06 S40 Brake Pad Replacement - Help Compressing Piston?

starrett7 · Post by **starrett7** » 23 May 2009, 15:19

I am replacing the rear Pads on the 06 S40 and the caliper piston is not compressing. I released the bleeder valve and put a C-clamp on to compress the piston and it won't budge. What am I missing here?

Thanks a million

Post by **vegasjetskier** » 23 May 2009, 16:01

Hmm. Never heard of releasing the bleeder valve. Are you sure you have the clamp on straight so that it will apply pressure directly in line with the piston axis? It takes quite a bit of pressure and you have to sustain it for the piston to retract because of the mechanical (hydraulic) advantage of the system. Can you post a pic of how your clamp is set up on the caliper?

Post by **vegasjetskier** » 23 May 2009, 16:22

Here's my super low-tech way to compress the piston. Maybe it will work for you, too.

I used the "poor man's piston compressor" (two screwdrivers) to push the piston back into the caliper all the way. I applied constant, firm, outward pressure on both screwdriver handles until the piston was forced all the way back into the caliper. Some people might say I shouldn't do this because of possible damage to the disc and/or pads, but I was replacing them both anyway, so it doesn't matter.

Post by **MadeInJapan** » 23 May 2009, 20:41

I've done mine the same way- make sure your brake fluid reservoir cap is open when you do this otherwise, the pressure in the line may be too much to compress the piston.

starrett7 · Post by **starrett7** » 23 May 2009, 23:08

Finally figured it out. The face of the piston has two small opposing recessed holes for a special tool to fit in. I just so happened to have a two pronged wrench that is for my makita grinder and it was a perfect fit. I turned the piston clockwise with the wrench while applying downward force and it retracted all the way. I used to own a Subaru that had spiraled spindle in the center of the piston and you had to turn it while also applying pressure to get it to retract. I suspect it is a new design for this caliper. Thoughts? Definitely it would not compress with just straight pressure on the piston. I did have my reservoir cap off the whole time. Turning with pressure did it. I can maybe post some pics tomorrow if anyone is interested.

Thanks for the quick reponses.

Post by **vegasjetskier** » 24 May 2009, 06:20

starrett7 wrote:Finally figured it out. The face of the piston has two small opposing recessed holes for a special tool to fit in. I just so happened to have a two pronged wrench that is for my makita grinder and it was a perfect fit. I turned the piston clockwise with the wrench while applying downward force and it retracted all the way. I used to own a Subaru that had spiraled spindle in the center of the piston and you had to turn it while also applying pressure to get it to retract. I suspect it is a new design for this caliper. Thoughts? Definitely it would not compress with just straight pressure on the piston. I did have my reservoir cap off the whole time. Turning with pressure did it. I can maybe post some pics tomorrow if anyone is interested.

Thanks for the quick reponses.

Yes, we would like to see the pics.

You might want to bleed the brakes since you opened the bleeder screw and may have got some air in there.

starrett7 · Post by **starrett7** » 25 May 2009, 18:04

Here are some pics and notes which show the procedure I used to complete the job.

1. Undo the cover on the parking brake lever
2. Undo the nut for adjusting the parking so the parking brake lead slackens. This will reduce pressure on the caliper piston.

Here is a pic of the tool volvo uses to compress the caliper piston. Probably unavailable to the average DIY'er

Here is the pic of the tool I used to compress the piston. It just so happens that I had a wrench which fit my Makita hand grinder to change the grinding wheel and it fit perfectly to align with the holes in the top of the caliper piston. I used a downward pressure (and I mean alot) while turning clockwise to retract the piston. I also doublechecked on volvospeed forum and volvo forums they confirm the same process. I know I was lucky and had a tool that worked. I also think that one could make a wrench by taking a strip of heavy flat stock and drill two holes the same distance as the recessed holes in the piston. Then take two small 1/2" to 3/4" long by 1/8" diam. bolts and put nuts on them leaving enough of the bolt extending out to fit into the hole. This should help all the DIY'ers to get by without having to go to the dealer and drop a wad of cash for the fix.