Moparts Tech Archive
Trans Vent Q'sTransmission vent relocation - Question
I heard of relocating the vent on 727 transmissions. What is the rationale behind this? Where do people usually put it? Tapping and plugging the original one 1/8 NPT seems easy enough while it is apart (spare trans).
Because when it runs out the vent, its hard to tell if its overfull,hot...or if you got a front seal/converter leaking.
This is the '78 Trans, I put a plug in the vent.
Look closely at the case in the pic below. The hole at the top of the case near the rear is a favorite relocation point for the vent. 1/4" NPT is the usual size with a hose attached to a nipple and up on the firewall.
Thanks John! That is helpful. And having it in the case is nice too, just in case the extension housing gets changed.
I know why it was done on mine. When I first installed my trans brake years ago, the thing would pump tranny fluid onto the ground during the burnout. Once we moved the vent I never had another problem.
Vent relocation is to prevent the fluid from sloshing out the front under hard forward G's. Also, the rear location allows easy attachment of a hose to route the breather opening up high, not easy with the front pump location. I drill the vent about 2" forward of the tailhousing flange.
Well, that is what I needed to hear. This transmission (and others I do), will have the vent relocated. I agree the hose going up will be a big help to avoid spills. I saw one guy bend a steel line along the case ending near the top front, then he attached a short hose.
I better look at my CSI trans sheild (one piece carbon fiber) to make sure the fitting clears it.
EDIT:My trans shield is still in the car, but from my picture (full size version), the shield is about 1.25" from the mating surface of the extension housing. I measured the case thickness at the extension housing mating surface, and it is 0.75". So, with a 1/4 NPT being about 0.54" dia, the center of the hole needs to be a minimum of 1.02" from the mating surface. This is nicely shielded by the sprag part of the case, which extends from the mating surface 1.40". So, I am going to put it between 1.02" and 1.13".
A helpful member emailed me this alternative location. It vents from the rear of the case, behind the divider to the extension housing.