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Old 04-14-2009, 05:31 PM
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Drum brakes not working

I replaced the wheel cylinders, the shoes, and the hardware on my rear drums but they are working! Im getting good fluid to them. I've bled them several times, but they just arnt working. I had it on the dyno and with the rear tires rolling at idle speed i stood on the brake pedal and they kept rolling. There is enough friction that a human cant turn the rear tires and if i put it in neutral it will slowly slow down. I've adjusted them to the point that its difficult to get the drum on and off. I put in a 10lb residual valve and still no luck. Any ideas?

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Old 04-14-2009, 05:52 PM
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You may have grooves worn into the backing plates where the shoes rub against it. The shoes might be getting hung-up in these grooves.

May be that the radius of the shoe lining does not match the radius of the drum. So there's only a small part of the lining actually touching the drum when the brakes are applied. It was common practice back in the day to "arc" or "radius" the shoes - which entails grinding the lining to match the exact radius of the drum, so it can make full contact.

This practice was mostly abandoned when the dangers of airborne asbestos was realized. Today, there are very few shops who radius brake shoes. even though brake linings are no longer made with asbestos. I live in a metropolitan area of over 1 million people, and there is only one shop in town that I know of that will still radius a brake shoe.

But, I could be totally wrong.

Joe G.
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Old 04-15-2009, 06:15 PM
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I hope not. shoes are new drums are fairly new
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Old 04-15-2009, 07:15 PM
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I would suspect the wheel cylinders are froze up and not extending the pistons all the way. A frozen cylinder will still bleed fine but not work correctly. It would be a long shot if both wheel cylinders are frozen but it's worth taking a look at.
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Old 04-15-2009, 07:27 PM
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I hope they arnt both frozen since i just replaced them both! Do the wheel cylinders come in different lengths? I wonder if mines could be to short....?
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Old 04-15-2009, 07:39 PM
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Quote:
Originally Posted by terminator0723
I hope they arnt both frozen since i just replaced them both! Do the wheel cylinders come in different lengths? I wonder if mines could be to short....?

I got distracted while reading your post and missed that you replaced the wheel cylinders so you could scratch that thought. Did they work fine before you replaced all the parts? What make & model vehicle are you working on? Is the master cylinder under the floor to need a residual valve? If the master cylinder is on the firewall in it's original location, you don't need a residual valve.
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Old 04-15-2009, 09:31 PM
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Car is a70 Chevelle. Yes everything worked fine before i took it apart other than the slightly leaking wheel cylinder. MC is mounted up high, althrough i still have a 10lb residual to keep the return springs from pulling the shoes back to far
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Old 04-16-2009, 02:17 AM
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You could pull one drum off at a time and have someone step on the brake very very gingerly so as not to pop the pistons out of the cylinders. See what's happening, or not happening as the case may be.
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Old 04-16-2009, 09:32 AM
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Quote:
Originally Posted by terminator0723
I hope they arnt both frozen since i just replaced them both! Do the wheel cylinders come in different lengths? I wonder if mines could be to short....?
They sure do ! and some times the parts guys might mix up and order, sell you front wheel cylinders .. Had it happen to me, the actuator, the ends that contact the shoes were incorrect .
The cylinders themselves maybe the same can not exactly remember but the actuators sure are different .

I would defiantly check that idea you have there.. and as a side note go to a different part house just so you do not get the same salesman . Salesmen typically dislike the idea that they just might not know it all after all ...

And I might add I am talking a GM rear here also ...

Last edited by pepi; 04-16-2009 at 09:41 AM.
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Old 04-16-2009, 10:06 AM
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Quote:
Originally Posted by pepi
as a side note go to a different part house just so you do not get the same salesman . Salesmen typically dislike the idea that they just might not know it all after all...
I understand what you're saying, but no way! If they made a mistake, no biggie, stuff happens.

But I'll be dammed if I would avoid the place because it might upset the help!

You might, however, want to ask for the "manager" of the place.

OT- My local parts stores know me by name, and it's not unusual for them to swing the monitor around so I can see what's there, as I sometimes have non- OEM things going on and they trust my judgement.

My point is, it really helps to build a working relationship w/your parts house, anyway- as long as it's not an adversarial one. lol
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Old 04-16-2009, 11:42 AM
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Quote:
Originally Posted by cobalt327
I understand what you're saying, but no way! If they made a mistake, no biggie, stuff happens.

Agreed I was coming from the point that a second set of eyes could from an independent source look up the parts and not be predisposed and already have in their mind what the customer was seeking. The word avoid was not used or never go back, it does pay to ask more then one source for answers .

Part folks most of the time answer questions from the reference point of I have heard or seen this before, and that is not troubleshooting. There is a HUGE difference in that path to the repair.. There are part swappers and there are troubleshooters, strive to be the latter, it makes for a better mechanic

I have delt with parts folks for quite a number of years professionally and with my personal projects. Parts people are way high on my list of good guys . Hope this clears the air for ya....

So what do you think his brake problem is, have an opinion on that the subject of the tread?
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Old 04-16-2009, 12:26 PM
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this may be a stupid question but did you adjust them right in the first place? tighten the adjusters till they won't tighten anymore then back off x amount till the shoes are just barely off the drum then drive and bed them then adjust again???

change the master to a different(maybe larger) cylinder size?

you may have done/checked this so may be stupid questions but thought i'd ask
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Old 04-16-2009, 01:49 PM
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Quote:
Originally Posted by cakraft
this may be a stupid question but did you adjust them right in the first place? tighten the adjusters till they won't tighten anymore then back off x amount till the shoes are just barely off the drum then drive and bed them then adjust again???

change the master to a different(maybe larger) cylinder size?

you may have done/checked this so may be stupid questions but thought i'd ask
The way i adjusted them was I tightened them till the drum was very difficult to get on and i couldent turn the rear tire any more. I shoulden't have to change the MC for them to work, as they worked before... No question is stupid... Usually it's the small incidental screw ups that cause the problems!
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Old 04-16-2009, 03:30 PM
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ok,the master cylinder part was a poorly worded question. i meant "did you change the master to a larger bore master?" sometimes people do this and don't realize that they lose a little pressure. but judging by your response you didn't change the master.

forget how hard it is to put the drum on and just concentrate how hard it is to turn the wheel/tire when adjusting the brakes.

the way i like to do drums is put all the brake crap on and kinda smack everything till it's kind of centered with the shoe plate touching the pins on top and the adjuster backed off so the it's easy to put the drum on. then put the wheel/tire on and tighten the adjuster till it's impossible to turn the wheel/tire anymore. then back off the adjuster till the wheel/tire is free to turn but just a LITTLE BIT of drag is ok. take the car for a short drive around the block making sure to come to a couple of complete stops the adjust them again. done it a couple hunerd times over the years and it always comes out right.knock on wood.

you said you changed wheel cylinders and i'm sure that you bled them but there is a slight possibility MAYBE that somehow air got into the master. did you bleed the master after you changed the wheel cylinders then bleed the wheel cylinders?

if you covered all this then it's one of them "HMMMMMM" things.
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Old 04-16-2009, 05:20 PM
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I had plenty of drag on them to the point you had to struggle to turn the tire then i back it off some. then I fired the car up and let the tires run and slammed on the brakes as hard as i could... for the most part they stopped.. just not completely. They'd like pulse.. Stop go stop go and that was with me holding firm pressure on it. As far as the master cylinder.. No I havent bled that. How do you go about that? Pump up the brakes and loosen the line a bit? The bore of the master cylinder should be the same as the one I took off unless they gave me the wrong one.
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