i have a 99 trans am 4l60e tranny car shifts smooth no grinding . the trans level is good no burnt smell looks clean i can put it in drive get on it fine when i just cruise it and about 35 to 40 mph and hit gas rpm's rev up and i go now where so i didn't want to screw anything up so just brought it home but goes in gear good l1 l2 and reverse have a circle d 4k stall anybody know what might be going on ?

 

The lack of punctuation and grammar discourages anyone from answering; it is unclear when your problem occurs.
Please detail in what shifter positions and in which gears the trans is slipping.

If when it downshifts to 3rd, it is likely the 3/4 clutch.
If when it downshifts or accelerates in 2nd, it could be the band.
Depending upon the shifter position, it could be the forward sprag.
In all cases, low fluid level or low line pressure will cause slippage.
A bad converter will cause slippage in all gears and shifter positions.

Unless the fluid level is low, you might as well take it to a trans shop for analysis on their scanner. While we might be able to diagnose the problem from the requested details of gear/shifter, it probably needs a rebuild.

 

Yes I would say its will need a rebuild either the 3-4 clutch is slipping or the input sprag and yes clear descriptions can do wonders.

 

Sorry guys i guess what i mean is it goes in gear fine seems like 1 and 2 then when going into 3rd the rpm's rev up and the cars not going anywhere so im guessing your right 3-4 must be going out i don't know much about transmission but it was just rebuilt about 6 months ago per previous owner.

 

In that case this is very similar to another current thread where the 3/4 clutch is gone:
https://ls1tech.com/forums/automatic...806-4l60e.html

In many cases the original 3/4 clutch lasts 100,000+ miles and then fails a few months after a rebuild. IMHO this is because the rebuild is rushed and not enough time/effort is spent carefully checking for potential leaks in the 3/4 clutch hydraulic circuit. I list some of the potential leak areas in post #3 of that thread.

From the comments and feedback I read here, members have much better success with performance transmissions from e.g. PerformaBuilt, FLT and RPM than from local rebuilders. You pay just a few hundred dollars more, but they are built more carefully with quality parts, 3/4 clutch improvements and a shift kit. Obviously there are also good local rebuilders, but it is hit-or-miss and even good trans mechanics often have little experience with performance parts, shift kits, etc.

 

Yes 3-4 gone complete rebuild with z paks $1700 big ones grrrrrrrrrrrr!!!!!

 

can't believe Redline clutches and kolene plates would go that easy

 

While the Z-pak is no longer the preferred setup, when properly installed and the trans properly rebuilt, it should last a long time with anything under 500HP. There is either a leak in the 3/4 clutch circuit or the line pressure is too low due to a bad PCS, engine sensor or tune.

As I said in another thread yesterday, a trans pressure gauge is as critical for diagnosing trans problems as a volt/ohm meter is for electrical problems.

You can purchase a trans pressure gauge on ebay for $45 or have a local shop hook it up for a drive. I would highly recommend this as otherwise, if the underlying problem is an engine sensor or tune, even the best rebuilt trans will quickly fail. Also, a proper rebuild should replace the PCS (Pressure control solenoid, also called EPC) because they are known to fail or just get flaky.
Hopefully your $1700 rebuilder will warranty this problem.

 

thanks good info