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garynortheast
BSB novice
Joined: 30 Apr 2006
Posts: 2246
Location: Mid Wales
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 Posted: Tue Jun 24, 2008 7:29 pm Post subject: Rebuild of front calipers |
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Well, finally bitten the bullet after nearly three years of procrastination! The brakes on my 71F have never been overly confidence inspiring, there's always been a lot more lever travel than I like especially as the pads wear down. The problem is 22 year old pistons in the calipers with a degree of corrosion on them which doesn't allow the pistons to creep through the seals to take up the pad wear. The answer is new pistons and seals which I ordered last week from Robinsons Foundry. Not cheap unfortunately - £160 all in! Still, it means I'll finally have decent brakes which is what I really could do with for the trip down to France. Don't fancy those mountain roads and hairpin bends with a brake lever that comes back to the bar!!
Step one - First buy your pistons and seals.
Doesn't look like much for £160 does it, but if it means I have decent brakes at the end of it then I'll be a happy man!
I did replace the seals when I first got the bike but I cleaned and reused the old pistons which, with hindsight, was a mistake. In fact, I split the calipers and replaced the small seals in between the two halves of both the front calipers as well. The seal kits I have contain those little seals again and I was thinking about splitting the calipers and replacing them again but not really sure that there is any gain to be had from doing that. Think I'll just deal with the pistons and associated seals, should sort the brakes out.
As an aside, does anyone know where I might get a set of these caliper pistons made up in s/s? |
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garynortheast
BSB novice
Joined: 30 Apr 2006
Posts: 2246
Location: Mid Wales
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| Posted: Thu Jun 26, 2008 9:35 pm Post subject: |
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Phew!! That was a long and thoroughly unpleasant job! It shouldn't have been - it sould have taken just a couple or three hours to pop the pistons out, replace the seals and fit the new pistons. But the pistons and seals were in a real state and I started the job yesterday afternoon on my own. I quickly discovered that it's very useful to have a second pair of hands and I struggled to get one of the calipers rebuilt alone. Today my FiL came over to lend a hand and between us we did the other caliper in half the time.
The main problem was that the pistons were stuck to the seals as they were corroded so it took a long time to get each piston out. I popped each piston out seperately, replaced the seals, fitted the new piston and then moved onto the next one. I retained the other three pistons in place in the caliper with a clamp made of two strips of steel bolted together over the piston opposite the one I was replacing. I used an old piston pushed in between the other two pistons to stop them moving while pumping out the piston I wanted to remove. The long bit was trying to pump up enough pressure to move each piston in turn and free it from the seals. It got easier as more new pistons and seals were put in place.
Bleeding the brakes was definitely a two person job as well. I started off by pumping the lever a few times and then slackening the master cylinder banjo bolt to clear any air from there. Then one at a time, I lifted the calipers up as high as the brake lines would allow, rolled them around while gently tapping them all over with a small steel bar to help move any air in them around to the bleed nipple. Finally while keeping the bleed nipple in the highest position and with my FiL pumping the brake lever for me, I bled the air out of each caliper. I also went around all the metal joints and junctions in the system with the steel bar, again tapping all the way up to the master cylinder to help dislodge any air bubbles. Finally I tied the lever back while I went in for dinner.
And? I now appear to have decent brakes which start biting soon enough to get two fingers under the lever without squashing them. I'll have to watch my step when I go out on it for the first time now then or I'll end up grabbing the usual handful and be on my ear! |
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garynortheast
BSB novice
Joined: 30 Apr 2006
Posts: 2246
Location: Mid Wales
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| Posted: Fri Jun 27, 2008 7:45 pm Post subject: |
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Wahay!! I've got brakes!! Took the bike for a ride into town this afternoon (even though it was raining) just to see how the brakes were and they're great. Never had brakes this good since I've had the bike. So nice to have a bit of resistance at the lever now and feel the bike achieving a very rapid slowdown with not too much lever travel. Should do me for the ride round the mountains in France (and here in Wales).
I'm a happy man - but then it doesn't take much to please me! |
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andyk3
Site Founder
Joined: 15 Dec 2005
Posts: 21680
Location: Widower to a Nintendo DS
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| Posted: Fri Jun 27, 2008 8:15 pm Post subject: |
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dont it feel good to have brakes  job well done gary |
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garynortheast
BSB novice
Joined: 30 Apr 2006
Posts: 2246
Location: Mid Wales
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| Posted: Fri Jun 27, 2008 8:21 pm Post subject: |
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| It does too mate. I don't know how I put up with 'em like it for so long, I guess you get used to it. It did make me look hard at where I was going and try to anticipate what was coming up having crap brakes. But I'd had a couple of close calls lately so on the whole I think I'll stick with having decent brakes! |
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garynortheast
BSB novice
Joined: 30 Apr 2006
Posts: 2246
Location: Mid Wales
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| Posted: Wed Jul 23, 2008 8:58 pm Post subject: |
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Well I've just fitted new sintered metal brake pads all round and it has completely transformed the brakes.
They were a lot better after fitting the new pistons and seals in the front caliper but I still felt they should be better. I had to push the pistons in a long way to fit the new pads and it seems to have sorted something out - possibly dislodged an air bubble in the system somewhere. The front brakes are now phenomenally good!!! The lever only needs a gentle pull to make the bike stand on it's nose. I've just been out to try them out and two fingers on the lever are all that's needed at any time.
The back brake is OK but it's now on my to do list for this winter. I'm going to replace the pistons and put another set of new seals in as I think I can probably make it as effective as the front brakes. |
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ashman
moderator
Joined: 09 Apr 2006
Posts: 6465
Location: Land Ahoy
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| Posted: Thu Jul 24, 2008 4:10 am Post subject: |
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Nice one Gary, good job  |
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andyk3
Site Founder
Joined: 15 Dec 2005
Posts: 21680
Location: Widower to a Nintendo DS
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| Posted: Thu Jul 24, 2008 5:13 am Post subject: |
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another job well done mate  |
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croc
Burnout King
Joined: 11 Feb 2008
Posts: 177
Location: Derby
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| Posted: Thu Jul 24, 2008 12:44 pm Post subject: |
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| horrible job to do mate ive done it but well worth while in the end, good job mate |
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P3tchy
BSB novice
Joined: 22 Aug 2007
Posts: 2038
Location: MK
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| Posted: Thu Jul 24, 2008 3:10 pm Post subject: |
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Much easier to use an airline and blow the pistons out.
And btw alloy pistons are much better foe dispersing heat than SS ones. |
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garynortheast
BSB novice
Joined: 30 Apr 2006
Posts: 2246
Location: Mid Wales
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| Posted: Thu Jul 24, 2008 9:14 pm Post subject: |
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Problem with the pistons for my calipers is the age of the bike. It's hard finding anything but the standard parts for it without paying a fortune. And the standard bits ain't cheap either.
Will look into the alloy pistons though. |
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