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.