Differential / transmission vent

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rtadams89
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Differential / transmission vent

Post by rtadams89 » Sat Feb 20, 2021 9:26 pm

The vents on my A5 look like they could use a replacement. I see 2 such vents, one on the front differential and one on the transmission. Both appear to be 1/8 npt. Is that all of them? The front differential one is east to get off. The one on the transmission is installed in a recess and I can't get to it with a wrench; is there some trick to getting that one out?


rtadams89
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Re: Differential / transmission vent

Post by rtadams89 » Mon Feb 22, 2021 9:24 pm

As an update: I got the rear transmission vent off. I ended up snapping it in half and then using a socket to remove the remaining portion that had wrench flats on it. After removing it, I can see that the cap was somehow expanded, which prevented a socket from fitting over it in the first place. The replacements I put in (and the original front axle vent) allow a socket to fit over them normally, so there were easy enough to install.

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Re: Differential / transmission vent

Post by markrdje » Tue Feb 23, 2021 4:52 am

So someone put the wrong size vent/part there
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rtadams89
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Re: Differential / transmission vent

Post by rtadams89 » Tue Feb 23, 2021 9:05 am

It was still a 1/8 npt vent, it's just somehow the moveable "cap" part of the vent was larger than the wrench flats of the base part. Every other vent I've seen (including the one on the front axle and the two replacement ones I sourced) had the wrench flats of the base just slightly larger than the "cap" so that a socket can fit over the cap and engage the flats. I can only assume the cap somehow expanded after installation -- though I'm not sure how -- as I don't see how it could have been installed without use of a socket.

Chuck W.
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Re: Differential / transmission vent

Post by Chuck W. » Tue Feb 23, 2021 11:53 am

Bear in mind that those are NOT vents, they only open to let pressure out. Under normal conditions, they remain closed to keep water out.
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rtadams89
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Re: Differential / transmission vent

Post by rtadams89 » Tue Feb 23, 2021 12:01 pm

At the risk of being pedantic, they are "VENT ASSY" according to the TMs, and the modern replacements are "axle vents", "differential vents", etc. But yes, they are supposed to allow pressure out. I don't have the reference docs near by, but if memory serves me, they are supposed to open between 1-3 PSI. Ended up replacing mien with Dorman 924-262 to somewhat keep the original look. I'm sure you know this, but for anyone else that stumbles on this thread: If you don't care about authenticity, you can replace the vent with a hose running up to a high point or to the airbox...did that with a few M35A2s, as they built up a lot of pressure in the axles when these vents clogged.

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Re: Differential / transmission vent

Post by Chuck W. » Tue Feb 23, 2021 12:06 pm

2530-832-6844 Vent assemblies - cap should be spring-loaded. These were common on just about all M-series vehicles.

The point I was trying to make is some people may think the "vents" are bad because the cap is tight and does not spin freely. If you can lift the cap slightly and it springs back, it's probably OK and just needs a good cleaning. I understand that in your case, one of yours was damaged and had to be replaced and the Dorman product is about the only choice. I don't know of any vendors who sell the spring-loaded pressure relief vents new. I checked McMaster-Carr and they didn't list them. Might find some good used ones.
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