How do these 915 dogteeth look?

[Beetspeed]

I have encountered some grinding in 2nd and 3rd and decided to replace any worn items I would find.

Both gears stacks (1/2 and 3/4) are out now and this is how they look:
1/2:


And 3/4:


Second gear teeth are obviously rounded, but the others look rather good. Strangely enough, I think 3rd even looks better than 4th (?)...

So, I plan to change all 4 synchros at least and nr. 2 dog teeth.
Should I renew anything else as well?

Thanks for your input,
Best regards,
Walter

BTW Its a 1976 915/40, mag case and with mechanical speedo..

[dick911]

Hello Walter,

Yep, they really look bad. Dogteeth must be sharp. Better to look first to new dogteeth and compare your synchros with new ones before you buy them. Most people will invest in new synchros and forget the (more) important dogteeths....

Good luck,

Dick911


Hallo Walter,

Ze zien er slecht uit! Dogteeth moeten echt scherp zijn om goed te kunnen schakelen. Voordat je nieuwe onderdelen gaat kopen kan je beter de huidige synchromesh ringen vergelijken met nieuwe exemplaren.
Veelal zijn de synchromeshes nog goed terwijl de dogteeth (zoals bij jou...) helemaal rond gesleten zijn.

Men roept heel vaak "effe nieuwe synchromesh ringen erin en hij schakelt weer als boter" ... nou, niet met de dogteeth zoals die van jou eruit zien.

Gr.

Dick

[Geo9146GT]

Unless you have money to burn, i wouldn't replace any of the
synchro hubs(dog teeth?). Replace the synchro rings, and inspect the slider teeth(not visible in your pic). If they are in the same shape as your synchro hubs, they'll do fine.

[ed martin]

If you look at a few recent posts regarding this subject, you will understand that the sharpness of the dog teeth and the teeth in the slider are super critical for smooth shifts. Yours look shot to hell.

[Jim Sims]

"sharpness of the dog teeth and the teeth in the slider are super critical"

Once the gear is engaged the torque is carried by the flanks of the teeth not by the points. What I'd like to determine is how important length of the teeth is to establishing the initial mesh and whether teeth could be resharpened. I know of at least one well respected Porsche mechanic who is reported to file the teeth sharp again. I wonder if a good saw sharpening shop could carefully redress the teeth on a slider and synchro hub (dogteeth).

[Beetspeed]

Here's another picture of a now dismantled first gear:



To avoid a lot of 'still not too detailed' pictures of 5 synchro rings: They are very, very good! Only 3rd had some marking on the outside (but was also very sharp on the inside grooves).

I have the distinct idea that in the not too far past, all synchros and probably some or all dog teeth have been replaced...
The sliders however are shot, both 1/2 and 3/4:

I will at least replace the sliders, 3rd synchro and dog teeth of 2nd.
First really seems very decent, been replaced before and will never be used to shift fast with...

Thanks,
Walter

[ed martin]

I'm a little confused looking at your first gear dog teeth. If I'm not mistaken, the points on the first gear dog teeth are asymetrical, not symetrical as your picture shows. Maybe someone with more experience can chime in here. The difference between good dog teeth and worn dog teeth is very subtle. This topic is covered in another recent post. If your second gear dog teeth are worn, then chances are your first gear are probably worn, they are the gears that get the most use. You can reuse the old parts, but once you get it all back together your going to wish you had done the right thing and replaced them.

[Jim Sims]

1976 915's were built with symmetrical dogteeth on first gear; the change to the asymmetrical configuration occurred in 1977.

[Beetspeed]

Originally posted by ed martin
[B]I'm a little confused looking at your first gear dog teeth. If I'm not mistaken, the points on the first gear dog teeth are asymetrical, not symetrical as your picture shows.

I still have the old style, symmetrical, 1st gear dog teeth...

Actually, shifting to and back to 2nd and 3rd was the problem. Shifting into 1st was very good. I think with the new 1/2 slider it will not become worse

Tnx,
Walter

[lvporschepilot]

is it possible to file the old dogteeth until the are sharp again, or is that just too ghetto?

[dvkk]

You wouldn't be able to file the dog teeth, they are hardened more than any file. If they were ground to a new sharp point, their overall length would be reduced such that the sides would be shorter. This is not a good thing when it comes to holding the slider engaged while the power is on.
A rounded dog tooth means you have to shift slower to avoid grinding.