Some work on the MG Metro brakes was finally done. I got all the parts sandblasted by a mate (for a small amount of coin) but hadn't touched them for 4 weeks since I picked them up. Some surface rust had already started to appear so I brushed them some rust converter (35% Phosphoric Acid), cleaned them up and painted them.
If anyone is repainting brake parts, take the time to mask off any areas which will be mated together later (eg Steering arm to hub) so that the metal is flat & clean when it's bolted back together. Also mask off any threads disc surface. Note the non-painted sections in the pic below
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While the paint was (black - engine enamel) drying, I started pulling out the pistons from the calipers so that the seals can be replaced. It's normally a pretty easy job by inserting air compressor nozzle in the brake line inlet and carefully applying some air. One or more pistons will pop out. BE CAREFUL of this because they can release at a high velocity so don't leave your fingers in there! When each piston pops out, insert it back into the recess a small amount (so it can be removed by hand later) and clamp it in place with a G-clamp, so when you apply more air then the other piston(s) will pop out.
One caliper was relatively easy. The other caliper had 2 pistons which refused to budge by giving it a blast of air (As it turned our later, rust had got under the hardchrome of the pistons and wouldn't let the piston move past the seals). Applying a higher air pressure didn't seem to work so I used liquid instead! Well close enough - grease. By coincidence, my grease gun had the same thread as the main brake line inlet on the calipers so I screwed it in and pumped away. Slowly but surely the pistons were forced out and I cleaned the grease out of the calipers by soaking them in petrol for an hour or so to break down the grease and blew it all out of the lines with the air gun.
Then it was paint time with a silver enamel - specifically for brake calipers. The bleed nozzles and inside the piston area were taped off before painting. The obligatory before & after shot :
If anyone is repainting brake parts, take the time to mask off any areas which will be mated together later (eg Steering arm to hub) so that the metal is flat & clean when it's bolted back together. Also mask off any threads disc surface. Note the non-painted sections in the pic below
.
While the paint was (black - engine enamel) drying, I started pulling out the pistons from the calipers so that the seals can be replaced. It's normally a pretty easy job by inserting air compressor nozzle in the brake line inlet and carefully applying some air. One or more pistons will pop out. BE CAREFUL of this because they can release at a high velocity so don't leave your fingers in there! When each piston pops out, insert it back into the recess a small amount (so it can be removed by hand later) and clamp it in place with a G-clamp, so when you apply more air then the other piston(s) will pop out.
One caliper was relatively easy. The other caliper had 2 pistons which refused to budge by giving it a blast of air (As it turned our later, rust had got under the hardchrome of the pistons and wouldn't let the piston move past the seals). Applying a higher air pressure didn't seem to work so I used liquid instead! Well close enough - grease. By coincidence, my grease gun had the same thread as the main brake line inlet on the calipers so I screwed it in and pumped away. Slowly but surely the pistons were forced out and I cleaned the grease out of the calipers by soaking them in petrol for an hour or so to break down the grease and blew it all out of the lines with the air gun.
Then it was paint time with a silver enamel - specifically for brake calipers. The bleed nozzles and inside the piston area were taped off before painting. The obligatory before & after shot :
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