Differences between dogbox, dog teeth, syncho, 915, G50, modern gearboxes

[J P Stein]

Originally Posted by Matt Monson

JP,
Have you seen what Britain has done with the gearbox since? I'll see if I have pictures. 2 Spd 930 dog box now.

I haven't seen the guts of his 2 speed. I was surprised to learn that he converted the 930 to a 2 speed. Can he swap it back to a 4 speed?

That beastie would be a hell of a track car with a couple more gears. The Porsche crowd would be in for a shock......that is an excellent case for "Modern". He's pulling 380HP at the wheels for now (@ 2.0L) at (WAG) 1/4 the price of Porsche power.

[javadog]

Originally Posted by J P Stein

...but you still couldn't power shift it. (right foot flat to the floor, side step the clutch pedal while going for the next gear).

I would never shift any gearbox that way, even a dog box. You need at least a momentary cut in power, if nothing else to keep from over-revving the motor, so I think that's outside the scope of this discussion and not an indictment of a Porsche gearbox.

Probably a good thing you took out 1st and reverse from your gearbox...

JR

[J P Stein]

Originally Posted by javadog

I would never shift any gearbox that way, even a dog box. You need at least a momentary cut in power, if nothing else to keep from over-revving the motor, so I think that's outside the scope of this discussion and not an indictment of a Porsche gearbox.

Probably a good thing you took out 1st and reverse from your gearbox...

JR

I admit ya gotta be quick.....practice helps....I did learn how to rebuild a T-10.
I tried to do it "once" with a 901 box.....I got off gently.

Your statement shows a lack of experience...... maybe OK in theory.

I now have a Miata. That 6 speed is almost as slick shifting as a T-10. I've never driven a Porsche with the BW syncro set up.......and ,as a result, with hold opinions
of them.

[javadog]

Originally Posted by J P Stein

Your statement shows a lack of experience...... maybe OK in theory.

a lack of experience... no, don't think that's the case. I have plenty of that.

I just choose to treat my gearboxes, and everything else, like they should be treated. I don't drive (or ride, in the case of bikes) like a Neanderthal...

I'm out of here, I think. Sugardude has his questions answered and I can't stand to listen to red-breard's acid trip again...


JR

[Matt Monson]

Originally Posted by J P Stein

I haven't seen the guts of his 2 speed. I was surprised to learn that he converted the 930 to a 2 speed. Can he swap it back to a 4 speed?

That beastie would be a hell of a track car with a couple more gears. The Porsche crowd would be in for a shock......that is an excellent case for "Modern". He's pulling 380HP at the wheels for now (@ 2.0L) at (WAG) 1/4 the price of Porsche power.

Definitely not reversible. It's hydraulic clutch and directly actuated on the shift rod. There is no longer a selector rod in it. Really good details and pictures are in this thread:

World's Lightest 930 Transmission

[red-beard]

Holy crap! The old transmission part prices are out of control. I remember complaining when sync band went from $20 to $40. Wow. Rebuilding a 901 will be mighty expensive these days.

[Matt Monson]

Originally Posted by red-beard

Holy crap! The old transmission part prices are out of control. I remember complaining when sync band went from $20 to $40. Wow. Rebuilding a 901 will be mighty expensive these days.

Price a 1st/R slider for 901 or 5th/reverse for 915. Crazy expensive these days.

[masraum]

Originally Posted by Matt Monson

It's seem there's only one choice. My LSD.

Checked out your site. Looks like you do have both clutch and torque biasing type. That's what I was asking, if you had an opinion/recommendation for an enthusiastically driven street car.

[kusiobache]

Originally Posted by Geary

Two things are going on with the earlier Porsche system:



As the shift sleeve ages, it develops a ridge on each and every engagement tooth. This essentially narrows the gap that the corresponding dog teeth must plug into. Those sharp little ridges slowly replace smooth tooth flanks as the initial contact point.

Sorry, but could you elaborate on how/why it narrows the gap? I would think the engagement teeth wearing down would increase the gap, unless you are saying the dog teeth make less contact?

[sc_rufctr]

[J P Stein]

Originally Posted by masraum

Checked out your site. Looks like you do have both clutch and torque biasing type. That's what I was asking, if you had an opinion/recommendation for an enthusiastically driven street car.

I went with a torque biasing diff from Guard many moons ago and never regretted it.

A top notch product which, unobtrusively, dose it's job.

Matt is now the HMIC there.

[masraum]

Originally Posted by J P Stein

I went with a torque biasing diff from Guard many moons ago and never regretted it.

A top notch product which, unobtrusively, dose it's job.

Matt is now the HMIC there.

That's what I was thinking. My last car, turbo miata, had one, and it seemed to work well on the street.

[Geary]

Originally Posted by kusiobache

.. could you elaborate on how/why it narrows the gap? I would think the engagement teeth wearing down would increase the gap, unless you are saying the dog teeth make less contact?

The pointer shows the spot where material is scuffed and peeled over by the Porsche synchro band. This sharp spot is found on each and every tooth of a worn out shift sleeve.

If you were to test how smoothly new engagement teeth plug into a new shift sleeve and compare this against the worn out parts, the difference is quite evident.

[notfarnow]

I refreshed my 915 over the winter, and was so damned proud of myself that I couldn't bear to just put it in the garage until it went in the car.

Hoping to get the car buttoned back together this weekend, and I am REALLY anxious to see how it shifts.

I've had the more typical Borg Warner style transmissions/synchros apart before and it is pretty intuitive when the parts are in your hand. However, even after having the synchros apart in my 915 transmission, I still don't really get it.

[Geary]

Originally Posted by Geary

The pointer shows the spot where material is scuffed and peeled over by the Porsche synchro band. This sharp spot is found on each and every tooth of a worn out shift sleeve.

If you were to test how smoothly new engagement teeth plug into a new shift sleeve and compare this against the worn out parts, the difference is quite evident.

Another clearer stock photo showing the deburring and removal of all sharp edges. This is generally a waste of time with worn sleeves, as the working dimensions are already on the high side.

[red-beard]

Here is a worn slider - Photo is nearly 15 years old!

The slider wear in two ways: 1) The sync band contact spreads metal, making the double pointed areas wider, making it harder for the dog-teeth to engage. And the pointed areas wear against the dog-teeth, rounding, usually because the sync band is worn and not making good contact.



Sorry this first gear slider is a little out of focus, but you can see the rounded points.



The dog-teeth are softer than the slider, so they wear out faster...

[red-beard]

A good shot of a rounded, worn slider



Here is my attempt to clean up a 1st gear slider in a 901. I used a file in between the grooves to bring them back to spec. Then I used a dremel to repoint the triangular area. At the time, 1st gear sliders were not just expensive, they were hard to find. A repointed slider with a good sync band and new dog-teeth restored function.

[kusiobache]

Originally Posted by Geary

The pointer shows the spot where material is scuffed and peeled over by the Porsche synchro band. This sharp spot is found on each and every tooth of a worn out shift sleeve.



If you were to test how smoothly new engagement teeth plug into a new shift sleeve and compare this against the worn out parts, the difference is quite evident.

Originally Posted by Geary

Another clearer stock photo showing the deburring and removal of all sharp edges. This is generally a waste of time with worn sleeves, as the working dimensions are already on the high side.

Originally Posted by red-beard

Here is a worn slider - Photo is nearly 15 years old!



The slider wear in two ways: 1) The sync band contact spreads metal, making the double pointed areas wider, making it harder for the dog-teeth to engage. And the pointed areas wear against the dog-teeth, rounding, usually because the sync band is worn and not making good contact.







Sorry this first gear slider is a little out of focus, but you can see the rounded points.







The dog-teeth are softer than the slider, so they wear out faster...

Thank you both very much for the pictures and enhanced explanation.

[red-beard]

901 gear stacks before being put back in a transmission



Some fun pictures - really broken stop blocks and brake bands

[Geary]

Originally Posted by red-beard

Great shot, James .. mind if I borrow it?