78 GS750 Rear Brake Issue

[freakyteeth]

My rear brakes lock up. The pedal stays down and doesn't automatically spring back or retract. Spring isn't broken, seems the master cylinder plunger is a little tight. I can hook my toe under the pedal to unlock it. Do I just need new pads or do I need to rebuild/replace my rear master cylinder?

[Suzuki mad]

Try greasing the spindle that goes through the frame first.

[freakyteeth]

I lubed the spindle with WD40 but it didn't loosen.

[Suzuki mad]

You will need to pull the lever, spring, and then the whole unit out from the frame. Once done you can clean the spindle of all the old rubbish and grease it. WD40 may free it slightly but won't make it move smoothly.

If that doesn't change the locking brakes then its check the rear calliper seals, pistons for aluminium and rust growth. If that fails to solve the problem then its a master cylinder rebuild.

[Steve]

I lubed the spindle with WD40 but it didn't loosen.

Please don't confuse WD-40 with a lubricant.

Yes, it has some lubricating qualities, but its purpose is as a WATER DISPERSANT, hence the "WD" in its name.

As Suzuki mad suggests, remove the brake lever (you have to remove the clamp bolt completely, not just loosen it) and remove the linkage to the master cylinder. I don't remember if there is something that holds that spindle into the frame, but remove it by whatever means necessary. Use a wire brush or emory cloth to clean the spindle, then use a good multi-purpose grease and put it back in place, then re-attach all the other hardware. Chances are, this is all you will need.

.

[doctorgonzo]

"I don't remember if there is something that holds that spindle into the frame"

Reassembled my rear brakes last night, no, there isn't. It just slides through the hole in the frame.

[piester]

I had this exact same problem. Turned my rear brake into a parking brake pretty much. Took the pedal off. Unhooked the rear pivot from the plunger and took the spindal off. Cleaned both the spindal and the hole it goes into with a wire brush and then very fine sand peper. Then greased them up and putt it back together. Works better than ever. Don't forget to unhook the little wire spring that pulls on the brake light trigger before you take the spindal out.

[freakyteeth]

Thanks for the advice. I'll report back after I affect the steps you've recommended.