915 downshift problem/question

sfoster13 · 02-25-2007, 09:01 AM

New clutch, rebuilt 915, Wevo coupler, Wevo 915 shifter

Less than 1,000 miles on the work - mostly track miles, this is a track only car at this point. Once the rebuild work was done I noticed I had trouble downshifting from 5th to 4th. All the other gears going up or down are fantastic. Just doesn't want to go into gear. I thought it was just tight from the rebuild and it would work itself out but it hasn't. Any ideas what it might be? Doesn't feel like an alignment problem on the coupler and it goes into 4th easily when going up rather than down shifting.

jbscheff · jbscheff's Garage

I have the exact same problem on my un-rebuilt 915. I find that if I nudge the stick into third (but don't let up on the clutch), I can then put it into 4th. Not the fastest shifting by any means, but it seems to work. I am really interested in what this board identifies as the cause / fix.

Jim Sims · 02-25-2007, 09:27 AM

Sounds like a problem with the 4th gear synchro assembly - it only works well in one direction. Perhaps reassembled incorrectly. Were the 4th gear brake bands and synchro ring replaced as part of the rebuild?

sfoster13 · 02-25-2007, 10:22 AM

Yes they were.

dentist90 · dentist90's Garage

Is it hard to pull out of 5th, or only trying to go into 4th?
Jim Sims observation is correct, but i'm sure only 1st has the assymetrical brake band. A previous owner of my car had installed the brake band backwards in 1st... made at speed downshifting impossible (without matching revs) and prematurely wore out the synchro ring.
Have you tried double clutching and blipping the throttle when shifting 5 - 4? If so, did it help? Doing so takes some of the work from the synchros... might provide a clue.

Jim Sims · 02-25-2007, 10:52 AM

It is possible to assemble any of the synchro's incorrectly, not just first.

Eagledriver · 02-25-2007, 10:56 AM

My transmission is difficult as well on that shift. I've found that If I shift quickly and with above normal force it will go in consistantly. It's when I try to baby it in that it is reluctant. Double clutching seems to help on mine but there is only one place on the tracks I run that has that downshift and there is no time there for the double clutch.

-Andy

dentist90 · dentist90's Garage

Quote:

Originally posted by Jim Sims
It is possible to assemble any of the synchro's incorrectly, not just first.

Uh oh.

sfoster13 · 02-25-2007, 02:44 PM

Not hard to get out of 5th, hard to get into 4th. Haven't tried double clutching because I don't have time for many of the turns on the tracks that I run. I'll give it a try and see what happens.

Eagledriver · 02-25-2007, 07:24 PM

If you have a stock SC I'm suprised you need 5th gear on the track. What tracks are fast enough to use 5th?

-Andy

sfoster13 · 02-26-2007, 02:45 AM

Watkins Glen

jakermc · 02-26-2007, 02:28 PM

I was having trouble downshifting from 3rd into 2nd under heavy load on my track car. I replaced the stock tranny mounts with the WEVO semi-solid and it completely fixed the problem. You might have the same problem if the issue only occurs when downshifting, give it a try.

sfoster13 · 02-26-2007, 02:30 PM

I've got the Wevo tranny and engine mounts installed. That's the thing that's killing me. All this work/money and still having trouble.

jakermc · 02-26-2007, 02:47 PM

Cant you downshift from 5th to 4th on the street when driving at a moderate to slow pace versus the hard braking/heel&toe downshift on a race track?

Try and determine if the load on the engine and tranny is a factor.