GS550ES Front Brakes Lock Up (Again)

[Guest]

I scored a nice 86 GS550ES from the original owner about a month ago. He put the bike away in 08 and I have gotten it to run and drive, but the front brakes keep giving me issues. I have ridden it a bit but don't feel safe without the front brakes. The brakes were locked when I got it, and I new I needed to flush the old fluid. After doing so, they locked up. I used a 2x4 and a c clamp to free them, but I also inspected the piston to make sure there was no corrosion. It was completely clean.

I thought the issue might be the return in the master cylinder. After struggling with it, I put a new master on it. Today I installed it, bled all the air out, and by the time I finished the brakes were locked again.

I know it has to be something to do with how long the bike sat, with the fluid gathering moisture and all. It's worth mentioning that I have taken the caliper apart more than once, but it is tedious and frustrating finding the issue.

Any advice helps. Thanks!

Evan

[Cipher]

you stripped and cleaned the calipers and purged the old fluid from the system and it still locks?
Is there corrosion on the pistons?

I had a front caliper that locked up single disc front bike.
I seperated the halves to get it off the bike and clened and flushed it and it never showed and problems.

Seals were good though.

[Nessism]

Something doesn't sound right if you broke down the calipers and replaced the master. You best replace the brake lines since they are sure to be lined with scale but that's not likely the problem. Maybe the caliper sliding pins are binding up? You need to lube them with heavy black caliper grease if you haven't already done so. Also make sure the return port in the master is open. Last thing, I'd replace the caliper seals with new OEM parts. Do not use K&L or any other aftermarket caliper seals since they can be sketchy.

[fbody_mike]

When the brakes are locked, crack a bleeder and see if there is a large rush of escaping fluid followed by the brakes releasing. If so you have problems with the lines or master.
There are no sliders with this caliper, it is the opposed piston type.

[landrover1]

I went out a cracked the bleeder again. Lots of fluid did drain, but the problem persists. I think I will find some new seals and use the 2x4 solution in the meantime. Last time I broke down the calipers, I noticed the piston would only return when it was almost completely ready to pop out. I find that odd and I hope that may help. Thanks for all the suggestions.

[fbody_mike]

Did you actually remove the pistons and inspect the bores? Just a small amount of build up on the walls will seize a piston. Inspect the groove where the seal seats too, dirt in there will cause problems like this too.

[Cipher]

When the brakes are locked, crack a bleeder and see if there is a large rush of escaping fluid followed by the brakes releasing. If so you have problems with the lines or master.
There are no sliders with this caliper, it is the opposed piston type.

The pads glide on hardened steel pins and if corroded a pad can get cocked sideways.
accelerating wear and maybe a source of the problem. Polish em up and use a smidgen if brake grease not regular grease.

[hillsy]

Corrosion inside the calipers also occurs UNDERNEATH the seals. This pushes the seals onto the piston and can lock them up.

You need to remove the piston, remove the seals, scrape out the gunk in the grooves and re-fit. If the seals have been pushed into the pistons for some time they might leak after this....so if you are going this far in, new seals are probably the best option.

[landrover1]

There was a fair amount of corrosion under the seals as I found out. I will get rid of it before I get my rebuilt kit in. Any suggestions for cleaning the rust? Steel wool?

Thanks for all the help so far!

[Cipher]

pretty sure the onl;y safe way to fix this is new pistons.

[Cipher]

Part# 69100-27821

Desc PISTON SET -SU

USD Price 47.92

[roeme]

I think it's high time providing pictures. There's too much guesswork involved for us here.

- Rust on the calipers? Aren't those aluminium? They may corrode, but they don't rust.
- So, rust on the pistons? Then it's time for new pistons, depending on how they look, you may put that off for a while, but not too long.

I've rebuilt brakes that have been locked up good and corroded. It really depends on the nature of the damage. In my case, I had pistons that were chipped a bit on top and bottom, but the face which slides along the seals was good. In the same vein, I had calipers that had a fair amount of corrosion damage, but the seal groove was fine - apart from dried out, crusty brake fluid.

Ultrasonic cleaning, bit of elbow grease and a brass dremel wheel got those back.

Hence why we require pictures.

[Brendan W]

Do both lock up ? If so the common components are the first things to go after.
Stretching credibility a bit that both calipers would have the same tipping point if corroded.
Old hoses break up inside and have been known to act like one way valves.

[landrover1]

Yes, both brakes lock up when the front brake is pressed. I am out of town for a few days but on Monday I will post pictures. I was thinking it may be something with the lines, but I will try seals first. Thanks.

[mmattockx]

There was a fair amount of corrosion under the seals as I found out. I will get rid of it before I get my rebuilt kit in. Any suggestions for cleaning the rust? Steel wool?

Thanks for all the help so far!

Steel wool will damage the aluminum of the caliper body. Brass wool is fine, the less aggressive Scotchbrite pads will also work. For cleaning up the seal grooves a brass brush on a dremel works well.


Mark