reducing drum brake drag

[Gregte]

It just occurred to me that drum brakes tend to have an amount of drag that varies from light to moderate to light etc. over time as they periodically adjust themselves. To jack the car up and turn a wheel by hand really points this out.

Ha anyone here come up with a solution to the problem regarding the automatic brake adjusting mechanism setting the brake shoe adjustment such that the shoes drag on the drum?

[gteclass]

unfortunately that little bit of drag is federally safety mandated and you will never pass a safety inspection without it.

[ttoyoda]

It just occurred to me that drum brakes tend to have an amount of drag that varies from light to moderate to light etc. over time as they periodically adjust themselves. To jack the car up and turn a wheel by hand really points this out.

My rear drums do not have any noticable drag. Certainly not to where I can detect it with the wheel on. Are you perhaps sensing the intertia of the wheel and thinking that is brake drag?

[Gregte]

Originally Posted by ttoyoda

My rear drums do not have any noticable drag. Certainly not to where I can detect it with the wheel on. Are you perhaps sensing the intertia of the wheel and thinking that is brake drag?

No, I am referring to actual drag of the shoes on the drum. That drag will be very minimal or even non existent just before the shoes have worn enough for the automatic adjusting mechanism to click a notch. but just after it does that there is often drag.

My experience with this is from my own vehicles and from thousands of vehicles I have serviced etc. (gas station work).

One solution to this problem would be to remove the automatic adjuster levers and then just adjust the brakes manually every so often but that does not appeal to me at all.

To keep disk brakes from dragging, a slight amount of lateral bearing play does the trick as this allows the wheel to wobble left to right forcing the calipers to spread the pads away from the rotor. But drum brakes are of course a completely different design.

[ebacherville]

why they even use drums at all is a total mystery to me , discs are far more efficient and far easier to work on .. with the invention of discs the drums should have been dropped completely.. I don't get it , anything over 30 years old should be discs all the way around.

[getnpsi]

When chevy went back to drums after 4 wheel discs in trucks, the trend of large wheels came around. That is awesome marketing, knowing that brakes only last 10,000 miles on those custom trucks and suv's. It's THE MAN.

[ttoyoda]

To keep disk brakes from dragging, a slight amount of lateral bearing play does the trick as this allows the wheel to wobble left to right forcing the calipers to spread the pads away from the rotor.

I disagree with that theory. The square o-rings used inside the calipers as piston seals have enough spring-back that they pull the piston away from the pads. Otherwise, brakes would always drag until the brake rotor turned a few times, and that is demonstrably not the case.

No, I am referring to actual drag of the shoes on the drum. That drag will be very minimal or even non existent just before the shoes have worn enough for the automatic adjusting mechanism to click a notch. but just after it does that there is often drag.

If you say so. Regular use of the parking brake is needed in my cars to make the adjusters move. I have not noticed any drag, other than what is in the bearings and the bearing seals.

[ttoyoda]

why they even use drums at all is a total mystery to me , discs are far more efficient and far easier to work on .. with the invention of discs the drums should have been dropped completely.. I don't get it , anything over 30 years old should be discs all the way around.

Because it is very easy to incorporate a cable operated parking brake in the design. Disk brake calipers with a parking brake unit built in (subaru used to do this on the FRONT calipers, the [children of unmarried parents]^*) are a pain to rebuild. Regular calipers are a 10 minute job to rebuild if you rush. I would rather do drum brakes than fight with disc calipers with parking brake klude-ons.

* word filter

[Gregte]

Originally Posted by ttoyoda

If you say so. Regular use of the parking brake is needed in my cars to make the adjusters move. I have not noticed any drag, other than what is in the bearings and the bearing seals.

My newest vehicle is 14 years old, and that is also when I quit working on cars other than my own. I don't have any experience with anything newer but all cars I had ever known of required applying the brake while backing the vehicle to actuate the automatic adjusters.

There is a simple explano at:
http://auto.howstuffworks.com/drum-brake2.htm

It talks about the reverse braking type and the parking brake type of adjusters. I had never known of the parking brake type before reading your post.

[diesel_john]

I pinned the adjusting wedge so it can't over adjust. also have small stainless steel springs holding the front pads off the disc. i check them often and adjust if needed. in addition i drill a small hold in the wear face of the drum to let out dust which can cause drag. but then i try to drive without using brakes. a set of pads usually last me about 90.000 miles.

[MechEngVT]

Disc brakes typically have more drag than drums. The springs in drum brakes pull the shoes back away from the drum surface. Obviously if your adjusters have spread them a bit too far they still drag on the drum surface, but their tendency is to not contact the drum.

Calipers have no mechanism to spread the pads away from the disc after brake actuation. Many caliper designs have o-rings on the slides in an attempt to prevent knock-back where rotation and flexing of the disc (or wheel bearing) will push the pads away from the disc. A lot of drag racers use drum brakes because it is easier to set them so that they will have no drag and leave braking performance to the 'chute.

Making a parking brake meet safety standards with discs is a pain in the rear. The force required to clamp a rotor and hold it is so high that it is only user-friendly with power-assisted hydraulics. Parking brakes can't be hydraulic because of the risk of fluid leakdown causing a park brake failure, but the mechanical force required is rough. My truck has 4-wheel disc brakes but the rear discs have a park brake drum surface on the inside rear of the rotor with the mechanical cylinder and shoes behind the rotor. It's 2 brakes in one, which is more costly (not to mention heavier, and forces large diameter rotors, thus large heavier wheels).

[rbhollabaugh]

The cars I drive (old Citroens) have manual adjusters on the rear drake shoes. You only need to adjust them every 20k or 30k miles.
The brake shoes on our other car (Honda) have auto adjusters and, yes, they will drag a bit here and there. But the drag is sooo small I can't see it causing any measurable loss of MPG. If that's what you are after.

[ttoyoda]

It talks about the reverse braking type and the parking brake type of adjusters. I had never known of the parking brake type before reading your post.

And I had never known about the reversing type. Thanks for the tip.

[Concrete]

Diesel John,
do you have any pictures of your disk break mods
particularly the pull back springs?

[RP-CLMBR]

I found that when you put new soes on if you dont turn the drums to ruff sand the shoes to fit and then dont hit hand brake while rollig backward suddenly or this will actuate the aouto adjuster I may go back and eliminate the auto adjusters cause iIuse the hand brake a lot on hill take offs, like dsle john said let the road do your brakeing drive for every one way up in front of you,and the brakes will stay clean and free rolling
My dad had made some spring steel clips for a 81 starlet mod back in 89 or so and he would roll up to a light and time it to where gravity did the work and finish it with the hand brake, Oh try pushing a car that has sticky calipers a mile, I think disk brake drag cost as much as day time electrical recharge,if not more, If the speed limits were still 55 I would have four wheel drums on my crx hf, but for pulling a tree chipper and load of mulch, I am glad my mitz fuso has dual front calipers when you need them is when they pay you back for the drag

[RP-CLMBR]

Oh look at the honda insight it has rear drums,