From single to dual

[Melmac]

I’m going to convert from single to dual brake line on my GT6, it seemed easy enough. Bought the master cylinder from Rimmers and discovered that it needs two different sizes of nipples. The front one is bigger than the rear one. How come?

[Nick Jones]

I expect it is so that the circuits cannot be mixed up when the master cylinder is changed, though I can't say I remember seeing this on anything else (never had a dual circuit Triumph).  Presumably the smaller ones are the usual 3/8" UNF and the larger ones 7/16" UNF?

[Melmac]

I think you may have a point there, and yes, you are right about the sizes. Thanks Nick.

[Nick Jones]

7/16" fittings are sometimes used on clutch hydraulics, but often with larger (1/4"?) pipe - so care needed when buying fittings as the 7/16" UNF for 3/16" tube may be moderately unusual. 

How are you splitting your circuits?  I presume front/rear as the steering geometry is not suited to diagonal split and will pull horribly to one side if one circuit fails?

[Melmac]

The holes for the pipes in the master cylinder looks similar, but if I need larger pipe for, in this case, the front brakes Im in trouble. The calipers have 3/8. My plan is to use the existing 4-way junction for the front brakes by plugging the connection to the rear breaks. Then I just have to change the nipple for the master cylinder to 7/16 and the front brakes are ready. The pipe from the rear I just extend right to the master cylinder.

[Nick Jones]

No, that was my point.  I'm sure the actual brake pipes will be the usual size (3/16").  What I meant was that it may be hard to find the correct fitting with 7/16 UNF thread and 3/16 hole rather than 7/16" with 1/4" hole as used more commonly in clutch systems.

But it seems Automec do them - so you should be ok

https://www.automec.co.uk/products/brass-brake-pipe-fitting-male-7-16-x-24-unf-3-16-pipe

[Melmac]

Wow, thanks for the link Nick. It was this problem with 7/16 thread vs 3/16 hole that could have made my simple plan not so simple.

[spitfire6]

Hi melmac,

 What size the bore for the master cylinder? I think I need to take this route on my car.

Cheers,

Iain.