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Post by Deleted on Feb 11, 2020 17:38:13 GMT
One of the front brake calipers on my CB400NC is leaking despite new pistons and seals. I was lucky enough to buy a box of odds and sods last week that contained a caliper and I decided to refurbish it. However, one of the two pistons was missing and the other was seized solid.
I tried penetrating oil for several days, heat and brute force without success. There was not enough of the piston proud of the bore to get grips on it. I cut some small channels in the top of the piston and used an old chisel as a bar to twist the piston and I got some movement so I knew the piston was at least rotating in the bore.
I have an old piston from refurbishing the (now leaking) caliper so I fitted that using the old seal that was still in place. I tried to blow out the stuck piston with an air line using a wood block to keep the the other piston in place but even 100 psi would not shift it. I sealed the banjo bolt with a collar and washers so that I could fill the removable pot with brake fluid. Then, I compressed the moveable pot in a vice using a socket. After some grunting by me the seized pot began to move and eventually came out. It is amazing how efficient the old seals were in both the seized and moveable pot. This shows the power of hydraulics.
Before using the vice I tried attaching the caliper to the bike and using the master cylinder to push the piston out but without success. I doubt that the master cylinder would have produce enough pressure to pop out the caliper piston.
Dennis
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Post by JonnyHonda on Feb 12, 2020 8:50:48 GMT
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stevegbr
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Post by stevegbr on Feb 12, 2020 9:22:59 GMT
put the caliper in to boiling water and leave it for a while, because you have two different materials they will expand at different rates, while still hot use compressed air and hopefully it will blow out, but be cautious at all times. be safe.
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Post by JonnyHonda on Feb 12, 2020 9:39:11 GMT
put the caliper in to boiling water and leave it for a while, because you have two different materials they will expand at different rates, while still hot use compressed air and hopefully it will blow out, but be cautious at all times. be safe. Same principle when replacing bearings, I remember once replacing a bearing in a CB750, the one in the middle of the engine, heated the crankcase and freeze sprayed the bearing and it fell out, to replace I put the crankcase in the oven and the bearing in the freezer. |
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Post by duffer on Feb 12, 2020 11:40:34 GMT
Did the same thing putting new main bearings in the AJS crank case. Turns out that British bike crank cases make the oven stink and the chips taste of Castrol for months ! I was in the dog house for years after that one !!
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Post by bodie on Feb 12, 2020 19:09:55 GMT
isn't it great that in this world of bloody health and safety we can still do just about anything we want in our sheds or garages like burning things with big scary flames using all sorts of dangerous things with compressed air ,waving big drills and electric god knows what with plugs on and all without hard hats ,gloves and masks if you so wish  |
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Post by JonnyHonda on Feb 13, 2020 8:45:42 GMT
Yer, but that's because we're careful for the right reasons, I mean, who wants to wait for 4 hours in A&E with the missus telling everyone how stupid you were with a blow torch and a compressed air gun
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Post by Deleted on Feb 13, 2020 20:31:27 GMT
Ironically, I used to be a safety rep at work and preached safe working, then I would go home and cut the hedge with a corded trimmer whilst hanging off an unstable ladder!
I am a bit more careful now but not much. Blowing out a seized brake pot with an air line can be exciting and there is a satisfying bang when it lets go.
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Post by duffer on Feb 13, 2020 21:34:37 GMT
I had to weld up my first tank on the two bike restoration. Had to make it "safe" first. As I love a little drama sometimes so I took a leaf out of the hillbilly book. No faffing about with inert gas nor nuthin...... yeehaa !! Haven't seen the cat for weeks..  www.youtube.com/watch?v=gbZt_9URtnw |
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ian
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Post by ian on Feb 13, 2020 21:41:09 GMT
Ironically, I used to be a safety rep at work and preached safe working, then I would go home and cut the hedge with a corded trimmer whilst hanging off an unstable ladder! I am a bit more careful now but not much. Blowing out a seized brake pot with an air line can be exciting and there is a satisfying bang when it lets go. Only done it once, it worked a treat, only I put my fingers in to catch the piston - took ages to free them, and it hurt!  |
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Post by marktrower on Feb 13, 2020 23:30:58 GMT
Stripping down machines at work spent a full week getting a boom pin out jig made and a 90 ton Jack the pin 60cm long and 15cm wide ,all the pressure we could get on the pump then the 14lb hammer you would hear a loud crack it would move about 1/2 mm then start again do I miss it do I f**I.i youse a adapter I have made it as a grease nipple fitted a grease gun goes to 28000 psi and you can control what you are doing and unlike air grease does not compress
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Post by Deleted on Feb 17, 2020 12:49:28 GMT
Very creative - and safer.
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Post by davefirestorm on Feb 17, 2020 15:07:46 GMT
Here’s another method😁 It’s the rubber seal that causes the bugger to lock into the Caliper.I used a tool attached to airline ( as in picture )to grind inside of piston away in area the seal is to get at the seal,takes bit of time but works.I Also managed to hold a Caliper in a Chuck on a Myford lathe and bore the piston out past the seal ( very light cuts lol ) Where There’s a Will There’s a way is very true saying.  |
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