Rear 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?

 

Replace the master cylinder, it sounds like it is byp***ing under pressure.

Dave

 

the master cylinder has been re cently replaced too

 

the flex hose on the differential has collapsed.change the hose.problem solved.

 

Yep.they collapse internally,so the hose may look ok from the outside.

 

Same problem I had on a truck, rear flex line bad

 

Are the brake parts factory parts? Does the car have a proportional valve? Did you change the master because of this problem? I have had bad master cylinders right out of the box.

 

How much pedal do you have when you push on it hard?

I've run into situations where the guy bleeding the brakes didn't follow the normal method of brake bleeding and that causes problems.
By normal I mean having a helper pump the pedal "slowly" Hold the pedal down while you open the bleeder screw and keep it held down until you close the screw and give the "OK" to pump em again.
Other methods using a pressure bleeder or a Mity-Vac to vacuum bleed them work well most of the time too.

Are all the pieces of brake hardware in their proper places ? When I was doing brake and front end work in shops this was the biggest issue with guys cars who had tried to do a brake job at home and couldn't get things to work right. That includes having the primary shoe on the front side and the secondary shoe on the back side.

 

still say flex hose.

 

I havent check the flex hose yet. Ill replace that next.
No electric connections on the proportional valve.
Master cylinder was replaced because it had a small leak.
I've got good pedal. It goes down just a hair and gets hard.

 

Yea, lok at the flex hose. Had that problem when putting my rod together, thought they sold me bad Master cyl.

 

A little more info would help. What car? What parts? Power brake booster or not? Stock setup or modded?

 

I agree with mr48chev. brake shoes in the wrong position. also, some older vehicles needed the shoes ground to the correct arch of the brake drum.

 

Car is a 70 Chevelle. No booster. Stock setup pretty much. From MC to the proportional valve straight to rear split then off to individual wheel cylinders. Fronts go to valve then of to individual calipers.

Shoes are primary (the one with a lot more padding) is on the rear towards the back and the secondary (less padding) towards the front of the vehicle.

Do the wheel cylinder or wheel cylinder arms come in different lengths? Im wondering if my wheel cylinders could be to short?

 

next time say what the car is.label the thread off topic..this is a little underhanded to get advice for an off topic car...

 

Dont worry about that ****, I learned stuff from this thread.

 

then let's open it up for the camaro crowd,the new challengers etc...i don't ask questions here about my ot cars. if it's ot....state it's ot

 

Give me a freakin break! His question is valid and applies to many drum brake systems, hot rod or other wise. Cut the guy some slack.

 

ok guys..i had my 66 chevelle as an avatar and was given hell. i asked about a 454 build and was given hell. all i'm telling this guy to to do is announce it as an off topic car as i do and others do for courtesy.period....i was the first to give him advice on his brakes....didn't do anything to cut him slack for. so get back on your soapbox somewhere else.

 

no soap box here.....

You are the one who said the guy is "underhanded" for asking about an off topic car. It's not like he asked how to install his new cold air intake on his mitsubishi eclipse!!! He asked a question about a brake system that in one form or another could be found on a ton of 'on-topic' cars on this site. The model of the car actually has little bearing on the specific nature of his question. You just felt like bustin' the guys balls. end of story.

 

It isn't that it is an off topic car but it's nice for those of us who are attempting to help sort things via the web to know exactly what someone is working on.

By the way on drum brakes the shoe with less material to contact the drum is the "primary" shoe and the shoe with more llining is the "secondary shoe".
The primary going in front an secondary going in the back just like the barrels on a 4 barrel carb.

I was more concerned with the hardware it's self being hooked up wrong or not in place.

Check the hose and see if it is working right or bad and I'd check the lines to make sure none have a tight kink or have been flattened for some reason.

You might have to take it out and drive it a bit up and down the driveway or the street and work in the shoes.

 

Some gm brake shoes the slot where the rod from the wheel cylinder goes is deeper[different series &cores get mixed up at remanufacturing]the wheelcylinder piston may be bottoming out on the safety stops on the backing plate???

 

Could be screwed up. any obvious ways to spot misplaced springs?

 

Check the adjustment on the shoes.First you need to make sure that the E-brake equalizing bar is in the relaxed mode.If your E-brake cable is stuck and not pulled back all the way,this bar will not let the shoes go in the right place.Then you can adjust the shoes accordingly so there is a slight amount of drag.If this step is not done correctly your master cyl. will have too far to travel before it can engage the rears.Dan

 

All the ebrake stuff is gone. I adjusted the brakes till it was very difficulit to turn the tire then backed off a bit then I got in the car, fired it up, and put it into gear and let it idle. Then I slammed on the brakes. It partially stopped. It was more so of a pulse. It stopped and would turn a hair stop and would turn a hair. And that was with me holding as much pressure on the brakes as possible!

 

I probably have a photo at home in a manual but my scanner is on the fritz lately.

Most motor manuals, Chiltons or the Haynes manuals should show a picture (either photo or drawing) of how the brake hardware goes back on.

If you still have the old shoes I would compare them to the new ones and see if the slots for the pins that go in the cylinders and push out the shoes are different.

I'm ***uming that the drums are in decent shape and not grooved by metal to metal contact from worn out lining before.

Usually if one of the springs is in the wrong palace they won't retract right and hang up.

I can't think of much else at the moment.

 

hmk ill get a manual and take them apart and put them back together tomorrow and see if that does the trick....

 

I recently had the same issue with my OFF TOPIC (don't want to get in trouble with the HAMB police) 89 Caddy daily driver.The problem was with my proportioning valve, while bleeding the system I had to pull the little pin out on the valve to allow fluid to flow through, and get behind it enough to hold pressure, then I had rear brakes, otherwise it was the same thing as you, stand on the brakes and nothing.

 

Hmm... Ill give that a shot!

 

that's a good idea. I did a brake job for my brother on his toyolet. he came back and said the brakes didn't work very well, I dis-***embled the proportioning valve and found it gummed up. cleaned it and re***embled and brakes were fine, I had forgotten about it until you posted. good call!