Fixing a dragging brake?

[giro]

What causes a brake to drag, and how do you fix it?

This tank my gas mileage has sucked. That could be from a lot of things (we've done mostly short trips, still has winter blend gas, and have used 4wd in the snow quite a bit), but there's also a smell like brakes. I think it's from the driver's side, likely from the rear but it could be either.

I've replaced the front brakes a couple times over the years, though I'm not familiar with the rear drums. They haven't been replaced in the 65k that I've driven it, though the previous owner gave me a pair of unopened ones in his "toyota parts" kit.

What causes a brake to drag, and how do you fix it? I have a little spray on the underside of the truck in the middle, I think from a brake line. But I don't think there is anything new there....I think those stains date back at least 7 years and possibly from before I owned it....and the brake fluid in the reservoir doesn't seem to go down. Basically I don't think there is a leak to worry about, and just crawled under the whole length of the truck a week ago when painting some things.

Any suggestions on what to look for or what to do? I'm guessing something is just sticking and a few hits with a rubber mallet could fix it and spraying around a little lube on non-braking parts, but sometimes does one need to bleed the brakes or anything like that?

 

[nevada]

get each end jacked up and verify a brake is dragging first.

the bell cranks are well known for seizing up on these. that would be the first thing I checked.

make sure the arm is all way in against the stop. maybe even have a helper pull, and release the parking brake, while you watch the cables/levers. make sure they are fully returning.

 

[giro]

I had 20 minutes before school pickup, so got under the truck and took a look. I think the former leak I thought I saw was just grease from the U joint (or whatever it's name is), and one of those lines is for putting it in 4wd. The parking brake sounded fine, pulling on the lever the cable connects to and releasing it.

10 minutes left, so blocked the front wheels and jacked up the back. Spun the wheels....I hadn't realized that when one wheel went one direction, the opposite would go the opposite (The truck was in gear, if it matters). But sure enough, there was a noise on the driver's side rear wheel. When spinning in the drive direction, this noise which sounded like some resistance was when the valve stem was between about the 5 o'clock and 3 o'clock position.

It will likely be visible unless it's something like a bearing. I'll lift it up again now, take the wheel off, and take a look.

 

[wallytoo]

rust is a significant "cause" of brake drag. for the front calipers, they seize on the pins. for the rear drums, there are a bunch of places that rust can affect.

the parking bellcrank, as noted above, is one place. however, when you jacked up the back end, and spun the wheels, it seems from your post that it wasn't particularly difficult to rotate them. if they more or less easily turn, brake drag isn't likely, although you should test it out by jacking the rear after driving it for several miles and see if that makes turning the wheels more difficult.

bad/clogged wheel cylinders can also cause drag. i would guess that broken brake hardware (mounting pins, springs, adjusters, etc) can also contribute to brake drag.

 

[giro]

Thanks WallyToo. I put it up again today, took the wheel off, and slowly got the drum off. Nothing obvious, though a bit more wear on the bottom of the front brake lining, and a little bit more on the bottom rear brake lining. Basically 5mm and 6mm vs 6.5 mm on the top of both the front and back linings. All huge compared to the 1mm minimum listed in the FSM. It looks like the upper part is for the parking brake while the lower part is for the normal brakes, so that makes sense that there's be more wear on the bottom edges.

With the drum off nothing dragged. I cleaned the drum and pads a little, and then put the drum back on. If I pressed hard on the drum, it didn't hit anything. If instead I barely held it on, it did hit something like it did before. So I pushed it on hard, put on the wheel, made sure to tighten down the lugs in a good pattern, and it's not scraping at all now.

I decided to lift up the front. This 4runner has the ADD/automatic locking hubs. Spinning the front wheels is much harder, and has a decent amount of drag. Basically giving it a hard half spin let's it go another quarter turn. Both sides behave the same, and neither affects the other. While the half-axle spins with the wheel, it doesn't look like the drive shaft moves, so it looks like the differential is disengaged as it should be.

Is this resistance (doesn't seem to be brake drag) expected? It's been a while since I did the front brakes so I can't remember if this is how it was. But in the FSM on SA-19 it shows using a spring tension gauge to check the preload. It looks like that's what I'm seeing here.....though I'm guessing at that.

The vacuum lines on the ADD seemed a little floppy...I'm still worried that other things might have got cut when my fan exploded a few months ago. But since the electric wires from it are separate, and I've seen the 4wd light go on and off when shifting into and out of 4wd, I'm guessing that things are working fine.

Once I air up the tires (hadn't checked in a long time, and all were low to differing degrees) I'll have to check for any odors after driving. Maybe this little dragging was all there was. I'm betting against that, but we'll see.