How should rear caliper pistons react when lever pulled? Both act differently now...

Hello!

I've changed a lot of rear brakes on cars with rear screw-type calipers, I know how to rotate the piston and how to service them.

As of right now, I'm having 2 used calipers on my work bench which are about to go on my mk4.

My concern is that: On one of the calipers, if I rotate the lever by hand, the piston will pull out slightly and when releasing the lever, it will stay at it's new position (I.e. If I pump the lever, the piston will eventually pop out of the caliper's housing)

On my second caliper, If i rotate the lever by hand, the piston will pull out slightly and when releasing the lever, the piston will retract to it's previous position (I.e. If i pump the lever, the final position of the piston will be the same as when I started pumping.)

I'm not 100% sure of how the system works exactly and how should the piston act. I think I may have a problem with one of the calipers.

Can anyone point out how it should act? thanks a lot!!

g.b.

have you disassembled the calipers ? i just rebuilt a set and there's not much to em' inside

I'm talking about the rear calipers, there is some mechanisms hidden behind covers held by snap rings which I do not feel like removing. One one the caliper side, one inside the pistion.

that's what i'm referring to ... i rebuilt front and rear GLI calipers... you eject the rear pistons by actuating the parking lever or by using a caliper tool, then remove the snap ring deep inside ... the lever is removed via the nut and then by prying the lever off it's tapered splines ... after that the parking brake mechanism slides out

I believe the retracting one acts correct.I mean it makes sense that as you release the p brake, the piston should pull back.

guillaumeber said:

I'm not 100% sure of how the system works exactly and how should the piston act. I think I may have a problem with one of the calipers.
Can anyone point out how it should act? thanks a lot!!
g.b.

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The piston should pull back a little bit when the lever retracts and hits the stop. I have a bad one right now and have to order a caliper today.

My lever is retracting, but not all the way to the stop. If I give it a little tap with a hammer until it hits the stop, the piston retracts slightly and releases pad pressure.

I've been through it before...the e-brake mechanism in the back of the caliper seizes up from salt and corrosion. I took this one apart and cleaned/lubed a couple years ago, but the socket that holds the rear seal in place corrodes away, so the caliper is junk.
The passenger side calipers last a little longer than the driver's side. I can't fault this one, at 14 years old and with almost 400,000 kms it had a good run.

Rembrant said:

I've been through it before...the e-brake mechanism in the back of the caliper seizes up from salt and corrosion. I took this one apart and cleaned/lubed a couple years ago, but the socket that holds the rear seal in place corrodes away, so the caliper is junk.
The passenger side calipers last a little longer than the driver's side. I can't fault this one, at 14 years old and with almost 400,000 kms it had a good run.

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As said here, most likely there is crazy corrosion behind this seal, take the lever off, pull the seal out if you can and clean the crud there, I generally use some motor oil for penetration and put the lever back on and move it as the cable would, and then push some grease in there as best possible, push the seal back into place and it will probably be good for another year or two..

Thanks guys!

The corrosion thing is the problem with my old calipers, this is why i'm replacing them.

The ''new'' (used) one i'm installing are coming from a state where they don't seem to see any road salt, the levers move freely and they goback to their stops without hesitation.

I think I may not have been clear enough. The caliper piston that does eventually pop out from the caliper housing act as the following: When the lever is pulled, the piston will come out about 1.5mm, and retract a bit when released to about 1mm from starting position. Resulting in a travel of about 1mm left from each stroke.

The other caliper piston moves about 1mm when the lever is pulled but when the lever is released, it will come back 1mm to it'S original position.

I think I might just install them on the car and see what happens but that concern me a bit thinking i will probably install a bad caliper on a side.

I am following this thread. How did the two calipers play out and how should they work?

My parking brake lever now comes up to about 45 degrees and still does not hold the car. This happened over about two weeks of light driving. When the wheels are off the ground I found the drivers side engaged when the brake was set but although the lever on the passenger side caliper moved its full range of travel that side's wheel still spun freely. I am suspecting that the passenger caliper is not self adjusting. Tomorrow I will check to see if the piston turns and moves. Does this behavior make any sense?

My answer is: Surprised? (I just couldn't resist! [response after seeing the thread title])

andyboy, each caliper is it's own unit. They can independently fail. Been doing any brake work?

andyboy said:

I am following this thread. How did the two calipers play out and how should they work?

My parking brake lever now comes up to about 45 degrees and still does not hold the car. This happened over about two weeks of light driving. When the wheels are off the ground I found the drivers side engaged when the brake was set but although the lever on the passenger side caliper moved its full range of travel that side's wheel still spun freely. I am suspecting that the passenger caliper is not self adjusting. Tomorrow I will check to see if the piston turns and moves. Does this behavior make any sense?

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Check to make sure the slider pins are not seized, and that the brake pads are not stuck in the carrier.

I have had repeated caliper slide issues in the past. The previous owner may have greased the shafts at some point but did not replace the boots, so I had one side stuck and my inside pad was worn off at a serious angle. P-blaster and a small impact got the rusted pin out and with sandpaper, grease and a new boot all seems to be well so far.

With the driver's side caliper in the correct place and the passenger's side turned all the way out, the e-brake handle acted oddly for the first 5 or 6 pulls; I will guess it was due to the e-brake needing to "set" the caliper on the passenger side.

I removed the cable from the parking brake lever on both calipers, doused them both with P-blaster until they moved freely by hand. I decided the parking brake cables must be the problem. While replacing the cables and inspecting them I decided they were not the problem but replaced them anyway.

I put a parking brake arm spring on each caliper and I am betting that will fix the problem. I think the arm not returning to rest was messing with the self adjusting. It takes about 2 weeks for this problem to reoccur so then I'll see.

A big unrelated issue was that the two new brake cables were 1.5" difference in length from each other. Of course I didn't compare them before installing them so I wasted a good 2 hours of head scratching and fiddling before pulling them out and comparing them. Grrr.

Springs did not fix problem. After some light driving one caliper started locking up and the other one would not retract even with the added spring. That's enough nonsense. Replaced both rear calipers.

I can't seem to catch a break. Replaced the rear calipers with rebuilds from Autozone and both dragged but especially the driver's side. I had worked the emergency brake lever on one, before installing, since that was my interest.

I thought maybe that was bad luck inducing so after driving a few days and wheels getting real hot, I re-pushed the piston back in on both calipers. That helped quite a bit but both wheels still warm up with local driving and very little brake usage and the driver's side actually gets hot after highway driving.

I did not adjust the parking break cable(s) as it says in the manual. I just left the cables a little slack so that the levers on the calipers rest against the stops. With the rear wheels in the air the drivers side has noticeably more drag that the passenger side, on a hand spin the drivers side will spin 1.5 revolutions to 2.5 on the passenger side.

Any ideas? I had never checked wheel temps or hand spinning on my car before. Is this common?

From what I have read here and other places you have created a new problem;

andyboy said:

Replaced the rear calipers with rebuilds from Autozone

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I have to agree on the rear calipers from auto parts stores. It's really luck of the draw if you get good ones or not.


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