Front brake lever firm - finally

[Guest]

Sharing my experience with the front brakes on the GS850G.

After replacing and rebuilding all the front brake system, the brakes are finally firm and the lever does not go to the grip. The problem was the pistons had too much resistance. They would more forward and just spring back. This wasted all the lever travel bringing the pads up to the rotors.

Here are my tips for rebuilding the calipers.

Get new the rebuild kit with the piston. The kit cost about $16 each. New seal and boot is something like $6 or more. So spend the extra $20 ($10 per side) and get new pistons.

Clean out all the corrosion and scuzz in the caliper where the seal and boot fit. I used a pick tool to scrap the groves. I think this was the real problem. The seal was too tight because it was not able to fit fully into the groves in the caliper.

Wet sand the caliper bore with 400 grit.

This may not have made much difference, but I did move the piston in and out a few times using a bike floor pump. This way I knew that the pistons were moving fine.

Also make sure the caliper pins slide easy. I had to clean out all the old grease and replace the swollen rubber on the lower pins. I used motorcycle fuel line to replace the rubber.

Once this was all done the they bled easy and quickly using just the lever - no mityvac.

The lever pull in about 1/2 inch then firms up and I cannot pull it to the grip.

Here is the long story. When I got the bike the front brake worked but didn't seem very good. I could, using most of my strength, pull the lever to the grip. Not a big deal since I planned on rebuilding the whole system.
I did the following:
Rebuilt the MC with non-OEM kit.
Rebuilt the calipers replacing the seal and boot. I didn't replace the pistons even though they were pitted.
New OEM hose with new crush washers.

After all that they didn't bleed with the lever. Using the mityvac didn't seem top fix the problem either. Wasted a quart plus of brake fluid.

I suspected the calipers were springing back wasting the lever throw. This is when I fixed the caliper pins. Still no good.
I got an OEM MC kit. Found I had the outside seal on backwards. I don't get how fluid didn't leak out. Still no change.
Did the tie the lever down trick several times. No change.
Parked the bike after riding home when I had the front brake lever pulled to the grip and was still going to roll into the car in front of me. Ordered the new pistons since that was the only part that had not been replaced.

All this time it felt just like there was air in the system. Even pumping the lever see the firm the system up. But really it was sticky pistons. Now that I think about it I could always see the calipers move back to their staring position when i released the brake.

There has been much frustration and this has taken many months to fix. I hope this helps others.

Any thoughts or comments are welcome.

[Rover]

This is a common problem,I'm sure many will benefit.
Thanks.

[SeanGSUK]

He guys, thanks for all the input.
Checked over the calipers today, no pitting or rust on the pistons they move freely in and out and in a circular motion with no fluid loss. The disks are straight and true. I pumped the lever a few times to lock them against the disks and locked the lever back, then I tapped the calipers with the wooden end of a hammer for a few minutes alternating between the two, then tapped the braided lines up to the junction. Then tapped the junction for about 30 seconds, then tapped along the length of the tube up to the master cylinder then tapped the cylinder and hay-ho a couple of bubbles came out. I repeated this process a couple of times, I didn't get any more bubbles but the lever feels a lot firmer now and doesn't pull back to the bars. I am leaving the lever tied back again overnight, hopefully any more air will work its way up. I also used some PTFE tape on the bleed screws as I thought air might be getting in there somehow, don't know if it made any difference but I thought it worth mentioning. Good luck fellas!