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Best method to replace rubber sealing for caliper piston?

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.
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Best method to replace rubber sealing for caliper piston?

Post by LOB » Mon Apr 01, 2019 1:02 am

Front caliper. Do I need to take the piston out or can this be done with the piston in place using a tool without sharp edges? I've used petroleum based caliper grease which caused the rubber gaskets to expand. I thought all types of caliper grease where supposed to be compatible with rubber (it should have been silicone grease). The pistons are in good condition so it's not necessary to remove them for polishing.



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Re: Best method to replace rubber sealing for caliper piston?

Post by LOB » Mon Apr 01, 2019 4:18 am

Looking at the caliper restoration package there's another thin o-ring that supposed to be on the piston so I guess I have to push out the piston.



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Re: Best method to replace rubber sealing for caliper piston?

Post by Cookeh » Mon Apr 01, 2019 4:59 am

Yep, gotta get the piston out. Definitely worth replacing both seals whilst in there.



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Re: Best method to replace rubber sealing for caliper piston?

Post by cn90 » Mon Apr 01, 2019 8:24 am

Search for the DIY I posted in forum for tricks.


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Re: Best method to replace rubber sealing for caliper piston?

Post by tardcart » Mon Apr 01, 2019 9:07 am

The real problem is rust, if the bleeder screw is seized and broken you cant fix that.forget heat and drilling. I dont know how they do it at the rebuilders, probably some hot lye bath. also if the groove that holds the boot seal is rusted up you could soak the caliper in vinegar for three days, but who is going to bother? If the piston is seized use the break pedal to force it out, air won't do it and is very dangerous. the piston will fly and oil will go in your eyes. Its like pulling a stump with a nylon rope. the stump is coming after you. If the piston is corroded you cant polish that out. the original were Crome plated. if the plating is gone it will rust immediately and is probably pitted. You cant really buy a piston. either na or substandard or very expensive.



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Re: Best method to replace rubber sealing for caliper piston?

Post by JimBee » Mon Apr 01, 2019 2:58 pm

I've done several and I second most of what tardcart says.
The first thing to check before going further is the bleeder screw. If it's seized, you wouldn't be able to bleed it even if you could otherwise rebuild it. If you're near and junk yard, you might find a decent used one. Again, first thing to check is the bleeder screw. The second thing to check is whether the dust boot appears to be in tact. If it isn't the piston will likely be rusty. Then does the piston move freely. Use a heavy screw driver to force the piston back by levering on the pad. If the bleeder screw is open, you'll see fluid spurt out. If it passes all 3 tests, it's probably usable.

If the caliper is off the car, you'll need to use pressurized air to force the piston out. MAKE SURE if you do this, you use a STOP such as a brake pad or piece of plywood so the PISTON DOES NOT FLY ALL THE WAY OUT. cn90 shows this, I believe.

If you get the piston out and it isn't rusty, and the bleeder screw is operable, you can clean up the two grooves in the caliper housing that accept the rubber parts. The internal seal groove and outer-more groove that holds in the ridge of the dust boot. The third groove is near the head of the piston, the outer rim of the dust boot seats in that groove. As suggested, cn90's tutorial leads you through most of that.

However, last time I viewed the tutorials—YouTube included—none I could find guides you through the last step: reinstalling the piston AND the dust boot properly. Unless you have some special magic touch, it's about impossible to get them both installed without some sort of special aid because the inner rim of the dust boot needs to be seated in its groove—but if you seat it with the piston out (which is easy to do) then you can't get the piston in through it without damaging the dust boot. You can use a cross section of a coffee cup like I did. If you don't get the new dustboot properly seated moisture will get behind it and rust the piston and you're back to square one. Maybe somebody who has successfully done this, will say, Jim, just do it like this! And show it in a video. A neat slight of hand and it's in. I will gladly eat my words!

What's really frustrating is that the new seal and dustboot (from O'Reily Auto Parts) only costs a few dollars. Still, it's money and time wasted if you can't install the dustboot properly.

I'm going to write this up how I solved it with pictures when I have time, maybe later spring.



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