Hi all i have a 68 chevelle with power drum. my problem is on long trips 15 miles or so both my rear brakes smoke i have new shoes and cylinders booster and master cylinder.any local trips everthing is good i just cant figure this out. the car rolls fine but it looks like the wheels are on fire when i stop at lights.i checked the adjustment and it's good it's like the fluid is expanding when hot and pushing the shoes out and rubbing the drum. thanks

Here are some things to check. each wheel has a long and short shoe. I can't recall from memory which goes to the front of the car, so check your manual, or post again and I'll check mine. Take the shoes off again and check the 4 spots where they rub the backing plate. Sometimes this rub block has a groove worn into it and won't let the shoes return easily. They must be filed flat and use some white lithium grease on each rub block so the shoes slid back easily against the backing plate.
It might be wise to install new springs. A complete spring kit only runs around 10 bucks a side.
My last thought is proportioning or combination valve if your car has one. Some years, and I think 68 may be one, has a metering valve instead of a combination valve. Anyway, for drum brakes, the combination or proportioning valve has a residual valve built into it to hold about 2 pounds pressure in the drum brake system, so the brakes shoes stay close to the drum for the next application. Maybe your residual valve is holding too much pressure to your rear wheels and this is causing the rears to rub against the drums at all times. Go to a great brake sit, MPBrakes.com for more info on brake residual valves, combo, or proportioning valves. Complete this post once you have solved the problem so what you learned will benefit others.

BHawk,
Small shoe to front, Large shoe to rear.
Blue,
Is your E-brake hanging up? That can also cause this problem.

Thanks for the info bhawk. And as for my e-brake the cable is broken. I have what looks like a valve block bolted to the frame just below the booster. Thursday (thanksgiving day) instead of turkey i'm going over the brake system. One thing i forgot to mention is this car was manual drum i put a booster on and the padal only travels at most 1 1/2 i'm also going to check the booster rod again
Happy thanksgiving to all !

Two things to check now that you mention your addition of a booster. There are 2 holes in your brake pedal. One hole is for power brakes, the other for manual. Can't recall which, so check out the mpbrake site, they have the answer.
Also, I read alot of posts about booster rod length. It must be exact or you have problems. Search "booster pin" or "booster rod" in the archives on this site to read about the issue. Good reading is the disc brake conversion articles archived in separate section on this site. Good luck.

Originally posted by bhawk:
Two things to check now that you mention your addition of a booster. There are 2 holes in your brake pedal. One hole is for power brakes, the other for manual. Can't recall which, so check out the mpbrake site, they have the answer.
Also, I read alot of posts about booster rod length. It must be exact or you have problems. Search "booster pin" or "booster rod" in the archives on this site to read about the issue. Good reading is the disc brake conversion articles archived in separate section on this site. Good luck. The LOWER hole is used for the power brakes.

WOW, yeah after reading that recent addition, I am thinking distribution block as well.

But just in case that's not it, jack the car up and see how easy/hard the drum turns. The brakes shouldn't be but maybe barely touching now and then. Adjust as needed. Both sides.

I agree with making sure you have new springs, and I always clean the adjusting device and lube it. I can find a whole spring kit for about $3.00

Also, did you clean the pads AND the drum before putting the drum on? What's the chances there is some grease or other contaminants on the pads causing the smoking?

Slowdown!!! :D

Well i checked the booster rod and i'm useing the long rod which is good because the master slides down to the base of the booster so thats good, it's not pushing on the master. Then i checked the booster pedal pivot point and it's on the bottom hole.But is there a difference between power drum master and manual drum master.And is it normal for the pedal to only move about 1 1/2" total travel. Thanks

Blue,
When the brakes smoke does the pedal get soft ?
Any loss of braking? How are the axle seals? Maybe
gear oil is leaking onto the shoes.Until the shoes get completely soaked with gear oil you'll have normal braking but they'll smoke when you come to a stop.

the brakes work fine just a LOT of smoke when i stop. and the seals are good just replaced them about 2 months ago along with the shoes,cylinders and half the brake system. it did this before all the work but i thought i might of repaired it but it's back. the only thing that is not replaced are the rubber lines front and back and only because they looked good. i can do local driving all day and it's good, just extended hwy speed does it.

Try backing off the rear adjustment a couple of clicks.If the smoking stops it was mechanical , If it still smokes its a hydraulic problem. Don't
back the adjustment off too far or the pedal will be low.
Happy Thanksgiving :D

blue chevelle,did you go to the www.mpbrakes.com (http://www.mpbrakes.com) site yet. Click on troubleshoot. They have 5 things that cause drums brakes to drag. Booster pin that is too long is first on the list. They mention shimming the master out by 1/32 of an inch, then seeing if problem goes away. They have other causes, including too much fluid in the master cylinder. I strongly suggest you run their causes and fixes first, then report back to us. We want to help you fix your problem, and learn in the process.

well wednesday afternoon i went to a local autopart store (mom-n-pop)to pick up the rubber lines and told him what my problem was after a few minutes of i dont know he called a buddy of his. He told me that if the rubber lines are original that the rubber line to the rear could be collapsed. and told me to remove it and try to blow through it if you could it's good if you cant replace it. i tried and no luck so i replaced it (the new one i can)took the car for a long trip about40 miles and so far so good. this week end i'm going to test it again. dont know why i didn't think of this but i'm praying it's fixed. thanks for all the help

Sometimes when you get a snag,it takes awhile to get the line out. graemlins/clonk.gif I have see that happen many times on the front of cars but never on the back.Also when I have seen this happen the wheel would lockup right now.Never really understood how fluid could go one way but not the other(amount of pressure I guess)sure would like to see what the inside of a line looks like when that happens.Now, if this happens to me I will know one of the first places to look for the problem thanks to TC.

the only thing i can think of is that pedal pressure can push the fluid through the line but then the fluid on it's own cant return and there is pressure built up. not enough to slow u down but the shoes are just touching the drum. as for the hose i cut it the long way and the rubber inside was peeling away from it self. it's probably the original line from 68