Diagnosing a Sticky Caliper

[The Critic]

How?

Mom woke me up early this morning to alert me that there's a burning brake smell from the 96 SL2 (106k miles).

Took it for a test drive, no audible pulling, pedal pulsation, or brake noise. Parked it on the driveway, put it Neutral, released the brake, and the car rolled back normally.

Jacked up the car, spun all four tires. They all moved, though the LF and LR ones didn't seem to move as easily as the others.

How can I tell if I have a sticky caliper? I did lube the slide pins about three months ago with permatex synthetic caliper grease and bled/flushed the system with fresh fluid.

Thanks.

 

[benjamming]

First, are you sure it's a brake smell?

 

[The Critic]

I can't smell it. Mom says she does. But then again, I do have a slight cold today...

 

[surfstar]

Tell her to release the parking brake before driving.

take it for a good drive and see which one heats up the most?

 

[Merkava_4]

Usually the car will pull hard to one side real hard, like as if it was badly out of alignment; but that's more of a symptom of a frozen calliper, not so much one that just sticks once in awhile.

With the car up on jacks and the wheels removed, you should be able to rotate the rotor fairly easily by just grabbing a lug and turning it by hand; a slight drag is normal, but if it takes a lot of effort, your calliper is sticking.

Sometimes an old collapsed calliper hose that is restricted can cause the fluid to get trapped; preventing the calliper piston from releasing fully.

Two things that can cause a calliper to stick:

1. The calliper slides pins needing grease.
2. The calliper piston not moving freely inside its bore.

 

[MaximaGuy]

Quote:

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With the car up on jacks and the wheels removed, you should be able to rotate the rotor fairly easily by just grabbing a lug and turning it by hand; a slight drag is normal, but if it takes a lot of effort, your calliper is sticking.

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Should it be rephrased like...


With the car up on jacks and the wheels removed and tranny in neutral, you should be able to rotate the rotor fairly easily by just grabbing a lug and turning it by hand; a slight drag is normal, but if it takes a lot of effort, your calliper is sticking.


In Park it is quite hard to rotate the tires, the tranny will stop the rotation in no time.

 

[chefwong]

Hi Merkava_4,

Just short of physically lifting the car and checking how the wheels spin, are they any obvious telltale ideas. In my case....I recently had a frozen caliper that went all the way into the rotor relatively fast.

I was having slight pulsations when braking, which I ignored due to the fact that I was up for a brake job and dismissed it as a warped rotor. Literally, it just got so bad that the anti-rattle clip was gouging the rotor. Granted....I knew the brakes pads needed changing, but the last time I looked, it did have 1/4 life in them. The car did not drag or pull hard to any one side however at all. Would the behavior be different bearing it was a AWD vehicle ?

 

[Merkava_4]

Quote:

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I recently had a frozen caliper that went all the way into the rotor relatively fast.

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That's exactly what happens when a calliper freezes; just the way you described it. As far as I know (and I don't consider myself an expert, but just a weekend mechanic) there's no way to know ahead of time when a calliper is about to freeze up until it's too late and the rotor is chewed up. On a more positive note - it's extremely rare for more than one calliper to freeze up at one given time.

Quote:

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I was having slight pulsations when braking, which I ignored due to the fact that I was up for a brake job and dismissed it as a warped rotor.

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I would've thought the same way you did; I would've just thought the rotors needed turning.

 

[alanu]

If your concerned that the piston is siezing remove the caliper.

google this tool

Lisle 25750 Dual Piston Brake Caliper Compressor

Lisle also sells a single piston caliper compressor. These tools are the cats ---- for leverage in compressing a piston.

OR use whatever method you choose in compressing the caliper.

IF you have difficulty compressing the piston crack the nipple on the caliper. If its still difficult to compress the calipe YOUR CALIPERS ARE SIEZING. If the nipple made the piston compress easily its likely that your brake hoses are acting as a check valve and not allowing fluid to go back to the resevoir.

Depending on how the master cylinder is plumbed you may have a master cylinder issue. Not very common in this case.

 

[another Todd]

If your caliper is sticking your rotor should be discolored from heat. If the piston is sticking both pads will wear evenly but faster than the others. If the slide is sticking (assuming single sided piston or pistons) than the outside pad will be worn more than the inside pad.

 

[Merkava_4]

another Todd, that's some good info; thank you sir.