Frozen caliper pins caused excessive wear on a Chevy I had. It had a single piston and depended on the caliper being free to move. If this is your problem you should be able to hear the brake dragging when you spin the wheel.

Chuck

 

too many variables to help here, BUT should be free with "slight" drag after 2 full turns. Figure less than 20 inch pounds to get it to rotate on a smaller car, 50 to get the F250 turning then drop to about 15 to keep it turning. less is always better. I'll bet you either frozen slider pins or caliper slides, especially if it just snowed there. warm is always bad. If in doubt, it is time to change the bearings.

 

If you jack a FWD car up and spin the wheels there may be quite a bit of drag from the excessive half-shaft angle. Also, you are experiencing added drag from at least some of the transaxle parts.

 

Pull your vehicle after a drive up where you can work on it. Lift it up and see how hard it is to turn the tires. Get to the calipers and retract them so the pads are loose. Try turning the tires again and see if you can feel the difference, that at least will tell where the drag is originating from.


Roy

 

ok, turns out that pads seemed to be 'dragging' a little... there was audible scraping when spinning by hand. Not horrible, but there.

I removed calipers, wiped rust and grit off, cleaned the areas where the pad 'ears' touched and added a touch of brake caliper grease just to make sure everything could wiggle a little better and buttoned it all back up with my NEW carbotech ax6 pads ( I want to see if they are grippy enough to not need vacuum booster ).

system seemed to 'scrape' less after replacement.

I debated on whether to peel back rubber caliper boots and add grease, but I did not because I was afraid to rip the boots....

...will report results later.

 

On my bug the front wheels could do 20 revs, (with drum brakes adjusted for no dragging) now with disk brakes they do 2. The rears have never done more than about 5.

 

a bug would be completely different... with drums and tranny on the rear. But your info regarding maybe 2 revs with disc, versus maybe with drum NOT connected to a tranny sound about right.

My rear wheels, having drum brakes and no tranny, do spin LOTS better than the front. The front at least don't sound like they are dragging anymore, so we'll see. Other possibility that occured to me is that I had CV joints replaced, and perhaps the mechanic replaced transmission fluid with something too thick, or thicker than the 'royal purple' I had in there.

 

Don't forget the caliper guide pins. I have one seize once. I have also had guide pins with chewing gum consistency grease, and severely worn guide pins. You should be able to push the caliper back and forth by hand on the guide pins.

Can you push the piston back in with your thumbs? It takes a strong squeeze, but I have been able to do this on all my cars that didn't need a caliper replaced.

Also make sure there is no looseness in the front hub -- if the wheel clunks back that can induce brake drag.

Unlikely on a front wheel drive, but I did have a rear wheel drive where the rear wheels would telescope out on turns, and wear the rear brakes very quickly as a result. I had to put a spacer under the brake disk to fix that.

 

caliper pins (bolts holding caliper on?) seem fine in that caliper can move back and forth once caliper piston was pressed back a little.

I could not press caliper by hand, and I have strong hands. I had to use a C clamp to retract the piston.

The 'ears' of the pads rest in these little spring steel clips which were pretty gritty and grimy. I cleaned and put a dab of grease so that pads have a better chance of being able to bump off contact w/ rotor.

seems to have helped, but I am thinking I need to pull them back apart and grease under the caliper boots?

 

So, how many watts does 20 lb-in of drag torque gobble up?

It may be 'down in the noise'. With a 2:1 ratio in energy consumption the mystery energy drain is not a subtle effect.

 

well..... 20 in-# of torque is 2.26 watt-seconds

 

So at 30 mph avg. speed at 120 seconds per mile = 271 w-s/mile = 0.08 w-h/mile.
Seems like something else is sucking energy out of this vehicle.
400 w-h in 120 sec. is 12kw, 16 hp. The 8 hp of lost power has to show up as heat, light, noise or mechanical work. F'r sure this is no taillight stuck on, but it could be a faulty reading.

 

Dan,

I used silicone grease on my caliper pins and had no further problems with brakes as long as I had the car. A remote sensing IR thermometer would be handy for diagnosing problems like these. They are quick and easy to use.

Chuck

 

well..... 20 in-# of torque is 2.26 watt-seconds

I guess you are converting to N-m then to W-sec? Doesn’t work that way. Work done by torque is the product of torque and angular displacement – how far you rotate the torque wrench. The length unit in your calculation is where you grip the wrench, and with the force you apply determines the torque. Power is work per unit time so the product of torque and angular velocity, or 2.26 * wheel rpm * 2 *pi/60 = 0.237 * wheel rpm, so about 840 * 0.237 = 200W for 12” dynamic tire radius and 60 mph.

 

You could just pull the car slowly on level ground by hand or by using a winch or block & tackle, and use a hardware store spring to measure the drag.
Storm door snubber springs have a spring constant of about 45 lbs per inch, but measure it first. Valve springs are really stiff.

 

are you serious?

I am all about scientific process, but this does not seem like an accurate or repeatable test for what I am after.

I think this is one of those times when a simple spin-by-hand and an audible test of 'do I hear brake drag on rotor anymore' is close enough. Answer so far is that after preliminary cleaning of pad ear 'holders' things seem to be much better.