Brake caliper problems

[sparkymark567]

Hi, I'm looking for some advice on what best to do about my brakes (sorry for long post).

I bought the bike privately a few months ago and then noticed that the front brakes were not very good. The bike only has 8000 miles on the clock so it has probably been sitting around for some time.

I decided to disassemble the front calipers. I could not remove the pistons by myself because the pistons were too tight. My dealer has now removed the pistons for me. On inspection, there was a lot of gunk where the old seals used to be. I think some of this might be from the old seals as the pistons were removed with heat. I also found one of the piston bores to be slightly damaged and I suspect that this was caused by my dealer. All of the pistons (except one) were removed by drilling a hole in the top and threading through a bolt. I suspect that the damage to the first bore was caused by removing the first piston by some more crude method.

I decided to ignore the slightly damaged piston bore (not sure this was a good idea) as the damage is well below the seals. I cleaned the calipers as best as I could (6 hours), but could not remove all of the dirt from where the old seals used to be. Not wanting to spend my whole weekend cleaning the calipers, I decided that they were not too bad and eventually refitted new pistons and seals.

After refitting the calipers, and bleeding the brakes, the lever still felt a little spongy. I left the brake lever tied back to the bar over night to see if the brakes were leaking. When I returned in the morning it was obvious that one of the calipers had leaked.

I am not sure what to do for the best:

1. Take the calipers apart again and clean them more thoroughly.
2. Buy new or second hand calipers
3. Take the calipers back to the dealer and get them to finish the job.
4. Anybody know where I can send the calipers to have them done properly?

I have already spent £180 on new pistons and seals (+£35 for the dealer to remove the pistons). I decided to buy the new pistons and seals, instead of second hand calipers, because I wanted the brakes to be perfect. I didn't want to buy second hand ones....because I could not be sure of the condition. So I'm really in a right mess now.....and above all I just want to start riding the bike. Any advice/ideas would be helpful, thanks.

[RedexRobB]

Damn

Personally i would get the caliper off again and find out where its leaking and why, then go from there. Sounds like one of the calipers is ok so you did half a good job You never know you may have just nipped one of the seals when putting a piston back in. Did you cover the pistons in brake fluid before installing them?

Have you thought about fitting braided lines and maybe also getting a master cylinder rebuild kit?

[Northern ANdy]

why oh why didn't you just pop the pistons out by taking the calipers off and pumping till they bloew out.

[masterofinsanity]

i'd go with robB and strip them again and find out where they are leaking from.Let us know how you get on.Alternatively check out the know your stuff forum and look at the brake upgrades available.

[rene]

why oh why didn't you just pop the pistons out by taking the calipers off and pumping till they bloew out.

because if one is more stuck than the other then it will just force out the less stuck one

[masterofinsanity]

i always use a duplo brick to wedge them they are spot on size for this job. so wedge 2 pistons and if u put a pad in one side that'll wedge 3 pistons and push the sticky bugger out.

[sparkymark567]

Thanks for your replies.
I did lubricate the seals first with DOT4, but it's possible that I did pinch one of them.

I have stripped callipers back down again.
The damaged piston bore, was not to be so bad after all. It is more of mark than a deep scratch.....so probably not my dealer's fault.
When the pistons are tight/seized they can shudder down the inside of the bore.

I have been reading around a bit....and I believe that the callipers need to be really clean in order for the seals to work properly.
So this time I cleaned them thoroughly, used an Ultrasonic bath and Isopropanol (which is OK according to the manual).
After the ultasonic bath, there was still a lot white residue, which I cleaned away by hand (took me ages).

I am now just waiting for 1 new piston seal, which I will compare with the pattern seals (I'm not taking any chances this time)

When I started taking the calipers apart......I never thought it would take quite this long. If I had known then what I know now......I might have paid for new callipers.
At least I have learned to check the brakes properly before buying a second hand bike!

[RedexRobB]

Hopefully youll get it sorted. Do you own an ultrasonic bath? Where can you get them from? You also learned how to strip and clean calipers!

let us know how you get on

[sparkymark567]

I borrowed the ultrasonic bath from my work. It's a fairly simple thing about the size of a large toaster. They are not very expensive though, about £50. You need to be careful what solution you use, as some some are alkaline based and therefore not good for aluminium.

[RedexRobB]

I saw one on tv once, it was in Jay Leno's garage, and he had a proper large one, about the size of two sinks. I would definately like to get one!