Brake feed pipe union thread

redrover

redrover

Well-Known Member
Hi Guys,

I installed my new CompBrake master cylinders yesterday. All went smoothly except for the brake feed pipe (from the reservoir), which I can't connect up. The flanged end of the pipe seats nicely, but the screw union can't pick up the thread. It's as if it's hitting a shoulder.

I have contacted CompBrake for the union specification, and they have confirmed it is a 7/16-20 thread (see attachment). My question is what is the thread of the standard union? I'm about to have a complete set of cupronickel brake lines made up, and basically need to try and work out if I need to specify a different union on the feed pipe (7/16-20 instead of whatever is on the car), or whether the cylinder itself is defective.

Thanks in advance
MichaelDSC_7272.JPGMASTER-CYLINDER-[SETUP-GUIDE]-DIAGRAM.jpg
 

Attachments

  • DSC_7272.JPG
    DSC_7272.JPG
    458.6 KB · Views: 12
Hi, Sometimes the shoulder at the start of the thread gets flared out by its tightening down against the flare of the pipe. It usually comes out but won't go back in. If it is you can either dress it up with a file or replace it. The only other thing to check is that it's actually 7/16" UNF by trying a bolt of that size, it could also be a metric thread as it's a new item, which is annoying but not unknown.

Colin
 
colnerov said:
Hi, Sometimes the shoulder at the start of the thread gets flared out by its tightening down against the flare of the pipe. It usually comes out but won't go back in. If it is you can either dress it up with a file or replace it. The only other thing to check is that it's actually 7/16" UNF by trying a bolt of that size, it could also be a metric thread as it's a new item.

Colin
Click to expand...
Ah, that's interesting. And to be honest, would tally with the symptom I'm experiencing. CompBrake have confirmed it's a UNF thread (unless it's defective, of course). I've got some new 7/16 UNF bolts - I'll try one of those. If it fits, I'll buy a new union to check that fits as well. If that all checks out, I'll be able to order the new brake line set with peace of mind, as it will be all-new unions.

Thanks for this
 
I have seen the end of the male tube nut (on the pipe from the reservoir) that goes into the master becoming flared outwards due to over tightening, and being very difficult to get back into the master inlet. If you can see that flaring, carefully file it back to straight, without marking the flared part of the pipe itself.
 
Thanks JP.
I'll try that trick to verify that the union is the correct size, just flared from over tightening. The union will be replaced when I fit new lines anyway. I just want to verify that the size is correct.
 
In my experience the inlet hole (yellow plug) is one size bigger than the outlet hole, eg 7/16-20 inlet, 3/8-24 outlet, so they cant be confused. And I swear I wrote that before I looked at the diagram you posted!
Edit - can I suggest that you get the pipe connections threads to the cylinders started before you bolt the cylinders down hard? This will give you more flexibility in the alignment, and ensure you dont get anything cross-threaded.
 
Last edited:
From distant memory the P6 uses a particular Brake pipe thread. Check the thread pitch with a guage. If its 26 TPI It'll be British Standard Brass - all sizes us 26 TPI and no other thread types do.
 
jp928 said:
In my experience the inlet hole (yellow plug) is one size bigger than the outlet hole, eg 7/16-20 inlet, 3/8-24 outlet, so they cant be confused.
Click to expand...
Thanks.
That was my understand on the thread sizes too. I'm hoping it will just be a deformed flange on the old union. A new union will hopefully prove that, and I'll order the new brake line set only after I know for sure.
jp928 said:
can I suggest that you get the pipe connections threads to the cylinders started before you bolt the cylinders down hard? This will give you more flexibility in the alignment, and ensure you dont get anything cross-threaded.
Click to expand...
Good advice. I'll definitely do that.

mikecoombs said:
From distant memory the P6 uses a particular Brake pipe thread. Check the thread pitch with a guage. If its 26 TPI It'll be British Standard Brass - all sizes us 26 TPI and no other thread types do.
Click to expand...
That's interesting. The new brake master I've fitted has a 3/8-24 outlet, and that fits the existing brake line perfectly. It's only the inlet that's causing me issues, and hopefully that is just a deformed flange on the old union.
 
I recently bought a generic 5/8 clutch master cyl with 7/16-20 inlet, 3/8-24 outlet, and it fitted the std tube nuts fine, so I doubt Rover used odd threads there. Havent change the brake master ...yet, what bore is an S2 brake master?
 
My old clutch master was 0.7" bore, but there had been work in there before. The clevis pin to the pushrod was a bolt, with the back side of the clevis threaded - Dont know how Rover expected anybody to get a split pin the back, or the pin in from the back. Did NOT enjoy working in there at all!
 
I remember using an R clip in the clevis pin, I put the R clip on a length of lockwire so if I dropped it I could haul it back up again, it made installing it easy.
 
You must log in or register to reply here.
Back
Top