Brake system compatibility: 1980 Midnight special to 1981 Midnight Special

[DuenasMoto18]

Will the rear brake assembly from an 1980 MNS fit on 1981 MNS. If you swap the whole brake system to the other does it fit with no modifications?

[Rasputin]

The 81 has the linked front and back brake where the 80 does not. Some parts are the same and others are different. You would have to swap all the parts in the braking system to be sure it was correct.The front master cylinders have different part numbers although I am not sure of the difference but the 81 system only operates one front caliper where the 80 does both.

[cajun31]

Will the rear brake assembly from an 1980 MNS fit on 1981 MNS. If you swap the whole brake system to the other does it fit with no modifications?

First question is why do you want to do that? As Rasputin stated the two bikes are entirely different when it comes to the braking system. There is a lot of plumbing that would need to be replaced. If you were going to pursue that and unless absolutely necessary I wouldn't you would have to probably replace both the front and the back. On the rear connected to the master cylinder there is a proportioning valve that serves the rear caliper and the front left caliper. By the way the calipers are different on the front from the 80 to the 81. The forks are not the same either where and how the calipers mount.

[DuenasMoto18]

I’m looking at alternatives in case the complete 1981 OEM MNS system that’s in my bike now does not work properly. I bought it with seized right front brake, seized rear brake. The front left brake worked. I drove it home 50 miles on El Camino Real, in Northern California. That was about a decade ago, I’m finally going through the brakes now. My concern is putting everything together and the purge valve doesn’t end up working, what do I do then. I asked about the swap because from occasion I see complete braking systems on sale. The bike has only 14,668 miles.

[cajun31]

I understand your concerns. To better answer your original question, in order to modify what you have you would need to control both front calipers from the front master. Keeping in mind that the oem master was designed to only control one caliper. You might need to replace it with a larger one. You would also need the joint and associated hoses. This diagram shows you what all is involved on the front. Yamaha Motorcycle 1980 OEM Parts Diagram for FRONT MASTER CYLINDER | Partzilla.com. The back you would have to acquire the master cylinder from an earlier year that does not include the proportioning valve and just run a single line from it to the rear caliper. What you are thinking is doable and I remember someone actually did it. Just can't remember who.

[DuenasMoto18]

Thx Cajun31! Do any of the xs1100 rear master cylinder work for the application, or would it be better to acquire tthe 1980 MNS rear master cylinder. Do most people retain the old brake lines? The bike as only 14.5k miles but those lines are 45yrs old. Even when I removed the brake caliper seals the rubber still looked and felt good, did not deteriorate. Of course I’m getting rebuild kits and new pistons.

[cajun31]

The rear master cylinder is the same on all the xs1100's other than the 81 MNS that you have. So yes any year is good. Most of us replace those old rubber hoses with stainless. You can get them in black to match the look of what you have now. I would recommend replacing all the brake lines with new. You will immediately feel the difference in how much firmer your brakes are. Good choice to completely start with new pistons and seals. If you haven't already purchased anything I would also recommend stainless pistons. They will resist pitting a lot longer than the oem type.