synchro diameter

[alexandervdr]

on 1st gear I installed new dogteeth and new synchro. However, the synchro diameter is 85.96mm which is not within spec (86.37+/-.17mm according to Bentleys).

I already did 2nd gear and that was perfect within spec.

What can I do?

[Matt Monson]

What brand teeth did you use? They may be lacking the proper backcut and pinching the synchro too tightly.

[JackkTheMackk]

Went through this 2 years ago. OEM dog teeth from dealer were missing the back cut. I bought R&S dog teeth and they arrived with the proper back cut. I took some photos back then to show the difference.

[alexandervdr]

sorry guys for my ignorance, but what do you mean by 'back cut'?

[Matt Monson]

The synchro ring has curvature. If the engagement teeth are straight up and down they are too tight. They are supposed to have a 9° taper away to grab the synchro at angle, more in alignment with its curve c

[alexandervdr]

Originally Posted by Matt Monson

The synchro ring has curvature. If the engagement teeth are straight up and down they are too tight. They are supposed to have a 9° taper away to grab the synchro at angle, more in alignment with its curve c

clear, thanks!

[alexandervdr]

interesting closing on this topic: I did test with the old synchro ring, and the reading was identical to the new one ( 85.96mm). It still could have been the dogteeth. In confusion I checked with a specialist 915 shop, who works with the exact same parts supplier I work with. He's done multiple 10s of 915s and said not to bother at all because the new parts have different tolerances.

[Matt Monson]

Originally Posted by alexandervdr

interesting closing on this topic: I did test with the old synchro ring, and the reading was identical to the new one ( 85.96mm). It still could have been the dogteeth. In confusion I checked with a specialist 915 shop, who works with the exact same parts supplier I work with. He's done multiple 10s of 915s and said not to bother at all because the new parts have different tolerances.

Accepting that they are wrong, because a mechanic agrees that they are wrong, doesn’t make it right. The Porsche/German OEM synchro teeth have been wrong for more than a decade. Many mechanics have just accepted it, letting their clients deal with poor shift quality and accelerated wear.

[alexandervdr]

Originally Posted by Matt Monson

Accepting that they are wrong, because a mechanic agrees that they are wrong, doesn’t make it right. The Porsche/German OEM synchro teeth have been wrong for more than a decade. Many mechanics have just accepted it, letting their clients deal with poor shift quality and accelerated wear.

I agree with you. That being said, I did not have any problem shifting the 1st gear, and that was with the wrong setting, identical diameter to the new/wrong one I installed! I tried to identify a european source for the R&S dog teeth your recommended, but could not find one (yet). All the other shift gear synchro dimensions are spot within specs.

[kevingross]

Originally Posted by alexandervdr

I agree with you. That being said, I did not have any problem shifting the 1st gear, and that was with the wrong setting, identical diameter to the new/wrong one I installed! I tried to identify a european source for the R&S dog teeth your recommended, but could not find one (yet). All the other shift gear synchro dimensions are spot within specs.

Alex, I am not in the parts business. But if you are stuck locating a R&S asymmetric 1st gear dog ring (10.1550.312), PM me, I can help you out. I have eight on the shelf. (I service a lot of 915 transmissions.)

R&S does have a major distributor in Europe. I would be surprised if they are out -- US distributor has plenty on the shelf today.

[dutchcrunch]

so if i were to buy new gear set from porsche , i could have this problem??? thanks

[Matt Monson]

Originally Posted by dutchcrunch

so if i were to buy new gear set from porsche , i could have this problem??? thanks

Not the new finished gears from Porsche Classic (by Hoer). But if you buy the replacement teeth they sell, yes.

[dutchcrunch]

Hello Matt is Porsche classic a specific site??

[Matt Monson]

Originally Posted by dutchcrunch

Hello Matt is Porsche classic a specific site??

It's a division of Porsche. You can find it via porsche.com.

[kevingross]

Originally Posted by dutchcrunch

Hello Matt is Porsche classic a specific site??

https://www.porsche.com/countries/classic/?cslang=en

[dutchcrunch]

Thank you......

[dutchcrunch]

this guy does not even remove the cluster to replace shift coupling and synchro rings.




https://www.youtube.com/watch?v=L2cDuiOIKeA

[thetorch]

that's interesting. The video didn't seem to show how they torqued the pinion and input shaft nuts before installing the nose cone and the differential...hmmm

[Matt Monson]

That video doesn’t show much rebuilding at all. It’s more of a how it works video. One cannot replace synchros or shift sleeves (never heard them called couplers before) without disassembly. Furthermore, his little cartoon graphics show G50 Borg Warner style synchros, not 915 or 930 style split ring synchros.