Diagnosing brakes that drag

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Aug 11, 2006
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362
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Bedford, MA
I recently replaced rotors, pads, calipers, and all the soft brake lines on my 95 80 series after a front axle rebuild. Since the rebuild, I've noticed a slight dragging on the front brakes. When I back up, I have a slight squeal as well. After a short drive, I can barely touch the front rotor due to heat build up. In another thread, I read that the problem with dragging might be brake lines, calipers, MC, and booster. My brakes work fine, I don't see any leaking at the MC. How would I tell if the MC or booster is bad?
 
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Joined
Jan 16, 2013
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Atlanta, GA
I had a similar problem when I replaced all the brake axle components. Rotors, pads, calipers, lines on both front and rear axles. My truck wouldn't move forward on its own in drive they were so tight. I slowly bedded the brakes over multiple short drives. I didn't experience any overheating of the rotors, but would be careful with that since it could warp some brand new rotors. Soon everything wore in to the point it functions normally. I don't know about the MC or booster causing any issues when replacing all the axle brake components though. Take it just as my experience with changing out all the brake components, the brakes are significantly better than they were before with the 20 year old parts.
 
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Thanks. I've had them on for months, so I definitely think they've had time to seat at this point.
 
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Jul 20, 2004
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Chandler, AZ
It's normal for disk brakes to make slight contact. Define "hot" they operate at ~150F without use, much hotter when used, so not comfortable to touch. A hydraulic problem will usually greatly restrict coasting, take a lot of power to get going, cause big heat, like smoking, etc. The definitive test, drive till it's bound, then crack open each bleeder, the one(s) that shoot fluid are the problem.
 
Joined
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Thanks. I need to get a gauge, but hot meaning I can't keep my finger on them. No smoking. I'll try the bleeder technique. This is helpful, thank you.
 
Joined
Sep 15, 2016
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Chattanooga, TN
If the parts listed are new/good then you've eliminated many of the brake drag causes that I've experienced over the years.

Did you change the master cylinder or booster/etc.? If so are you confident that you adjusted the rod end that pushes into the master cylinder correctly? If that rod is too long it will prevent the master cylinder from returning completely and from fully releasing pressure in the lines. An easy way to test this is to loosen the 4 12mm bolts that hold the MC onto the booster until the MC slides out and away from the booster. This is easy to check and makes an obvious difference if the brake sticking is really noticeable but harder if it's slight.
I set this rod on my 80 last Winter and apparently set it too tightly because on my first warm weather/hot highway drive this year my brake pedal started to feel much harder and I started to see brake drag. A slight shortening of the rod and the brake drag was gone again.

The pins that the pads slide on also need to be clean/lightly lubed so that the pads don't stick on the those pins. This is possibly an issue in your case if you reused those pins from your old calipers and they are crusty.

Another common cause that is probably not relevant for you can be degraded/internally collapsed brake hoses. This usually impacts just a single wheel and you can check this by releasing the bleeder screw on the sticking wheel or loosening the brake hose to release the pressure.

Rusty/dirty caliper pistons can also stick and not return properly which shouldn't be happening with new calipers but I guess is possible if they weren't rebuilt/treated properly.

Good luck sorting this out!
 
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Jul 21, 2015
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Bend, OR
How old are the brake hoses? In the past I had old brake hoses (not on the cruiser) that failed internally and wouldn't let the fluid return back from the caliper very well after letting off the brakes. This caused the brake on that wheel to drag significantly and the wheel was hot to the touch.

During the troubleshooting phase I replaced the caliper, etc... before figuring out it was a bad hose.

On the other hand if this was not an issue before the rebuild I'd check your wheel bearing preload. If loose the brakes will drag and make noises.
 
Joined
Nov 9, 2012
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Olathe, KS, USA
Have you done a proper bed-in of the brakes?

45 MPH to 5 MPH with hard braking, do this 3 time in rapid succession. Stomp on brakes as hard as you can without locking. Ylu SHOULD see smoke after you are done.

After step one, then drive 3-4 miles for brake temps to normalize.
then do 45-5 three times, applying the brakes lightly and driving about 1/2 mile between each.

Do not lock the wheels and do not stop until you have driven some distance after the last stop or you may overheat the pads in one area.
 
Joined
Aug 11, 2006
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Bedford, MA
Great feedback. Thank you. My officemate mentioned the greasing of the pins as well. I suspect this might be part of the problem as everything is new. I wouldn't suspect the MC adjustment rod is out of tolerance as I didn't change the booster or MC. Either way, I'll check that as well. They are not grabbing to the point of smoking, but I do feel that they are not fully releasing, so I'll check the bleeder valve after a short drive. I've probably put 500 mi on since changing everything. I did not go through a specific bed-in process like BILT4ME mentioned, which might be part of the problem. I do have all new hoses, calipers, pads, rotors, etc. Thanks for this. I'll look into this as I have a bit of time. Thank you.
 

Squash

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Dec 8, 2006
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Sudbury, Ont. CA
Biggest issue is corroded caliper pistons.
With old pads they work because they're into shiny metal.
You replace the pads and now your caliper pistons ride in crud.
Clean your pistons or use new calipers.
 
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