The Stovebolt Site Forums The Parking Lot Big Bolts Brake line thread pitch

Looking for an answer - I'm installing a '3rd' generation Bendix booster (from the mid 1970's) on a 58 Chevy 2-1/2 ton truck, in place of the '2nd' generation one it had on it. Brake line taps are all the same size (cylinders and booster), but I notice a difference in thread pitch - the orig. wheel cyl.'s have a slightly coarser thread than the taps on the newer booster. What's the explanation?

....the lines I see in the local parts house have "standard American thread" on some labels and the other ones have "metric" on them. Thats about all I can tell you. I know what you mean by pitch but in my cases they have been regular thread or metric.

Heavyhauler was helping me with getting started on my brakes and he found out the following info:

"I found them odd tubing nuts for the crossover tubes on our brakes. They are 1/4" with a 20 thread pitch normal 1/4" tube nuts are 24 pitch anyway the only place that has them around here is Williams’ Oil Filter in Tacoma."

Here is their contact info:

Williams Oil Filter Service Company
1247 Puyallup Ave, Tacoma, WA 98421
(253) 655-0188

Fred

It's not uncommon to have different thread sizes on inverted flare tube nuts for brake systems.
Are you sure the tube nuts are the same diameter with different pitches? That sounds odd to me.

These are the only standard ones I know of:

1/4" line,
tube nut with 9/16-18, 1/2-20, or 7/16-24 thread

3/16" line,
tube nut with 9/16-18, 1/2-20, 7/16-24, or 3/8-24 thread

Grigg

I also have/can offer most sizes of tube nuts in stainless steel.
Here's a thread about them , and copper nickel brake line as well.

Grigg

Thanks Grigg, Achipmunk and Fred for the quick replies. Fred, I think I have what you mentioned: 1/4" line w/ both 20 and 24 pitches - they are both the same size, but let me re-check, because I can't remember if it's 1/2" or 7/16"....

Yes Fred showed you what I had found above. I found it to be rather odd that the brake shops around here didn't know about the different thread pitches on the tubing nuts. Since I have found that this is not as uncommon as it originally seemed although the finer pitch threads are more common and that is what you will find as pre made lines at the parts stores. You will most likely need to contact a specialty brake distributor to get the course thread fittings.

Oh by the way another alternative to the tube fittings with odd thread pitch is to use a banjo fitting and fluid bolt to standard tube fitting adapter.

Grigg you will find that the fittings on the rubber brake lines will have the course threads like these odd tubing fittings do.

Thanks Grant, for the further insight. In fact some of the wheel cylinders on this truck use banjo fittings anyway - but all pitches on the OEM parts, whether banjo fitting or direct line connection, are 7/16 and have the same coarser thread. However the Bendix booster, which also has 7/16 taps, is a finer pitch. I haven't done enough of this to have known about the problem ahead of time - what clued me in was checking the threads on all of the rebuilt components before installing them, including wheel cylinders, master cylinder and bendix booster. The truck is 1958 and the booster is early 70's, so the time difference may(?) explain the pitch difference, but I'm not sure that it's that simple. I guess I should feel lucky I didn't come home with a bundle of pre-made lines with the wrong fittings....

I looked in another catalog here and did find listings for 1/4" tube buts both 7/16" with either 20 threads or 24 threads per inch.

Grigg

Grigg I have now found that they are not so uncommon I can't believe that all the brake shops said that they don't exist even when I had an example?????

I looked for the 7/16-20 fittings and could not find them so I turned some on my CNC lathe.Heck of a lot cheaper to buy them.

I'd say they are not as often used, but certainly are available.
What I haven't found is any in stainless steel like I have most all the other sizes in.

Seems a little odd that 7/16-20 tube nut is hard to find, when that is a normal fine thread for 7/16 bolt.
The extra fine thread 7/16-24 which I would think is more unusual is in fact easy to find and common on tube nuts. Not a perfect comparison, one is a bolt and other a tube nut, but odd none the less.

Grigg