Z Madness

I have a 2000 Z-28 that I use for autocross. I recently installed a custom rebuilt 4L60E transmission. On second race (2 weeks after install), the trans brake is non existent. In first gear, I run out the gate but as soon as let off, RPM's drop to 1,000K, light throttle and the car just rev's, no engagement. If I stomp it, it will have a nasty hit. Also 2nd and 3rd gear does the same thing. 4th/OD is fine obviously since no transbrake. Any ideas? Is this a tuning issue (which is what the tranny guy is saying). Car was recently tuned remotely by Trifecta Performance and they indicate they didn't touch the tranny. Any help would be appreciated. Thanks!

Vince B

iTrader: (1)

When this happens what position do you have the shifter in? Also at the first race was everything OK? The reason I say this is if the over run clutch is not applied you will not have engine braking. You could have your builder install a sonnax hd 2-3 shift valve and this might help your issue while you have the shifter in the D3 position. However if you are manually shifting and you have this issue I would assume that you either have a broken over run clutch hub, failed OR clutch seal, or a failed OR clutch. Vince

Z Madness

All of this happens when moving the shifter in the selected gear. During our AutoX runs, I ususally start in 1st and will sometimes shift to second if I will be at the REV limiter for a while, then on the next tight turn, usually drop back into 1st as I squeeze the gas. It would be quite frustrating if this is a failed clutch (anything mechanical) since it is a newly rebuilt tranny (paid some big bucks).

The tuner did indicate that he increased the line pressure and reduced shift times. Any other ideas?

Vince B

iTrader: (1)

Did your builder install a shift kit like the transgo hd-2 kit? This kit should hold the trans in a specific gear despite what the computer commands. I guess looking at what is commanded when this happens via a scan tool might help you figure out what is really going on here. If you do have the hd-2 kit then I'm thinking your issue is internal. Any details on the build that you care to share. PM if needed. Vince

Z Madness

Vince, thanks for your great responses. My mechanic will be opening it up today. It was one of those things where the Tranny builder said it must be a tuning issue while the tuning guy said nope. After further review, it looks like it is mechanical and probably has to do with the clutch, as you suggested in the first post. Hopefully its not too serious. Will see.