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  #1  
Old 01-09-2010, 02:02 AM
BodhiBenz1987's Avatar
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Caliper advice .. again ... I think I know the answer ...

... I think I've asked this before, but my search skills are lacking tonight, I guess. It shouldn't be that hard to push the caliper piston in on a 124 caliper, right? As I recall, last time I did the brake pads on this car, I needed my dad to man the channel locks to get the piston started inward, then it was OK. This time I can't get the piston to budge. I tried a C-clamp, and tomorrow I'll try putting the old pad back in and using it to push back with a screwdriver. My inclination at this point is that it's a bit seized and maybe I should go for remans. I'd rebuild, but I don't really have a good facility to do so. It wouldn't break the bank to get remans ... maybe would be worth the peace of mind. Does my reasoning sound right? Or should I find someone with man-hands to try to muscle the old ones back in?
The boots don't looked cracked and the car was braking fine (but did chew up the pads a little fast). It's just ... stuck ...
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  #2  
Old 01-09-2010, 02:14 AM
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Try popping the bleeder and then push the pads in. if it goes much easier, it's time for new hoses or possibly a new master cylinder. This would also explain the fast pad wear, if the brakes were not fully releasing. If you have ABS, you really should open the bleeders to push the pads in anyways, you don't want to push all that crud in the lines back through the ABS valve.
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  #3  
Old 01-09-2010, 02:16 AM
compress ignite's Avatar
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Try a "C" WITH the old pad

You know if it's "Cocked" the least bit It'll fight you.
How far out were the Pistons run from normal operation area? (If at all)
[Were the Pads even CLOSE to Metal on metal ?]

If there's some corrosion on the Piston it may fight you still.
(In the Past ,if it was only surface corrosion, I'd take super fine Bronze Wool
to the pistons after removing them with compressed air)

Brakes are one of the things I will not screw around with.
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  #4  
Old 01-09-2010, 02:16 AM
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The solution could be a simple as removing the piston, cleaning it up, applying some caliper grease and reinstalling. (If I were going to remove the piston, I would install a new seal kit.)

Don't be intimidated by "rebuilding." Think of it as cleaning and resealing. Nothing to it.
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  #5  
Old 01-09-2010, 02:46 AM
DeliveryValve's Avatar
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Quote:
Originally Posted by tangofox007 View Post
The solution could be a simple as removing the piston, cleaning it up, applying some caliper grease and reinstalling. (If I were going to remove the piston, I would install a new seal kit.)

Don't be intimidated by "rebuilding." Think of it as cleaning and resealing. Nothing to it.
Yes it is not that hard to do this.

But if the piston is corroded badly, than a rebuilt unit would be needed.



.
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  #6  
Old 01-09-2010, 03:24 AM
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I did have the bleeder open when pushing it in ... the piston is out quite far. The pads weren't totally wiped out but were pretty thin. IIRC the last time I did it they were hard to get "started" but once they started moving, it got easier. I'll try again tomorrow with a larger C-clamp ... even with the pad the one I'm using kind of ends up at a funny angle. Even if I can get it moving though, I'd still be worried about how stubborn it was.
I'll go back and study the process of removing and cleaning the piston ... last time I considered it it looked like more than I could handle. It's just one of those things I don't want to do wrong and find out the hard way. I'd rather experiment with one that's going on a car I drive less frequently and vigorously.
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  #7  
Old 01-09-2010, 03:27 AM
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Quote:
Originally Posted by compress ignite View Post
Brakes are one of the things I will not screw around with.
I hear this frequently out of people, and I'm always made to wonder what other controls of locomotion in their vehicles they're cutting corners on.

"I won't mess with brakes, but f* that steering man!"

I agree that brakes are life and death but they are also a simple hydraulic system governed by the laws of physics like anything else.

Bodhi, is this the second set of pads? I have had more trouble with the second side I do because the added brake pad material on the other side forces the piston on that side further in and thus the piston on the side you're working on further out...
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  #8  
Old 01-09-2010, 03:40 AM
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Originally Posted by Archdukeferd View Post
I hear this frequently out of people, and I'm always made to wonder what other controls of locomotion in their vehicles they're cutting corners on.

"I won't mess with brakes, but f* that steering man!"

I agree that brakes are life and death but they are also a simple hydraulic system governed by the laws of physics like anything else.

Bodhi, is this the second set of pads? I have had more trouble with the second side I do because the added brake pad material on the other side forces the piston on that side further in and thus the piston on the side you're working on further out...
I think he meant he doesn't mess with brakes as opposed to the headlight door, or trim strips. And I do think of brakes as one of those areas where something very small going wrong can turn into something big fast (although of course there's other areas ... like flex discs, which I'll be doing too!).
On these calipers, there's only one piston each. I'm not quite sure the terminology to differentiate between these and the 123s, but on the 124 there's a portion of the caliper with the single piston in it that swings down over the brake pads ... so the piston has to be all the way in to even fit over the pads. It's not like the 123 where you slide them in over the pistons. My 123 was pretty easy to decide what to do with the calipers. They looked like they'd been pulled out of King Tut's tomb and nothing would budge for anything.
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2005 Jeep Liberty CRD Limited, light khaki/slate--110,000 miles
1995 S320, black/parchment--28,000 miles (Dad's car)
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  #9  
Old 01-09-2010, 08:05 AM
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The W123 has what is called fully floating calipers, the W124 has semi floating. The semi is much cheaper to manufacture and lighter. I think the AMG models still have full floating. The change to semi in the W124 is an example of the been counters taking over at MB. The surface of the piston that is exposed is best cleaned if you can, before retracting it. The braking system is much simpler than the fuel system. The ABS system is a different story.
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  #10  
Old 01-09-2010, 09:41 AM
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Quote:
Originally Posted by BodhiBenz1987 View Post
I'll try again tomorrow with a larger C-clamp ... even with the pad the one I'm using kind of ends up at a funny angle. Even if I can get it moving though, I'd still be worried about how stubborn it was.
The clearance between the piston and the bore is pretty tight, when you apply pressure to the piston its important to make sure the force applied is in-line with the bore of the cylinder in the caliper.

If you are applying force from a 'funny angle' the piston could jam against the cylinder wall and it would not move. Make sure the force is applied parallel to the bore of the cylinder.

Has the car had regular brake fluid changes? Since its been in your family since 1987 I'd guess it has and if so the piston should move with very little force - like maybe 10-20 pounds.
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  #11  
Old 01-09-2010, 09:46 AM
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Quote:
Originally Posted by layback40 View Post
The W123 has what is called fully floating calipers, the W124 has semi floating. The semi is much cheaper to manufacture and lighter.
The W123 and earlier cars have fixed calipers, floating calipers work fine for the base W124 and floating calipers are easier to service and are less prone to shudder from rotor surfaces that are less than perfect. They also have fewer moving parts and fewer seals to fail and leak.

Not everything that is older is better.
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  #12  
Old 01-09-2010, 09:47 AM
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Actually the 123 has fixed calipers.

I am not sure what the difference between semi floating and full floating calipers is. I only know of fixed and floating.

When I do brakes on my 123 I use a very large screwdriver. First I take a small screwdriver and drive between the pad and rotor. After creating a bit of room I take my 19" or so craftsman and drive it in and pry back the pads. If they won't mover for that monster they are stuck probably.

The other trick I use is if the pads are reluctant to slide down in I take them to my bench grinder and take a little off the sides until they drop right in.

The calipers, rotors and pads are all very rugged so you are not likely to hurt anything.

It all is very simple on the 123. Once you do it a few times it takes longer to jack up the car and remove the wheels than changing the pads.
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  #13  
Old 01-09-2010, 10:34 AM
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Quote:
Originally Posted by compress ignite View Post
Brakes are one of the things I will not screw around with.
I used to have this attitude as well. Certainly we have to know our limitations and not get into an area that we don't feel competent in but a number of years ago, I assumed that taking it to the "professionals" was the way to go. I left my Honda Accord at a chain that does brakes (mufflers is their main thing; they claim to have a certain touch) and walked around the shopping center, had a cup of coffee and came back. On arrival I was informed that they had a problem with my car. It turns out that the guy doing the brakes turned the car over to an inexperienced kid to finish up, lower down and drive out of the bay. Evidently he didn't bleed all of the air out of the line or didn't get the pedal pumped back up. He evidently gunned it and with no brakes slammed into a brick wall across the lot. Smashed the bumper, truck, lights, quarter panels, etc. They were apologetic and paid to have it fixed, but this taught me who handles my car when I take it to these professionals. Certainly we all have to start somewhere and I am not faulting someone for making a mistake, but there was clearly a lack of supervision here, and that is not what I am paying for when I take it to the professionals.

Bottom line is, I know that I will be more careful and meticulous than most people in a big shop who are probably under pressure to get to the next job.
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  #14  
Old 01-09-2010, 10:44 AM
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Also, If this is the 2nd side, and the resivour on the MC is full, there is no where for the fluid to go except out the tiny vent hole. So if you have added fluid since the last brake change, this could also cause a piston to be hard to push.
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  #15  
Old 01-09-2010, 11:07 AM
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Quote:
Originally Posted by layback40 View Post
The W123 has what is called fully floating calipers...
Calipers with opposing pistons have absolutely no reason to float.
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