915 Downshifting Issues

[IROC]

To start off, my car still has the original mag-cased 915 (never rebuilt) in it behind a warmed-over 3.2. It has about 150k miles on it.

During normal street driving, it shifts fine - no problems at all. I have been having an issue at the last two track events, though (the first track events with the 3.2 - this problem didn't manifest itself with the 2.7). When the gearbox gets hot, I sometimes have a hard time downshifting.

I heel/toe well and really take it easy on the gearbox when shifting, but I still have had a problem downshifting (primarily from 3rd to 2nd but also from 4th to 3rd once). It just feels like something is physically blocking the shift - no grinding - it's just not going into gear.

It seems to be heat related as the problem only occurs later in the sessions. Could it be too much heat causing something to expand or get out of alignment? Could it be a slightly mis-adjusted shift coupler? Once it cools off, it's perfectly fine.

Fresh Swepco and the level is fine. Clutch adjusted correctly, etc.

Obligatory pic:



Any ideas?

Mike

[Blanco]

Tranny bushings? Maybe going out of spec with all the race stress. Fine otherwise.

[Jim Sims]

You could try adjusting the shift coupler when the tranmission is hot and see what that accomplishes. However given the miles on the transmission and it's apparent service life I would suspect that the friction material on the synchro rings is gone. Since nothing is grinding you could consider doing an "economy rebuild" by only replacing the brake bands, synchro rings and seals. Cheers, Jim

[nixter]

BTW, that is one e****** georgous car.

nix

[IROC]

Thanks for the info, Jim. I suspect you're right. Lots of track miles on this thing, but it has not been abused, for sure. I think I'll "nurse" it along until a rebuild is unavoidable.

BTW, the bushings are "Club Sport" bushings that are only about 2 years old, so they should be in good shape.

Thanks nix!! :>) It's kind of "old school" with all the new-fangled stuff at the track these days, but I like it.

Mike

[RX911]

mike

i have simular issues on the street in up or down shifting into 3rd or 4th. i have new everthing from the shifter to the trans rebuild (by charlie). new clutch - cable and wevo motor and trans mounts. i have begun to think it may be an alignement issue between the trans and the shifter. with the torque on an up or down shift this mismatch is aggravated. i will try wevo coupler next as this may solve any binding as a stock one cannot.

[jeff1hughes]

Before trying high $$ wevo coupler, try 914 bushings in the coupler, they'll tighten it up for only $10 as a trouble shooting measure