Thursday, May 13, 2004
Front brake caliper overhaul
I'd noticed that only one piston seemed to be moving when the front brake was applied and as the bike is 20 years old it seemed wise to strip the caliper and replace the seals. A pair of odd pads suggested that the PO had noticed the uneven braking force but not dealt with it. A seal kit contains two types of seal for each piston plus an O-ring for the joint between the two halves of the caliper.
The caliper is held together by two 8mm Allen bolts which are tightened quite firmly. It might be possible to access the pistons via the disc slot but it is a lot easier if the caliper is split...or so I thought.
One bolt came undone readily, the other turned a little. So I added penetrating oil and turned a bit more. Gave up for a day and soaked it in engine oil. It turned some more and then head chewed up due to the high torque being used. So I drilled it off and welded metal onto the remaining stud and it turned some more. Great, that's got it. Not quite, it got stiff and then sheared.
I'll bet you saw that coming!
OK so now it could be drilled out and helicoiled, spark-eroded and retapped etc etc. Now I know that helicoils are 'stronger than the original thread' but do I trust it to hold together? If it's not square will the fluid leak one day? Don't know, but I'm not going to risk it especially when one of the pistons is rusted and would need a light emery paper rub to get to metal.
For £60 I'm getting a new caliper with fresh pads and seals!
There are several morals to this perhaps:
1. If it ain't broke, don't fix it. Well it was broke, but it's more broke now!
2. If in doubt don't force it. - If I'd stopped at the beginning it could have been possible to rebuild it via the slot (except for the halfway O-ring).
3. How do you value your time and safety compared to a new part? OK so nobody rebuilds a bike to save money but maybe it would be wise to assess every part of a job and decide whether to leave, rebuild or replace.
I'd noticed that only one piston seemed to be moving when the front brake was applied and as the bike is 20 years old it seemed wise to strip the caliper and replace the seals. A pair of odd pads suggested that the PO had noticed the uneven braking force but not dealt with it. A seal kit contains two types of seal for each piston plus an O-ring for the joint between the two halves of the caliper.
The caliper is held together by two 8mm Allen bolts which are tightened quite firmly. It might be possible to access the pistons via the disc slot but it is a lot easier if the caliper is split...or so I thought.
One bolt came undone readily, the other turned a little. So I added penetrating oil and turned a bit more. Gave up for a day and soaked it in engine oil. It turned some more and then head chewed up due to the high torque being used. So I drilled it off and welded metal onto the remaining stud and it turned some more. Great, that's got it. Not quite, it got stiff and then sheared.
I'll bet you saw that coming!
OK so now it could be drilled out and helicoiled, spark-eroded and retapped etc etc. Now I know that helicoils are 'stronger than the original thread' but do I trust it to hold together? If it's not square will the fluid leak one day? Don't know, but I'm not going to risk it especially when one of the pistons is rusted and would need a light emery paper rub to get to metal.
For £60 I'm getting a new caliper with fresh pads and seals!
There are several morals to this perhaps:
1. If it ain't broke, don't fix it. Well it was broke, but it's more broke now!
2. If in doubt don't force it. - If I'd stopped at the beginning it could have been possible to rebuild it via the slot (except for the halfway O-ring).
3. How do you value your time and safety compared to a new part? OK so nobody rebuilds a bike to save money but maybe it would be wise to assess every part of a job and decide whether to leave, rebuild or replace.
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