XS and XJ Rear Brake Master Cylinders

[MF_Rider]

G'day

Does anyone know if the XS1100 and XJ1100 rear brake master cylinders are the same, ie the parts are interchangeable?

thanks

[DGXSER]

Nope, they are different animals completely unless you have the 81 Midnight Special, that one and the XJ are the same. The XJ uses a linked system where the rear brake also powers the left (IIRC) front brake caliper as well. The front MC only works the other front caliper.

On all the other XSs the rear MC only works the rear caliper and the front MC works both front brakes.

HTH

[Jerry]

Not the same. In addition to having different bore diameters, (XJ has the larger bore) the XJ unit comes with a proportioning valve piggybacked on it. Low pressure activates the back brake, more pressure and the front-left caliper activates. The proportionoing valve is removeable, however. Some XJ owners have re-plumbed the system so the front calipers are run from the front MC and the rear from the rear MC, same as on other XSs.

The XJ unit also has a fluid level sensor in it. A warning light comes in in the XJ instrument pod if either the front or rear MCs is low on fluid.

So, the two units you mention are not interchangeable, but could be made to work if you have the time and inclination to do so. I think the mounting patterns of the two units is the same, but do not know this for a fact.

[MF_Rider]

thanks for the info makes much sense

Do you know if another bike other than the XJ shares the same rear brake MC as the 79 XS1100E?

cheers,

[DGXSER]

Well, there was never a 79 XS1100E. The E on the end indicates a 78 model. The 79 model year was the F year with the Special model being introduced as the SF.

That being said, I believe all of the XS1100 models except the 81 MNS mentioned earlier had the same rear MC.