Rear Brake Lockup

[wedoo2]

Late last week I had a rear wheel brake lockup. During my restoration I had rebuilt the rear caliper with a good clean up, new pads and seals. Last week I did notice a small leak of brake fluid and intended to tear everything apart. Went to fill it up with gas down the road and the rear wheel locked up and I released pressure on the brake lines and got home.

When I tore down the rear caliper I did notice some light pitting in one of the pistons which may explain the leak, even though it was very light. The other was pristine. I ordered new pistons and seals, but my question is what else should I look for? The caliper looks fine and there seems to be no obstruction and everything seems to have been put together right the first time. But I really don't want to have this happen again.

Suggestions?

 

[cowboyup3371]

When you did the calipers did you also clean out the master cylinder? Sounds like the return port clogged up.

 

[81ZUKI75]

After rebuilding the front caliper and master cylinder on my '81, I experienced periodic lockup until I replaced the brake lines. I believe that trash from internal deterioration/contamination was fouling the relief port in the master cylinder.

 

[Steve]

Both of those are good points.

The return port in the master cylinder is VERY tiny, can clog very easily.

When is the last time that anyone cleaned the inside of their brake lines? :-k
There just might be a reason that Suzuki recommended changing the lines EVERY TWO YEARS.

.

 

[wedoo2]

I am going to order SS brake lines because the front needs replacing too. Two questions, first is it necessary to replace the metal tubing or can I leave that on if it is clear? Could be that a standard set replaces that anyway. Secondly, I cannot find the return port. Is it in the space where the piston goes?

I guess three questions; I did a search last week for SS lines, who would you suggest?

 

[Jcgonzal]

Can't really answer your questions, but I have another theory on what caused the lock-up. I could be wrong, but I believe that if you have not expelled all the air out of the line then that air can expand as the fluid heats up, causing the pistons to be pushed against the rotor. Just a thought.

 

[BluePlateSpecial]

I guess three questions; I did a search last week for SS lines, who would you suggest?

On recommendations from a thread here on GSR http://www.thegsresources.com/_forum/showthread.php?t=114521 I went with http://www.anplumbing.com/ . Cost me exactly $100 shipped to do my front and rear lines on my 1000G, and that included a coupe of extra feet of hose and 2 extra ferrules because I had to make up an $8-$9 difference to qualify for the free shipping.

 

[tkent02]

Can't really answer your questions, but I have another theory on what caused the lock-up. I could be wrong, but I believe that if you have not expelled all the air out of the line then that air can expand as the fluid heats up, causing the pistons to be pushed against the rotor. Just a thought.

The brake fluid itself heats up and expands, if it can't escape through the compensation or return port the brakes will come on, making more heat. More heat means more expansion, more braking, more heat. The port is in the area of the MC where the piston first starts to cover when you just barely move the lever. Normaly it is open with no lever pull at all, so the fluid can come and go as it expands, then as you begin to move the lever the port closes, then after that if you pull more you start to build up hydraulic pressure to the brake.

It is a tiny port, maybe the diameter of a small sewing needle. Easy to block with a flake of rust.

If it is clogged or blocked it can lock up the wheel and dump you even if you don't touch the lever at all.

 

[cowboyup3371]

I am going to order SS brake lines because the front needs replacing too. Two questions, first is it necessary to replace the metal tubing or can I leave that on if it is clear? Could be that a standard set replaces that anyway. Secondly, I cannot find the return port. Is it in the space where the piston goes?

I guess three questions; I did a search last week for SS lines, who would you suggest?

Fortunately, my daughter's rear MC is still not back together (school work has kept her pretty busy every weekend) so I was able to take a picture of it for you.

In this first picture, the top hole will have the small return port:



In the close-up you can see the return port:



When you clean your master cylinder out, you need to use a single strand from say a 18-gauge wire to push through this (use brake cleaner before hand to help out). Use a flashlight to see it come through if it's hard to see for you.


I also tried the make your own style but had issues with them so I bought a set from Z1. I know there are several sources out there so take your pick.

 

[wedoo2]

This is awesome. I did not clean out that hole when I originally worked on that master cylinder. If you guys are going to Brown County, I have a beer with your name on it. I'll post up on this after the work is done.