94 4T60E - slip/grab/slip/grab on take off

[david3100]

When I press hard on the accelerator off the line, the front tires act as though they are crossing over one of those wet white strips on a downtown street. In other words, about three iterations of slip and grab. I have been easing off the line ever since I noticed this. I changed the fluid and filter using Dexron VI, again. This is the second spill and fill using VI. I changed the modulator to an adjustable some time back. Think I should switch back or is it more serious? Torque converter? When it shifts from 1-2, it is a bit harsh. Then, the other gears are normal shifts. By the way, I do get a smudge of gray off the pan magnet, but I consider it normal wear. I don't know the history exactly of the engine/trans, but it was installed about 60K ago and had 50K on it at that time. Thanks for any comments. Dave

[gpse3400]

One issue, then the other...

For the take off issue sounds like your transmission is going neutral momentarily. You could try raising the pressure on the vacuum modulator to see if it cures it, also you could easilly need a fluid filter change if you haven't done so within that milage, you would be WAY overdue.

1-2 needs some more description...is it slipping then engauging hard or is it immediately engauging hard?

[david3100]

I'll try just going back to the old modulator just to remove that variable. The 1-2 shift is abrupt. There is no slippage. Just bang, there's second gear.
Thanks for the reply.

One issue, then the other...

For the take off issue sounds like your transmission is going neutral momentarily. You could try raising the pressure on the vacuum modulator to see if it cures it, also you could easilly need a fluid filter change if you haven't done so within that milage, you would be WAY overdue.

1-2 needs some more description...is it slipping then engauging hard or is it immediately engauging hard?

[gpse3400]

Yeah if the modulator is not adjusted right it will hit the gears hard, 2nd predominantly. I usually adjust it till I hear the transmission pump whine at idle, of course with a connected the vacuum line. Then I back off 4 turns, but that was a firm setting. 6 turns should make it civil. But the stock modulator will make the shift firmness factory...naturally.

I misread completely, you did change the fluid/ filter already then.

So your only problem is that it has a harsh 1-2 shift. Yeah readjust the modulator or put the factory one back in.

[3400-95-Modified]

The firmness of the modulator should not cause your slip and grab issue thought. My shift is far from soft and I have no issues with it... I like my shifts firm.

[david3100]

It was the modulator. I had too many counter clockwise turns. Thanks everyone.

[gpse3400]

No problem Sir.

[bszopi]

At least it was an easy fix!

[david3100]

Intermittent- still happening.

At least it was an easy fix!

I may have lost my audience since it has been a while_ But, I have had this same symptom happen twice. Oddly, at the same intersection on my way to work. There's a right sweeping turn that comes to a red light. I sit there and idle for 60 seconds. Then, when I proceed through on the green, slip/grab and I ease on away. It hasn't happened for several days. I'll check my log since I can't remember the mileage since the last spill and fill. May be time.

[seagull]

slip grab...

i have the same transmission.

the problems i have started out the way you discribe your problem... it progressed to the point that now... my trans doesnt go into drive, I have to downshift to D1 and if i start off from a light i must father it very lightly or it will slip, then it pops into gear and i can put it in drive and it will shift all the way to D4 normally. but... it will not downshift past 3rd without going into slip... neutral.... then the process begins again...

must people think its the 1 way bearing that works with the center band in the transmission, its some kind of holder that holds a part of the planitary to keep the unit in Drive. not completely sure aboiut it but i located a 96 4t60e with a vaccuum modulator from a buick lasaber with 28,000 orginal miles in the junk yard that was a collision wreck from Gieco, it was hard to believe, i was very happy to find a 96 car that looked like it had been kept in a garage all those years, even the transmission tag is like it rolled off the assembly line.. clean... the interior was almost unworn... it was easiy to tell the mileage was orginal. a beautiful car except for the huge ripped scrape down the entire passenger side of the car.... must have been an old persons last ride before they took their license away.

when i get the trany apart i will report back what it was....

[david3100]

OK. Good luck with yours.

[Dave96z34]

That problem is a fun way to snap deferentials and axles. 4t65s do it to you need a rebuild.

[david3100]

I have to manually shift the auto now to keep it from slipping. Lucas did not help. Is there another trans besides 4T60-e or should I stay with it? Also, anyone have opinions on trans shops? I'm tempted to look into swapping mine out. But, I cannot get much height in my garage. If you know of a good writeup point me to it. Thanks everyone.

That problem is a fun way to snap deferentials and axles. 4t65s do it to you need a rebuild.

[deathamatend]

Here's a diagnosis: the 1-2 clutch drum o-ring seal is leaking and causing the clutch pack to temporarely lose pressure disengaging forward gear. Giving it gas builds up line pressure overcoming the amount lost to the leak. Transmission problems mostly show up at lower line pressure where fluid pressure is more critical to transmission operation.

[david3100]

Sounds plausible. Thanks.