My Pro-Built 700r4 is slipping in 4th under low-rpm high load lockup. It's a very rough sort of slipping, sort of like the feeling of driving on grooved pavement. I know something is slipping during this sensation since the rpm raises a bit until I let off a little. So this means it must be either 3-4 pack, 2-4 band, or TCC. I don't notice slipping in any other gear but it's such a specific range it's hard to say if there's a problem or not. I have noticed a sort of "rumbling" vibration sometimes on WOT acceleration which could be the same thing. I'll be checking pressure and probably putting a Sonnax Super Servo 4th gear piston assembly on in case it isn't holding like it's supposed to. I also bought another 2-4 band in case mine got fried. Any other ideas on what I can do to troubleshoot the issue?

 

'slipping in 4th under low-rpm high load lockup'. This is the torque convertor lockup clutch slip. What are you using to lockup the torque convertor clutch?

 

I'm just using the regular old ECM setup. I did install the quick apply check-ball in the input shaft. Last I checked the o-ring was in good condition but I'll check again when I pull the trans. Would it be a good idea to throw the old torque converter on there before doing anything else (besides verifying pressure of course) to see if the problem still happens?

EDIT: I've also seen a sonnax valve for the TCC which has a seal on the end. The site says "Excessive pump bore-to-valve clearance allows TCC signal oil to leak past the spool, preventing lockup or causing lockup to disengage when hot." Would this be something to look into or is it more likely a bad converter? Would it hurt to throw that valve in anyway?

 

Double check the torque convertor to flex plate mounting bolts. If they contact the torque convertor it ruins the surface that the TCC apply uses.

RBob.

 

So you mean if they screw in too far and hit the surface behind the blocks, right?

 

Yes.

RBob.

 

This isn't exactly related, but has anyone done the WOT 4th gear mod (with the little allen screws). I'm interested in how it affects the shift points of the various gear both at WOT and part throttle.

 

It will allow you to make WOT 3-4 shifts and will hold 4th gear and eliminate the 4-3 kickdown at high speeds (75mph - 80mph) the vast majority of times. It does not affect 1-2 or 2-3 shifts.

 

Ok, I'll probably hold off on doing that then since I don't really have a powerful enough motor to warrant it yet. I checked the pressures on the transmission today and they are at or above the expected values for all gears for both minimum travel and max TV travel. They also look fine when driving around, even in the low speed 4th gear lockup (was about 120 PSI if I remember correctly). I'm pretty sure at this point that I'll end up replacing the converter, especially since I have a shudder at WOT high rpm as well with it. I'll still put the other band, Sonnax 4th apply piston, and Sonnax lockup valve in since I have them. For now I'll put the old 12" torque converter back on until I can get a new converter. I don't know if the TCC is just warping when hot or what, but everything transmission side seems fine. I'll double check the old band and 3-4 pack since they're easy to get to when replacing the band anyway.

 

If you are getting a "shudder" at WOT in 4th gear, then it sounds like the torque converter clutch is not releasing. The torque converter clutch is not designed to hold at WOT. Try disconnecting the wire at the transmission and see if it still does this.

 

The f-body calibration has a forced lockup at 75 MPH. This is from the latest calibration (AUJP) for the '90 - '92 years.

Once above 75 MPH the ECM will not unlock the TCC, even at WOT.

Another example is the '90 Corvette calibration ANHT, the forced lockup is at 76 MPH.

RBob.

 

Don't think it's an issue with the clutch staying locked up as it happens in all the gears even from a dead stop (unless the clutch is somehow applying when it shouldn't be). Put the old converter back in and all appears to be well, so may just be a bad or poorly balanced converter.

 

I am experiencing the same issue with my pro-built, word for word. The car is not driven much so it's been years now, but I don't think it's converter, or the tcc solenoid, or the trans for that matter. I think it's got more to do with the software. I had a mail order tune remedy this issue, but recently changed proms and went with a completely different bin, and the issue has returned, though not as pronounced as before. Something I'll have to look into