2005 cts-v had a new trans installed in december along with new motor mounts, trans mount, ls7 clutch w/ ram fw, and a short shifter. After a couple of months driving I found that going into 4th from 2nd or 6th and even from 3 to 4 near redline shifts I would get a crunch going into gear. Basically the higher the rpm change the synchros going into 4th were crunching. My shop looked at it and figured the rebuild was off. Got another in now... same symptoms.

Some guys have had shimming issues with aftermarket flywheels, but my clutch is not dragging and goes into reverse fine, its only 4th.

Shop wants to pull the short shifter hoping the linkage is throwing it off. If not this then maybe the aftermarket transmount is causing the alignment to be off.. but aside from that we are unsure.

Does anyone have any ideas...

 

ls7 clutches are notorious for not wanting to shift at high rpm due to the self adjusting pressure plate and the fact they are very heavy , light flywheel and adjustable master to increase hydraulic advantage are both supposed to help.

I have one installed by previous owner in my 6 speed car- gotta be patient to shift her....

 

Wouldnt this cause it to do this in every gear though? its just a mystery that 4th is the only victim. It is the 1:1 ratio but I am not understanding how that could be affecting the shift. Anyone know?

 

The shifting issues you are referring to with the LS7 clutch only occur when switching master cylinders on an already broken in LS7 clutch, and they occur in all high rpm shifts. I had this issue as well when I switched from a stock master to a Tick.

The OP's problem sounds like something else...what, I'm not sure.

 

Ok well it turns out that the first trans crunched in fourth and the one they just installed is actually doing it in third. The shop swapped the short shifter out with no results. So I guess at this point it is another bad build.

 

sounded like multiple gear issues at wot , but reading closer I agree with you on that. But mine got ls7 clutch kit (with new ls7 flywheel)/new gm master/new gm slave at the same time so I cant agree that it "only" happens when switching master's on a broken in clutch...