I managed to get the rear rotor off and the caliper without removing the hydraulic line [I hung the caliper onto the coil spring with a coat hanger].

The problem emerged when I tried to put the new pads into position in the caliper. I could not move the pistons back in place enough so that I could slide the new pads into place. I was using water pump pliers to force the pistons back into place and my mechanic chum says I will need a c clamp to force them back, i.e., that they require considerable force to get them back into the caliper housing.

This does not conform to the video I was watching that blackbrick had been supplying me on another web address.

I was able to move the exterior piston back fairly well but I have had no luck with the interior piston. I am waiting to get a c clamp tomorrow but in the meantime I thought I would ask if anyone has found another solution to this problem.

Bob in Parksville

I'm late on this and probably will be repetitive.

I always pry/ push/ squeeze the piston back with the old pads and rotor on. Variations on Ken C's method. If a piston won't retract enough to install new pads, time for another caliper.

Same for every vehicle: I just did my Dodge truck; ditto an old LandCruiser I had; ditto a friend's Chrysler; ....

I have on my own 240s run for a while on a sticky rear caliper but it's a poor economy.

I didn't know about the fatal master-cylinder problem that Ken mentioned. Maybe because I bleed myself sans assistant and have never (via luck) pushed a pedal to the floor during the bleeding process.

--
240s: 2 drivers & parts cars

I just rebuilt one original rear caliper and one from the boneyard on my '80 DL, the other original had a piston stuck so bad I could neither force it in or blow it out with compressed air. Brakes are too important to be wanking on with prybars, etc., the pistons need to move freely and smoothly ro operarate properly. I recommend removing the offending caliper and replacing or rebuilding with a good quality kit.

re: "...Brakes are too important to be wanking on with prybars, etc., the pistons need to move freely and smoothly ro operarate properly...."

I agree fully.

If anyone sees a contradiction between your advice and mine (viz., [paraphrasing] using screwdrivers to pry the pads/pistons inward), it's a misunderstanding about the severity of the forces needed.

That is, if you really have to force it against some "grinding" resistance, or it's truly stuck, then it's time for a new caliper. On the other hand, there is always some difficulty in retracting the pistons merely because of the hydraulic pressures generated behind the piston, and relief only being through a very long, narrow pipe leading all the way back to the M/C's reservior. Moreover, as one presses on one piston, the opposite side's piston invariably pushes out, at least somewhat, further complicating matters.

It's this moderate but reasonable resistance to which I was suggesting a remedy. A truly stuck or stubborn piston clearly warrants a replacement caliper.

OK, will take note of the cautions provided. I did take the car out for a run but I will take another look at everything this week and see if there is anything amiss. I did have to take a fairly large lever to get the inner piston back inside its cylinder on the left side but it did finally move. . . but it might be time for a new caliper. The right side seemed to be OK. I haven't bled the system because I do not have something that will apply pressure to the reservoir while I bleed from the wheel. And I don't want to use somebody to pump the brake because of the potential danger to the master cylinder. The brakes feel fine and I know the fronts have been changed over by a local brake and muffler garage. Thank you all for your input. Much appreciated.

Bob in Parksville

I know exactly what problem your describing.

Over the years, I've discovered that it's really easy if you push in the piston before removing the caliper.

With the caliper still bolted in place, I use a long-handled, large pair of slip-lock pliers spanning the ears (the "loops" that the pins pass through) and caliper body to just nudge the pads away from the rotor, leaving a little gap on each side of the rotor. Then I take a couple of long screwdrivers and push them into each of the spaces and pry the pads back toward the caliper, forcing the pistons inward. The pair of screwdrivers are pried back, crossing each other as you pry back the pads.

It's best if you can use two screwdrivers at the same time, because as you push on only one side, the opposite piston tends to push out again slightly (although you can do this eventually if you keeping trying, each side, one at a time).

I'm just using the outermost edge of the rotor as a fulcrum, so it doesn't leave any marks at all on the rotor surface. But with this method I can force the pads, and therefore the pistons underneath, fully home with ease.

However, to do this the caliper has to be bolted in place, because I'm using the screwdriver against the piston, which in effect is against the body of the caliper, so the caliper must be held securely in place. You cannot hope to do this with the caliper dangling on a wire because it can swing and move.

Hope this helped.

Ken, John, Heck,

I used a couple of Model T springs, which are flat and about the size of the pad holder plus a large flat chisel [for a wedge] and, by putting the T springs up against the piston and driving the chisel in beside them, was finally able to move the piston back into its cylinder. It was very reluctant to move I have to add and it took me almost an hour of pounding and prying to get the cylinder flat with the side of the caliper.

I do have a Model T that I drive in the summer and I had an old spring cut in half to use as a tire iron. These worked well so I guess there is a point to owning the T!

I will now go out and see if I can get the rest of the brake together and then I will tackle the other one, forearmed with the knowledge you have imparted to me.

Bob

Ken,

I think I will follow your advice and reinstall the old disc and one of the old pads. Then if I damage the disc or the pad, nothing is lost. There is only one piston on the rear brake and I am probably creating a problem by levering on one side of it and jamming its movement.

Thanks for your very informative reply. Just what I was looking for when I posted the question.

re: "...There is only one piston on the rear brake and ...."

I'm afraid you're mistaken. There are two pistons, one on each side, in the rear calipers. The fronts, of course, have four pistons, two on each side.

Even without taking it apart and showing you, just consider: since the caliper is firmly bolted in place and unable to move, if there was only one piston then only one pad, on that side, could compress against the rotor. What would enable the pad on the other side, presumably without a piston, to move and press against the opposite side of the rotor?

I think that you're confusing the 240's rear calipers with a "floating caliper" (on newer Volvos) that has pistons on only one side -- the floating caliper is such because it's the moveable body of the caliper itself (made possible by "pins" on which the caliper slides) that enables pushing pads against rotors on both sides. But a 240's rear caliper cannot move, so it must have pistons on both sides.

And, if you look at your rear calipers, you'll see the pistons on both sides.

Ken,

Sorry. I was referring to the one side of the caliper, that there was one piston and not two that activated the pad. The alternative would have been four pistons, two to each side and I thought that is what might have been the case with later model 240s. You are right of course. Just a misunderstanding of what I was referring to.

Bob

John's advice below is spot on. Exactly how I always do it.

I don't understand how you'd get a C-clamp in there anyhow.. unless, perhaps the caliper is not bolted back up...

If that's the case, bolt that caliper back up, install your old pads, and do exactly what John said... Ideally, of course, you'd have done that with the old rotor still on the car. But, the risk of scratching or warping the new rotor is pretty slim.
--
-Matt I ♥ my ♂

Matt,

Exactly what I was thinking about, given the fairly close presence of the coil springs. I will reinstall the old rotor first, reinstall the caliper and then use one of the old pads to apply pressure to the face of the piston. I now have a better line of attack when I go out to tackle the job today. Thanks for your input.

Bob

I think convincing the piston to retract that last little bit is more about getting even pressure across the piston face than the amount of pressure. I use an old, very worn pad to distribute even force on the piston while gently squeezing with channel locks or gently prying against the rotor face with a large flat screwdriver.

john
--
1989 245 236K / 1993 945 127K

John,

This is pretty well what I will try today after reinstalling the old rotor and the caliper and using one of the old pads as a pry surface. Thanks a bundle for your input.

Bob

The advice you have been given so far is spot on. I just wanted to add my 2cents since I've had lots of experience with old stuck calipers on Volvos. Now that you will put the old rotor on--don't be afraid to apply a lot of pressure--I sometimes use a 3 foot long tire iron--and if if still wont retract you can pound a wedge between the rotor and the old pad--it will retract. The calipers can take a lot of abuse and not leak. After you get it back in all the way I'd recruit a helper to pump the pedal--get the piston moving in and out while flushing the brake fluid at that end of the line. -- Dave

I wholeheartedly agree that you should flush the old fluid out afterward, but I'm concerned about "using a helper".

The problem is the notorious "killed master cylinder" syndrome on these 240s. It seems that whenever someone asks on this forum that their brake pedal "goes to the floor", it almost always happens after they flushed the brakes using the "step on the pedal" method.

Your assistant has be to very aware to avoid pressing down on the pedal too far while the bleeder nipple is open, lest they push the M/C's piston into "no man's land" where it ruins the internal seal.

It's much safer to get the fluid flushed using a PowerBleeder or similar setup, to avoid toasting your M/C.

I just wonder if I need do this step. About six months ago I paid a garage to install new front rotors, calipers, etc. and they suggested that the rears needed attention as well. I wanted some professional eyes on the brakes instead of just my own and I was willing to pay for it.

I decided that I could handle the rears and thus the situation I find myself in at the moment. I am thinking that the system would have been properly flushed at that time.

I suppose that some detritus could be flushed back into the system when the pistons are pushed back into the cylinder and that could call for bleeding and I think I have a way of pressuring the system that I found on an English car website several years ago. I know that pushing the brake pedal to the floor can cause problems with the master cylinder and so will avoid that.

Regardless, thanks again for all of your input.

Bob

Dave,

Thank you for your two cents worth! Knowing that I can be quite forceful with the caliper is important information indeed. Mine does appear to be stuck and will probably require a lot of force. I wouldn't have thought of using a tire iron or a wedge to force the piston back. Much appreciated.

Bob

I'd like to further add--considering the "protect the master" (well deserved)slant of the posts following my post--my concern lies with removing any loose sediment caused by working the piston in and out--opening the bleeder with the piston extended should accomplish that when it is forced back--then the piston needs to be "pumped" back out to repeat the process. -- Dave