Front Brake Problem

[Jim R]

Just restored my 1982 GS1100G. The problem is the front brakes being spongy / not 100% effective.
I have literally replaced everything from the master cylinder to the pads and I am getting the same problem.
I have also tried Dot 3 and Dot 4 fluids.
I have found that the right disc is hotter than the left and I'm pretty sure this is the problem but can't figure out why. Is there any trick to getting both sides to squeeze the pads equally on the discs? Keep in mind, every part has been replaced and it is still doing the same thing.
I bought all original parts as replacements. There is nothing aftermarket except for the pads and fluid.
Any help is appreciated!

 

[GSX1000E]

From what you are relaying, it sounds like you have the square cut seal either mounted twisted or the groove that it resides in is not thoroughly clean and pushing it against the piston.

 

[Nessism]

Try pumping up the brakes and then tying back the lever to the bar over night. The constant pressure will help the piston move closer to the disc.

BTW, you haven't stated specifically but please confirm you replaced the pistons and seals in the calipers. Did you grease the sliding pins with heavy duty moly caliper grease?

 

[ShadowFocus603]

+1 for Nessism. Sounds like air in the system on the weak caliper side. Tying the lever back after pumping it up will help bleed the air out as well.

 

[Joe Garfield]

Is the suggestion to always replace pistons and seals during a rebuild? Even if they don't look too bad to begin with?

 

[Nessism]

Is the suggestion to always replace pistons and seals during a rebuild? Even if they don't look too bad to begin with?

I wouldn't replace the pistons if they look okay, but yes on the seals. Brake lines too.

 

[Jim R]

Thanks for the advice. I have done everything everyone has mentioned. I have 3 complete sets of rebuilt and NOS OEM parts from the master cylinder to the calipers.They are all doing the same thing. I have even tested the pistons with measured air pressure to be sure they move with the same amount of pressure. When I test the brakes, I ride the bike and brake hard several times. When I get off the bike, the right rotor is "hot" and the left is "warm". I assume this is the heart of the problem. The rotors are smooth and of equal thickness. I have bled them More than a dozen times in every way imaginable including pneumatically. I have also tied the brake lever to the bars overnight. I have even taken the "splitter" off and still the same thing. I was hoping someone had the same problem and knew of a miracle cure!

 

[JTGS850GL]

What pads are you using?

 

[Jim R]

I have 2 sets of OEM pads that have tons of meat on them and 1 new set I bought online. All do the same thing.

 

[Nessism]

Maybe the "warm" rotor unit has binding pins? Also, you might want to remove the pads and check to see if they are making proper contact with the rotor. Maybe the worn pads aren't making proper contact with the rotors for some reason.

 

[Joe Garfield]

Just an idea: maybe measure the space between each pad and the rotor - I wonder if the alignment between the calipers and rotors is the same on both sides, causing one side to engage more than the other. If a few different sets of brakes are doing the same thing, it makes me think the issue is either at the wheel, or hose restriction somewhere.

 

[Jim R]

I did think of that. They are the same on both sides. The problem seems to be that the left simply doesn't have the same amount of "squeeze" as the right.

 

[Joe Garfield]

If there is a way you can measure or see this on the stand (or rig it up in a way that's safe to road test), maybe try swapping the lines from the splitter to see if the problem in the splitter itself. If it isn't there, you might have it narrowed down to the one weak caliper at least.

Technically there would be a small pressure drop through the splitter between the right and left side hoses, but it should be pretty negligble since others don't seem to report the same problem. A blockage (reduced internal diameter) or bad seal at the banjos would make it worse.

My thoughts are just trying to isolate where the problem is since there hasn't been a solution yet.

 

[GSX1000E]

Here is a thought, as the problem seems to be limited to the right caliper, why not take it back apart and find the problem?

* See also post #2 in this thread.

 

[Jim R]

I have actually done that. I have even taken the T connection out of the equation. No luck.

 

[Jim R]

I have 3 complete sets of OEM calipers. All rebuilt with new seals etc. 2 by me. 1 by a bike shop. They all do the same thing.

 

[Nessism]

Have you tried new brake pads in that one side? Are the sliding pins greased and does the caliper slide easily back and forth on the hanger bracket? Sometimes the plastic collar around the pins swells up and causes binding too. Another thing is to confirm you used OEM caliper seals, not aftermarket?

One thing to consider is to put some miles on the bike and make sure the pads are seating properly. You can even drag the brakes under power to burnish in the pads quickly. Just give the brakes time to cool off.

 

[rustybronco]

I haven't read through the complete thread, but have you tried changing the caliper support brackets? The brakes on my '80 850 will pump up and I am almost 100% certain it's because the bore in the bracket is to large for the slide pins-allowing the caliper to cock and the rotor to push the pistons back further than they normally would be.

 

[Jim R]

Thanks for all of the effort and advice. I have 2 or 3 things to try when the weather allows.

 

[Grimly]

Worn pin mount holes in the brackets are a common problem. They allow the caliper to tilt and jam slightly - a giveaway is the slanted wear on the pads. If you haven't replaced the mount brackets, examine them closely for wear in the holes. As a guide, the amount of permissible clearance is only enough to allow the slightest of wobble - they can't be too tight, or it becomes problematical the other way, but since we're talking about 30+ year old brackets here you're unlikely to find any as-new ones, but you can find some very good, low mileage ones that will do fine.
As the miles totted up on mine, I became plagued with caliper sticking problems and it took a bit of sorting out. Mine are fine now, but I see no end to the inherent design flaw causing the same problem to recur eventually.
When they're sorted out properly with modern pad material, these are actually half-decent brakes, but it takes very little neglect or wear to let them backslide into being horrible brakes of the 80s.