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Transmission/Drive PCM Vent Valve |
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SharkSN 
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Joined: August-23-2010 Location: Sproat Lake Status: Offline Points: 119 |
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 Topic: Transmission/Drive PCM Vent ValvePosted: October-16-2010 at 4:05pm |
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I had this problem on my 87 and suspect it just happened again with the '97. About 41 DegF last night, pulled the tranny dipstick got a big pop.
The vent valve sticks in the closed position causing elevated transmission pressure and eventually front? seal blow-out. Tell-tale sign is a big puff (positive pressure) as the trans dipstick is pulled. Reason is the rubber flapper gets stuck onto the 1/4" vent pipe as the trans cools - during cold nights, or winter storage after being hot. I am going to just put a pce of hosing on there, tie wrapped up into the engine let the thing vent. also could put a wiper/washer check valve on the end but will not for now. |
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eric lavine
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Joined: August-13-2006 Location: United States Status: Offline Points: 13413 |
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Posted: October-17-2010 at 11:43am |
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normally and i suspect the same goes for the PCM transmissions, on the BW's the breather is designed to pop off when case pressure reaches 10 psi. alot of guys on the high HP, high rpm set ups will run a hose up high.thats of course the guy's that spin them at 6000 plus.
i have really never seen a front seal pop out with the suspicion of case pressure, but excessive pump clearance will cavitate the oil and foam and come out the breather. |
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"the things you own will start to own you"
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SharkSN
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Joined: August-23-2010 Location: Sproat Lake Status: Offline Points: 119 |
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Posted: October-17-2010 at 3:19pm |
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it's subtle and i doubt anyone would connect the two. but if it is happening to me, then it's happening to someone else. the spring on that vent is very weak, the rubber flap flimsy, my guess nominal +ve pressure would cause it to lift. but i can test it.
what is the the pull force of the dipstick - that's about 1" and probably 10lbs. I also had the same thing happen to a porsche differential. blowing gear oil out the seals. gummed up breather same sort of arrangement. |
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eric lavine
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Joined: August-13-2006 Location: United States Status: Offline Points: 13413 |
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Posted: October-17-2010 at 3:29pm |
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over the years i have seen a couple BW's push out the rear seal which is exposed to case pressure, unlike the pump seal which would not be affected by case pressure because the cavity is filled with oil, the only time i see the front seal popped is when the pump is shot on both the BW and PCM transmissions.
the rear seal on the pcm's gets pushed in up against a flanged area from the inside out and is impossible to be pushed out |
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"the things you own will start to own you"
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SharkSN
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Joined: August-23-2010 Location: Sproat Lake Status: Offline Points: 119 |
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Posted: October-18-2010 at 12:50am |
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got the spring here measured the spring rate, area of the valve, vent opens at = 0.3 PSI, so basically it's designed to be atmospheric. The KA-POP that I got pulling the dipstick yesterday showed there is a problem with that vent, no doubt.
And on my '87 trans the pop was worse than this time 'round. that happened after winter storage, then the leak sprung, then KA-POP, then oh-$hit. '87 trans was leaking off the front I am pretty sure. Dealer said he could fix the seal... I sold the boat through them after buying the '97. didn't care about it. |
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