 10:46 PM

Hello,

I am dropping my engine and tranny for the first time this weekend. I was hoping for some advice on the tranny. My symptoms: Overall the box shifts very well. Down shifts in all gears are not a problem in all gears except from second to first. You are probably asking why I would do that, but my 81 911SC is frequently my daily driver, and on the congested highway in the morning I often find myself crawling along at a very slow pace. Once second gear is at 1000 RPM I need to drop down or risk stalling. So I usually clench my teeth, but often it grinds, so I go back into second with the clutch in, then back into first. I hope I described it well.

The other problem is when I am at a stop and in neutral. When I try to go to first it will frequently grind. I usually now go from neutral, put the clutch in, go down to second then up to first. I was told this was the synchro.

So what am I looking at here? I want to rebuild this myself. I am thinking just replacing the first gear synchro, dog teeth, and leave anything else alone unless I see damage. The 915 had fresh Swepco 201 in March and still did this.

My mechanical abilities are improving. I had never done anything on a car, but then bought this and have caught the big bug! I can't wait to tear into the tranny and give it a try. I live in Seattle, so if I fail, I already talked to John Walker and he will recondition my 915.

Can you help me with advice?
Thanks!

Rob Channell · 10-17-2006, 05:21 AM

You can convert the asymmetrical dog ring on the 1st gear set to a symmetrical dog ring as used on 2nd gear. It makes downshifting into 1st gear while moving a much easier task. I do not know the details but had this done to my transmission when it was rebuilt several years ago by Dennis Aase. Maybe someone with a little more technical expertise can fill the details. I did find this link, but it makes me unsure of which option I have in my own transmission.

915 1st gear synchro upgrade parts list (long and boring unless you need the info)

john walker's workshop · 12:18 PM

1st can be fixed without a complete teardown. the trans can stay bolted to the engine. the end cover is removed, the 5th and reverse items under it are removed, the guide fork plate and center housing is removed next. that exposes the pinion and mainshafts. the two roller bearings on the end of the shafts are carefully removed, and then you can slip the freewheeling 1st gear off the pinion shaft. syncro, brake band and syncro teeth should be replaced on that part. the 1st/2nd shift sleeve is also a good thing to replace at this time. once that's off, you can slip the freewheeling 2nd gear off and check it's components. the 1st and 2nd pressed on syncro teeth are famous for loosing their teeth, so it's recommended (by me) to replace both 1st and 2nd teeth as a matter of course.

SP2 · 10-17-2006, 12:12 PM

Thanks John for the advice. I appreciate the concise message. I will do everthing slowly. I have lots of pictures from a p-workshop manual.

SP2 · 10-17-2006, 07:37 PM

Rob,

Thanks for the link, but it was a little confusing. Or at least way over my head at this point. Maybe when I get deeper into the rebuild I will understand these nuances.