Moparts Tech Archive

Automatic Trans.

Trans Vent Q's

451 Jim
Moparts Member
Posts: 2558
From: Lexington Park Maryland
Registered: Dec 2000

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).

I was thinking of putting it at location "2". Forward of that I think too much rotating stuff will throw oil at the vent.

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smokindatires
Moparts Member
Posts: 681
From: Valdosta,Georgia
Registered: Jan 2002
posted 11-15-2002 10:13 PM

Because when it runs out the vent, its hard to tell if its overfull,hot...or if you got a front seal/converter leaking.
Rob

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451 Jim
Moparts Member
Posts: 2558
From: Lexington Park Maryland
Registered: Dec 2000

This is the '78 Trans, I put a plug in the vent.

I have to admit, this vent design (after about '71?) seems pretty good. It has a plastic baffle on the inside with a nipple sticking out that should avoid surface splashes. Any chance this vent relocation was a product for the older design with a simple metal plate baffle on the inside?

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John Kunkel
Moparts Member
Posts: 2640
From: Rio Linda, CA, USA
Registered: Nov 1999

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.

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451 Jim
Moparts Member
Posts: 2558
From: Lexington Park Maryland
Registered: Dec 2000
posted 11-16-2002 05:21 PM

Thanks John! That is helpful. And having it in the case is nice too, just in case the extension housing gets changed.
Do you have any thoughts on why it is done, and if the old vent style vs the newer (pictured) vent makes any difference?

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nhra mark
Moparts Member
Posts: 157
From: St. Charles, MO
Registered: Apr 2002
posted 11-16-2002 05:27 PM

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.

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John Kunkel
Moparts Member
Posts: 2640
From: Rio Linda, CA, USA
Registered: Nov 1999
posted 11-16-2002 06:33 PM

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.
I think the plastic snorkel is an improvement over the tin baffle but it becomes brittle with age and breaks with any mishandling.

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451 Jim
Moparts Member
Posts: 2558
From: Lexington Park Maryland
Registered: Dec 2000

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.

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