Rear brake maintenance gone bad

[Espen]

Well I figured it was time to get some new rear brakes.

The old ones looked like this:



So i bought new disc`s, pads, and sliders.

New sliders..

The old ones were like total crap, the pads were full of cracks. And fell apart as soon as i got the pads out of the calipter.


Looks better huh?

[Espen]

But wait.. After a 5km test drive it smells like hot brakes..

Those were damn hot, thats for sure!

They must be hanging on... How can this happen??? Sliders are new and well greased. It also looks like the pads only touched the disc at the very outside of the disc.

[joshua43214]

I can't really tell much from the picture of the new rotor, but the picture of the old rotors show a definate problem.

Unless the car has been sitting for a very long time, the rear brakes apear to not be aplying. Brake hoses can be a common cause of this. Try starting the engine and very firmly aply the brakes. Shut off the engine and release the brake and see if you can freely turn the wheel. You should be able to rotate the rear wheels back and forth with no resistance taking up the differential slop each way. crack open the bleeder and see if the wheel suddenly frees up, if so, replace the lines.

If you assembled the slides into the mount before the caliper, the pads bay not be sitting properly on the mount, causing drag as well.

It is not unusual for the pad to only make good contact with the outer edge of the rotor until they are worn in. How hard did you get on the brakes on the test drive? many folks try to "burn in" the brakes too aggressively and smoke the brakes test driving them. The pads should be well seated before any attempt to burnish them in, 5km is just enough distance to seat them, not enough for using them hard.

[Espen]

The test drive was maybe a bit longer, i applied brakes very hard at once, i was told this was nessecary to seat the pads. I use the car to work today. (6km) Didnt get as hot as yesterday, but the left rearwheel was a lot hotter than the right one, wich was not hot at all.

the old rotors shows that only a small stripe of the pads are applying. the car was sitting the whole winter before i bought it.

The picture of the sliders is "lying" I did it like that first, later on when i tried to fit the new pads i realized that i had to first fit the "claw" on the back of my hub, then place the pads into the caliper, then connect the caliper and the "claw" together with the sliders.

I dint get your point when it comes to the conclusion that the lines must be changed. I start my engine and apply the brakes. stop engine, and try to push the car forth and back, i can feel the brakes are hanging on. Is this because of bad brake lines? I though it could be because the piston was not going all the way back.

You mean that it still is pressure in the system causing pressure on the pads against the discs? Im not so familiar with brake systems, how can bad lines cause the pressure not to go back when the brakepedal are released?

[genphreak]

Is it my imagination or is the right one the one that was really bad in the first pics? Is it possible that the caliper could be warped causing the pad to engage on the inside of the rotor (even when the brake pedal is not being applied) and not engage at all on the outside, causing that heat zone/heavy wear effect? Man I don't know how you could have survived on those pads the way the first lot looked.... ouch! Class pics btw

[joshua43214]

Sliding calipers always aply more pressure to the outer edge, that is why many people prefer fixed calipers since they aply more even pressure to the pad.

In practice, sliding calipers work fine for anything except for hard raceing since once the pad is worn in, it will just continue to wear at a slight angle. If the pad makes contact onthe inner edge of the rotor before the outer as shown in the old pic, it indicates a binding or dragging problem. Many shops would take one look at those rears and just quote calipers and hoses right off the top.

[Omega]

It looks like one of your calipers is not working correctly. The wear patterns on the old discs are not the same.

I would guess that looking at the photo of the old discs the one on the right is the caliper that is causing an issue. The disc looks heavily scored. I would also question the wear pattern as it looks like the groove is quite deep so this has happened over a long period of time.

If you are sure that the caliper slides and that the caliper piston will go in and out with no resistance, then check the flexible rubber brake hoses as Joshua recommends. These can sometimes collapse internally with no visible external damage.

[Espen]

The first pic is mirrored, you can see the exhaust part, the exhaust is on the left side of the car, it was mirrored as i took an "before" pic on the left side, and a "after" pic on the right side, easier to compare pics when they are of the "same side".

the calipers slide ok, the sliders are changed, the old sliders were not that bad though. It could be a binding piston, the old pads were very thin, so the piston have not been completely compressed for a long time. It may have caused rust and such. The brake fluid doesnt look good either, I think ill wait a couple of days, keeping an eye on the rear breaks and see if the problem still is there, if it dissapears, OK. If not, ill try to change my hoses and fluid. Still bad, then Im gonna pop out the pistons and check the inside of the caliper.

[genphreak]

Sliding calipers always aply more pressure to the outer edge, that is why many people prefer fixed calipers since they aply more even pressure to the pad.

In practice, sliding calipers work fine for anything except for hard raceing since once the pad is worn in, it will just continue to wear at a slight angle. If the pad makes contact onthe inner edge of the rotor before the outer as shown in the old pic, it indicates a binding or dragging problem. Many shops would take one look at those rears and just quote calipers and hoses right off the top.

Thank you Joshua, it is awesome being able to share knowledge from people like you on this board. Nothing beats the strength of practical experience on these cars, especially facing the likes of troublesome old calipers and stuff. I mean it when I say a big thank you for the contributions you make (and those of so many others with similar kinds of experience) that the more inexperienced but nonetheless lucky members like me get to read, learn and apply on our great and loved German beasties. Nick

[Javier]

fluid go forth but not back.

Javier