Transmission Slipping

[nroden]

My truck doesn't seem to want to shift into 3rd, the RPMs go really high and then you have to keep on letting off and it'll finally go from 2nd to 3rd. Then after you get up to about 45 MPH it slips (more you press the gas the faster the engine goes but the truck isn't going any faster). I hope this is nothing major, but it may be time for a new transmission. Its a TH-350. How much do you think a rebuild would cost at AAMCO or someplace like that? The current one has approx. 109,000 mi on it.

[Longhorn Man]

Do this quick test. Go drive your truck around the block. Shift it manually. Start off in first, and go untill the engine should shift at light throttle, then wait for just a second or two longer, then pop it into second.
Do the same thing for third gear.

If it seems fine when you do this, then you need to inspect/replace the rubber ends on the vacume line for the tranny modulator. You can see a hard line on the back of the engine...on top of the intake on the passenger side. Look follow that to the carb and inspect the rubber hose, then same thing underneath. (It may just be poped off)
If all this is good, and the tranny is still reacting the same way, replace the modulator. (cheap/easy fix)

[old gm blues]

Did you check the oil? My Th350 was leaking from the rear through the front tranfer case seal,so I never noticed any leakage, until I checked the oil lever from the transfer case and got a face full of dextron.

[68 Stepside]

If the truck doesn't wanna run over about 45 mph....but the engine still gains RPM's, the trans is definitely slipping. Providing the fluid level is correct, I would change the atf/trans filter, and hope that fixes the problem.

Let us know what you figure out.

[71Rat]

when u change the fluid if it is burnt and brown/black it is bad. sometimes if it is that bad and u change it, the problem will be worse.... sounds like u need a rebuild...... i do them at our school and the rebuild kit is only like $50... but i dont know what a trans shop would charge.... i am assuming ur looking around $800.

Best of luck
Rat

[Sweet72]

The no 2-3 upshift until you let off the accelerator is a vacuum related problem. As for the slipping, sounds like you have a internal problem, maybe as simple as a stuck valve in the valve body. Do what Longhorn Man said and take it for a run, then change the fluid and filter. Good luck

[ZOOMY]

With these old trucks, sometimes the valve body is gummed up. I put in a pint of "Sea-Foam transmission additive", & drive it for about 100 miles before changing the fluid. Works sometimes; sometimes not.