Trans Guru's can you diagnose this?

OK its a V8 GM TH350


Problem first arose when it started getting warmer out and after ya drove for like 20 mins and everything was nice and warm it would stop shifting into 3rd sometimes.

But shifted fine and smooth when cold.

Someone suggested a vac leak making the modulator not shift gears.

Found some questionable vac line n replaced all.


Well it didn't stop it. Trans shift right when cold, nice n smooth or fast n hard depending on how hard your on the gas. Its not a slipping problem.


Well yesterday it did it worse and didn't wanna shift out of first.


Though well maybe the modulator is bad as the car does shift right when cold.


Well I quickly learned that if I put it into park evey time I stop it will work fine and proper.


DId put some dye in it a bit back to find a leak but didn't find it.

Is this a sticky valve body problem?

Is there anything I could dump in there to losen up things or what do you think it is?

I know what a bad trans is like and they don't shift hard n right like that if bad.


Just seems to be like some sort of maybe gunk problem?

Gotta take dog to vet today so I gotta drive it. Gonna yank my reverse lights so folks don't freak when I toss it in park every time I stop but that is the only way to make sure when I do take off it will shift right through all 3 gears.

 

My 4l60e had a similar problem that I traced to sticking valves.
Just pull the pan and VB and clean it or get it cleaned.
A shop will try and sell you a rebuild.....

 

Got another tip and its woking for now.
All I gotta do is down shift n upshift when I stop 3-2-1-2-3 and all is well.

But make just a few stop without and it starts to wind 2nd out high which is the sign its gonna start pissin me off.

 

If you are losing third gear when it is warm, and the 1-2 shift does not change when cold or hot, then you are losing fluid to the third clutch pack due to inherent leaks. I have used the TransGo TH350-1-2 Shift kit. This will triple the oil to the third gear circuit. TH400's have the same problem and the chances are good that this type of Shift kit can solve this for awhile if the clutches are still in decent shape. I carry these Performance Shift kits for these transmissions. Let me know if I can be of help here?

 

Here is some more background info

Car had a bad thermostat that looked like someone stomped on it and stuck it back in. So it was stuc open in it for like 6-7 years and never ran more then 160-165 temp, bolts were stripped. Well I finally got tire of sucky heat this year and got some fancy bolt out sockets.

So now with the proper 195 thermo is when this all started.

Was thinking the trans is just to use to them lower temp as it never had problems before.

But once thermo was right and temps got warmer outside, and car is running around 200 is when its doing this stuff.

Thought of dropping to a 180 to try n help. Cause it will run lower, has monster rad, runnig lower temps is no problem.

 

If cold temps keep it working & hot temps create the problem, then most likely this is a sign that something is going away, slowly from the description. I would still put in the TransGo Performance Shift kit, to see if this will solve the problem. The 160 temp is good for the transmission.