1990 v1500 suburban 700r4 leaking when hot/hwy driving

[gmbellew]

Truck has just under 150k on it. 350 TBI, 700R4, NP241. All stock drivetrain.

My transmission has started leaking while driving on the highway. It doesnt leak much, if at all, on short trips around town. But if I get on the highway and it starts drenching the pan and dripping on the exhaust and cooking off. The leak appears to be in between the pan and the torque convertor area, although it is throwing ATF pretty good and the area from the starter to the rear axle has some fluid on it.

Fluid levels, checked with hot transmission, engine idling, sitting level, are in the upper end of the hashed area on the dipstick. A couple times I checked it after the latest incident and the levels were either jumping way up randomly or I was pulling the dipstick out and suctioning fluid up the tube, because sometimes the level read very high. It never did it when I would recheck it and slowly remove the dipstick.

Transmission shifts normally and TCC seems to be locking and unlocking normally.

I dont mess with transmissions, but I am wanting to get an idea on potential causes of this and what it will take to fix it.

For the mean time I plan to stay on short trips around town and save my pennies......

Thanks in advance for any insight.

 

[Matt69olds]

Go to AutoZone, advance auto, etc, and get a small bottle of A/C oil with the fluorescent dye. Add a little to the transmission, after a long drive use a black light to find the leak. The dye will make the leak so obvious Ray Charles could see it. Then you will have a better idea of how to fix it.

In the meantime, make sure the vent is clear. It’s on the passenger side of the trans, it’s a small tube at about the 2 o’clock position if your looking at it from behind the engine. Sometimes they get plugged with mud, dirt, etc. if the trans can’t vent, when the fluid gets hot and the pressure inside rises, it will push fluid out wherever it can.

 

[bucket]

I'd also install a trans temp gauge, just in case the fluid is getting cooking hot and burping out because of it. Even if that's not the issue, it's a good idea for anyone with a 700r4 to have a temp gauge.

 

[gmbellew]

When I get it to the shop, I'll get a gauge added and also a drain plug on the damn pan!