Sunday, September 15, 2019

Suzuki Bandit 1200 — Brake Caliper Stripdown.

Nissin Calipers Overhaul.
The Bandit has been a lot of fun so far, but one thing was niggling me. Although all the discs and pads looked quite new, the rear brake was squealing so loudly I was actively trying to avoid using it.

So a couple of weeks ago I thought I'd whip off the rear caliper, clean up the pistons and pads, and apply some grease to the backs of the pads. During the cleaning of the pistons, I noticed part of an O-ring sticking out on one side. The only thing I could do was unbolt the two sides of the caliper and remove the pistons to see what was going on.

The secondary O-ring (dust seal) must have been so dry at some point that it got caught on the piston and worked its way out. However it happened, I popped out the pistons, cleaned everything up in soapy water, blew it all dry and refitted the O-ring along with rubber grease. With careful refitting of the piston, all was well. Obviously this was done with both sides of the caliper, and then new brake fluid was flushed through. The back brake was then perfect... and silent.

What I did notice while the caliper was apart was the amount of orange, jellied brake fluid hiding within. There is no way this stuff is getting out unless you strip the caliper completely, which left me wondering about the fronts...

Picture quality is poor, apologies. It has aftermarket master cylinders fitted which seem to work ok, though the reservoirs are a little small, but this is the fluid! Scary stuff.

As much as I'd like to leave the calipers together and just wash the pistons, I think a rebuild is necessary to clean out the old fluid properly. I'm not replacing any seals unless absolutely necessary. Once everything is cleaned up, I'll make the call.

Pads, pins and clips are all in really good condition.

Pistons are dirty, and a toothbrush won't budge it. Thinly cut strips of 600 wet & dry is usually great for cleaning them off, but even that was struggling.

It was time to split them and clean it all up properly. Twenty-three years old and the pistons are still in amazing fettle.

It's always good to make sure the pistons are free to move, and lubed. But the main thing is to clean out the stuff behind the pistons. The fluid here has discoloured, and turned to a jelly type substance! 
After twenty-three years, the only real way to get these cleaned out completely is to strip them. Brake fluid flushes won't remove it because most of it will sink to the bottom.

I used a toothbrush, Ajax and several buckets of hot water to clean these out. Finally, they were blown out with an airline and they came up like new. I didn't remove the seals as there was no sign of corrosion. Earlier types of caliper, that aren't coated on the inside, would probably show corrosion buildup; on those you'll usually need to remove the seals, clean up the corrosion, and replace seals and, maybe, pistons.

The pistons were cleaned up with Ajax and Scotch pads, one had slight pitting which was smoothed out with 600 wet & dry. Other than that, they are in superb condition.

Every drilling and machined section was blown out several times. You need to make sure all moisture is removed. I went round the piston seals and O-rings meticulously, then gave a final wipe out with a rag soaked in brake clean. The seals feel good, supple and are unmarked.

My personal preference is to smear the seals and pistons with rubber grease before refitting the pistons. Try to turn the pistons as they go in to avoid picking up on the seals too. If they're in correctly they will slide nicely with no rough spots. I push them all the way in, wipe away the excess grease and then pull them back out slightly to check all is well (using a large, internal, circlip-type pliers).

Once the two flat-section O-rings are refitted to the caliper, I bolt them back together after cleaning and greasing the allen bolts. Final tightening can be done once they're remounted on the forks.

This little beauty already has braided lines on it, so with a quick clean up of banjo bolt and washers, they were ready for the pads.

I removed the brake fluid reservoir to clean everything out, then flushed clean fluid through. The action of the lever was extremely rough, which I initially thought was the piston in the bore (aftermarket cylinders). However, on the off-chance, I took out the pivot screw and greased all moving parts and that now feels great. I should also mention that I let clean fluid run through the lines before reconnecting the calipers, just to get rid of all of the old fluid.
It bled up easily and the feel at the lever is now perfect. I'll do a few miles on it and then flush the fluid again. The brakes on the Bandit are actually superb for a bike of this age. Very happy with it!

No comments:

Post a Comment