75 model front brake master cylinder option.

[5twins]

Well, I certainly hope an 11mm MC works out for you, please let us know. But like I said, I think it's going to be too small for your early two piston caliper, and have too much lever travel. Raymond is dealing with the later single piston caliper and an 11mm is fine on that one. Here's that chart that was posted earlier with some comments from 3M, the owner of Vintage Brake. I also highlighted the 650 sizes .....

As you can see, a 13 or 14mm MC is about ideal for the early two piston caliper, putting the ratio right around where 3M likes it.

 

[arcticXS]

On my RD350A, which uses the same 2x48mm piston caliper as XS2 to XS650C, I use a 13 mm Brembo MC, and it works great. A buddy used a 1/2" (12.7 mm) Grimeca MC on his RD, also worked great. I do believe around 12 mm is as low as one would want to go, possibly depending on the rigidity of the brake lines used. For sure, I would recommend a single piece brake line, and do away wiith the OEM brake light switch. The Brembo has mounts for a microswitch, or a banjo bolt with an integrated switch can be used,

 

[AlanW]

Thanks again guys. If I go for a single brake line, can someone please provide details of how to get the brake switch wired up if I’m removing the brake hose junction unit?? You’ll be aware that you are dealing with someone with limited technical ability here.

 

[SteveP]

I bought one of these, from eBay. You need to check if the thread is correct for the caliper you are buying.
I cut the connector off and put some bullet on. I seem to recall having to do the same on the wiring loom

 

[SteveP]

It replaces the Banjo bolt.
You can also get a version with the wires coming out at an angle, if that's more convenient

 

[AlanW]

So I’ll have an M10 x 1 banjo bolt at the MC end, a single, continuous brake line and a fitting to get onto the caliper to replace the steel brake line that’s the at the moment.? The pressure switch bolt you show will be the one at the MC end? I need to connect the wires into the loom?

 

[SteveP]

You need to check the thread on the caliper that you are buying.
The rest is right

 

[SteveP]

Sorry master cylinder thread not caliper.
That's where it fits

 

[AlanW]

Thank you

 

[SteveP]

I was eating my Christmas dinner and had a thought .
Most modern master cylinders have a brake switch built in. If that's the case with the one you are buying you will just need a normal banjo bolt.

 

[AlanW]

brake

Mine arrived Christmas Eve. No integrated switch so will need your option of banjo bolt with one built in.

 

[arcticXS]

Mine arrived Christmas Eve. No integrated switch so will need your option of banjo bolt with one built in.

Are there two 3 mm mounting holes for a microswitch, and a 5 mm bore for a plastic plunger?

 

[AlanW]

mm

Yes, I’m looking at this as an option???

 

[arcticXS]

Yes, that is the correct/ OEM brake light switch for Brembo Master Cylinder. A bit small and fiddly to work on, but once installed very stable and reliable.

 

[AlanW]

So I’ve sorted the master cylinder end. The caliper end is now causing angst - it is currently fitted with the metal pipe with a flared end - I believe it’s a m8 x1 fitting. BUT inside the caliper is some sort of olive for the metal pipe to fit up against.
According to the UK Aircooled forum - the early RDs used the same caliper - you can apparently heat it up and push the olive out???
Losing the will to live over this now. Any ideas greatly appreciated.

 

[arcticXS]

So I’ve sorted the master cylinder end. The caliper end is now causing angst - it is currently fitted with the metal pipe with a flared end - I believe it’s a m8 x1 fitting. BUT inside the caliper is some sort of olive for the metal pipe to fit up against.
According to the UK Aircooled forum - the early RDs used the same caliper - you can apparently heat it up and push the olive out???
Losing the will to live over this now. Any ideas greatly appreciated.

If the 75 XS is somewhat similar to the RD350, keeping the stock steel pipe and the corresponding "olive" is most likely a good idea, as there is very limited space between fender and fork slider. You should be able to find braided teflon brake lines that connect to the steel pipe. Pretty sure MikesXS and/ or Economy Cycle sell replacement steel pipes If necessary.

 

[AlanW]

Thought about that - Thanks - but I can’t seem to find a UK supplier -tried HEL and Venhill - that can supply an m8 female fitting to connect to the other end of the pipe going into the caliper.

 

[arcticXS]

Thought about that - Thanks - but I can’t seem to find a UK supplier -tried HEL and Venhill - that can supply an m8 female fitting to connect to the other end of the pipe going into the caliper.

Are you sure it is 8mm/ M8? I seem to remember the RD350 had M10x1.0 or M10x1.25 threaded connections. Venhill normally has a good selection of brake hose fittings.

 

[arcticXS]

https://www.economycycle.com/shop/y...d350rd40076-78-front-braided-stainless-steel/

 

[arcticXS]

Attached screenshot from Heiden Tuning, of the "hard line" . It definitely looks like both ends are identical, and as far as I know, the caliper connection is 10 mm. Did you by any chance measure the small thread diameter, i.e inside the female thread? That would not be correct. Nominal diameter is always measured as OD on the male thread. (Sorry if I am teaching you to suck eggs.....)