4T60E slipping; odd shift behavior

[big_news_1]

Have a rebuilt 4T60E in my 1997 Bonneville (I know it's not a 60 degree V6, but please bear with me ). This is the second rebuilt tranny in this car. The first rebuild acted strange from day one... slow shifts at high rpm/low vacuum and firmer shifts at low rpm/high vacuum (yes, that's backwards of what it should be), missed shifts, etc. It eventually developed a condition where it wouldn't shift gears when given more than 1/2 to 2/3 throttle unless I let off the gas. We swapped it out for the current tranny (which was rebuilt by the same person), and lo and behold this transmission has the exact same issues. We opened up the first tranny to see if we could figure out the problem, and found what we believe to be a bunch of clutch material in the bottom pan. Seems the trannies have some sort of fluid pressure issue where the clutches aren't engaging fully and are slipping quite a bit, causing slow/missed shifts and poor acceleration.

What could be causing this issue? I've already changed vacuum modulators, to no avail. If I use the adjustment screw in the modulator the low rpm shifts get firm (especially the 1-2 shift), but it still shifts really slow at higher throttle settings. I poked around on these forums and found a few mentions of electrical issues causing some problems, so is there any chance we've wired something wrong or I have a bad VSS? What should we be checking?

I've already surrendered to the fact that I'll probably have to do another rebuild, but if this issue is electrical then it won't do me any good. I'm pretty desperate to figure this out, so any comments or ideas are appreciated. Thanks in advance.

[IsaacHayes]

Valve body I bet. I bet he didn't rebuild it or fix it. There are parts of it that give way or something or are loose and cause issues. I don't know the details exactly (3400-modified would know) but I bet it's the valve body. I highly doubt it's an electrical issue. The computer tells it when to shift but it can't really mess up.

My friend had his dodge transmission rebuilt, and it won't down shift, and slips at times. He keeps taking it back and each time they just re-flash his ECM/trans computer and saying that was the problem. Guess what? It doesn't fix it.. The trans worked great before it broke and was rebuilt. They tell him it's not their work.. yeah right they just don't want to take it out and open it back up so they keep messing with the electronics hoping it will fix it...

So yeah I'd bet it's the rebuild/tranny. I've heard of shops rebuilding the 4t60-e and just replacing the clutches and they burn out the clutches in a few months due to not repairing the valve body and that other stuff...

[big_news_1]

The guy who did both rebuilds is a close friend, and I know he took apart the valve body. Could it be something he reassembled incorrectly that's causing the issue? I don't know enough about transmissions to even venture a guess. But I want to make sure it's not something silly like wiring or tuning before I bite the bullet and pony up for a third rebuild.

My understanding is the line pressure in the 60E is controlled by vacuum only. This would lead me to suspect a mechanical issue when seeing these symptoms, but is there something in the wiring or PCM that could cause the transmission to have low line pressure?

And yes, I need to take a reading of actual line pressure to see what it is under various conditions. Just want to know if wiring is a possibility.

[IsaacHayes]

If the original rebuild acted up and it was the original trans I'd suspect something was not rebuilt right. There is parts in the valve body I think that are prone to moving out of place and there is a correction kit for that.

3400-modified would be the one to ask he has rebuilt his and it's running good for a long while now. And he has a lot of power behind it.

PCM won't lower the pressure too low to cause problems. If anything in a limp home mode it would raise it to max. Wiring I can't see as being a problem.

[big_news_1]

Thanks for the info, man.

Anyone have thoughts on what specifically could cause this sort of problem?

[gpse3400]

The pump is not reacting to higher pressure that its requried. The pump is variable displacement and adjusts line pressure as required. The pump slide, regulator valve set or modulator valve might be at fault.

[MyLittleBlackBird]

Turns out that I'm the dumbass that grabbed the wrong gasket for the separator plate and channel plate or valve body. Had one of em right, but somehow managed to grab the wrong one for the other side.... It's true, I'm the fool that did it. Also, apparently the valve body and channel plate bolts need re-re-retorqued because somehow the ones installed and torqued to spec were loose and backed out...... Note for future reference I guess. I won't be doing another one of these for anyone except myself... until I get it right. I think that's what it came down to. The original poster of this thread got the downlow from the shop he took it to.

[IsaacHayes]

Well props for owning up to it! I guess then he is running good again then?

[MyLittleBlackBird]

Yes. He was driving yesterday. It was a nasty mess, but now he is going to try and tune out the partial lockup function, and then get back to modding.

[big_news_1]

No need to admit fault, man! It's all good!

Yes, the tranny is shifting properly, but we've got a torque converter issue that deals with the pulse width modulation lockup mode. After I tune that out and create a full-on lockup, everything should be right as rain.

Thanks to those who responded to my post.

[JohnnyReb]

ha ha ha ha, now I know I'm not the only one to do something like that. I grabbed the wrong gasket for the bottom side of a 700r4 once. Those rebuild kits ship with 3 diffrent gasket designs. One of those deals where it was pulled, rebuilt and reinstalled in one session. I blamed it on being tired. Fooled around 2 days doing line pressure checks and other crap before I happened to notice the correct gasket still laying in the box on the bench. Good thing is you will always rememeber next time and it won't happen again. I also rebuilt and installed one once only to find the vanes and vane ring assembly still in a box and the old ones in the trash. Wonder why my tq converter felt so sloppy when I slid it in.