924Board.org

[goc931]

[Lizard]

Goc931, CMXXXI has already corrected me if you reread
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3 928s,

[Smoothie]

Jeeze Lizard - you need to do the rereading. Goc931 not only read, he copied part of CMXXXI's post verbatim and seems to be in agreement with you that the popping out of gear can be due to worn dog teeth if they're keeping it from going completely into gear.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Lizard]

ok, that wasnt how I read it and I just read it again and seeing the same thing,
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3 928s,

[CMXXXI]

I'm no mechanical or automotive engineer, but having taken the thing apart, examined it long and hard, then reassembled it, I stand by my assertion.

I don't disagree that there might be a certain amount of axial "push apart" between the gear (with embedded dogteeth) and the coupling sleeve as torque is applied, but once the sleeve is engaged, the two are locked together as an assembly. The torsional forces turning the two are applied on flat surfaces "beneath" the beveled edges of the dogteeth and the beveled edges of the mating teeth on the sleeve. Once the gear and the coupling are engaged and "locked" together by the sleeve they are held together by a detent that engages in a slot in the shift fork shaft.

Perhaps a combination of weak detent spring, a worn detent and/or groove in the shaft, a worn groove where the shift fork rides, radial play along the shaft, together with extremely worn dogteeth on both the moving 1st gear and the shift sleeve could allow the thing to separate.

I'm putting my money on the belief the gear and the sleeve aren't fully engaging to begin with (for whatever reason[s]) if it pops out as power is applied

Click photos for larger images
Flat edges below beveled dogteeth mate with flats on sleeve below.

Flat edges below beveled edges mate with flats on gear above.

Gear and sleeve held together by shift fork (large "C" shaped thing on lower shift shaft) which is held in position by spring detent mating in groove in the fork's shaft.
That's the best I can explain it...
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'79 Eurospec 931

[goc931]

HI

CMXXXI - Shown on your top picture you actually have more teeth left than I had after my race weekend. I definately don't disagree with you, but on my gearbox this was the only flaw.

Lizard - I was actually trying to write that I agreed with you as Smoothie correctly points out.

However this was my second time I took down the gearbox and I'm starting to get rather good at it...unintentially.
Now I have new synchros for 1st and 2nd gear and much better dogteeth taken from another used gearbox bought on the German eBay.
The car had only 80000 miles on the clock before it crashed, or rather hit by another fellow driver.
Next time I'm changing it to an Audibox.

Best regards
Goran
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Porsche 924 -83, Race car
132hp, 950kg w/o driver

[numbbers]

What happens is that after the dogteeth are worn down, then even slow shifting will not prevent the grinding. Then all of the grinding will not only wear the gear set, but the vibration from it will cause the synchro ring to pop completely out of the gear. That sets up an interference gap so that the gears cannot completely engauge (mesh). Therefore they disengauge, usually under de-acceleration , but sometimes under acceleration. The cure is a new gear set. Very expensive. If you can get a good deal, it will be about $1000 US. But, it will more like run you about $1500. That is just for the gearset, you will still have to change it yourself. It is not too hard technically, just time consuming.
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1980 924 Turbo