3rd gear issue on a 915 trans.

[ginot912]

I got a problem with 3rd.

It engages fairly smooth, but it will slip out of gear if I let up on the throttle, other wise as long as I'm on it it stays put.

I've got Wayne's 101 and have done a search and will try to adjust the shift rod coupler.

The car has a OEM short shift with new bushings as the PO told me.

Could it be internal?? All other gears work great.

Thanks

Gino

[john walker's workshop]

pull up the shifter boot and be sure the shift handle doesn't butt up against the edge of the tower before it's all the way into gear. a coupler length adjustment would fix that. be sure the cylindrical bushing at the end of the shift handle is still in good condition, and check the side bushings in the shift coupler. if nothing shows up there, remove the shift guide fork plate on the bottom of the trans (i assume it's a 915) and see if the fork is loose on the plate. also check for little teeth on the drain plug magnet. that's the simple stuff.

[ginot912]

Thanks John

I'll check all that.

Gino

[ginot912]

Finally got to draining the transmission. The shift fork guide was tight but it is worn a bit on both sides.
Here's a couple of pictures.





Would the scoring be causing the slipping out of 3rd gear?
There was some fine shavings in the magnetic plug, along with some kind of gunk, no pict.

Thanks

Gino

[ginot912]

After reading old 915 posts for 2 hours it seems I'm in for a rebuild.
I've ordered a new fork, I'll see how it is on the way to the rebuild shop

Gino

[Mahler9th]

I have some similar damage on my 915 shift fork. I have been searching for the cause. Did yu ever find out what caused this? What was damaged in the transmission?

[Mahler9th]

Has anybody else out there seen this type of damage to a fork that wasn't loose?

[john walker's workshop]

that's from the nearest gear rubbing on the fork because the end play in that shaft is excessive, usually because the retainer (tensioning ) plate that holds the 4 point ball bearing tight against the diff housing is worn out. could also be the reason it pops 3rd.

[Mahler9th]

Is there a spec for end play?

[john walker's workshop]

yeah, zero to barely noticeable.

[Mahler9th]

Figured that. So far I have found the pinion shaft spacer (between fixed 3 and 4) to be 30-40 thou shorter than it should be. Will also be checking the spacer on the input shaft (late style).

[john walker's workshop]

check shaft end play. the gears will always have some.

[ginot912]

Tranny has been spit

3rd and 4th gear slider is worn really bad on 3rd side,

Yes that would make slip out of 3rd.

here's a picture of the 3rd side


now one of 4th for comparison


Gino

[Geary]

Wow. That's as worn as I've seen. Aside from the loss of all tooth tips, it's worthwhile observing the amount of metal that's been displaced on each tooth (the little bulge you see on every tooth). There hasn't been room for the gear's engagement teeth to fully engage for many thousands of miles.

This odd wear is usually caused by speed shifting, but can also be greatly accelerated by the use of synthetic oil.

[ginot912]

Must have been speed shifting as other teeth on 1-2, 4 and 5th
are Ok, well at least much much better.

Was surprised at the "buldges" myself.

Gino