# Brake drag



## bblocher (Jul 30, 2008)

Ok I just answered my own question here so thought I'd share. My wife has an 08 Prius so I figured the brakes on this are the answer I'm looking for! I jacked up a rear tire (front wheel drive) and spun the wheel really good and sure enough it kept spinning for a long time. Basically whatever wheel bearing resistance was there slowed it down over time.

Next I jacked up the front of my project car (rear wheel drive) and gave each front wheel a good spin both returning equal results. The wheels only spun for a couple seconds. Each rotation you could hear the pads rubbing against the discs for just small amount of time but it still stops the wheel very quickly comparitively. I'm guessing this is just disc warpage and I can turn them to fix the problem. 

So if you're looking to squeeze out those extra miles, jack up your car and see what your brakes are doing. It might make a big difference. What do you guys think?


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## ww321q (Mar 28, 2008)

Check the wheel bearing spindle nuts to I usually tighten all the way then back off less then a quarter turn (whatever hits the right slit in the crown retainer . Then grab the top and bottom of the wheel and check for to much play . And also don't over pack your wheel bearings . J.W.


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## Telco (Jun 28, 2008)

Another thing that contributes to brake drag is old hardware. Any time you replace the pads on disk brakes you should also replace the bolts and slides. They come in a kit. Yes, you CAN reuse the old ones, but the used bolts will have been heated and cooled across a great temp differential repeatedly and will eventually deform. It doesn't take much bend in these bolts to start causing the calipers to hang, and it just takes a bit of hang to start inducing drag. 

After you do the brakes and bearings, the front tires should turn for about 15 seconds, and it should spin down in a smooth, quiet manner. If the tire starts making noise and the slowdown speed is not smooth, then there is more to be checked.

Incidentally, it's been my experience that when you turn disks, especially on the newer vehicles, it makes them thin enough that a single panic stop will warp them. Not to mention that nobody seems to know how to properly turn them anymore. Instead of doing a brake job, then repeating a month or two later, I just go to the dealer and pick up a new set of rotors which will then last a couple of years. Unless there is a problem with vibrating brakes or deep grooves in the rotors, I also don't turn the rotors when I put new shoes on. It doesn't take that much life off the shoes to wear into the rotor wear pattern.


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## dimitri (May 16, 2008)

Brian,

I had same exact issue with Miata, done lots of research on the subject. Design of this type of brake caliper does not have any mechanism to push pad away from rotor when you release the pedal, so the pads continue to slightly touch the rotor surface. Other designs of brake systems have springs that push pads away, so the wheel spins freely.

Its not that big of a deal actually, when car is all done it rolls from slightest incline when brake pedal is released.

One thing to watch for is slider pins on the caliper, make sure they are clean and well greased, so caliper can easily slide and not stick.


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## Coley (Jul 26, 2007)

Haven't run into any disc brakes that have return springs on the calipers.

The main idea of slight contact with the rotor is to keep road debris off the pad faces, sand etc.

I also turn my rotors when replacing pads, UNLESS they are very smooth and even surfaced.

Checking master cyl pushrod adjustment, so that the fluid pressure is off when your foot comes of the pedal, is very important also.


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## madderscience (Jun 28, 2008)

Some car disc brakes DO have return springs. some of the early Toyota MR2s did (I figured this out, and tracked down the hardware and installed it) and it did make a noticeable difference for me and another fellow with an EV based on an early MR2.

A couple pictures:
http://www.amphibike.org/index.cgi?page=pages/3_wheels/mr2/efficiency#heading_4

I suppose not all cars will have this, and disc brakes will always drag a little bit, but perhaps with some creativity a similar setup can be installed on your honda.

I bet the prius has drum brakes in the back, those are much easier to set up for zero drag.


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## bblocher (Jul 30, 2008)

madderscience said:


> I bet the prius has drum brakes in the back, those are much easier to set up for zero drag.


Ah damn. I just assumed 4 wheel disc brakes. I'll check it out later this morning and see. That'd be a bad comparison if so


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## TX_Dj (Jul 25, 2008)

Another thing to consider, which madderscience alluded to, is that most cars use a "floating" caliper, that is to say that the caliper has one side that is "fixed" and the other side provides a clamping force that draws the piston and fixed side together.

When you release the brakes, one pad or the other will remain a little in contact with the disc, keeping a little friction in the setup.

I've not seen them except on sport bikes and high-end sports cars, but there are "fixed" calipers with pistons on both sides, which not only provide a more positive braking action, but also when the cylinders retract they tend to pull the pads off the disc. These may or may not be available for your application, but if they are, they are COSTLY... 

For example, I can get a full competition brake setup for the S10, but the whole setup will cost about $3000. 

The best bet is to do what others have suggested here... replace the pins with your pads, and make sure the pins are lubed lightly with anti-seize compound, which will help to ensure the pads get off the disc in a more timely manner. Also make sure your bearings and races are in good condition, and that the bearings are properly packed. Too little packing grease will cause the bearings to heat and expand, increasing drag, and too much packing grease will cause the grease itself to heat and expand, causing more drag as well.

If you have drums in the back, make sure the adjusters are in a good position (not over tight) before you re-assemble, and make sure that the return springs are in good condition and that the brake proportioning valve is working properly. Once re-assembled, you should not hear your drums rubbing the shoes, but may after a few times of backing out of the driveway (most modern drum brakes have automatic adjusters, which will try to click the adjuster each time you press the brakes while going in reverse. If the adjuster has enough slack, it WILL click on more adjustment, but should NOT click on enough to "bind" the brake)...


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## bblocher (Jul 30, 2008)

I checked the prius. Sure enough drums in the back so that wasn't a good comparison. However, my front wheels do seem to rotate well until they hit that small spot that drags. All four are disc on this car. They are the type where one side is stationary and one side presses in.

I retested the fronts which do have the slightest drag but it's really not much and after using the brakes a few times they were exactly the same so that's good. I lifted the rear next and they had a very consistent, yet very minimal drag, but not from the brakes, just the rear diff and the hanging drive line resting on a little support brace.

I think over it all they are fine. I could probably turn or replace the front discs but not sure how much I'd really get out of it. I think I'll wait until I see what my range is before I go spending any money there just yet


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## ISellMiataParts (Sep 24, 2008)

The miata has return springs, they're there only to keep vibration noises from annoying the customer, by why not try upgrading the gauge to a stronger spring?


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