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-   -   Mopar 904 trans pressure (https://classracer.com/classforum/showthread.php?t=70541)

ss3011 07-30-2018 04:38 PM
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 .

nhramnl 07-30-2018 04:44 PM
Re: Mopar 904 trans pressure
 
Quote:
Originally Posted by ss3011 (Post 568724)
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?

CMcAllister 07-30-2018 05:00 PM
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.

ss3011 07-30-2018 06:42 PM
Re: Mopar 904 trans pressure
 
Quote:
Originally Posted by nhramnl (Post 568725)
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 .

devo340 07-30-2018 07:14 PM
Re: Mopar 904 trans pressure
 
Quote:
Originally Posted by CMcAllister (Post 568715)
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.

devo340 07-30-2018 07:19 PM
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.

ss3011 07-30-2018 08:22 PM
Re: Mopar 904 trans pressure
 
Quote:
Originally Posted by devo340 (Post 568737)
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.
The two 904 transmissions are built the same ? Do they happen to have aftermarket bellhousings ?

CMcAllister 07-30-2018 08:38 PM
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?

dartman 07-30-2018 09:08 PM
Re: Mopar 904 trans pressure
 
Quote:
Originally Posted by ss3011 (Post 568644)
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 .
x2 happen to me now I run 1/16 plate between motor and trans.

devo340 07-31-2018 06:10 AM
Re: Mopar 904 trans pressure
 
Quote:
Originally Posted by ss3011 (Post 568743)
The two 904 transmissions are built the same ? Do they happen to have aftermarket bellhousings ?
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.


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