'81 GMC Transmission issues

Reply

  #1  
Old 02-06-03, 04:40 PM
short_circutz
Visiting Guest
Posts: n/a
Unhappy '81 GMC Transmission issues

I have an '81 GMC Rally STX van that I am currently having issues with. 350 c.i., not sure if it's a TH350 or TH400 tranny....

Before winter came, the Van was last backed into my driveway.

At this point I was experiencing a loss of transmission fluid, and it had to be topped up every time the van was to be driven. The van was driving fine otherwise, all shifts were smooth, and there, all gears forwards and revers were acting normal.

There was transmission fluid all over the front/top of the engine. No tranny fluid on the outside of the rad, cooling lines were dry on the outside, no fittings were leaking, the only thing I could figure is that the tranny fluid was being spit up through the filler/dipstick tube.

About a month into the snowy season (the van had been sitting in the driveway for about a month at this point), after some snow removal to be able to get the van out of the driveway, only the forward gears were present.

The following symptoms are present:

1) When the van is in park, the transmission is still putting a load on the engine, as it does not rev freely, and the van appears to want to try to move forwards, but "park" still locks the van from moving.

2) When reverse is selected, the transmission still puts a load on the engine, but the van does not move anywhere.

3) When neutral is selected the van wants to go forwards. When driving somewhere on the road, if it is left in neutral, the transmission does not shift out of first gear, and when a certain speed is reached it feels like it isn't engaged at all, as if you take your foot off the gas, it does not de-accelerate.

4) When in drive, it appears to function properly, shifts are still smooth.

5) 2nd and 1st could be manually selected successfully.

At this point, a local "tranny shop" would not even look at it unless we were willing to have them replace it with a rebuilt unit.

We brought it to a lube place to have the fluid changed (stood outside the vehicle and watched them do it, the type of process they used replaces the fluid in the torque converter also), and they advised us before they started the process that they did not feel chances were very good that it would cure the issue. We took the gamble, and, although the transmission has fresh fluid in it, the issues are still present.

Is there anything that I could look at to rectify these issues, other than replacing/rebuilding the tranny? The van is getting to be rough bodywise, and other than the tranny, is excellent mechanically wise.

I am technically inclined, and could get into repairing the issue if it isn't too "major".

Thanks in advance for any help!

Travis
 
Sponsored Links
  #2  
Old 02-06-03, 05:54 PM
Joe_F
Visiting Guest
Posts: n/a
What was the condition of the fluid that came out? How many miles?

Try changing the tranny modulator---little vacuum valve on the side of the tranny. Also, check the vacuum line going to the carburetor as well.

Failing that, wasted tranny---rebuild time.
 
  #3  
Old 02-07-03, 02:31 PM
short_circutz
Visiting Guest
Posts: n/a
Would that also cause fluid to come up the dipstick/filler tube?
 
  #4  
Old 02-07-03, 02:39 PM
Joe_F
Visiting Guest
Posts: n/a
Overfilling can do that. How is the fluid level? Must be checked hot.
 
  #5  
Old 02-07-03, 02:43 PM
short_circutz
Visiting Guest
Posts: n/a
Checked hot, engine running, level surface,and I filled properly each time i had to add fluid, hence the "There was transmission fluid all over the front/top of the engine. No tranny fluid on the outside of the rad, cooling lines were dry on the outside, no fittings were leaking, the only thing I could figure is that the tranny fluid was being spit up through the filler/dipstick tube" in my original post.

Would a plugged filter cause the issues I'm having?
 
  #6  
Old 02-07-03, 03:06 PM
Joe_F
Visiting Guest
Posts: n/a
I doubt it, plus you just had the fluid and filter changed, no?
 
  #7  
Old 02-07-03, 03:10 PM
short_circutz
Visiting Guest
Posts: n/a
A local "tranny shop" wouldn't touch it unless we wanted to re-build or swap out the tranny....we were originally gonna get a fluid/filter job done, and they wouldn't do it....

Fluid has been changed but the filter hasn't.
 
  #8  
Old 02-07-03, 03:27 PM
Joe_F
Visiting Guest
Posts: n/a
That's like putting on dirty socks with clean underwear. LOL.

Replace both again. Failing short of that, and a bad modulator, wasted tranny more than likely.
 
  #9  
Old 02-07-03, 03:31 PM
short_circutz
Visiting Guest
Posts: n/a
Thanks for all the ideas and advice. I think I found another tranny for just the right price anyways.....FREE!!!!, lmao

I might get the LT-1 that it's attached to also....

Thanks again for the quick responses...I'll try the modulator valve idea, it is something that crossed my mind....
 
Reply


Thread Tools
Search this Thread
Display Modes
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -7. The time now is 04:21 PM.