Sticky proportioning valve?

[larrys]

I put new brake pads on my Cal this year. Although it worked just fine the rear brake system has never been touched since new so I thought that it would be a good idea to flush the system with new brake fluid. Bled from the master cylinder to the proportioning valve, no problem. Bled to the rear caliper, the caliper is not releasing. I bought the kit and rebuilt the rear caliper. Went through the bleeding procedure per the shop manual, no joy. Bleeding the front caliper, that works just fine. The rear caliper is still not releasing. If I let it sit a few hours, it frees up. WTF? I suspect a sticking proportioning valve. What does the hive think?
TIA,
Larry

[guzzisteve]

The valve on your bike only has a series of holes in it, there is no valve like you think. The EV has a valve like the back of a pick up on the swingarm, it has a valve. You need to pull pucks out & clean. If you have newer rear brake with pistons next to each other there is no dust seal. If you have the older brake caliper with a piston facing each other, it has a dust seal. One reason they say to clean fluid every year.

[moto]

The exact model of your bike matters. Which one is it?

[larrys]

The exact model of your bike matters. Which one is it?

It's in my signature line. '95 California 1100.

[larrys]

The valve on your bike only has a series of holes in it, there is no valve like you think. The EV has a valve like the back of a pick up on the swingarm, it has a valve. You need to pull pucks out & clean. If you have newer rear brake with pistons next to each other there is no dust seal. If you have the older brake caliper with a piston facing each other, it has a dust seal. One reason they say to clean fluid every year.

I noted in my first post that I rebuilt the rear caliper. The bike has 3 Brembo F08 (27mm) calipers.
Larry

[moto]

It's in my signature line. '95 California 1100.

Your bike does have a proportioning valve, not the simple, multiport manifold of the first generation integral braking system.

Guzziology (1st. ed., version 5.1, page 19-55) lists it as "four way proportioning", part number 2766-8561, a
type that has a complex, internal proportioning mechanism. Complex, at least, in its principle of operation.

You can find a very clear discussion of the disassembly and cleaning of of the general type here:
https://www.thisoldtractor.com/mg_manuals/instructions_brake_proportioning_valve.pdf

Be careful following the instructions. I ruined one of these by trying to use a 3mm instead of a 2mm punch, if
I recall that correctly. The author of the instructions did much better.

I don't know whether your problem bleeding the system is caused by anything in the proportioning valve. These systems
seem inherently difficult to bleed. You might look around for more bleeding advice for them. Maybe in Guzziology.

Good luck.

[larrys]

Your bike does have a proportioning valve, not the simple, multiport manifold of the first generation integral braking system.

Guzziology (1st. ed., version 5.1, page 19-55) lists it as "four way proportioning", part number 2766-8561, a
type that has a complex, internal proportioning mechanism. Complex, at least, in its principle of operation.

You can find a very clear discussion of the disassembly and cleaning of of the general type here:
https://www.thisoldtractor.com/mg_manuals/instructions_brake_proportioning_valve.pdf

Be careful following the instructions. I ruined one of these by trying to use a 3mm instead of a 2mm punch, if
I recall that correctly. The author of the instructions did much better.

I don't know whether your problem bleeding the system is caused by anything in the proportioning valve. These systems
seem inherently difficult to bleed. You might look around for more bleeding advice for them. Maybe in Guzziology.

Good luck.

Thanks for the link. Good stuff there. Fortunately, I didn't have to take that path. I started disassembling things to get the valve off of the bike. I removed the rear brake hose and went to blow some compressed air through it just to clear it. Oh my, NO air flow through the hose... Well, there's the culprit! The 31 year-old hose had deteriorated inside and was plugged. Stepping on the brake pedal would force some fluid to the caliper, but the obstruction in the hose would keep the caliper from releasing. Well, off to the local hydraulic repair shop where they made a new hose for me for $40. The brake system bled just fine after replacing the hose and the old girl is back on the road.
I have encountered this deteriorated brake hose issue before on a 20 year-old truck and on an early 80's BMW R65 that I worked on. Something to consider if you have an older machine and the brakes start dragging.
Thanks for the responses!
Larry

[guzzisteve]

Glad you found it, rubber don't last forever. I have changed all mine long time ago to braided. Good luck.