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1949 Buick Roadmaster Dynaflow problem(s)


Flying Norwegian

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The Dynaflow trans in my 49 Roadmaster has been compleatly overhauled with new front pump, clutches, bands, seals end gaskets.

I am not able to ble to fil more than 8 quarts into the transmission and when I try to drive the car it moves in all gears but whit a lot of slipping.

As far as I understand that must mean the converter is not filling up.

What can be the reason for this?

 

I have measured the pressure of the front pump and it is aprox 100lbs at idle (400 rpm) When I increase the rpm past 550, the preasure drops to aprox 10lbs.

According to the manual the front pump should cut out at 2500 rpm as indicated by preasure drop to 20 lbs as rear pump cuts in.

What triggers this transission between the front and rear pump?

Are this two «problems» related?

All the measurement was made whith car on jackstands and rear wheels free to rotate

 

Have taken the transmission apart 2 times now and have not found any abnormalities.

Do not want to take it apart again before I have a fairly good idea of what might be wrong.

 

Any ideas apreciated

Thank you

Vegard

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1 hour ago, Flying Norwegian said:

The Dynaflow trans in my 49 Roadmaster has been compleatly overhauled with new front pump, clutches, bands, seals end gaskets.

I am not able to ble to fil more than 8 quarts into the transmission and when I try to drive the car it moves in all gears but whit a lot of slipping.

As far as I understand that must mean the converter is not filling up.

What can be the reason for this?

 

I have measured the pressure of the front pump and it is aprox 100lbs at idle (400 rpm) When I increase the rpm past 550, the preasure drops to aprox 10lbs.

According to the manual the front pump should cut out at 2500 rpm as indicated by preasure drop to 20 lbs as rear pump cuts in.

What triggers this transission between the front and rear pump?

Are this two «problems» related?

All the measurement was made whith car on jackstands and rear wheels free to rotate

 

 

Just to verify:

When you increase the rpm to 550 and the pressure drops, is this with the transmission in gear and the rear wheels spinning?  Of course, even if this is how you did it the 10 lbs sounds incorrect and like a failure in the accumulator.

And have you inspected the dip stick to make sure the cap has not moved from the correct position on the shaft?  The cap on my 56's trans dip stick has loosened its grip and will easily slip up the shaft thus letting the dip stick drop lower into the pan and giving a false full reading. 

 

 

 

 

 

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What does the service manual say about fluid capacity?  It sounds like low fluid (my 55 dynaflow needs 10 quarts --- 12 quarts if dry transmission).

I don't know what the transition from front pump to rear pump is, but on one of mine when rebuilt it was found that the rear pump had not been operating probably since the last rebuild (no performance issues).

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JohnD1956

The transmission in D and wheels are spinnig.

I have also measured the preasure in the high accumulator and it is correct at 95 lbs at idle, 1000rpm and 1800rpm

 

old-tank

The fluid capacity according to the manual is 11 3/8 quarts (dry), I can only fill 8 (9) quarts before it starts pouring out of the dipstic tube

 

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OK, I don't know why there is a diminished capacity.  Next, check that the pickup tube is leak free.  If like a 55 the rubber collar does not seal well without an added clamp.  That early transmission does not have detentes in the transmission, so check the linkage adjustment; if the valve body is between gears all will howl and slip.

 

 

1674785068_dynaflowtemplate.thumb.jpg.bd8bcdb5d5fcc339c708e54ccd800d8c.jpg 

Check all of the pressures before disassembly again and if needed focus on the input shaft at the ring grooves and of course be sure rings are present.  Be sure the correct clutch and steels are present and oriented correctly.

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5 hours ago, JohnD1956 said:

The cap on my 56's trans dip stick has loosened its grip and will easily slip up the shaft

Two fingers on the stick and two fingers holding to cap in place. The doctor held me up by the ankles and installed that information with a slap of his hand on day one.

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2 hours ago, old-tank said:

OK, I don't know why there is a diminished capacity.  Next, check that the pickup tube is leak free.  If like a 55 the rubber collar does not seal well without an added clamp.  That early transmission does not have detentes in the transmission, so check the linkage adjustment; if the valve body is between gears all will howl and slip.

 

 

1674785068_dynaflowtemplate.thumb.jpg.bd8bcdb5d5fcc339c708e54ccd800d8c.jpg 

Check all of the pressures before disassembly again and if needed focus on the input shaft at the ring grooves and of course be sure rings are present.  Be sure the correct clutch and steels are present and oriented correctly.

I have done a little experiment to see if the input shaft rings are sealing.

I drained the oil and left the drain plug out, then I pumped oil in through the oil cooler supply line to try and fill the converter that way. The oil that I pumped in drained out through the oil pan drain hole fairly quickly. My theory is that the input shaft seal must be leaking for that to happened. What do you think?

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1 hour ago, Flying Norwegian said:

What do you think?

I never thought of that but maybe I should have.  Drain the torque converter and measure what came out.  Try to fill through the supply line, drain and measure again and determine at what point it drains from the pan.  You probably will not be able to totally fill the torque converter since there will be air in there.

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6 hours ago, old-tank said:

I never thought of that but maybe I should have.  Drain the torque converter and measure what came out.  Try to fill through the supply line, drain and measure again and determine at what point it drains from the pan.  You probably will not be able to totally fill the torque converter since there will be air in there.

I am pretty sure the converter is not filling up, the question is why?

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9 hours ago, Flying Norwegian said:

I am pretty sure the converter is not filling up

Or draining too fast?   If not full I would expect excessive vibration and very foamy fluid.  The converter fills instantly on startup:  on one of mine if left sitting for a few days the converter leaks back into the pan (rings on input shaft) and when started the fluid pumped into the converter displaces the air in the converter back into the pan and blows fluid out the filler tube.

Another consideration that will be hard at this point to track down is that some wrong gaskets were supplied or multiples were in the "kit", the wrong one(s) were used.

Mudbone had that issue that he discussed somewhere, either in his restoration thread HERE or in the mudbone videos on dynaflow.

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3 hours ago, avgwarhawk said:

Possibly wrong gasket or misplaced check ball? 

The transmission have been taken apart and put together twice (by 2 different people) and behave exactly the same every time. I can drop the pan and take out the valve body and check the gaskets and ball, doing this is not a big job. I find it unlikely that this is the reason, but I must consider everything at this time.

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4 minutes ago, Flying Norwegian said:

The transmission have been taken apart and put together twice (by 2 different people) and behave exactly the same every time. I can drop the pan and take out the valve body and check the gaskets and ball, doing this is not a big job. I find it unlikely that this is the reason, but I must consider everything at this time.

 

One would think a gasket was not an issue but I remember in Mudbone's video(Old Tank linked above), there were several gaskets with many cut outs.  It took some looking over each for the correct gasket.   

 

You stated two different people rebuilt the transmission.  I would surmise the first rebuild missed something.  The second rebuild only replicated the missed item in the first rebuild.    

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16 hours ago, Flying Norwegian said:

One more piece of information I almost forgot.

There is almost no flow through the oil cooler.

When I attach a pressure gauge to the line going from the transmission in to the oil cooler in effect blocking the oil flow I get NO pressure (0psi) in any gear and “all” rpm

 

Is there any flow through the cooler if compressed air is used?  In short, is the cooler clogged?  

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45 minutes ago, avgwarhawk said:

 

 I'm a bit confused.  The port at the transmission tested fine yet there is little flow through the cooler?  

To clarify, the pressure test of the front pump was taken at the test port on the drivers side.

The flow and pressure test of the cooler was taken at the hard line that go from the transmission to the cooler on the passenger side.

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4 hours ago, avgwarhawk said:

Since you stated the cooler had very little flow I would look to use a rubber hose/clamps to route temporally around the cooler.  Take the cooler out of the system to check if perhaps the flow with the cooler installed is to little for proper filling of the converter.  

  

I have already bypassed the cooler with a clear plastic hose. Problem slit exist.

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20 hours ago, old-tank said:

There should be a vent on the upper part of the transmission center section.  If plugged it might not allow enough fluid into the transmission.  Whatever the cause or reason there is not enough fluid in it.

Good point, I will check it. Enclosed is a picture of the vent, how do I remove it without damaging it?

DSC_0458.JPG

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On 11/9/2020 at 7:42 AM, Flying Norwegian said:

have measured the pressure of the front pump and it is aprox 100lbs at idle (400 rpm) When I increase the rpm past 550, the preasure drops to aprox 10lbs.

This sounds like it is sucking the pan dry when you bring up the rpm

2 minutes ago, Flying Norwegian said:

It is just pressed in. Took it out and is was not blocked.

One last (probably not;)) suggestion: add some tranny fluid at that vent location.

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When the transmission was overhauled many years ago I changed the front pump and backing plate.

The new pump is different from the OEM pump and have a bushing to support the small pump gear the gear is modified to make room for the bushing.

Se enclosed picture of similar pump. The modified gear on the right, the OEM gear on the left.

Do anybody know of any issues with this type of modified pump?

Can this modified pump be the reason the converter is not filling up?

image.jpg

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I have never opened a Dynaflow and thus have no direct experience from which to draw a conclusion on your question regarding the modified gear in the oil pump.  But in reading my '56 Service manual I would say you are right that the modified gear would be a source of low oil pressure. 

The original gear in your picture looks like the gear shown in my manual.  Full and flat on the beveled side.  And the manual calls for a tight clearance between the face of that gear and the pump as well as between that gear and the pump cover.  According to my manual checking across the face of the pump there should be between .001 to .0025 clearance between the gear and the surface of the pump.  But the manual also says to check the pump cover for "depth of wear"  And to replace it if the cover shows scoring and or wear in excess of .001.  It would seem to me that the hollow area on your modified gear is in direct violation of that setting.

 

However, you indicate this trans has been rebuiilt twice, and that leads me to question if it ever worked right with that modified gear in place?  If so, then my observations would seem to be inaccurate. 

 

And, as one with no practical experience with the subject at hand,  I would defer to those who do this for real.  

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Like John, I've not been into a dynaflow past having the valve body off. You mention back at the start that pressure is good at low idle, then drops off. Could it be the control valve that switches to the rear pump - which I understand is to take place about 2500 rpm, is not working and switches it right away?  Just thinking out loud. 

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1 hour ago, Oldtech said:

Like John, I've not been into a dynaflow past having the valve body off. You mention back at the start that pressure is good at low idle, then drops off. Could it be the control valve that switches to the rear pump - which I understand is to take place about 2500 rpm, is not working and switches it right away?  Just thinking out loud. 

II don't understand how the switching to the rear pump work. Please explain.

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How did it function before the rebuild?

100 psi at idle:  nothing wrong with the front pump

Forget the rear pump.  It turns off the output shaft only when the car is in motion.  No change in function even if inoperable like I said before.

I would still like to see more fluid in that unit.

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I was looking for pictures of your transmission and found this:  HERE

So, now I know what you have.  What is the fluid level when off, idling and higher rpm?  Maybe jack up the passenger side and stuff more fluid in or add some at the vent?

You may have to move on to a different transmission (this one is kinda high priced for a "core")...there are others out there.  

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