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I need some advice from some more experienced Volvo mechanics regarding failed caliper dust seals.
From my Brickboard reading and discussions with Volvo Mechanics and IPD, as near as I can tell rebuilt calipers for 240s have the following problems. First, most of the cores used for rebuilds are approaching junk status with repeated rusting in use and cleaning for rebuilding having now removing metal from critical areas. Second, replacement pistons are not available for rebuilds, so the pistons are also simply refinished and reused. This means rebuilt calipers have sloppy tolerances and are more likely to fail with stuck pistons way before pads and rotors wear out. This has been my experience with my 1992 240 wagon. Three of the 10 rebuilt Centric caliper pistons locked up and ruined the pads and rotors with low mileage (less than 10,000) and more than 75% of the pad thickness left on the normally operating calipers. With typical Volvo safety margins, the brakes never actually began to fail, just started to make an terrible racket.
On close examination of the calipers I found most of the failed pistons also had obviously failed dust seals that had poped off of the lip on the caliper casting and exposed the pistons to water, dirt and salt. I presume this happened because the lip in the caliper castings that the dust seal snaps over has lost critical dimension from rust and cleaning cycles, such that the seals will no longer stay in place. Recomendation on Brickboard to put some silicone grease under the dust seals seem like a bad idea, since this approach will simply make it even easier for the dust seals to pop off of the casting lip as the pads wear.
So here is what I am planning to try next. First I bought rebuilt powder coated calipers from NuGeon (NHT powder-coated calipers, QBR Brake, Inc.) with the hope they will "cherry pick" calipers for such expensive parts. Second, I plan to glue the outer edge of the dust seals to the the casting/power coat with the best high temp glue I can buy. Third, if possible without damaging the seals, I will try to put a little silicone grease between the piston top and the dust seals after the glue has hardened around the outside of the dust seals. Fourth, I will take the pads out once a year in Spring, clean everything off and inspect the dust seals and make the sure the pistons still move easily. Fifth, I will replace the pads (they are relatively cheap and easy to swap out) and the dust seals the minute any one of the 10 dust seals shows signs of popping off.
Does this approach make sense? Anyone else tried gluing the outer edge of the seals in place? Is there a better approach? I currently have all the new parts on the bench and plan to put everything back together in the next few days.
As always, thanks for your advice.
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