Turbo 350 issues

[77 k 20]

Hello all. I have a 77 k20 that keeps spitting the dipstick out of the tube a couple inches after driving it. I thought changing the fluid and filter as well as cleaning the vent would help. Nope still does it. Hasn't been an issue until now since selling my other truck it's become the only truck on the property. Any ideas or suggestions would be appreciated muchly.

 

[squaredeal91]

Sounds like you're breather/vent on top of transmission is plugged. Probably Mudd dobbers. Happened to Mt friend. Was on the highway and all asudden transmission fluid blew out of dipstick tube and on the exhaust and it pretty much burned to the ground. Not trying to scare. Just warn.

 

[77 k 20]

My trans has just a hole in the top of case above shift linkage. On my other turbo's they've either had a metal tube or a vent like an axle vent in that spot. My truck came from Montana and was a serious work truck there. Hard to say what it's been thru and what changes/deletes were done. Thanks for the advice and after Thanksgiving dinner I'll go take another peek in that area.

 

[squaredeal91]

If the hole is plugged Might be able to clean out the hole by hand twisting a small drill.

 

[77 k 20]

I was reading other posts about this same issue and I found a great thought that I'll share. After cleaning the hole take a small amount, a couple psi, of compressed air from compressor insert the line into the fill tube and hopefully it will push whatever is blocking the vent hole out. Keep the psi down so that you don't bulge the pan and blow gaskets and seals. I'll let ya know how that works when I'm done.

 

[NickTransmissions]

I was reading other posts about this same issue and I found a great thought that I'll share. After cleaning the hole take a small amount, a couple psi, of compressed air from compressor insert the line into the fill tube and hopefully it will push whatever is blocking the vent hole out. Keep the psi down so that you don't bulge the pan and blow gaskets and seals. I'll let ya know how that works when I'm done.

It's literally impossible to blow out the pan, pan gasket, front seal, stator sealing rings etc with shop air (id love to see pics if you manage to do so)..You'll just push whatever is clogging that vent (if anything) deeper into the pressure relief circuit inside the pump, potentially creating more problems.

And when you say "fill tube" are you referring to the dipstick tube? If so blowing air into the dipstick tube will move a little fluid around in the pan, nothing more.

If your pressure relief/vent circuit in the pump and/or case is blocked by debris or anything, trans will have to come out, pump removed to clear it.

 

[77 k 20]

Nick Thank you for your thoughts and insights. I'm kind of at a loss for other options. What thoughts might you have to my problem of the dipstick moving out the tube when driving and your suggestions to solve the problem? The trans works fine and shifts solid like it may have a kit in it Thank you for your time.

 

[NickTransmissions]

What thoughts might you have to my problem of the dipstick moving out the tube when driving and your suggestions to solve the problem?

You're welcome - See my response above:

If your pressure relief/vent circuit in the pump and/or case is blocked by debris or anything, trans will have to come out, pump removed to clear it.

This assumes internal fluid pressure is forcing its way up the tube and pushing the dipstick out.

Is it overfilled? How many quarts were added at last service and how many total in the trans?

 

[77 k 20]

I just changed the filter and gasket and put in 9 qts which left me at the bottom of the fill line on dipstick.

 

[NickTransmissions]

I ... put in 9 qts

Well.....found the problem.

Here's a capacities chart

ATI Fliud Capacity for Automatic Transmissions and Torque Converters

These charts show the fluid capacities for varoius automatic transmissions with OEM pans, as well as a variety of torque converter diameters. Aftermarket deep pans may require more fluid. Please note that the charts show the fluid capacity for a new converter. Generally a converter that has been...

atiracing.com

You have like 3-4 quarts too much in there, lol.

 

[77 k 20]

With all due respect then why does the dipstick show 1 pint low?

 

[squaredeal91]

With all due respect then why does the dipstick show 1 pint low?

Then it would lead me back to clogged vent scenario. Or someone put the wrong stick or tube in. The th350 has the hardest to find dipstick and tube because it seals different than most other gm trannys. I used to get calls for them where I used to work.

 

[NickTransmissions]

With all due respect then why does the dipstick show 1 pint low?

Do you have an aftermarket deep pan and/or large aftermarket trans cooler installed that would dramatically increase capacity over stock?

What size (diameter) converter do you have and what is your particular transmission system's total capacity, to the best of your knowledge?

 

[77 k 20]

I'll go tear into it today and report my findings. Thank you both for your insight and thoughts.

 

[77 k 20]

Well here's what I found. As far as I can tell the vent orfice is open. Was able to take some wire and stick it in about an inch or so. Never really found a hole that the wire would go into the transmission. The pan is a stock metal pan not any deeper than my old 350 turbo in my 72 K10 It does have a standard size cooler in front of the radiator in line with the one in the radiator. As far as the convertor it appears to me as a stock replacement size and type. Rethinking when I filled it up I'm sure I was wrong about the 9 qts but 7 qts for sure. My dipstick still reads 1 pint low now and driving into town and back. Thanks again for your advice. Nick do you have a stock turbo 350 pan with a drain plug in it and if so would you be willing to part with it. I can't find one up here.