Disc brake drag

[metroschultz]

Most new cars have some sort of retraction mechanism;
whether it's the return spring like Daox' Toyotas (all Toyotas for that matter, and most Fords and so on)
or the X square piston seal (which works quite well)
You need to make sure all the parts are moving freely and you are not hearing a bearing noise or other rotational scraping.

[Christ]

A larger master cylinder could compensate for the "double pump" effect.

[MazdaMatt]

Mech, thanks for that info - i didn't know there was a system that pre-loads the brakes after knockback. Sounds genius, but I wouldn't want it on my race car... automation is scary - especially when it is made by dodge!

Come to think of it, my pads have springs, too... they offer about 6-7 pounds of force (estimated, thinking back to my last brake change), which is definately not enough to push the pistons back.

[MazdaMatt]

Originally Posted by Christ

A larger master cylinder could compensate for the "double pump" effect.

although we're off topic.... it isn't quite that easy. I have spent a number of hours discussing this issues with my racing community at large and the solutions are rare and expensive. Your solution results in a different feel every time (not acceptable at 100mph heading towards a wall between two cars) and a heavier pedal. Defiantely a discussion for a different thread... a different forum, for that matter.

[DonR]

Kart calipers are twin pistons (one on either side of the rotor). A kart chassis experiences a lot of flex, which can put a lot of drag on brakes. I also would not want this on a full size race car.

Don

[MechEngVT]

Originally Posted by DonR

Kart calipers are twin pistons (one on either side of the rotor). A kart chassis experiences a lot of flex, which can put a lot of drag on brakes. I also would not want this on a full size race car.

Don

Karting isn't a good comparison to full-size "real" cars. Karts have to have chassis flex as they have no suspension. Having a suspension divorces brake mounts from chassis flex, but you still have to deal with bearing clearances and hub/rotor flex. In a street-driven car that does not see a track or Autocross you won't likely see flex inducing any perceptible knock-back.

[bikin' Ed]

The brake rotors on the front of my Dakota were warped pretty bad. Last Saturday, I replaced the rotors, cleaned and lubed the caliper slides, adjusted the rear brakes.

In my week of driving, my average mpg city went from 20.5 to 21.3--according to the on board computer. (It also makes using the brakes safer and causes less vibration.)

For those of us who try not to use the brakes too much, the dirt and crud accumulation is something to check out periodically.

[DifferentPointofView]

It seems my Jeep's brakes don't touch at all when I let off the pedal. The pads have less than 50% on them though which could explain that, but, nonetheless, coasting is forever on that thing, even in neutral. They come off the discs with such a small gap between the pad and rotor I don't think I could see it without getting eye right up to it.

[Piwoslaw]

Reposting from a different thread:

Originally Posted by Piwoslaw

I've been hearing a squeeking/scraping sound from the front wheels for quite a while, but recently this has gotten very loud. After returning I asked my mechanic brother-in-law to have a looksy and it turned out that the brake pads were sticking to the discs. Lots of grime and rust (from salt, and from sitting outside and not driving for weeks at a time), so he cleaned each pad, filed it down a little and greased it and that made a huge difference! After I drove into his garage we both had to push to barely move the car, now I could roll it by myself. Three of the wheels wouldn't spin more than half a revolution when rotated by hand, now they do 2-3 revolutions. I haven't driven yet, but I expect much longer coasting distances. I'm sure this has been steadily chewing away at my milage.

A few days later:

Originally Posted by Piwoslaw

Those dragging brakes were really causing havoc! Yesterday and today I did a total of over 130km of city driving, and the car's computer showed 4.3 l/100km on both trips. That's the first time in 2 months I've seen less than 4.8 l/100km, and the ride is noticeably quieter So brake dragging reduced my FE by 10%.

[Vekke]

When I loosed up my brakes car rolled so much better that I had to brake when I come to my home. I glide to stop. It is about 700 meters, first 300 hundred downhill and rest gentle uphill. When brakes were dragging I needed 40 km/h speed at the top of that last hill to be able to get to parking space. When I loosed my brakes I could drop the speed to 30 km/h and still need to brake to stop at my parking space . On the downhill I gain same top speed even starting with lower speed. Due to less friction I have much more speed at the end...