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Disc brake fun

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Thanks all. Snow should be over by tonight, so next test will be a long (50 mile) drive tomorrow.

I've heard of the collapsed hose problem before, but I use the brake when parking the car, so I'd think there's no "relax" period for the caliper to release.

Both the left and right rear wheels have the same very slight "drag"; same in early morning when cold, or immediately after a long drive. There's a suggestion that there should be no drag at all, but if the pads remain lightly touching the rotors even when brakes are released, seems a slight drag would be normal.

Maybe the temp difference left vs. right is just due to the right pads/caliper being slightly out of whack. Please send me more whack.

Weird!
 
A few thoughts from my wee mind...

Sources of heat are friction, or something external applying heat.

Sources of friction: 1. parking brake pads. But you said you removed these to test, and the problem did not go away? One test could be to test e-brake effectiveness right when you drive off vs. a few miles later. If there is significant fade, could point to rubbing pads. Drive up to 20 MPH, and count how long it takes to stop. Having adjusted the parking brakes on my car (same disc / drum setup), all I can say is it is both an imprecise science and a difficult (at best) task. As such, a misaligned parking brake is not surprising. 2. Main disc brake pads. But you say only the drum gets hot, and not the disk itself (having said this, thinking as I type, this could be only b/c the disk has less mass and will cool faster). 3. Bearing. But you say you replaced the bearing? However, if the bearing went "bad" due to misalignment, and not simply b/c it wore out, the misalignment might still exist, and could be causing the heat with a new bearing. I am far from smart enough on this last topic...

Sources of heat: Exhaust leak? Fire? (Hope not!!) Hot tires b/c you drive like Mario? (I am stretching here, I really can't think of any external heat sources near the rear wheels, other than exhaust.)
 
Thanks Mike.

Tomorrow will be "interesting", with the long test drive (if it ever stops snowing/sleeting).

1. parking brake pads. But you said you removed these to test, and the problem did not go away? One test could be to test e-brake effectiveness right when you drive off vs. a few miles later. If there is significant fade, could point to rubbing pads. Drive up to 20 MPH, and count how long it takes to stop.

Parking brake shoes - you can't remove the shoes and drive without the cable flopping around inside the drum. But ... I did back off the adjusters three times more than usual, so there's no way they can be rubbing against that drum. I sure agree with you on the "fuzzy" adjustment of the parking brakes, but as I've fully backed off the shoes, I can't see it could be the parking brake.

2. Main disc brake pads. But you say only the drum gets hot, and not the disk itself (having said this, thinking as I type, this could be only b/c the disk has less mass and will cool faster).

The RR rotor/disk *does* get hot, but not nearly so hot as the parking brake drum.

3. Bearing. But you say you replaced the bearing? However, if the bearing went "bad" due to misalignment, and not simply b/c it wore out, the misalignment might still exist, and could be causing the heat with a new bearing.

That's an interesting idea. Sure hope it's not a hub/bearing alignment problem. Wonder how I'd ever check that out?
I am far from smart enough on this last topic...

Same here!
 
A couple of things.

1. The parking brake pads and the disk brake pads are not the same pads - you have the mechanical e-brake system and the hydraulic braking system, so, trying to stop with just the e-brake tells you nothing about the actual brakes.

2. Having said that, you reminded me about something - this year I had to replace the emergency brake cable on my 2010 Soul - the cable was binding and the rear wheel was locking up - it was literally draggin - but basically not releasing. In Ontario they use more and more liquid slurry to melt the snow/ice on higways instead of rock salt. This slurry gets up into the cable and binds it. He was telling me about an Escalade that he did - took him weeks to figure out because the cable would freeze - the brakes wouldn't release. The guy would drive to the shop - by which time the cable had thawed - problem gone. It was only when they left the truck overnight at the shup and the mechanic drove it the next day.

3. Finally, coming back to the hydraulic brakes - while it seems odd on a newer car, could the brake hose have perished inside? Certainly on our older cars it keeps the calipers from fully releasing.
 
Sorry if I wasn't clear. The parking brake system is a shoe and drum system. There are no pads in the parking brake system.

That frozen/corroded parking brake cable idea is certainly a possibility, but with the parking brake shoes fully retracted, and the parking brake cable loose and untouched, I can't see how the parking brake shoes could be causing the problem. Actually, I wanted to do a test drive with the parking brake shoes completely removed - but that would leave the cable and attachment clip dangling loose inside the rotating rotor/drum, which I felt wasn't safe to do.

You mention that on your car, "the cable was binding and the rear wheel was locking up - it was literally draggin - but basically not releasing"

You mean the parking brake was not releasing? or the service (disc) brake?

Regarding the hydraulic hose, I suppose that's always a possibility on an eight year old car. But the caliper and pads don't get hot - only the rotor and drum. And that's immediately after a 25 mile drive. Park the car, immediately touch the rotor face, parking brake drum, caliper, and pads. Only the rotor and drum are hot. That's why I can't see it's the hydraulic system - the hydraulic system operates the pads, not the parking brake.

A 100 mile test drive planned for today. If I don't report back, look toward Connecticut for a plume of smoke.

TM
 
Parking brake wasn't releasing.

Good luck! (nice knowing you :devilgrin: )
 
There is a square seal surrounding each piston. When you step on the brakes, the piston is extended and the square seal deforms slightly. When the pedal is released, the seal returns to normal and pulls the piston back. Yes the pad is always in contact with the rotor.
 
"Actually, I wanted to do a test drive with the parking brake shoes completely removed - but that would leave the cable and attachment clip dangling loose inside the rotating rotor/drum, which I felt wasn't safe to do."

So you were not able to do a test drive without the shoes installed. I thought that you had. Since this is the case I would say that you have a shoe dragging in your parking brake. I would try adjusting the brake until the shoes make no contact at all on that side and then see how things go.
 
Back from the long drive without disaster.

RR rotor/drum still hotter than the other three wheels.

Parking brake shoes are retracted as much as possible, so not contacting the drum.

Tomorrow I'm pulling the caliper again, and checking if there's any possibility the guide pins are sticking.

Would I cause any problem if I (1) "polished" the guide pins with fine sandpaper, and (2) put on a touch of high-temp grease?

Thanks.
Tom M.
 
NutmegCT said:
Would I cause any problem if I (1) "polished" the guide pins with fine sandpaper, and (2) put on a touch of high-temp grease?
Click to expand...
Tom, the YouTube videos on Altima rear brake pad installation all show those pins being lubed with brake grease. I've done 2009 Infiniti (the same Nissan family...looks like the same brake) brakes and the pads I bought came with a packet of grease for the pads where the ends are held in those clips and for the pins.
 
Thanks Jay. I've used the lube before when replacing pads, but never after just "inspecting" the pins.

This might actually improve the situation. Rain will continue until Thursday, but Thursday we'll see how this goes.

TM
 
Back to how it works. The o-ring in the disk brakes has a square x-section. When the brake fluid pushes the pot forward it doesn't roll the o-ring, rather the o-ring slightly deforms. when you release the brakes the o- ring relaxes and pulls the pad back a very tiny bit.
When the pad wears a bit more the pot moves more than the normal deformation of the Ring and the pot slides forward adjusting the brake.
Yisrael
 
catfood said:
My understanding is there is nothing to retract the pads. Any slight imperfection in the 'staightness' of the discs is sufficient to lift the pads off the disc.
Click to expand...

There us a square seal around the piston. It deforms slightly when the brakes are applies and returns to it's original shape when the brakes are released, retracting the piston a smidge.
 
Tom, I had that same thing happen on one of my trucks and found that the piston and cylinder were corroded enough to not let them fully release the pressure on the pad. A new set of calipers were installed and the problem went away. Of course that was around the 200 K mark! Also this truck went in the fields at times picking up a lot of dirt. PJ

I forgot to say that some of the dirt had fertilizer in it, not good on metal items. :rolleyes2:
 
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