Valve stem size?

[Steve Jelf]

These stems (Schrader 724 & 725) are the size used on all the current metal stem tubes. It looks to me like ¹⁵⁄₃₂ - 27, but I don't trust my less than perfect vision. I wonder if anybody has a stem handy that they can check to see whether I'm right.

[CudaMan]

Here is a page from a 1930s Schrader catalog that shows the dimensions of several stems, including 724 and 777.

It says the major thread size for a 724 stem is 0.482-26.

For a 777 stem, it is 0.406-28.

Hope this helps.

[Scott_Conger]

For What It Is Worth:

Schrader threads are unique in all of the world. When you see a "decimal" value x "thread count" listed on any document INCLUDING a FORD print and SCHRADER documentation, you CANNOT go by that and expect to have a custom mfg make you the right thing if you're looking for a tap or a die. With that said, it is possible to have a tap made, lets say, for a valve stem cover, and end up with a cover that threads onto a valve stem (sloppily). An example of that is FORD's drawing of a valve stem cover of "15/32 x 26". That results in a cover which threads on, but it is NOT the actual size that Schrader specifies. Thread diameter and pitch are not SAE standard, they are a hybrid between the UN-series and M-series series screw theads.

Schrader Taps and Dies are available if you look hard enough...I know, because I have made some parts for myself that I needed, and invested an enormous amount of time on the project (and bought a few wrong taps along the way before I learned the special Nomenclature associated with them)

In my quest to make the best parts possible, I've found that it is easy to make a quality product...it just takes a lot of research, $$ and time. And often times you end up with a product that no one will pay for, but that's the way the game is played.

[Original Smith]

Even though the valve stems will work, neither were ever used by Ford.

[Steve Jelf]

Even though the valve stems will work, neither were ever used by Ford.

Correct. Ford used the smaller Schrader 777.

[Altair]

This is an original Ford valve stem.

[CudaMan]

With the bridge washer installed upside down.

Here are some more Schrader 777 pics.

[Steve Jelf]

Mark beat me to it.

[Altair]

[attachment=1.]

Both stems are from the same maker both have 28tpi

[Original Smith]

Most of the repro bridge washers I've seen are not made correctly, and my guess if you used one they might be prone to a future leak. Also keep in mind there are two sizes of them.

[Steve Jelf]

For those who haven't seen it, this picture shows what Larry mentioned.

Most original bridge washers, like the three on the right here, have raised ridges that press into the rubber of the tube to grip it securely and make a good seal. My guess is that the two on the left were made before anybody came up with the ridges. Current reproductions are made without ridges too, because the makers assume they will be used only with modern stems vulcanized into the tubes.

[Scott_Conger]

Steve

I don't think there was ever a time when "ridges" hadn't been thought of. There are several period suppliers who supplied "the ridges" as a separate and unique part. I have several of such pieces, and they were used with, and without the standard "winged" bridge washer. They are shown in multiple trades magazines and literature.

I cannot recall the source of the below photo, so cannot verify that the bridge washer is vintage or not, but the compression washer is.

[CudaMan]

Period picture with the "ridges" on a separate part from the bridge washer:

[Scott_Conger]

Thanks Mark!
I could not locate that ad on my computer

And now for the actual Schrader Universal hardware (got out to my shop this AM...BRRRR)

[Steve Jelf]

In Mark's illustration showing two separate pieces, the latest patent date is 1900. I suspect Schrader made their bridge washers that way first, and later combined them in one piece. I have both types with the Schrader name on them, though most bridge washers of either type are unmarked.

[CudaMan]

By the way, the Model A Ford vendors sell a bridge washer with the proper dimpling to clamp the rubber tube. It is much wider than a typical Model T bridge washer, but can be cut down to the proper size and shape with a cutoff wheel in a dremel tool. Just be sure to deburr all of the cut edges so that they can't cut the tube.