Break problem (1 Viewer)

[perk]

It sounds like I've got a pad that partially drags on the rotor, but I'm not sure. A little background...I recently (approx. 500 miles ago) replaced front rotors and pads (100 series) while servicing birfields. I had to sand down the pads to fit. They still touched rotor a tiny bit, but I went ahead and ran them. Any slight grinding/rubbing was not noticeable after initial test drive and bedding. Within the last couple weeks I began noticing a light grinding sound from front PS that sounds like a pad is partially rubbing, I say partially because it is not constant, it is intermittent, like whiiisshh...whiiisshh...whiiisshh. There has been slight pulsing or grabbing that has persisted at low-speed braking since install. The slight grinding sound is only noticeable when initially driving at low speed with no pressure on brakes, it seems to go away after a little driving and braking.
I took the tire off tonight to take a look. The pads are touching the rotor, but it doesn't like they are putting any pressure on it. Should there be space between rotor and broken-in pads? The rotor/hub does not turn easily, it takes a bit of muscle (alot more than 6.4-12.6 lbf) Is this ok, or is my preload all F'd up? I neglected to bleed the brakes after the install, although... is it necessary to bleed the brakes if the lines were not removed? Could this be at the heart of my grinding or grabbing problems?
I'm also wondering if my calipers need rebuilding. What are the signs and is it difficult to rebuild calipers?

Thanks for any thoughts on these matters,
Perk

 

[perk]

Anyone out there got any insight into this? A little direction at this point would be very appreciated.

 

[perk]

I retracted calipers with pliers and this created about 1-3 mm of space between pads and rotors except for one area. The top portion of the inside pad on the DS remains in slight contact with rotor. Does this indicate a caliper rebuild is in order? Is there a problem with sanding down the DS inside pad to create some space, IOW, is a little differential wear between the inner and outer pads a bad thing? Should the calipers be fully retracted when the brakes are not being applied?

I also need to amend a previous statement...the pads were putting pressure on the rotor because when I got the calipers retracted, the rotors turn at approximately 15 lbf, is this ok, or do I need to go in and reset my preload.

Startin to wonder if all the tech gurus are tired of giving free advice,
Perk

 

[tarbe]

The pistons do not "retract" when you let off the brake. The pads are going to drag on the rotors ever so slightly. This is normal.

 

[Scamper]

Perk -

Sounds to me like a caliper rebuild is in order. It's not "quite" true that the calipers don't retract, as I recently learned here myself. There is a square rubber gasket on the capliper piston. When the piston slides out as you brake, the gasket deforms, making the square rubber gasket more rhomboid (if you don't remember your geometry, a rhombus is like a square or rectangle which is leaning over). The deformed rhomboid gasket wants to return to a square position, so it does actually apply a small yet significant retracting force on the pads--just enought to eliminate the pressure you are finding.

Caliper rebuild kits are cheap and Dan can set you up with some. It's a one- job that will take you a few hours to do for both side, including the

 

[perk]

Thanks Tarbe, Scamper...
I'm going to include the kit in my next order from Dan. I don't have compressed air, so I guess I'll make arrangements with a shop...what exactly should I ask for?
I wen't ahead and bled the brakes and this seems to have helped with the pulsing while braking at low speeds, still a little, but better.

 

[sixsracing]

You don't need compressed air to do the job. You can have someone depress the pedal ever so slightly and work the pistons out evenly using a block of wood to keep the pistons travelling at the same distance until they get right to the end of the bore. Then just take them out with a pair of needle nose pliers staying close the the very edge of the piston.

 

[Kalawang]

You're driving an 80 with 100 pads and have been doing so for a short while ? If I understand correctly, 100 pads are slightly bigger than 80 pads. If that is the case, pull off your wheels and look at the edge of your rotors and see if they are shiny and bright as against the rest of the rotor. Look at all your rotors. They don't all come to this state at the same time.

I have that problem with my very old 80 because the new 80's sport bigger rotors and bigger pads than my old one. Yet these days I can no longer find any small pads and so have had to use the bigger ones with the above result. When the oversized pads are installed, the outer perimeter of the pads do not actually get used and so are not worn down. After some time the outer perimeter gets a bit of an overhang on the rotor and periodically in movement actually makes contact with the rotor edge causing the shininess and some intermittent noise. If allowed to continue the noise becomes continuous.

The solution is to simply remove the pads and grind off the protruding edge and keep using the pads until you can economically replace them with the correct size. You might have to do this 2 or 3 times before you use up the pads enough to require replacement.

If you have some slight pulsing on your brake pedal, run your fingers along the side of the rotors and see if they have become uneven, i.e., developed some ridges and no longer present a perfectly flat surface to the brake pads. If so, I think the best option is to replace the rotors.

If neither of my solutions are yours, I wish you the best of luck finding yours and hope you will be kind enough to share it with the rest of us.


Kalawang