Fmx Leaky Tranny Question

Discussion in 'Classic Mustang Specific Tech' started by 04mustang70, Mar 21, 2014.


  1. 04mustang70

    04mustang70 Member

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    1. Hi all! I have a 1970 Mach 1 with a 351W and a FMX Trans. I have owned this car for about 30 years and drive it fairly often in the summer months. My problem is there has been a slow leak coming from the front of the bellhousing when I park the car. It drips a few after parking then stops. I have some skills in wrenching but less in diagnosing. Could this leak be from the convertor? I know theres fluid in the converter and if it is leaking are there seals that need to be replaced or do you just buy a new converter? What else could it be? Im sure theres a front seal for the transmission shaft that could be leaking? I think it could be the converter because after sitting for a while it takes the car to go in gear after putting it in gear especially reverse. Any help is appreciated as I plan on dropping the transmission soon to fix this leak that has been there for quite some time.
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  2. dennis112

    dennis112 Active Member

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    First make sure it is transmission fluid that you are dealing with. The rear main seal of the engine can leak into the bellhousing too.

    The converter is probably fine as they are a sealed metal unit. There really isn't anything you can replace on it anyways. It could be the front shaft seal that you mentioned (quite likely) or possibly the front pump outer seal. After 30 years the front shaft seal is probably dried up and should be replaced. The pump outer seal is more involved but, unlike the front seal which has the rotating converter to seal with, the pump seal is a stationary devise so I wouldn't go there yet without first trying the shaft seal.
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  3. 04mustang70

    04mustang70 Member

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    Its definitely tranny fluid. The tranny was rebuilt in 1997 but I would agree that it is the front shaft seal. Is that seal replaceable by a do it your self guy like me or does it involve disassembly of the tranny or special tools? I would take the tranny out myself and take it to a shop if needed. It seems to operate fine and doesn't need a rebuild.
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  4. rbohm

    rbohm Founding Member

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    the seal is replaceable, but it does require some tear down of the trans. mostly pulling the trans out, removing the torque converter, and the front pump housing to replace the seal in the housing. if you pay attention to what you are doing, and you have a shop manual you can reference, you can do the job yourself. expect to take the weekend though to do everything.
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  5. 04mustang70

    04mustang70 Member

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    Thanks for the reply!
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