Differential vent

[Tom Endy]

The subject of a differential vent for a Model A with a Mitchell overdrive installed has been discussed on the barn a number of times. The attached document is further to that discussion. I have also discussed the subject with Steve Mitchell. This document is posted on the web site of the Santa Anita A's Model A Ford Club of Arcadia, California

santaanitaas.org

https://www.santaanitaas.org/wp-cont...ntial-Vent.pdf

Tom Endy

[Tom Endy]

A barn member contacted me asking what a Tudor basement is. The attached document describes what they are.

My grandson is now a senior in high school, and he has been driving his Model A to school every day for the past several months.

https://www.santaanitaas.org/wp-cont...r-Basement.pdf

Tom Endy

[David in San Antonio]

Thank you for the explanation of the basement. I had the same question.

[JayJay]

So bottom line, Tom: are you recommending that a differential vent be installed when installing a Mitchell, and if so is the drilled out plug with the Alemite vent an acceptable method? Thanks.

[Synchro909]

If there are concerns about water entering the rear end through a simple drilled hole in the plug in the Mitchell tube, why not drill it and install an elbow and a piece of PVC tubing like Mitchell puts on the O/D itself? The other end of the tube is attached to the under side of the floor. You can be as creative as you like on how to shield it from water splashes.

[8EL]

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Originally Posted by Synchro909

If there are concerns about water entering the rear end through a simple drilled hole in the plug in the Mitchell tube, why not drill it and install an elbow and a piece of PVC tubing like Mitchell puts on the O/D itself? The other end of the tube is attached to the under side of the floor. You can be as creative as you like on how to shield it from water splashes.

Something like this perhaps.....

[Synchro909]

Originally Posted by 8EL

Something like this perhaps.....

Yes, something like that but I was suggesting putting it in the plug to access the grease nipple in the tube.
Do I see a couple of adaptor plates in the background to fit a 1928 Chev head to a Model A engine?

[8EL]

For a "in the car" add on it would be easy to put it in the fill port like you say, I don't know if you would have an issue with oil spinning off of the ring gear and exiting the vent cap however. I had the differential down for an overhaul so I just machined it into the RH axle housing to get it away from the ring gear.

The cylinder head plates I made to fit 455 Oldsmobile big block engines to simulate the internal stresses applied to the block when the heads are installed on the engine. Incorporated in the cylinder boring and honing processes which yields a perfectly round bore, they assures the same bore dimensions when the head is installed. They are often referred to as "Torque Plates".

A leak-down test on a new overhaul with very low run time mind you does quite definitely validate their usefulness of the intended purpose....

[Y-Blockhead]

Originally Posted by 8EL

For a "in the car" add on it would be easy to put it in the fill port like you say, I don't know if you would have an issue with oil spinning off of the ring gear and exiting the vent cap however.

I believe Synchro is referring to the plug in the Mitchell Torque Tube. No where near the ring gear.

The Alamite vent is designed to prevent water and dirt from entering. Best to KISS it.

[8EL]

Gear boxes need to be vented, that seems pretty simple. The one I installed is for that same intended purpose, lightly spring loaded to prevent any foreign substances entry, while not allowing any pressure to build in the gear box.

[P.S.]

Now that Mitchell has been including the threaded cap on the rear torque tubes, that cap just needs a tiny hole drilled in it, or left a little loose to provide plenty of air pressure relief for the rear differential.

[Bruce of MN]

I got my Alemite fitting, but I think I'll add some elbows to the tapped hole in the Mitchell torque tube plug to make it vertical in place. Maybe a tube and make a little bracket to hold it vertical, as suggested above.

[Bruce of MN]

I tapped a 1/8"npt hole in the plug in the torque tube and used a pair of brass street elbows to hold the vent vertical. I tried it with a tube, but it was going to be more work to keep the vent upright and more pieces to fail.

[JayJay]

I spoke with Steve Mitchell about this modification to the output shaft tube plug. I asked him what he thought of it, and if he had any problem with warranty if it was installed. He said that he could see in a well sealed differential how venting might be a reasonable idea, and told me that he had no issues at all if an owner wished to make this mod. I am finishing up the rebuild of the diff to which I am attaching my new Mitchell O/D (finally got it a couple of weeks ago, started last May 2023, yay!) and will drill, tap and install the elbows like Bruce did.

The Mitchell Mfg. shop is in Colusa, CA which is about 2-1/2 hours drive in a modern car for me. So my bride and I made a one-day road trip and went up to pick up the overdrive. Spent a while just talking with Steve and Cindy, they are a thoroughly delightful couple whose dedication to their business is remarkable. Steve has a lot of stories about when the business was younger and his dad and mom were running it. All the best wishes to them.

[Ray in La Mesa]

To vent my Dif with a Mitchel, I had a 45* brass elbow & drilled & tapped the greasing access plug on the back torque tube till it was aimed up then screwed in a Zenith carb float valve. Works great, allows pressure to escape & seals so nothing can enter. Too simple!

[Planojc]

I vented my 39 about midway on top of the axle housing, exact same place as the vent on my 51.