Excessive disc brake drag?

Posted By: 68LAR

Excessive disc brake drag? - 11/17/14 07:41 PM

I've asked this question before and never did get an acceptable answer.
Stock drum rears
Stock disc front end (A body spindles and calipers // B body rotors)
Non power
Stock master from '95 Dakota. (aluminum body, plastic reservoir)

All pieces are in the stock location. Master is above the calipers and wheel cylinders.

Problem is,.. It seem like there is excessive pad drag at the rotors. Any body have a solution for this problem???????
Thanks for any constructive input.

Posted By: feets

Re: Excessive disc brake drag? - 11/17/14 07:45 PM

The first question is how much drag do you get? There will be a bit of drag on them.

Do you have the springs installed over the pads? They help prevent unnecessary dragging.

In a properly designed brake system one inch of pedal movement only provides about .004" of pad movement. If the pads are too far away from the rotors you will end up with a soft or spongy pedal.

Posted By: 68LAR

Re: Excessive disc brake drag? - 11/17/14 08:45 PM

No springs on my calipers or pads. They are the slider type.
Brake pedal moves about 1" max. Nice high hard pedal.
I've had plenty of experiences with disc brake systems in my life time. My drag just seems to be a little more excessive than I've noticed on other cars.
I realize that there will be a certain amount of drag with disc brake systems.

Since I'm working with a conversion brake system, is this inherent of going this route?

Posted By: John_Kunkel

Re: Excessive disc brake drag? - 11/17/14 08:52 PM

Single-piston floating calipers depend on the distortion of the square-cut rubber ring to retract the piston ever so slightly, a small amount of disc runout helps...by nature they drag more than calipers with mechanical retractors.

If the rotors are really hot after a drive with minimum brake use there might be a problem.

Posted By: Grizzly

Re: Excessive disc brake drag? - 11/17/14 09:20 PM

I pulled my hair out with the same issue as you, but all stock components.

It STILL drags to much for my liking.

Here is the thread, I start out just wanting to re-build a caliper, but if you read the whole thing it will at least give you an idea of what I tried.

Help.

Posted By: dragon slayer

Re: Excessive disc brake drag? - 11/17/14 09:43 PM

Stuck caliper, collapsed hose, stuck master cylinder piston. G

Posted By: 68LAR

Re: Excessive disc brake drag? - 11/17/14 09:59 PM

Quote:

Single-piston floating calipers depend on the distortion of the square-cut rubber ring to retract the piston ever so slightly, a small amount of disc runout helps...by nature they drag more than calipers with mechanical retractors.

This is exactly what I'm dealing with. Everything is new. Except for the calipers. They are NEW, in the respect that they don't have much mileage on them, but have been on the car for several years. I drive the car, maybe 1K a year. You see where I'm coming from??
I have heard that the Square Ring seal on the piston may cause an issue like this, but kind of discarded that thought because of usage.

Posted By: LAR_414

Re: Excessive disc brake drag? - 11/17/14 10:10 PM

Just a quick thought. Could the wheel bearings be set with too little free play (too tight)? A little on the loose side where the bearings may have some play, would help push the calipers back in a little, as the wheel spins.

Just a thought.....

Posted By: RapidRobert

Re: Excessive disc brake drag? - 11/17/14 10:19 PM

I had 74 A sliders & one of em (LF) had what I thought was too much drag. I replaced it with a $15 rebuilt caliper & problem solved. It had significantly less drag than the one it replaced did

Posted By: Paul_Fancsali

Re: Excessive disc brake drag? - 11/17/14 11:31 PM

Just fixed that issue the new calipers were NAPA and would barely spin. Took them off went and bought Advance Fixed do they drag yes, but not too bad Be careful that your master cylinder is not the source of your issue Many drum brake master cylinders passed off as disc in the reman world.

If you want drag free brakes use four piston disk brakes They are like unadjusted drum brakes and stop fine I rebuild my own

Posted By: TJP

Re: Excessive disc brake drag? - 11/18/14 02:31 AM

open a bleeder and see if it squirts fluid and then see if the drag is significantly reduced.

If so now you have to establish why,
1. Internally collapsed hose
2. Wrong residual valve in the master
3. M/C pushrod too long.

Posted By: Rick_Ehrenberg

Re: Excessive disc brake drag? - 11/18/14 05:17 AM

Also look for worn adapters (brackets). Sometimes the pads wear a groove that hinders retraction. Mill basturd (hadda misspell, Moparts would not allow correct!) file fixes that, also provides more inner pad clearance causing inner shoe to seize and crack pad material off when very hot.

Rick

Posted By: RapidRobert

Re: Excessive disc brake drag? - 11/18/14 05:53 AM

Rick is that correct or not correct that you want the one pad to have some side to side clearance (so it can float)? And the other pad you want to bend the end L tabs so you have to snap it into place on the caliper?

Posted By: loaderpro

Re: Excessive disc brake drag? - 11/18/14 05:57 AM

Check the residuel valve. Most disc systems use a 1-3 lb valve for disc systems and some do not use any. Put in the lighest valve, if that doesn't do it then remove it alltogether. Check though to make sure after doing this you do not lose the pedal. Apart from that as others here have mentioned, be sure the pistons will retract fairly easy with the bleed screw open. if not then you need to disassemble/clean and rebuild your calipers.

Attached picture 8334673-pomona.jpg

Posted By: 68LAR

Re: Excessive disc brake drag? - 11/18/14 03:51 PM

Let me take all the suggestions one by one.
1. Wheel bearings are adjusted properly. With no pads the rotors spin freely.
2. Brackets are brand new. Purchased from Dr Diff and installed last week. Had the same issue B4 that.
3. No residual valve that I'm aware of. Standard A Body to B body disc brake conversion.
4. Inside pad is floating on bracket. Outside pad snaps into caliper.
5. Everything you guys are suggesting is pointing to the calipers. I find that hard to believe, but facts is facts.

Thanks for all the input.

Posted By: Supercuda

Re: Excessive disc brake drag? - 11/18/14 03:58 PM

Quote:

Check the residuel valve. Most disc systems use a 1-3 lb valve for disc systems

Residual pressure valves are used in some DRUM setups, not disc.

Posted By: gtsdude

Re: Excessive disc brake drag? - 11/18/14 04:44 PM

Maybe you checked already, but make sure your pedal is coming back all the way. When I changed over to manual brakes and aluminum master on my 68 dart my front brakes were dragging too. After bleeding them half a dozen times I just happened to grab the brake pedal and pull it up. Over the years it wore into a spot and would not come back on it own.

Attached picture 8334872-dart1.jpg

Posted By: TJP

Re: Excessive disc brake drag? - 11/18/14 05:42 PM

GTSDUDE, I know the history on your Dart,

Posted By: feets

Re: Excessive disc brake drag? - 11/18/14 06:44 PM

I'm still not sure what you call excessive drag.

Is there some way you can quantify the problem? Can you turn the wheel by hand? Can you spin the wheel without it stopping immediately upon release?

Posted By: 68LAR

Re: Excessive disc brake drag? - 11/18/14 07:20 PM

Quote:

I'm still not sure what you call excessive drag.

Is there some way you can quantify the problem? Can you turn the wheel by hand? Can you spin the wheel without it stopping immediately upon release?

If I spin the wheel with a good hard spin, it will rotate on its own for about one revolution.

Posted By: stumpy

Re: Excessive disc brake drag? - 11/18/14 07:27 PM

Sounds pretty normal to me.

Posted By: shanker

Re: Excessive disc brake drag? - 11/18/14 08:18 PM

Quote:

Quote:

I'm still not sure what you call excessive drag.

Is there some way you can quantify the problem? Can you turn the wheel by hand? Can you spin the wheel without it stopping immediately upon release?

If I spin the wheel with a good hard spin, it will rotate on its own for about one revolution.

that's fairly excessive I would think too....it would cause excess heat and faster wear on the pads/rotor.

I had a similar issue with a bad rubber brake line, have you changed those too?

Posted By: 68LAR

Re: Excessive disc brake drag? - 11/18/14 08:52 PM

Quote:

that's fairly excessive I would think too....it would cause excess heat and faster wear on the pads/rotor.

I had a similar issue with a bad rubber brake line, have you changed those too?

I forgot to mention, I installed brand new rubber brake lines when I did the original conversion about 6 or 7 years ago. Again remember, I had this issue from the onset and the car is driven less than 1K miles a year. Probably closer to around 200 miles/yr..

Posted By: John_Kunkel

Re: Excessive disc brake drag? - 11/18/14 09:05 PM

Quote:

If I spin the wheel with a good hard spin, it will rotate on its own for about one revolution.

Sounds better than normal to me.

Posted By: dragon slayer

Re: Excessive disc brake drag? - 11/18/14 09:40 PM

Regardless of the age of the calipers if there was any defect in the remanufacture of the piston or some water in the system the corrosion can form and bind the piston. There is no spring return.

I know a B body caliper can be had for $20, so it can be an easy fix. Does the car pull when braking or normal driving? If not, than maybe both are equal which can push you back to a MC piston not fully returning and preventing fluid return, or a meter valve(hold off valve) if you are using one with debris. G

Posted By: poorboy

Re: Excessive disc brake drag? - 11/18/14 11:33 PM

Quote:

Quote:

If I spin the wheel with a good hard spin, it will rotate on its own for about one revolution.

Sounds better than normal to me.

This really doesn't sound like much of a disc brake drag at all to me! Probably better then most! A disc brake drag is where you stop spinning the tire and it stops immediately, or you can barely get it to turn with the wheel.
I think your chasing something you won't be able to cure with disc brakes. Gene

Posted By: feets

Re: Excessive disc brake drag? - 11/19/14 12:51 AM

Quote:

Quote:

Quote:

If I spin the wheel with a good hard spin, it will rotate on its own for about one revolution.

Sounds better than normal to me.

This really doesn't sound like much of a disc brake drag at all to me! Probably better then most! A disc brake drag is where you stop spinning the tire and it stops immediately, or you can barely get it to turn with the wheel.
I think your chasing something you won't be able to cure with disc brakes. Gene

This is kinda what I had in mind when I read the first post. I asked about the drag but didn't get a quantified answer.

It sounds like his brakes are in great shape and there are no concerns.

Posted By: Rick_Ehrenberg

Re: Excessive disc brake drag? - 11/19/14 02:07 AM

Quote:

Rick is that correct or not correct that you want the one pad to have some side to side clearance (so it can float)? And the other pad you want to bend the end L tabs so you have to snap it into place on the caliper?

Exactly.

Rick

Posted By: RapidRobert

Re: Excessive disc brake drag? - 11/19/14 02:20 AM

Thanks Rick, you're the man

Posted By: 68LAR

Re: Excessive disc brake drag? - 11/19/14 02:24 AM

I'd like to thank everyone for their input. I hope we all learned something, I know I did.

Posted By: BDW

Re: Excessive disc brake drag? - 11/19/14 02:33 AM

Don't mean to be flippant, but at 200 miles/yr, why worry?
Unless they are getting red hot, I wouldn't be concerned.

Posted By: 68LAR

Re: Excessive disc brake drag? - 11/19/14 03:31 PM

Quote:

Don't mean to be flippant, but at 200 miles/yr, why worry?
Unless they are getting red hot, I wouldn't be concerned.

A good part of that mileage is at the track. I was thinking that I might be leaving some ET on the table with the drag. Maybe I was over thinking the who thing????

Posted By: poorboy

Re: Excessive disc brake drag? - 11/19/14 11:59 PM

Disc brakes traditionally have more drag then drum brakes. Back in the early 70s, some guys used to run the drum brakes with a loose adjustment on non-self adjusting brakes at the drag strip, in an effort to reduce brake drag. Exactly how much difference it actually makes would probably have to be subject to testing. The pursuit of the lowest ET had some guys doing some strange stuff over the years. The question is, how much are you willing to do for how much reduction in the ET?

Gene

Posted By: 68LAR

Re: Excessive disc brake drag? - 11/20/14 12:41 AM

Quote:

Disc brakes traditionally have more drag then drum brakes. Back in the early 70s, some guys used to run the drum brakes with a loose adjustment on non-self adjusting brakes at the drag strip, in an effort to reduce brake drag.

I was one of those drag racers..... When I found it harder and harder to stop is when I did the conversion.

Posted By: cedarmachine

Re: Excessive disc brake drag? - 11/20/14 04:23 AM

Quote:

Quote:

Check the residuel valve. Most disc systems use a 1-3 lb valve for disc systems

Residual pressure valves are used in some DRUM setups, not disc.

If the master cylinder is lower than the brake calipers, you will certainly need residual pressure valves. That said, stock disc applications shouldn't need them.