4T60E slipping in 1st gear

[Woosch]

My Bonneville just passed 95k miles. The transmission was working fine, but I left the car parked for a couple of days over Christmas, and when I went to drive it this weekend, noticed that it is really slipping in 1st gear. The engine revs, and the car barely accelerates. Once it gets up to speed and shifts into 2nd, and 3rd, there isn't any noticeable slipping. The shifts from gear to gear feel normal. The fluid is full, and it is Valvoline Maxlife ATF which I replaced about 20k miles ago, along with the filter.

Two years back I had a very sporadic transmission issue that went away when I changed the fluid and filter. At the time, this is what would happen: I'd be accelerating under light throttle in 2nd gear and I'd floor it enough to induce a downshift. 2nd gear disengages, but it doesn't downshift into 1st. The engine revs like it is in neutral. I let up on the gas, it shifts, and everything is fine. The link to that issue is here: http://www.pontiacbonnevilleclub.com/fo ... 30962.html

Any thoughts? I've searched the forums but don't see anything that sounds exactly like my current problem of the slipping in first gear. Any advice would be appreciated. Nothing like a problem during the holidays...

Thanks!

[Franksdad]

dude try shudder fix, its a little red tube http://www.lubegard.com/~/C-230/Dr.+Tra ... udder+Fixx

[Jrs3800]

First get an adjustable Trans Vacuum Modulator,install it and see how it feels and if it makes any difference.. Your stock unit may be going bad causing the line pressure to be too low.. For the price of a modulator at the parts store its worth a try..

[Woosch]

Thanks for the advice. I'll pick up an adjustable modulator and see if anything changes.

[Woosch]

First get an adjustable Trans Vacuum Modulator... Your stock unit may be going bad causing the line pressure to be too low.. For the price of a modulator at the parts store its worth a try..

Thanks, the Vacuum Modulator was the problem. I replaced it with a new one and the transmission is shifting without a hint of slipping. So relieved it isn't a bigger, more expensive problem.

Thanks again!

[Franksdad]

Hmmm would this be the same with a 2001 sle?

[J Wikoff]

I don't think the 4t65 has a vacuum modulator, does it?

[repinS]

It does not.

[Jrs3800]

First get an adjustable Trans Vacuum Modulator... Your stock unit may be going bad causing the line pressure to be too low.. For the price of a modulator at the parts store its worth a try..

Thanks, the Vacuum Modulator was the problem. I replaced it with a new one and the transmission is shifting without a hint of slipping. So relieved it isn't a bigger, more expensive problem.

Thanks again!

Glad to hear it.. You can actually dial up the pressure a tad to gain a firmer shift and a little less clutch slip between the shifts.. Glad to hear that the trans is shifting normal now.. when the weather warms up drop the pan and do a filter and fluid change..

[Woosch]

when the weather warms up drop the pan and do a filter and fluid change..

That's next on my list. Once the weather warms up enough for me to pull a '58 out of the garage and make room, I'll get it done. The current filter and fluid have about 20k on them.