Front Brake Troubleshooting - Calling all brake experts

[jswhite]

Hi All, it's riding season and I cant ride my 81' GS650G. Please Help

My front brakes work, but work too well and work when i'm not squeezing the lever. It feels like the front brake lever has constant pressure on the pads, which is reflected in the fact that I cant even push it in neutral because the brakes are on so much. The bike began with normal pressure and the bike was able to coast, but the more I used the brakes the more they got tighter and tighter, now I cant ride it...No Bueno

I rebuilt the master cylinder, replaced the brake lines, and replaced the rubber in both of the calipers. I talked to a shop about it and they said it could be the round rubber seal, in the calipers which meets the sides of the piston, is too small, and I was possibly given the wrong one when I bought it. I do not doubt this because I was given the wrong piston for the master cylinder too.

Has anyone heard of this? I could always rip apart the calipers and put new rubber seals in, but it is nice to hear from someone who has experience before I do.

BTW this is only on the front brakes, the rear are working as they should

Thank you for all the help

 

[mnferwerda]

If both calipers are binding, it is most likely the master cylinder. If only one is binding, then it is that caliper. Master cylinders can be tricky to put together correctly. I've done it wrong several times myself...

 

[roeme]

Either there is a problem with some plugged port, as written by previous posters. Or bad rubber has swollen up (but that would mean horrendously wrong supply of parts!).

Bleed the brakes once more. If they don't free up, its probably the seal in the calipers. If they do, the problem is likely in some other part of the system.

It would be weird if it's some swollen up rubber, because that would mean you've got rubber that is _not_ appropriate for use with brake fluid.

 

[Steve]

My money would be on a plugged "compensation" port in the master cylinder. It's a very small port, easily plugged and easily overlooked during an "overhaul".

The compensation port is supposed to be open from the brake lines to the reservoir until you squeeze the lever. The first movement of the lever will cover the port to seal the lines so you can build pressure. The port is open to allow fluid to flow through as it warms up and expands in the calipers. If it is plugged, pressure simply builds up in the calipers, not allowing you to move the bike.

.

 

[fastbysuzuki]

I'm with steve on this the pressure is not being released back into the reservoir when the lever is released because of a blocked return port possibly wrongly fitted or incorrect parts.

 

[hillsy]

If you crack open the bleed nipple on the caliper and the wheel frees up then it's more than likely the blocked return port as mentioned above.

 

[jswhite]

Perfect, thank you everyone. Looks like it is most likely the compensation port which isn't allowing fluid to go back to the reservoir. I remember trying to clean this, but the hole was so small I didnt have anything which would fit through.
Any suggestions on how to clean this port? Thinking wire smaller than the hole and softer metal not to damage, where do I get something like that?

 

[Steve]

Cut a short section of wire, peel back the insulation, use one strand of copper wire. It's stiff enough to poke through the crud, but softer than the master cylinder body, so no damage. When you are done poking, spray some brake cleaner through there with its little straw, then follow up with a blast of compressed air.

If you have the piston out of the bore, you should be able to shine a light in there and see that the port is open.

.

 

[bwringer]

I've used a guitar string to clean out stubborn compensation ports. I played bass in a busy bar band a while back, so I collected a goodly supply of broken strings from my guitar player...

The copper strand is a better approach overall, since you can't damage anything with it, but sometimes it's still tough to get through a really solid deposit of whatever the heck that stuff is. And you might have to rummage through your random wire collection and try a few to find a strand small enough to fit but big enough to have a little stiffness.

 

[hillsy]

Pretty sure I got this tip from this forum - clip off a strand of wire off a wire brush and push it into the end of a matchstick. Perfect tool for clearing small holes in carbs and the like.

 

[jswhite]

I was able to get that other hole open, after working at it for a while, it was all gummed up and closed. That might be the problem

Have another question...how much are the brakes supposed to grab when spinning the wheel on a jack?
After fixing and putting in neutral, spun the front and back wheels. Back spun pretty free with some minor scraping from the pads, but the front still caught enough to slow the wheel as if the brakes are on. Assuming that means the front still needs some work?

 

[chuck hahn]

I use the wire brush wire for doing carb jets and master cylinder returns. I hold it with hemostats though.

 

[chuck hahn]

If the hole is open and they still grab its time to break down calipers and clean them. Remove the pistons seals and clean the groove the seal seats into. Scale build up pushes the seals tighter and tighter against the pistons...thus they dont release enough when you let off the lever. ALSO, clean the carrier pins for the pads.