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Thread: TH 400 w/ Coan Trans Break blows ATF out of vent

  1. #1
    Junior Member SHOW GUEST
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    TH 400 w/ Coan Trans Break blows ATF out of vent

    Anyone got an idea why ATF blows out the vent tube on top of my TH 400 on a pass? Ran it up on the break and through the gears on stands but no leaks or fluid from vent. Possitive about coming out of vent, put a temp bottle on it and captured 2 or 3 ounces each pass. Has TCI deep pan, run Pennzoil ATF at normal level on dip stick. Even tried to drop 1 quart ATF. Still came out of vent. Trans shifts fine.

    Car does wheelies, runs low 9's. Blown 427 SBC 900 hp.

    Too much pressure? Too much heat? Too much ATF? Need baffle in pan?

    Dave

  2. #2
    Senior Member RACING JUNKIE
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    how hot is it getting ?

  3. #3
    Senior Member RACING JUNKIE
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    THe center support bolt is leaking pressure in the case.

    If it has been raced alot the case is sure to be wallered out where the center suport bolt goes. So it will pressureize the pan and vent

  4. #4
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    Quote Originally Posted by hammertime
    how hot is it getting ?
    Don't know temp yet. I know that sounds stupid but I have raced it since for a few years and just didn't get a temp guage on it yet. Will do this season.

    I do have a good B&M cooler mounted under the car with it's own fan.

    Dave

  5. #5
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    Quote Originally Posted by kwkracing
    THe center support bolt is leaking pressure in the case.

    If it has been raced alot the case is sure to be wallered out where the center suport bolt goes. So it will pressureize the pan and vent
    That's an interesting possibility, but the case was just changed out last year after an ear flew off the torque converter and destroyed the case. Still pushed fluid out of the vent.

    Only change we made to the set up is we upgraded with an additional torrington bearing (I think) between the direct and the intermmediate clutch, but didn't change the clutches. Wish I had now. 20/20 hindesite that might have eliminated one possibility.

    I guess it's still possible that it's leaking internally however. Is there any way I can tell if the bolt is leaking, and is there a fix if it is?

    Also is it possible that there is pressure coming from the valve body not sealing to the case, or some other common internal pressure leak? There is no gasket on either side of the Coan valve body, just metal to metal contact.

    Dave

  6. #6
    Senior Member RACING JUNKIE
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    The only way to check the center support is a visual, th400s like to waller that hole out where it seals. It only takes a little and the case leaks. One other thing is to take a punch and swell out the end of the governor tubes so they fit snug in the case and valve body.

  7. #7
    Junior Member SHOW GUEST
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    Quote Originally Posted by kwkracing
    The only way to check the center support is a visual, th400s like to waller that hole out where it seals. It only takes a little and the case leaks. One other thing is to take a punch and swell out the end of the governor tubes so they fit snug in the case and valve body.
    Thanks for the info. I'm going to take it out to install a braided line in place of the vent tube that will go to a small catch can tank on the firewall. I'll check out the center bolt hole to see if it's hogged out. The governer tubes have been taken out of my trans when we installed the new Coan trans break manual shift valve body. I'll look at places that might be pressurized for obvious flaws.

    Thanks again, Dave


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