Mopar 904 trans pressure
 

Need a transmission guy.
Just killed the thrust bearing in a new engine, 3rd time.
Twice with the old engine.


People keep pointing to the transmission cooler pressure.
I need someone to look at the readings I got.
Let me know if there is a problem.


Pressure line to the cooler;
Engine @ idle Engine RPM @ 2000
P-0 P-5PSI
R-25PSI R-50PSI
N-45PSI N-48PSI
L-28PSI L-42PSI
2-25PSI 2-50PSI
3-28PSI 3-55PSI


RETURN LINE


P-5PSI P-8PSI
R-40PSI R-45PSI
N-40PSI N-40PSI
L-28PSI L-45PSI
2-28PSI 2-45PSI
3-35PSI 3-45PSI


MAIN LINE PRESSURE FROM THE CASE


ENGINE @ IDLE ENGINE @ 1500RPM
P-5PSI P-14PSI
R-5PSI R-14PSI
N-5PSI N-15PSI
L-5PSI L-15PSI
2-15PSI 2-29PSI
3-15PSI 3-16PSI


Anyone know if these numbers are good?

Re: Mopar 904 trans pressure
 

Your mainline pressures do not make sense, you must have the gauge in the wrong port or the valve body you have doesn't supply pressure to it. Try checking it at the front servo in 3rd.

The cooler return line pressure is fed back into the transmission for lubrication, what you're seeing is a little high. Is the converter regulator valve (the one next to the main relief valve) still functional or has it been locked out?

904's don't normally take out the thrust due to the smaller diameter converter neck, much easier on things than a 727.

Jim Mantle V/SA 6632

Re: Mopar 904 trans pressure
 

I didn't think the main line pressure looked right.
No expert here, but I would have thought it would be more.
I used the center port on the right side per an ATSG book I have.

Re: Mopar 904 trans pressure
 

If your converter balloons , you will probably damage the thrust bearing . Converters can balloon if there is too high a pressure being fed into the converter , or if the converter shell is just not strong enough . The fluid that is inside the converter will be at a much higher pressure than what is fed into the converter , and goes higher , the higher the rpm the converter is spun . Most converter builders furnace braze the pump fins to the shell , and weld anti-ballooning plates on the pump shell , and also on the cover . Also make sure you have some pull up on the converter to the flexplate , usually .090" is adequate .

Re: Mopar 904 trans pressure
 

Exactly what I was going to suggest. Happened to me once, with the same outcome (burned-up thrust bearing). The advice above is spot-on.

Re: Mopar 904 trans pressure
 

If I read this correct, the issue here is no clearance and or actual pressure on the flexplate because the converter ballooned. Right? If so, that should be easy to check.

Re: Mopar 904 trans pressure
 

The way it works is there is some amount of spline lock inside the conveter , If the converter balloons then it forces against the flexplate , which is actually designed to flex slightly . If it can't , or if the converter pilot bottoms in the crank , then the forces go way up and could fail the thrust bearing . If there is enough endplay in the converter then even with spline lock there is enough clearance to cover up some small amount of ballooning . Many aftermarket flexplates are super stiff so they don't flex much , so with those flexplates it is critical to have enough pull up . Usually .090" is enough to be safe .

Re: Mopar 904 trans pressure
 

The converter balloons under pressure then returns to it's original size. Checking clearances, pull up, and dimensions after the fact may not reveal a problem.

Re: Mopar 904 trans pressure
 

Now that's some good info there. Never considered it can return to it's original size. Thanks

Re: Mopar 904 trans pressure
 

Not wishing to be argumentative, but I have never heard of a ballooned converter returning to its original size when fluid pressure is taken away. Think of ballooning as reforming the converter's metal shell by hydraulic pressure. Once the metal has been "stretched" to it's new size, it has no ability (think "memory") to return to its original shape.

Re: Mopar 904 trans pressure
 

To figure that out , you would need to know the dimensions when the converter was brand new . I have talked to more than one converter company that says that their converters are built with tighter endplays new , and it will change to their desired endplay after a couple three runs . That would indicate some permanent ballooning , but good point that it could balloon more , during operation , then return back .

Re: Mopar 904 trans pressure
 

Then why anti-ballooning plates?

Re: Mopar 904 trans pressure
 

I expect the converter shell is able to flex to some degree before yielding to the point where it is permanently distorted, especially if it lacks anti balloon plates. If the pull out distance hasn't changed, then the converter hasn't been blown up out of specs - as long as the pump isn't also damaged. Excessive internal pressure in the converter will also force it forward. I may be wrong but 50PSI in the cooler lines sounds a bit high. I would pull the pump and check it for evidence of excess loading on the gears against the reaction shaft support as well to help figure out what's occurring.

Re: Mopar 904 trans pressure
 

The original application for an 8" converter was an Opel way back in the 1960's . It wasn't designed for the kind of HP that is being put to it in most of the racing applications currently . The anti ballooning plates are meant to beef up the shell , it works in conjunction with furnace brazing the pump fins inside the shell . Most modern OEM converters are furnace brazed from the start . The older converters , just had the fins staked in .

Re: Mopar 904 trans pressure
 

Interesting to know.
Sent this convertor back to ATI, they told me that it hadn't ballooned.
Had it freshened up & sent back.
Put it back in, 10 passes, lost the thrust.
Chalked it up to the crank repair.
Had a new engine built, all I used from the old one was the rods & pistons.
New block & crank.
Had another custom convertor builder look at it, no signs of ballooning.
9 passes later, lost the thrust.
I have used two different transmissions, checked for binding & the trans, drive shaft & differential was used in another car with no concerns.

Re: Mopar 904 trans pressure
 

The only constant is the convertor.




I will be doing some comparasion & taking mearsuments when the engine comes out.
I do have a spare Turbo Action convertor to compare it to.

Re: Mopar 904 trans pressure
 

The two 904 transmissions are built the same ? Do they happen to have aftermarket bellhousings ?

Re: Mopar 904 trans pressure
 

I don't do these things everyday, but I know some guys who have fought this with a high RPM Torqueflite combination. I would ask someone about those cooler line pressures. 50PSI at 2k - hard to tell what it is as the RPM go up. I do remember that some people were using a pressure relief system to dump fluid from the cooler system directly to the pan to limit that pressure. Flexplate to crankshaft bolts leaving marks on the front of the converter? Verify the clearance there for reference before unbolting everything. Converter snout not bottoming or jamming in the crankshaft flange bore? Front trans pump chewed up?

Re: Mopar 904 trans pressure
 

x2 happen to me now I run 1/16 plate between motor and trans.

Re: Mopar 904 trans pressure
 

No, stock cases.
One came out of my bracket car that has 10 seasons on it & the other is the one that came in the Stocker.

Re: Mopar 904 trans pressure
 

I just recently saw this problem on a customers 360 Drag Pak engine.
It was caught in time before the crank was damaged.
The root cause was not the converter but the converter pilot hub not having adequate clearance and bottoming in the crankshaft .030" before the converter reached the flexplate .
I was able to increase the clearance by using a .125" mid plate as a spacer and then using .125" spacers between the converter and flexplate .
The proper fix will be to machine the pilot hub deeper when the engine is apart for freshening . In this case the crank was a Scat crank , but I checked the depth against a stock 360 and it was within .020".
Converters do not actually balloon with modern shells and reinforcements ,but rather they try to push out of the pump .Excessive line pressure can be a factor, but the key word is excessive
Usually this movement is absorbed by the flexplate ,,but when there is no free movement in the crank pilot hub ,the thrust takes the load.

Re: Mopar 904 trans pressure
 

Update; Found the ATI convertor that is in the car is bottomed out in the crankshaft. Have a spare Turbo Action convertor & checked it & had .102 clearance between the convertor snout & the crank. Real close to the problem identified in this thread.

Re: Mopar 904 trans pressure
 

Call ATI...their pilots are screw on, and can be bought in differing lengths.

Bill

Re: Mopar 904 trans pressure
 

Mike that is great news.

Re: Mopar 904 trans pressure
 

Talk with ATI, they will have to move the lugs on the convertor to get the Clearance that I need.

Re: Mopar 904 trans pressure
 

You should inspect the front pump in the trans. If it was pushing forward on the thrust bearing, then it was probably pushing back on the inner gear of the pump.

Eddie Bolton