I'm getting ready to fix some problems a had before I put the gta up last fall. Namely no 5th or 6th gear. 1st though 4th works fine as does reverse but if you go to 5th or 6th the shifter will stay in place but it has a high pitched whine/grinding sound and no gear. From the manual and exploded diagrams it looks like the 5th/6th gear shift arn is held in place on the rail by a pair or c clips. could one or both broke or come off? Or am I looking at a rebuild?

 

Was anything going on with the car before you put it away with this issue last year?

From your description, it sounds like the 5/6 driven gear (Item #61 from the Service Manual) has stripped the splines off of the mainshaft. The 5/6 shift fork is held on by a clip, but it only retains it going forward (into 6th), the solid linkage moves it into 5th if the clip is there or not.

I think you're in for a rebuild for a new mainshaft and the driven gear.

I have takeouts of both if you get it torn apart and verify that's the issue.

 

I got this trans used off ebay and the guy I bought it from didn't Know much about it. He said he got it from a junkyard for a street rod project but didn't use it. I'm hoping to get it out and torn down sometime next week. I'll let you know what I find and I'll get in touch with you about those parts. Now are you talking the mainshaft or the extension shaft(part no. 128?). I can see the splines on that in the picture and they look pretty easy to damage.

 

The 5/6 driven gear rides on the mainshaft (Item #23). I've seen 4 T56s with this same issue, all LT1s. The later LS1 and CT/GTO/etc. units seem to have tighter tolerances, but it could also be milage related..

 

I'm going to try to get it out and torn down this weekend instead of next week. How much would you want for a good mainshaftand driven gear?

 

PM sent