Front brake woes

[swhomrig]

Hello All,

I've been having troubles with the disc brake on GS450 ever since I changed the pads quite some time ago. I'll do my best to walk you through the process.

The Bike: '86 GS450L, 30k miles, had been sitting for quite some time before I bought it.

What's happened since I bought it:
1. I went to replace the brake pads as the old ones weren't in great shape (not super worn down but just looked generally bad after sitting for so long).

2. The first problem I encountered was that it was difficult to push the piston back in to fit the caliper over the disc. I flushed the system out and I was finally able to get it all back on (with some force).

3. Since then, the front wheel has never spun freely. You can hear it contacting the pads when the front wheel is off the ground and spun. It makes a squealing noise at speed unless gentle pressure is applied to the brake. I've heard this squeal is typical and can be prevented by adding special grease to the backs of the pads. This did not help.

4. Recently, things have become worse. I've been getting the sensation of losing pressure occasionally. One day, the brakes were squealing particularly bad so I thought I might be able to set them in there by squeezing on the lever particularly hard. The brakes made a noise I'd never heard before (perhaps describable as a popping? or snapping? I'm not really sure how to describe it) and since then, whenever I apply the brakes, the front "twitches" to the right. The harder I apply the brakes the more it twitches. While the bike is still "rideable" I've since stopped riding it as this seems really bad.

Any thoughts on what's going on here? How to fix it? I don't know much about brakes. I'd rather not take it to local mechanic.

Possibly related info:
The bike appears to have been in an accident at some point. There is a dent on the left side of the tank and I discovered the old handlebars to be bent when I took them off.

Also, I have noticed that it seems the alignment is not quite right: when the bike is traveling in a straight line, the handlebars seem to be slightly off center.

And, I'm not sure if the disc is warped...any suggestions on how to check this?



Thanks everybody,
Scott

[t3rmin]

If it's pulling to one side when the brakes are applied, then probably only one of the calipers is working. I'd pull 'em both apart and inspect. Z1enterprises.com has caliper rebuild kits for a good price.

[chef1366]

Yep! Rebuild time. You have a frozen caliper piston. I wouldn't ride it or you might take a trip over the handle bars.

[Nessism]

On the surface rebuilding the caliper seems daunting but in reality it's a pretty easy job. Pop the piston out by pushing it out with compressed air and then clean all the gunk out. Inspect the piston carefully and replace if it's pitted. Install new seals after lubing internal parts with clean brake fluid. Last thing to do is lube the pins that the caliper slides on with high temp grease.

[swhomrig]

On the surface rebuilding the caliper seems daunting but in reality it's a pretty easy job. Pop the piston out by pushing it out with compressed air and then clean all the gunk out. Inspect the piston carefully and replace if it's pitted. Install new seals after lubing internal parts with clean brake fluid. Last thing to do is lube the pins that the caliper slides on with high temp grease.

I'm not sure I really understand that. How does that work? I saw in another post someone mentioned getting the piston out by squeezing the brake lever. Does this work too? The closest thing I have to an air compressor is a bike pump.

[koolaid_kid]

Yes, squeezing the brake will force the piston out also. You can clean the inside of the caliper and the outside of the piston with a fine wet-r-dry sandpaper (I use 600), using brake fluid as the lubricant.

[DimitriT]

I'm not sure I really understand that. How does that work? I saw in another post someone mentioned getting the piston out by squeezing the brake lever. Does this work too? The closest thing I have to an air compressor is a bike pump.

I've used the brake lever to pop out the piston. Be ready for a big messy caliper full of brake fluid, though.

My advice.. if you like the bike and want to keep it and ride it, do yourself a favor and overhaul the complete brake system: rebuild the master cylinder with new cup and piston, new stainless steel braided hose and banjos, new caliper seal, piston and dust boot.

But before you invest in all this I would look into the frame and figure that out. No point in putting time and money into a bike with a crooked frame.

[Unclesol]

You definitely have at least one seized caliper, and from the sounds of your last response, it might be a good idea to find a gsr member close by to give you a hand. If you're not sure what you're doing, brakes are one thing you don't want to mess with. Otherwise, find a factory (or Clymer) manual for your bike, as they have pretty good step-by-step instructions for most jobs like this. Once you understand how the caliper works, it is farily straightforward.
Good luck...

[swhomrig]

So, I got the piston out. Theres a little bit of corrosion on part of the piston and the inside of the caliper. Its not much, but I imagine it wouldn't take much to mess up a fragile system. It looks like it could be taken off using the wet sand method mentioned above. Is this a terrible idea? I don't plan on keeping the bike much longer so I'd rather not shell out the cash for a new caliper or piston...but I also don't want to be killed by a brake failure before I sell the bike.

I had a caliper rebuild kit lying around. I had ordered one I long time ago when I started all this but didn't put it on when my Haynes manual said that the job was to be performed by a professional. I really hate when they say that. Anyways, it turns out that the kit is the wrong size - piston seal and piston boot are too big. I guess someone goofed when they filled my order. I've got new seal and boot on the way from bike bandit. Hopefully everything will go smoothly once those arrive.

As far as redoing the whole system, I think I'll hold off as I don't plan on keeping this bike much longer. I'll be selling it when I finish my 400 project. In the mean time, I'll just limp this 450 along.

Thanks for your help!

[TooManyToys]

Your main problem is most likely within the calipers O-Ring groove. The O-Ring fits in a tangential cut groove but is somewhat loose fitting. As the piston is installed the O-Ring tightens up to maintain a static fluid seal, but there is still some travel to the ring in and out. As you apply the brake, the O-Ring slides to the tighter radius of the groove, sealing against the higher fluid pressure and distorts forward a small amount. When you release the brake, the O-Ring returns to a square shape and back of the groove, retracting the piston a small amount. This is called seal roll back and is only about 0.020 to 0.030". But it's what keeps the pads away from the rotor.

Usually over time enough dirt, dried brake fluid, oxidation, or dried assembly lube clogs up this area. And it's not soon after that the piston freezes in the caliper bore.

Try to find a small brass brush that will fit in the caliper piston bore so you can clean out the groove when you do the rebuild.