915 transmission 1st gear issue? Has anyone seen this?

hasaramat · 04-29-2018, 01:49 PM

These pics are of a first gear on a 1980 911 sc. The gear teeth are new and the synchro is new. The problem is that when it is assembled the diameter of the synchro is almost .5mm out of spec too small. If I put this in it will grind in first. The parts are new. Wrong gear teeth diameter? The part number on the box was correct. The synchro is the right size. Bad manufacturing? Or am I missing something obvious? The gear teeth and synchro control the outside diameter of the assembly correct?

DRACO A5OG · DRACO A5OG's Garage

What brand are they?

kevingross · 04-29-2018, 06:19 PM

My first suspicion would be the dog teeth, because they should be controlling the installed diameter of the synchro. Are they new, and who made 'em?

Trackrash · Trackrash's Garage

The inside of the dog teeth will need to be cut to 9*. AHIK

hasaramat · 04-29-2018, 06:47 PM

Brand is Rouch & Spiegel for both the gear teeth and the synchro and they are new. I don't think I want to cut on new gear teeth. You would think that it would fit correctly for $129

Matt Monson · 04-30-2018, 04:55 AM

Sounds like an older set of teeth. r&s has been back cutting their teeth for a year or two. They will need to be cut.

Trackrash · Trackrash's Garage

You can verify the back cut by comparing the new with your old gear.

hasaramat · 04-30-2018, 06:17 PM

Is this back cutting something that is new. Would this be done on a good lathe. I just ordered a new set of teeth. Why would anyone make our sell parts that need to be cut when new. That is really a trashy product. I bought two sets of teeth about 2 years ago and this was one of the sets. Can't send them back

Trackrash · Trackrash's Garage

I cut mine on my lathe using a tool post grinder.

Matt Monson · 05-01-2018, 09:12 AM

Quote:

Originally Posted by hasaramat

Is this back cutting something that is new. Would this be done on a good lathe. I just ordered a new set of teeth. Why would anyone make our sell parts that need to be cut when new. That is really a trashy product. I bought two sets of teeth about 2 years ago and this was one of the sets. Can't send them back

It's not new. The German OEM replacements have always been delivered without the backcut as well. We have used them in the manufacture of our new gears for more than a decade and add the backcut as part of the finishing process once they have been pressed on to the gears.

Originally R&S was making them identical to the German ones, but they listened to feedback from their wholesale customers and changed the design a year or two back. It appears that you have a set that predates the design change.