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Old 02-01-2003, 01:42 PM
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Post Rear Drums Overheat & Lock Up/Smoke

In my 69' Camaro my rear drums have been overheating when driving for about 10 minutes. They get very hot, and I have to pull over. The breaks expand and freeze up and I have to wait until they cool off before I can get going again. When they get hot, the car starts shuddering badly and I can't go over 30 MPH.

As soon as this started happening I replaced the shoes (badly burned) and all the springs from a spring kit. I followed my manual and backed the pawl screw off 1 1/2 turns from when they were just dragging when spinning the drum by hand. I just went for another test drive and they overheated again.

Can anyone help me figure why they keep dragging and overheating? The shoes and springs are good so it must be in the piston or something. When the car is cool they do not drag at all and the car rolls fine.

Joe

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Old 02-01-2003, 02:13 PM
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If your adjustments are correct, it sounds like you either have a wheel cylinder that is sticking or a brake hose that has broken down on the inside and isn't letting fluid flow back toward the master cylinder. I personally, would completely go through the braking system, replacing all rubber parts, wheel cylinders, etc.. These parts (if they are original) are 34 years old now and really need replaced anyway! Does this occur more on one side than the other?
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Old 02-01-2003, 02:25 PM
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The car was completely rotisserie restored last year. Every thing is new, from the master cylinder all the way to the backing plate. However, when I had the drums off to replace the breaks & springs, the piston assembly on both sides look to me like they are the the originals. The manual said that the pistons should have a slight amount of break fluid on the actual piston that pushes against the shoes. I saw only one piston out of both pairs that had any fluid on it. The other three pistons were dry.

Both brakes seem to overheat equally now, although the first time this happened the right brake is the one that smoked and locked up. This time, both drums were equally too hot to touch after a 10 minute drive. I was setting the new brakes by doing several hard braking from about 45 MPH. After that, they started to get hotter and hotter when driving around. So, it seems that after using the brakes, it keeps a little pressure on the drums until they get hot and expand.
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Old 02-01-2003, 02:42 PM
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Hey Prima! I'd start with 2 new wheel cylinders and go from there! Is your avatar your Camaro? Very Nice!!! You never know anymore, some of these machines are 30,000 mile originals and some are total restorations! Good Luck! This may sound juvenile, but, are your self-adjusters installed correctly? They should adjust the relationship between the shoes and the drums when the brakes are applied in reverse.

[ February 01, 2003: Message edited by: OddRodder ]</p>
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Old 02-01-2003, 03:08 PM
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This may sound stupid but are the wheel the cylinders the clynidrical objects that are in the center of the brake shoes that push the pistons out against the shoes? I am sure they are but I need to be sure. I figured out how to replace the shoes and springs so I am getting there on some of the general machanics on my car.

What is involved in replacing the wheel cylinders? I suppose the brakes would need to be bled if they are replaced?

How can I tell if the self adjusters are really working? I think they are because you can only turn the pawl screw one way and it's like a ratchet. There is a tab that touches the pawl screw thumb wheel that won't let it reverse and loosen. I think it is OK.

Yes the Avatar is my Camaro and I really love it. This is the only major problem I have had since I got it 6 months ago.
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Old 02-01-2003, 03:23 PM
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Yes, the wheel cylinders are fairly simple to replace. You will want to remove your brake shoes to do it though. Otherwise there should be two bolts (and the brake line of course) to remove on the backside of your backing plate! Yes, you will need to bleed the brakes ( try a vacuum pump one of the best tools I ever owned)! The reason that I asked about the adjusters is, I seem to remember a friend of mine installing the adjuster (Threaded gear with slotted ends) backwards and having problems similar to yours!
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Old 02-01-2003, 03:48 PM
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OddRodder, thanks for your advice! OK, I am going out to get new wheel cylinders. I already own a mityvac. I got it to troubleshoot my RS hideaway vaccum headlights. This will be the first time I have bled brakes on a car though. I have done it on a motorcycle before. Any advice on bleeding before I dive in?
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Old 02-01-2003, 03:52 PM
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It's pretty simple with the mity-vac! Just don't let the master cylinder run dry while you bleed the brakes!
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Old 02-01-2003, 03:55 PM
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I forgot to answer your question regarding if the adjusters were backwards. I will double check them when I get the drums off. The manual says there is a R and L stamp on them.
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Old 02-01-2003, 07:06 PM
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If that don't fix it, it could possibly be the proportioning valve up by the master cylinder. It equals out or proportions all the fluid in the lines. You may have to replace it.


Kevin
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Old 02-02-2003, 02:09 PM
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OK, I just finished replacing the wheel cylinders. The old ones were definately sticking. The Mity Vac didn't do as well as I expected. I never was able to draw much fluid with it. Finally I got the wife to step on the brakes for me and they bled fine after a couple of pumps.


I noticed that the left side drum drags a little when turning by hand even with the pawl screw completely in. Also, the drum seems to be slightly out of round as it binds up when spinning it about half way around. I went for a test spin and found that the right drum is cool all the time now (this is the one that smoked previously). But the left drum became too hot to touch.

I think that I should turn the drums. Because the shoes are new with a lot of meat on them, I am unable to back off the pawl screw any more, and the drum is dragging and slightly out of round, I think this would cause the drum to get hot. Do you think this is a good idea? I want to get everything out of the way before working on the proportioning valve.

The adjusters were correct stamped R and L.
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Old 02-02-2003, 10:12 PM
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Yeah, I would take both drums in to have them checked! Heat alone can cause warpage and distortion! Sounds like your on the right track! I have never had problems using the vacuum pump to bleed brakes, did you open the bleeders far enough? If the right side brake is working properly now, you have pretty much ruled out the proportioning valve.

[ February 02, 2003: Message edited by: OddRodder ]</p>
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Old 02-03-2003, 10:03 PM
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I had the drums turned today for $16 bucks and they look good. I put them on tonight. The left side still seems to drag a little unevenly when turning by hand so I am not sure what's up with that. The right side turns smoothly. Had some snow today and more is supposed to come down tomorrow night so I will have to wait for a test drive.

Yes the bleeders were open OK at about half a turn because I had good flow when the wife assisted by stepping on the brakes. I did have to put teflon tape on the bleeder threads because air was leaking through the threads when using the Mity Vac. After that it held pressure. The wierd thing was that I tested the Mity Vac directly on the brake line before connecting to the wheel cylindar and got good flow. So I can't figure why I couldn't draw it through the bleeder. At times I would get plenty of bubbles and then nothing. Anyway, past history on bleeding the brakes.
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Old 02-04-2003, 07:29 PM
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(1)Make sure the brake shoe's are in the proper location. Short shoe(short lining) goes toward's the front of the car, the long shoe(long lining) goes to the rear plus the emergency brake arm hooks to that shoe.(2) back off on the emergency brake cable adjuster.( It may be holding the shoes out too far.) <img src="confused.gif" border="0">
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Old 02-04-2003, 08:52 PM
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Another possibility is that you have a bent left axle. If you have access to a dial indicator, run it on the outside of the axle flange aand check for runout.And it certainly doesn't hurt to check to make sure that your e-brake cables & hardware are in working order.If you have a cable or return spring weak this will also toast your brakes.
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