Traction Owner’s Club › Forums › Technical › Brakes › BRAKE PIPE UNION SIZE
Does anyone know the brake pipe union thread size on the master cylinder?
This is for a Slough built Light 15 1950 .
Philip,
I only have metric thread gauges but, having measured the banjo bolt from the nose union (feed to brakes) with a micrometer, I am fairly confident that thread is ½” diameter x 20tpi.
B…….
Hi Philip
If it is the same as my 1949 Light 15 then the brake pipe size is 1/4″ and the union thread is 7/16″ x 20tpi UNF.
Cheers Richard
Philip,
If it is not too late ……
I am not familiar with non-metric threads so after I read Richard’s post, I had to look it up. It seems both 7/16” and 1/2″ unf are 20 tpi, but the former has a nominal major diameter of 0.438″.
However, as I said, I checked the male thread on a banjo fitting with a digital Vernier and the major diameter was definitely ½” (actual reading 0.502) with a 0.05″ pitch and those are definitely the dimensions of a ½” unf thread.
The hardware I measured was from a Light 15 so, having seen Richard’s reply, I re-measured the banjo male fitting and then confirmed it was compatible with a selection of other “stock” cylinders, mostly ex-French models.
That confirmed the ½” unf thread to be the common to all of them which is what I expected because Club spares only lists one reference for all models. However, it also confirmed the unit from which I had originally taken the banjo bolt was not an “odd” one that had been retro-fitted at some time.
I have subsequently corresponded with Richard off piste. He tells me has just been working on his brakes and, although the master cylinder was not accessible, he ran a 7/16″ unf tap into one of the other unions where the brake pipe goes to the rear of the car. Although it was a good fit in that union, my measurements still suggest the master cylinder outlet has a different thread, i.e. ½” unf.
If nobody else can offer precise information, I would suggest obtaining a sample of both a ½” and 7/16” male thread and trying both in your master cylinder.
B……
I have a brand new Bendix master cylinder on the shelf, it is 1/2″ unf 20tpi, checked with a 1/2″ tap also tried the 7/16″ in my view imposible to interchange. Hope this helps.
Philippe
Thanks, Phil.
B….
And so, having now answered the initial question, that raises a further question from me …..
…… why did Philip require this information ? Does he need to replace the banjo bolt?
B…..
…… why did Philip require this information ? Does he need to replace the banjo bolt?
He’s plumbing in a brake servo (details on Facebook)
Simples!
Ta,
B….
I have just sent a picture of my master cylinder (it wouldn’t accept any text) which shows the banjo bolt going into the master cylinder but there is also the sleeve bolt? holding the pipe into the banjo and this is 7/16 unf. I have just fitted a servo and I was lucky to find a 7/16 unf sleeve bolt which took a 3/16th brake pipe as I couldn’t find a servo which took the 1/4″ brake pipes fitted to my Citroen.
Cheers Richard
Finally all plumbed in. The original male unions were finally found to be M11 x 1.25 and it was not possible to find fittings in this size. 7/16 UNF is very close so a M11 x 1.25 tap was run through two inlets of A 7/16 UNF ‘T’ to connect to the original pipes. Then easy to connect up with the pipe from the servo with a 3/8 UNF adapter. The other pipe from the servo was connected to the original banjo with another adapter. Just need to remove the manifold and drill and tap 5/8 UNF for the vacuum pipe.