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Here's the situation:

Initially

Changed a wheel/tire, and snapped a hub stud. Had to take off the brake caliper on that hub (driver's side). No problem with that, but then all of a sudden my front end was really jumpy. It was time to change the pads and rotors for my front disk brakes. Also, when I put all my weight and force on the brakes it definitely went to the floor with the pedal. I don't recall this ever happening, though I can't say for sure.

Brake Change

So then I changed both rotors and all pads for my front disk brakes. I noticed that my driver side pads had very little pad left (I changed these about 9 months - 12 months ago) and my passenger side had plenty of pad left. I would say drive side had about 1mm of pad left, and passenger side had 3.5 to 4mm of pad left.

I also noticed something odd. When I was trying to compress the caliper piston on the driver's side caliper, it was extremely difficult. I eventually got it, but it wasn't nearly as easy as the passenger side.

After the Brake Change

When I immediately drove the car afterwards, the front end shake was gone. But I noticed something odd. My driver side wheel has this awful smell, and when I got done driving it (I was hard on the brakes to test out and make sure it was stopping well, and it was) it was lightly smoking at that wheel. I thought it might have been the brake cleaner just burning off.

But then a day later, the smoking and smell continued, but stopped later in the day with about 45 miles down.

Question

What could have been causing this? Does it sound like my driver's side caliper is just getting stuck, causing it to ride the pads and wear them down? Is that why it was smoking/smelling?

Why was the driver's side caliper piston so hard to compress with a C-Clamp? Could the caliper be going bad?

Could air in the line cause the caliper to get stuck and/or go to the floor?

Could this possibly be a master cylinder issue? But I would think if it was a problem at the master cylinder, it would cause an issue for both front brakes. Am I correct in saying that the master cylinder has a connection for the front that shares the same fluid/pressure?

Any ideas are much appreciated.

Vehicle: 1994 Mercury Villager.

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3 Answers 3

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It sounds like the caliper is sticking. If the piston is sticking then you would end up with one side worn down more then the other. Also, a piston should compress with a clamp, if it is that hard then that also points to it sticking. The smoking then could be from the pads being in constant contact with the rotor (if it is in that strong of contact). You probably would also notice the vehicle pulling to the side of the sticking caliper. Air in the line would not cause nor would a bad master cylinder.

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    +1 for sticky caliper. I'd think the smoke is likely due to some oil/grease from the recent maintenance that is now burning off.
    – mac
    Aug 1, 2012 at 16:31
  • Always difficult to elaborate a diagnose w/o seeing the components but I guess your description is accurate enough to assess a front left caliper issue. In most cases the root cause for this sticking effect is the caliper piston seal design itself and/or the grease that is used for it's rollback. In that case I would dismount carefully the caliper and piston, clean it and remount a new seal with the appropriate quantity of grease on the piston lipseal. I would also make sure that the caliper slides properly on its 2 guiding axis (must be also grease inthere+the cap must be sealing properly).
    – hornetbzz
    Dec 12, 2014 at 10:47
  • This should also result in a large difference in temperature between the left and right brakes – enough that you should be careful about getting burned. Also, you should be able to hear the pads dragging on the side with the stuck caliper.
    – dlu
    Jul 30, 2016 at 19:47
  • @Matt, the front pistons should compress with a clamp, but it is common for rear pistons to be the screw type on some vehicles. It may be helpful to mention that in your answer to others or atleast specify that the clamping procedure is specific to this vehicle (which does not have screw type rear calipers)
    – finleyarcher
    Aug 10, 2017 at 22:25
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I do not think that air would cause this behavior. I had the same issue with my 1999 Toyota Tercel (a lot of smoke from the wheel well), and the caliper was seized, I changed calipers, pads and rotors.

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  • Air in the line will prevent the caliper from closing and will allow it to easily be pushed away from the disc. Quite the opposite of the symptoms here. I concur that it's most likely a stuck caliper. It happens. I've replaced 4 calipers across our 3 cars that were stuck beyond a simple rebuild. 2 others were saved by regreasing the slide pins.
    – Brian Knoblauch
    Jul 31, 2012 at 19:09
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A bad Power Brake Booster will also affect the pedal action. As you use your brakes you are allowed to pressure your brakes to stop but they will not retract (open) because you either have a clog in one of the brake lines or you need a new Master Cylinder, Or you may need a New Power Brake Booster. Another tell tale sign of faulty M/C or faulty PBB:-- You may be able to release the Brake tension by loosening the bleeder valve at the brake hydraulic box which is likely to be within 18 inches of your Master Cylinder. Look for a harness of metal tube lines. If you see this harness then look for a bleeder valve somewhere on the hydraulic box body and crack the bleeder valve just a bit. if you remain quiet you should hear the stuck brake pistons dis-engaging with momentary clicks. when you have done this re-tighten the bleeder valve when the noise stops. After you have done this your brakes will be loose again but you will still need to change one of the latter auto parts. You can also choose to rebuild your own caliper but if the piston is really pitted you should consider a new caliper and possibly the rotor. If your rotor was heating up it may have warped and will cause a shaking. new calipers and pads will not stop the shaking. look at it this way, after a new caliper, rotor and pads your only options would be: Your inner & outer Tie Rods, Wheel Balance, or front end alignment.

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  • And how is it that you don't introduce air into the brake lines when opening the bleeder valve you talk about? Are you supposed to do this every time you use the brake? How else are you going to relieve pressure if what you are saying is correct? While a bad booster will affect pedal travel, this answer does not come close to providing useful information which the OP needs to fix their issue.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Nov 29, 2015 at 12:22

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