TH350, shifting weird, leaking and low.

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naminator

Apprentice
Thread starter
Jul 21, 2020
53
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Ok, stupid question but are you checking the fluid level with the engine running?

You should be checking it with the fluid warm not hot, engine idling, in park, on a level surface.

I checked with the engine off, I checked with it idling and cold, I checked with it idling and warm (but it seems to be overheating) and always in park on a reasonably level surface. The last time I checked it and it was super low, it was warm, running and parked on a level surface. This time, engine warm, rowed the gears, drove a bit, idling and parked, after 1 bottle of lucas and maybe 200ml of atf, it was high.
 

Wraith

Royal Smart Person
Jan 13, 2013
1,512
113
DFW, TX
Fluid needs to be checked with a warm vehicle on a level surface, you can circulate the fluid with the car in neutral, should read high when cold without running the vehicle. I'd pull the pan, the mark for full should be at the edge of sealing surface, make sure that mark is correct to start, I've seen many marks off if the dipstick has been changed.
 
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naminator

Apprentice
Thread starter
Jul 21, 2020
53
18
Fluid needs to be checked with a warm vehicle on a level surface, you can circulate the fluid with the car in neutral, should read high when cold without running the vehicle. I'd pull the pan, the mark for full should be at the edge of sealing surface, make sure that mark is correct to start, I've seen many marks off if the dipstick has been changed.

I am thinking of dropping the pan, but haven't. It has a TH350 and a 307 v8. I have no clue if anything in this car is what it seems.
 

pontiac guy

G-Body Guru
Oct 28, 2016
583
93
Royse City, TX
If a car sits long enough the converter will drain back a fair amount of fluid into the pan. Then it's common to leak passed the seal on the dipstick tube. It will drain back some every time you shut down. That's why it reads higher engine off. It is possible that the car drained back from sitting and leaked. Once you started driving it you filled the accumutor and clutch Pistons as well as the assorted fluid passages. A typical GM trans holds about 12 qts including the converter but a fluid change nets you 5. 5 qts is actually just the pan and some of the various passages. I'd fill it drive it and figure out what exactly is going on before getting to far into it. It should stop taking fluid unless it's leaking it or drinking it thru the modulator hose. You can check the dipstick seal by removing the bolt from the back of the motor and pulling the tube up. There is actually a molded bushing looking seal that was used by the factory. I have no idea where to get one. Aftermarket tubes have an O-ring they use to seal it. I've never had any luck using an o-ring on a factory tube. I always used to rob a parts trans.
 

naminator

Apprentice
Thread starter
Jul 21, 2020
53
18
If a car sits long enough the converter will drain back a fair amount of fluid into the pan. Then it's common to leak passed the seal on the dipstick tube. It will drain back some every time you shut down. That's why it reads higher engine off. It is possible that the car drained back from sitting and leaked. Once you started driving it you filled the accumutor and clutch Pistons as well as the assorted fluid passages. A typical GM trans holds about 12 qts including the converter but a fluid change nets you 5. 5 qts is actually just the pan and some of the various passages. I'd fill it drive it and figure out what exactly is going on before getting to far into it. It should stop taking fluid unless it's leaking it or drinking it thru the modulator hose. You can check the dipstick seal by removing the bolt from the back of the motor and pulling the tube up. There is actually a molded bushing looking seal that was used by the factory. I have no idea where to get one. Aftermarket tubes have an O-ring they use to seal it. I've never had any luck using an o-ring on a factory tube. I always used to rob a parts trans.
I figured it may be leaking because it was sitting without running. I know it would be higher when not running, but that didn't explain the incredibly low level after sitting and not driving for a while, outside of idling a bit. I added the trans slip fix just in case and haven't noticed new leaks so far. I plan on driving it a bit, getting an inspection on the car and hopefully the fluid levels will stabilize.
 

pontiac guy

G-Body Guru
Oct 28, 2016
583
93
Royse City, TX
I figured it may be leaking because it was sitting without running. I know it would be higher when not running, but that didn't explain the incredibly low level after sitting and not driving for a while, outside of idling a bit. I added the trans slip fix just in case and haven't noticed new leaks so far. I plan on driving it a bit, getting an inspection on the car and hopefully the fluid levels will stabilize.
If it sits for long enough you could drain all the fluid above the centerline out of the converter, plus all the passages not protected by a check ball. That's a lot of fluid. So let's say 3-4 qts at the low end. When you fill an empty trans you are supposed to manually shift it through all the gears to fill the valve body and accumulator and servos. It doesn't just suck up. If you lost a lot I would expect it to be low once or twice before it stops asking for more
 

303'505rollin

G-Body Guru
Sep 4, 2020
699
93
Colorado2newmexico
You can get a 5 qt jug of fluid at Walmart for 17$ DeX 3 compatible. I always let it run in neutral for a few after adding fluid then reverse then go through the gears lowest first then check again. I had a problem when I swapped the 200 metric for a t350 that reverse never kicked in until I let it circulate for a few, maybe it had to work out any air that may have trapped but it was fine after
 
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