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> Brake Pad Dragging on Front Rotor, Speader Spring Installed Wrong?
VWTortuga336
post Sep 13 2015, 08:24 PM
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Just installed freshly rebuilt calipers with new pads and hardware on my '74. Now the pad closest to the inside of the car seems to be rubbing on the rotor. I was thinking maybe I had the spreader spring installed incorrectly, but I can't even push the pad back any further by hand either.

Any thoughts on what would cause this?

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Cupomeat
post Sep 13 2015, 09:12 PM
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I doubt it is the spreader spring.
Remove the spring and see if you can move the inner piston.

I had this recently and had to rebuild them. Since you say yours are rebuilt, perhaps an error was made?

Good luck
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bandjoey
post Sep 13 2015, 10:29 PM
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Isn't there a metal plate that sits on the piston as a part of the rebuild kit on front calipers. Liike an automatic venting clearance piece. Do you have that installed ?
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bandjoey
post Sep 13 2015, 10:35 PM
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Picture from PMB. Thank you. Your 914 brake expert. Eric is the rebuild God of brakes Do you have these parts installed?


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stugray
post Sep 14 2015, 07:11 AM
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Push the piston all the way in using a C-Clamp (make sure the reservoir does not overflow).

Then try again.
Those are late calipers so should still have the "knock back pins".
They are probably resisting too much (only because you said they were just rebuilt)
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Dave_Darling
post Sep 14 2015, 08:59 AM
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Are those the right spreaders? They don't look that much like mine...

--DD
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stugray
post Sep 14 2015, 09:05 AM
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I don't believe the "spreaders" actually do anything to help the pistons push out.
The knockback is achieved by the natural runout in the rotor as it flexes.
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mgp4591
post Sep 14 2015, 09:17 AM
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QUOTE(stugray @ Sep 14 2015, 09:05 AM) *

I don't believe the "spreaders" actually do anything to help the pistons push out.
The knockback is achieved by the natural runout in the rotor as it flexes.

That and the square cut seal between the caliper body and the piston. The seal holds back the fluid but it can't overcome the fluid pressure when the pedal is depressed- it only flexes slightly when the brakes are actuated then after the pressure is release, the seal pulls back on the piston until it the flat part is on the piston surface. Gives it a couple of thousandths for the pad to move away from the rotor surface. If the pad isn't dragging on the rotor face, drive it a few miles (20 or so), then check the clearance again. You'll know if the piston is hanging up or not. Good luck!
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VWTortuga336
post Sep 14 2015, 01:27 PM
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I tried pushing the piston back into the caliper. It has some movement, but won't stay in. I just springs back to it's original position. I should also add that when I looked into this issue more, I noticed it was all 4 pads (both on each caliper) that are rubbing. None of them really put any significant amount of drag on the rotor, but you can hear it.

Is this normal for newly rebuilt brakes? As I mentioned, these are freshly rebuilt calipers with new pads and hardware.


I am also still concerned that I did something wrong with the spreader springs. Something just doesn't look right (IMG:style_emoticons/default/confused24.gif)
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r_towle
post Sep 14 2015, 01:36 PM
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Bleed the brakes again, if the piston won't stay in you may have air in the system
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VWTortuga336
post Sep 14 2015, 02:17 PM
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QUOTE(r_towle @ Sep 14 2015, 02:36 PM) *

Bleed the brakes again, if the piston won't stay in you may have air in the system


I probably should have mentioned this to begin with (IMG:style_emoticons/default/hide.gif)

I don't have all the brakes put back on the car or fluid in the system yet. I'm in the process of going through and replacing the MC, soft lines, pads, etc...
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stugray
post Sep 14 2015, 02:32 PM
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QUOTE(VWTortuga336 @ Sep 14 2015, 02:17 PM) *

QUOTE(r_towle @ Sep 14 2015, 02:36 PM) *

Bleed the brakes again, if the piston won't stay in you may have air in the system


I probably should have mentioned this to begin with (IMG:style_emoticons/default/hide.gif)

I don't have all the brakes put back on the car or fluid in the system yet. I'm in the process of going through and replacing the MC, soft lines, pads, etc...


Then if you are pressing the piston in and it is coming back out (more than 1/16") then the system is sealed and the air pressure is pushing it back out.

Nothing to worry about - unless the system is supposed to be open and the air is getting trapped when it should not be.
Open the bleeder and do the experiment again.
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VWTortuga336
post Sep 14 2015, 03:57 PM
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I removed the bleed nipples, no change. Pistons are still springy.
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porschetub
post Sep 14 2015, 04:49 PM
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QUOTE(VWTortuga336 @ Sep 14 2015, 02:24 PM) *

Just installed freshly rebuilt calipers with new pads and hardware on my '74. Now the pad closest to the inside of the car seems to be rubbing on the rotor. I was thinking maybe I had the spreader spring installed incorrectly, but I can't even push the pad back any further by hand either.

Any thoughts on what would cause this?

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I can see the pins aren't fully "home"but that won't cause it,are you brake hoses good or are they new ?.
Old brake lines can swell inside and cause this problem,they can appear fine on the outside .
I have different brakes but they dragged on the pads ,bleed all 4 corners several times and the problem went away, try repeat bleeding.
The only other thing could be the piston seals ?,are they the correct size if not the pistons don't retract after system pressure is released, remembering they only move a very small distance, good luck.
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r_towle
post Sep 14 2015, 06:28 PM
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Finish the job, then troubleshoot it.

With no fluid, the rubber seals have friction.
It will stop when you are done.
Replace all the soft rubber lines, that may be another issue, but the dry calipers will behave like that with no lube...
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