mason@vax.ftp.com (Nark Mason) (02/03/90)
About 2 months ago I replaced the brake pads on my TR250. The old ones were almost compeltely worn so I had to push the pistons back into the caliper body to make room for the new pads. About 30 miles later, while driving up a large hill, I pushed down on the brake pedal and almost nothing happened. I took this opportunity to rebuild the brakes, among other parts, and found out what had caused the failure. The pistons had rusted and pitted up to, but not past, the sealing gasket in between the caliper body and the piston. When I pushed the pistons back into the body the seal was now resting on the pitted area of the piston which didn't make a good oil seal, and the brake fluid squirted out through the rust. I guess the piston boot can be expected to keep out only *almost* all of the moisture.
robbp@pyrthoth.pyramid.com (Rob Pryor) (02/03/90)
>. . .I replaced the brake pads on my TR250. The old ones were almost >compeltely worn so I had to push the pistons back into the caliper body to >make room for the new pads. About 30 miles later. . .I pushed down on the >brake pedal and almost nothing happened. I . . .found out what had caused >the failure. The pistons had rusted and pitted up to, but not past, the >sealing gasket in between the caliper body and the piston. When I pushed >the pistons back into the body the seal was now resting on the pitted area >of the piston which didn't make a good oil seal, and the brake fluid >squirted out through the rust. I guess the piston boot can be expected to >keep out only *almost* all of the moisture. I had a similar problem with my Healey back a few years ago, only I found pitting both on the pistons and the caliper body, in the grove where there seal rests. As new calipers were $300 each, I succeeded in convincing myself that new pistons, at $50 each, would fix the problem. They didn't. Some calipers are 3-piece where the cylinder that holds the piston bolts on to the main caliper body. I believe Jag calipers are this way. The Healey has a second type of caliper which is 2-piece, split down the middle, with the piston cylinder cast into each half. The 3-piece style can be bored and sleaved at a reasonable price, but I couldn't find anybody who could do the Healey calipers. I know the manual warns against splitting the halves, but there has got to be a way to split, bore and sleave, and re-assemble them and have them work correctly. -- _____________ _____________ Robb Pryor, \____________\_____________/____________/ Pyramid Technology, \__________ __________/ Mountain View, CA 94039 \________ AUSTIN-HEALEY ________/ VOICE:(415) 335-8465 \___________________________/ USENET:robbp@pyramid.com
augi@cbmvax.commodore.com (02/03/90)
> > About 2 months ago I replaced the brake pads on my TR250. The old ones were > almost compeltely worn so I had to push the pistons back into the caliper > body to make room for the new pads. About 30 miles later, while driving > up a large hill, I pushed down on the brake pedal and almost nothing > happened. I took this opportunity to rebuild the brakes, among other > parts, and found out what had caused the failure. The pistons had rusted > and pitted up to, but not past, the sealing gasket in between the caliper > body and the piston. When I pushed the pistons back into the body the > seal was now resting on the pitted area of the piston which didn't make > a good oil seal, and the brake fluid squirted out through the rust. > I guess the piston boot can be expected to keep out only *almost* all > of the moisture. > Yeah, it seems like british cars have this terrible disease where the calipers rust fiercely. The only permanent solution is to get your old calipers resleeved in stainless or brass; it costs about the same as new calipers, but is more permanent. I'm absolutely convinced that the problem with british cars isn't the engineering per se, but it is the material science. SU carb's have 1 adjustment screw that is always seized, simply because it is a brass screw in an aluminum body (I know that Webers do this all over the place, but somehow they don't corrode in Webers. I have a suspicion that Webers use a clever alloy instead of pure aluminium). Take apart a Lucas switch sometime. The contacts are _copper_! Yeah, copper is a great conductor of electricity, but it makes a crummy switch surface. I think most good switches use gold. Stuff like this is all over the place in british cars, and is probably the ultimate cause of a large percentage of the flakey failures in these cars. Joe
Eric Dashman <dashman@rti.rti.org> (02/06/90)
Re: pitted wheel cylinders, master cylinders, calipers. There's an outfit in Virginia called White Post Restorations (I think that's right) that does resleeving. They did my 3000's brake master. They're a highly reputable shop. I don't know if they resleeve calipers, but a phone call to them might be in order. Reston, VA rings a bell somewhere. They have advertisements in Hemmings, Cars & Parts, Car Collector & Car Classics, etc.. Eric Dashman
robbp@pyrthoth.pyramid.com (Rob Pryor) (02/06/90)
Re: pitted wheel cylinders, master cylinders, calipers. >There's an outfit in Virginia called White Post Restorations . . . that >does resleeving. They were the first people I called. >They're a highly reputable shop. Yes they are. I have been impressed with the brake master cylinders that they have done for me. >I don't know if they resleeve calipers. . When I called, they only did the 3-piece calipers. Robb Pryor@pyramid.com