1954 Power glide burps transmission fluid

[John S.]

Re: 1954 Power glide burps transmission fluid

In a previous post I have posted a picture of a valve body which I keep as a spare. I am going to address the two rings on the valve body that mate with the clutch drum. The rings have approximately the thickness of a grocery receipt in free play as they fit between the grooves.. When fully compressed the rings have approximately 30/1000" free play between the inner diameter of the ring and the outer diameter of the area inside the grooves. Does this create a non-leaking seal? You might slow down the torque converter draining, but you are not going to stop it at this point.

[Joe R.]

Re: 1954 Power glide burps transmission fluid

Having studied the cross-section of the entire unit the purpose of the vent is not obvious to the engineer in me.

The high point for fluid in the tranny is the top of the torque converter. Since fluid flows down hill to seek equilibrium it seems to me the fluid would be passing the rings on the clutch shaft and clutch drum, which are the first obstruction encountered, into the body. I thought that it is wear on that shaft and drum that is the problem.

A vent in the tail piece would actually promote such a flow as does the filler tube, which also acts as a vent. (Doesn't that answer the question of why Chevy did not vent the transmission? It is vented.)

Speaking of vents. It is interesting that one post called for the vent to be a tube higher than the torque converter. Whereas the other thinking is a vent as low as the tail piece is sufficient. Looks to me that fluid draining past the rings could actually come out a vent that low.

I still say the additional vent is not needed if the metal parts are within tolerance. But it might be a less expensive fix.

I don't think we armatures are going to solve this but it is an interesting conversation.

I agree with most of your observations. The heart of the matter is that when the engine is running, the front pump in the transmission keeps the torque converter full of fluid. When you shut the engine off, all that fluid in the top half of the torque converter wants to drain back down into the transmission.

I believe that all Powerglides have an anti-drainback provision, but I don't know the specific implementation of it and I don't know if the design of this anti-drainback provision changed as the Powerglide evolved.

What I do know is that when this anti-drainback provision starts to leak, the torque converter will slowly drain back into the transmission and the fluid level will rise considerably. If the leak is very slow, it may take a month or more for full drainback, but if the leak is faster, it may take only a few days.

The rising fluid level will start leaking out wherever it can find a path, such as the shifter shaft, speedometer connection, and the connection between the dipstick tube and the case. All of these locations are above the normal fluid level and may not leak much under normal operating conditions, but being submerged in fluid can greatly increase the leakage rate.

You can "reset" the drainback mechanism by simply starting the car and letting the pump re-fill the torque converter. To completely cure-it though, the anti-drainback mechanism has to be correctly repaired.

Once the fluid has drained back, the apparent "fluid level" shown by the dip stick will be far above normal, and the bottom of the dipstick tube will be immersed in the accumulated fluid. When the engine is started, it seems plausible that turbulence in the transmission might cause fluid to be pushed out the dipstick tube.

It also seems plausible that if there was an air vent at the high point of the transmission case, trapped air could be released as the fluid drains back and displaces the air. Releasing the trapped air might allow the resulting fluid level in the dipstick tube to be lower than it would otherwise be. It might also allow the start-up turbulence to develop less pressure inside the transmission case, further reducing the changes of pushing fluid out the dipstick tube.

Overall, I think the root cause of the problem is a leaking anti-drainback mechanism, but I suspect that a vent at the top of the transmission case might help to reduce the consequences of a leaking anti-drainback mechanism.

[Dan P.]

Re: 1954 Power glide burps transmission fluid

Get the car up to about 35 miles MPH and put it in neutral shut the motor off.Preferably down hill. After the motor stops put drop it in gear and see if the motor turns over. If it does not the pin that drives the rear pump is sheared off . If it starts pull the governor out to see if the gear is worn out .As far as the fluid leaking out . It is the converter draining back. Some times a new front pump bushing fixes the problem .This is a common problem . I have tried many things to fix it . I had a 55 passenger car that i rebuilt the transmission.Never had a problem for over 10 years . One day i decided to get the car up tp 60 MPH .After that it started draining back . There is a converter drain back valve in the valve body . But you have to pull the transmission out to check it . Never got around to doing that .They use to make a check valve that went in the coolant line to correct the problem . Check with Classic Chevy they had them years ago

[John S.]

Re: 1954 Power glide burps transmission fluid

I agree with most of your observations. The heart of the matter is that when the engine is running, the front pump in the transmission keeps the torque converter full of fluid. When you shut the engine off, all that fluid in the top half of the torque converter wants to drain back down into the transmission.

I believe that all Powerglides have an anti-drainback provision, but I don't know the specific implementation of it and I don't know if the design of this anti-drainback provision changed as the Powerglide evolved.

What I do know is that when this anti-drainback provision starts to leak, the torque converter will slowly drain back into the transmission and the fluid level will rise considerably. If the leak is very slow, it may take a month or more for full drainback, but if the leak is faster, it may take only a few days.

The rising fluid level will start leaking out wherever it can find a path, such as the shifter shaft, speedometer connection, and the connection between the dipstick tube and the case. All of these locations are above the normal fluid level and may not leak much under normal operating conditions, but being submerged in fluid can greatly increase the leakage rate.

You can "reset" the drainback mechanism by simply starting the car and letting the pump re-fill the torque converter. To completely cure-it though, the anti-drainback mechanism has to be correctly repaired.

Once the fluid has drained back, the apparent "fluid level" shown by the dip stick will be far above normal, and the bottom of the dipstick tube will be immersed in the accumulated fluid. When the engine is started, it seems plausible that turbulence in the transmission might cause fluid to be pushed out the dipstick tube.

It also seems plausible that if there was an air vent at the high point of the transmission case, trapped air could be released as the fluid drains back and displaces the air. Releasing the trapped air might allow the resulting fluid level in the dipstick tube to be lower than it would otherwise be. It might also allow the start-up turbulence to develop less pressure inside the transmission case, further reducing the changes of pushing fluid out the dipstick tube.

Overall, I think the root cause of the problem is a leaking anti-drainback mechanism, but I suspect that a vent at the top of the transmission case might help to reduce the consequences of a leaking anti-drainback mechanism.

Joe, Pictured is the valve body. Point out the "anti-drainback provision". (it's called a pressure regulating valve)

[Perry M.]

Re: 1954 Power glide burps transmission fluid

I brought this thread back to the top because I don't think the issue was resolved. These transmissions didn't burb transmission fluid when new so what caused them to burb at a much later date. I don't believe it was due to the lack of a vent. Maybe the addition of a vent was a cheap fix but what actually failed internally to cause the problem? As asked by John, please point out the anti-drainback provision in the valve body so we can determine if there is a possible fix to the problem with it. If anybody knows of an old timer in the Pacific Northwest area (Seattle) that used to rebuild these units, please let me know.

[Joe R.]

Re: 1954 Power glide burps transmission fluid

I would gladly point to the anti-drainback valve if I knew where it is, but I don't. All I know is that there is reportedly an anti-drainback valve somewhere in the design. And, I *think* it may be accessible with the transmission in the car.

Hopefully someone who really knows these old transmissions will be able to tell us where the valve is and how it can be serviced.

I do agree that finding and checking the anti-drainback valve should be the first order of business when trying to fix the burping problem, but it is also possible that drainback leaks can develop elsewhere as wear increases the tolerances in certain sleeve bearings. This possibility was alluded to in some earlier posts. Fixing those bearings would likely require removal of the transmission.

So, let's hope that someone can tell us where the anti-drainback valve is, and whether it can be serviced with the transmission in the car. It seems to me that checking the ant-drainback valve should be the first step in trying to fix this problem.

[John S.]

Re: 1954 Power glide burps transmission fluid

I would gladly point to the anti-drainback valve if I knew where it is, but I don't. All I know is that there is reportedly an anti-drainback valve somewhere in the design. And, I *think* it may be accessible with the transmission in the car.

Hopefully someone who really knows these old transmissions will be able to tell us where the valve is and how it can be serviced.

I do agree that finding and checking the anti-drainback valve should be the first order of business when trying to fix the burping problem, but it is also possible that drainback leaks can develop elsewhere as wear increases the tolerances in certain sleeve bearings. This possibility was alluded to in some earlier posts. Fixing those bearings would likely require removal of the transmission.

So, let's hope that someone can tell us where the anti-drainback valve is, and whether it can be serviced with the transmission in the car. It seems to me that checking the ant-drainback valve should be the first step in trying to fix this problem.

Valve to torque converter is in valve body. Certainly not accessible with the transmission in car.

[Joe R.]

Re: 1954 Power glide burps transmission fluid

Valve to torque converter is in valve body. Certainly not accessible with the transmission in car.

I guess I'll have to study up on Powerglide terminology. I thought the "valve body" could be removed by simply dropping the pan on the transmission. I seem to recall removing the valve body on a Powerglide to install a shift kit to make the 1-2 shift more crisp. But that was almost 50 years ago, so my recollection may be mixed up with a TH 400 that I eventually used to replace the Powerglide.

[John S.]

Re: 1954 Power glide burps transmission fluid

I guess I'll have to study up on Powerglide terminology. I thought the "valve body" could be removed by simply dropping the pan on the transmission. I seem to recall removing the valve body on a Powerglide to install a shift kit to make the 1-2 shift more crisp. But that was almost 50 years ago, so my recollection may be mixed up with a TH 400 that I eventually used to replace the Powerglide.

no pan on a 54 powerglide

[Joe R.]

Re: 1954 Power glide burps transmission fluid

That explains it. The only Powerglides I'm familiar with are the ones from the 1960s.

If there is no pan on a burping Powerglide, it sounds like the transmission would have to come out of the car to get to the anti-drainback valve, even though we are still not quite sure where that valve is on the 1954 version.