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dtbaker61 10-03-2012 05:16 PM

tips/tech to eliminate brake drag
 
I'm looking for tips/techniques on eliminating brake drag and how to tell whether its brake drag or bad bearings causing my front wheels to heat up....

My vehicle is not getting as good efficiency as I would hope, and the other day I noticed that my front wheels get quite warm after relatively short drives around town without much braking. Much warmer than rear wheels which are drum brakes.

When I raise wheels off ground and spin, there is audible rubbing on discs and the wheels only make one or two revolutions given a pretty good heave my hand. Rear wheels spin much more freely.

How free CAN disc brake wheels spin? especially FWD that is spinning CVs and tranny guts even when in neutral?

best tips/techniques for reducing drag and getting calipers to move easily and let pads off discs?

Daox 10-03-2012 05:36 PM

First thing you can do is jack the car up and try to wiggle the tire. A bad bearing should allow some play. If you still can't tell, take the brake caliper off and rotate the hub by hand and see if the noise is still there.

Oelmensch 10-03-2012 05:53 PM

Unfortunately, as they do not employ return springs and adjustment hardware like drum brakes, disc brakes will usually have some degree of drag when not engaged. Beyond the extended position of the caliper piston(s), there is nothing to relate the pad distance to the disc, so they always have very minor contact while not in use and applying a product to reduce that drag would essentially also reduce their braking effectiveness and thus safety.

As for the temperature of your front wheels, it is likely a combination of the wheel bearing friction, and hotter air exiting the engine bay passing through the your wheel wells on top of any heat being generated by braking that makes them feel warmer. If your front wheels are out of alignment, that could also contribute to tire temperature, but I wouldn't expect that to be significant at the wheel unless things were really misaligned.

Daox has a good suggestion for checking them in the previous post, I would definitely do that too. You can usually hear/feel them with the car in neutral and all the hardware in place, but not always.

JellyBeanDriver 10-03-2012 06:56 PM

It doesn't take much braking to heat up the rotors. I'm surprised as to how much they retain their heat so unless you know for a fact you didn't use the brakes at all, I wouldn't put much value in the fact they are warmer than you think they should be.

In regards to making them as loose as possible, the caliper seal can only pull back the piston so far. Anything compressible between the piston and the pads can take up some of this pullback distance and result in the pads dragging more than not.

What was a eye opener for me was working on a friend's Metro. His front tires were nearly friction free when turning, but mine were much tighter. Ends up he didn't have brake shims installed, but I did AND I also had CRC brake silence compound. I ditched the shims, cleaned off the CRC goo, and now mine too are nearly friction free.

Frank Lee 10-03-2012 07:56 PM

Quote:

Originally Posted by Oelmensch (Post 331842)
Unfortunately, as they do not employ return springs and adjustment hardware like drum brakes, disc brakes will usually have some degree of drag when not engaged. Beyond the extended position of the caliper piston(s), there is nothing to relate the pad distance to the disc, so they always have very minor contact while not in use and applying a product to reduce that drag would essentially also reduce their braking effectiveness and thus safety.

As for the temperature of your front wheels, it is likely a combination of the wheel bearing friction, and hotter air exiting the engine bay passing through the your wheel wells on top of any heat being generated by braking that makes them feel warmer. If your front wheels are out of alignment, that could also contribute to tire temperature, but I wouldn't expect that to be significant at the wheel unless things were really misaligned.

On older vehicles the piston seal is supposed to retract a little bit on release. Some (many?) newer calipers do have return mechanisms.

Wheel bearing friction is for all practical purposes nothing, and wheel bearings aren't going to heat up noticeably unless there's something wrong with them i.e. no lube, or they are very, very heavily loaded.

Alignment has nothing to do with wheel temperature especially towards the hub.

If the front wheels are warmer than the back ones it is because of brake drag.

3-Wheeler 10-03-2012 10:09 PM

Quote:

Originally Posted by dtbaker61 (Post 331837)
I'm looking for tips/techniques on eliminating brake drag and how to tell whether its brake drag or bad bearings causing my front wheels to heat up....

You did not mention what type of car you have, but I have worked on several Honda's over the last two years, and each one has/had brake pad sticking issues, so I consider this a design flaw in the braking system.

It turns out that the pad fits so tightly in a "nest" that any amount of rust causes the pad to stick in the "nest" and effectively causes the pad to lock up. The worse the amount of rust, the more prevalent the sticking becomes.

I just worked on my wife's Honda Fit this weekend, and her pads were at the onset of this phenomena. The brake pad on the piston side of the caliper was especially stuck in the nest. I had to use a rubber hammer to move the pad out of it's nest.

One "cure" for this issue is to grind about .020 inch from the end of the supporting backplane for the brake pad.

Once this is done, the pad slips into the nest easily as it should.

Cars that I have seen so far with this issue:

Honda Civic, Honda Fit, and Honda Insight.

Jim.

ron 10-03-2012 11:14 PM

good ideas ,tight fit from rust? also try some ceramic pads they should be more stable when hot. dow chem made a silicone gel/grease, try coating the metal parts that rust and grab the pads,just be careful not to get it on the dics or pad areas

tommyt 10-03-2012 11:27 PM

What Sometimes helps is to replace the front rubber brake hoses. They can deteriorate and restrict oil flow in both directions. U won't feel a difference in braking ability but the brakes won't release as well. Also, your calipers might need to be replaced. If the brake doesn't slide back and forth on the guide pins real easily then u have a problem. Clean and grease the guide pins and see if that helps. If not, buy new calipers.

Frank Lee 10-03-2012 11:41 PM

Quote:

It turns out that the pad fits so tightly in a "nest" that any amount of rust causes the pad to stick in the "nest" and effectively causes the pad to lock up. The worse the amount of rust, the more prevalent the sticking becomes.
My F150 was particularly sneaky in that regard... the pad guides are stainless clips that clip on the big cast iron caliper mounts on the spindles; so far, so good. I discovered the brakes dragging and upon investigation found what you did- binding pads... but how? The pads were clean and so were the stainless clips. :confused: I finally figured out to pull the stainless clips off and have a look underneath. All still looked OK but in fact there was a nice rust build-up under the stainless that put the squeeze on the pads. The rust was so compacted that it looked like the cast iron surface of the caliper mounts but some work with a scratch awl at first, then wire wheel on an angle grinder revealed the rather thick layer of rust. :mad: I greased that area up and put it all back together.

That was a few years ago and it's all still good. Grease is a great rust preventative; just use it sparingly around brake parts so there is no chance of it migrating to the braking surfaces.


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