Eric:

probably time for a caliper rebuild (by which I mean replace the piston seal and dust boot).

One piston is sticking, so that it doesn't exert as much force on the rotor, OR the other three are dragging and not retracting. One stuck is more likely, even more likely if someone ran the rotors too thin and the backing plate hit the anti-rattle spring.

Rebuild on these calipers is easy -- remove caliper and drain brake fluid. Stand caliper in a vise, pry off the dust boot and remove from piston, then use two same prybars (from Autozone, etc) to hook the lip where the dust boot fits on the piston and lift piston out of caliper. Note the orientation of the piston. Your's will probably have a heat sheild -- the piston sticks through it part way round. You must put the piston back in the exact original orientation, so look closely.

Take a "twisted" pick (the funny one in the four pick set from AutoZone, etc) and pull the piston seal out. Spray out bore and caliper body with brake parts cleaner, then wash piston with brake parts cleaner. Inspect piston and bore for scratches, gouges, or galling -- usually none -- then the part of the bore above the seal for dirt, corrosion, or rust. If that part of the bore is dirty enough that the piston won't drop back in without intereference, you can clean it wil brake parts cleaner and some scotchbrite -- DON'T use scotchbrite or ANY other abrasive anywhere else!

Flush completely and wipe out bore, then coat new seal with brake fluid and install. You will probably have to use the pick to roll the last bit in, make sure it's not twisted or the piston will cut it going back in.


Coat piston with brake fluid and insert in bore. Double check the orientation, as you cannot rotate it without the special too. Place a short board through the caliper across the top of the piston, and with the caliper on the floor, push the piston back down in the bore. It will be VERY stiff until you get it through the seal. Alternatively, you can start it with the board, then use a C-clamp to press it down. It helps to twist back and forth a tiny amount to get the piston over the seal. The piston should "bounce" back some when you release pressure -- if it doesn't, you 've rolled the seal, remove piston and inspect. May take a couple tries to get it in, don't force it.

Install dust boot by snapping over the piston, then use a pair of channel locks to push it down all round -- you may nave to use a pair of vise grips to hold one side to start it on.

Press the heat shields in after you are SURE the piston is in the correct posistion -- I don't think you can get them off intact if it's not right!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!