Mopar 904 trans pressure

[Hacksaw]

Originally Posted by ss3011

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 .

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.

[ss3011]

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 .

[CMcAllister]

Originally Posted by Hacksaw

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.

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.

[Hacksaw]

Originally Posted by CMcAllister

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.

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

[nhramnl]

Originally Posted by Hacksaw

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

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.

[ss3011]

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 .

[nhramnl]

Originally Posted by ss3011

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 .

Then why anti-ballooning plates?

[ss3011]

Originally Posted by nhramnl

Then why anti-ballooning plates?

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 .

[CMcAllister]

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.

[devo340]

Originally Posted by CMcAllister

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.

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.