ohio

So when I put on my new aisin hubs, I noticed what I think is my front brake pads not fully retracting. The wheels were really hard to turn by hand, and there was a consistent metallic scraping sound when I did. Couldn't see any space between the rotor and pads either.

I'm assuming the pads can just be pushed back further into the caliper and then the piston seals will readjust themselves for proper retraction... but to be honest I don't know. I've only ever played with mountain bike disc brakes.

How do I fix this and make sure it doesn't happen again? It's killing my gas mileage, and will soon kill my pads and rotors... although it didn't cause overheating and fade even on a 100mi trip.

Hyperlite

Bump......

You know I it's still a mystery to me also. Disk brakes are suppose to rub a little and form a glaze, but mine have always been like you describe....and worse. I have replaced both rotors 4 times last year (2003) and each time the pads stick.
Make sure you don't have silt or sand in your rear drums cause that's how I destroyed a set of rotors. It caused the drums to stop working and it fried my front pads.
You can get the fpads to go into the caliper by:
1. Bleeding the brake lines
2. I use 2 large vise grip clamps on each pad and pushed the pistons in, which forces the fluid in the caliper back into resevoir.

However after pumping the brakes it goes right back to sticking. So I really don't have a clue either.

MTL_4runner

The calipers should retract smoothly in the bores (use some channel locks and if it won't budge, replace it). The pads should ride on the rotors but not apply any (very tiny bit is ok) pressure (so you should never see any light between the pad and the rotor). Semimetalics do also tend to make a scraping sound when the wheel spins. As for losing gas mileage, I would be curious if you actually see any difference or if you are just assuming since the pads apear to be rubbing. On the highway the rotor wobbles a tiny bit which tends to push the calipers back into the bores and you never really lose any mileage from it doing that (also why when you step on the brakes on the highway at high speed, they are very soft as first).

ohio

Well, I would expect some very light rubbing, but in this case with the wheels off I could only turn the hub/rotor by using some body weight on the wheel-mounting studs (yes, even with the ADD hubs off so it's ONLY the wheel bearings or brakes that could be rubbing). That seems like more scraping then there should be. On bikes and motorcycles, you might hear some scraping, but the wheel will still spin from it's own momentum. There was no way they'd do that on my truck...

My experience with those brakes is that the square seal (piston seal) dictates how much retraction there is so it's non-adjustable... it just seems strange to have THIS much rub.

toy283

Not gonna happen. If you look at the brake system, there is nothing to retract the pads except the movement of the master cylinder back to its normal position. Before it gets to that position it vents to the reservoir and any movement stops. In addtion to this, rotor runout may push the pads back a little as well. There is a reason for this. The brakes need to be self-adjusting. i.e., as the pads wear they need to readjust themselves for optimal operation. If they retracted fully into the caliper there would be a long soft peddle every time yopu touched the brakes. As the brakes wear, this would increase to the point where you'd to push the peddle several times to get any operation at all. As such, the pads are gonna constantly rub on the rotors. The eefects on mpg, power, etc are negligible and far outweighed by the ability to stop when you need to.

ohio

I'm not saying they should FULLY retract... I understand how self-adjusting open systems work. I'm just wondering if the degree of friction I have is normal.

MAIS0N

The degree of friction you describe is not normal. When the front end is up on jack stands with the transmission disengaged it should require very little effort to spin the wheel. If you can't do it with one finger, something is sticking.

lcopelan22

It sounds like the pistons in the calipers are frozen. I'd just replace them both and have the rotors turned and see what happens. I think when I replaced mine they were like 20 - 30 dollars each with a core at Advance Auto. But don't quote me on the that cause it's been a little while.

sfrolich

There's something called parallelism... There is supposed to be some small amount of it so the disc is thicker in some areas more than others. The thicker part of the disc will open the calipers and make the thinner parts not rub. I remember this from auto school way back when

TechWrench

The way the calipers are supposed to work is, when the pedal is pressed down, the fluid pressure forces the piston out to press the pad against the rotor. The seal between the piston and wall of the caliper is usually a square cut 'O' ring which will flex as the piston is pushed out. The 'O' ring should have enough tension to pull the piston back slightly when the pedal is released. This allows the pad to stay lightly in contact with the rotor as it freewheels. If you have a single piston caliper, it is often referred to as a 'floating' caliper. This simply means that as the one piston is pressing its pad against the rotor, the body of the caliper is being pushed away from the rotor which pulls the other side and its pad against the opposite side of the rotor. So, in a floating caliper system, if the mechanism that allows the caliper to float gets stuck or frozen, the caliper will not release properly and could keep pressure on one pad against the rotor. Another common cause of dragging pads is a restriction in the brake hoses to the calipers. Many vehicles have a clamp holding the brake hose in place. And they often use a rubber bushing between the clamp and the hose to prevent chaffing. But I have seen where the metal clamp will start to rust on the inside edge, and cause the rubber bushing to eventually press into the brake hose hard enough to cause a restriction. This acts like a one way check valve. It allows fluid to pass when pressing the pedal, but doesn't allow the pressure to drop enough when the pedal is released which causes the pads to rub too hard.

So, all this being said, you should have someone who is knowledgable in brakes check them over. You might just need a good cleaning and lubrication of the moving parts to make it all right. I wouldn't let it go too long, you could wind up having to replace the rotors if they get over heated and warp, or just get worn down.

Good luck........

rosspa75

When I first got my 90' runner the brakes would gradually build pressure as I drove and stopped and drove and stopped, The master cylinder was not fully backing off to release all the pressure. A small amount of pressure would build up and build up until the truck would barely move w/o giving it alot of gas. Overnight the pressure would bleed off and be normal in the morning,

The fix.....if you pull your master cylinder loose and look at the actuator rod coming from the brake booster, there is an adjustment. It looks just like a "cap" nut however look close it adjusts (mine does anyway). It doesn't take much for this rod to be out of adjustment. To fix it I first held the master cylinder back up to the brake booster to listen for the sound of the shaft contacting the inner piston actuator. If I heard it tap together I'd adjust it a little more. I adjusted it until the contact was just out of reach of the rod but by only a fraction of an inch. Dont forget to tighten the adjustment "keeper" nut. It was a 20 minute job.
P