Disc brake iissues
#1
Huh   Here I go again, after getting the "won't go" problem resolved, ran into another.  I also converted the rear brakes to disc and having issues with them.  Brakes are real soft, have to pump them up 3-4 times to get them to work.  Had it up to 5 or six but after adjusting the calipers with spacers for alignment, it got a little better, but there is too much space between the rotor and pads.  We also adjusted the piston out some which helped but still have to pump up them up.  Not real sure what to do.  We did power bleed the brakes also.  Have a new master cylinder with a  proportioning unit on it.
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#2
I've never tinkered with aftermarket rear disk brakes.  Do you have the correct master cylinder for rear disk and front disk brakes?  Disk brake calipers usually require more fluid volume flow than the wheel cylinder on drum brakes.  It's odd that the pistons pull back so far after releasing the breaks.


On stock calipers there is a square cut O-ring that seals the caliper piston to the caliper.  During brake application, as the piston moves a little, the square cut O-ring deforms slightly, then when the brakes are released the deformed square cut O-ring returns to its normal shape and pulls the piston back.  As the pads wear, occasionally the piston will need to move further than the square cut O-ring can deform and the piston will slide past it a little and basically self adjust.
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#3
I agree with 69 Mach1. You shouldn't have that much distance between the pads and rotor. And once they moved out to the disc's they should stay there, and only pull back enough to loosen their grip on the rotor. approximately .030 or thirty thousandths of an inch. Think like 2 match book covers. so if they are pulling back an 1/8th inch or more? That's not a good thing. If all else works, then you might make a phone call, or two, and see if all the parts are correct for the rear kit that was installed. Hope it helps.

JTS
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#4
(08-19-2019, 03:39 AM)1969_Mach1 Wrote: I've never tinkered with aftermarket rear disk brakes.  Do you have the correct master cylinder for rear disk and front disk brakes?  Disk brake calipers usually require more fluid volume flow than the wheel cylinder on drum brakes.  It's odd that the pistons pull back so far after releasing the breaks.


On stock calipers there is a square cut O-ring that seals the caliper piston to the caliper.  During brake application, as the piston moves a little, the square cut O-ring deforms slightly, then when the brakes are released the deformed square cut O-ring returns to its normal shape and pulls the piston back.  As the pads wear, occasionally the piston will need to move further than the square cut O-ring can deform and the piston will slide past it a little and basically self adjust.
I drive a truck for a living and when I get home hopefully on Friday, will do some more checking and hopefully resolve the problem.  There was a new master cylinder and proportioning valve put on it , so seems kind of strange to have this problem.  Thanks for the info and will let you know!!!
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#5
(08-19-2019, 06:49 AM)JTS71 Mach1 Wrote: I agree with 69 Mach1. You shouldn't have that much distance between the pads and rotor. And once they moved out to the disc's they should stay there, and only pull back enough to loosen their grip on the rotor. approximately .030 or thirty thousandths of an inch. Think like 2 match book covers. so if they are pulling back an 1/8th inch or more? That's not a good thing. If all else works, then you might make a phone call, or two, and see if all the parts are correct for the rear kit that was installed. Hope it helps.

JTS

Thanks JTS for the info, we are going to get back at it this weekend and there will be some phone calls made before then.  I am wondering as you are if I have the wrong "stuff".  Will also let you know what we find out.....thanks again!!!!!!
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#6
It crossed my mind that the other thing that causes a caliper piston to retract too far is a warped rotor.  In your case they would have to be unusually severely warped.  But maybe something else is causing them to not run true.
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#7
I want to thank you all for the info.  I did get the problem resolved.....I hope.  A friend found a You Tube video to see if it might help and seems it did.  In it, it showed and with the audio, disconnect the caliper from the mounting bracket, put it on the rotor, then remove the e brake bracket from the caliper and also the cable, then turn the nut under the bracket in until there is no play.  Well as I said, so far so good.  I even drove it most of last weekend....lol  Thanks again !!!!!
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#8
Cool Glad to hear you fixed it. There's always answer, sometimes it's easier then others, but there is always an answer. Good Luck with it.

JTS
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