Author Topic: Should the rear drum brakes???? (Read 3423 times)

1onehotTA · « **on:** October 18, 2006, 06:37:58 PM »

With the rear tires off the ground, should my rear brakes lock when someone hits the pedal, mine do not, unless someone hits the brakes numerous times. I have replaced the rear cylinders, and front calipers and master cylinder as an upgrade, Im sure they are bled, do I have a bad combination valve, or are they supposed to be that way and work only when the car is moving somehow in conjunction with the front braking system, or only when the car is running, im confused on this somewhat. I would think they would lock anytime the pedal is pushed, the front brakes lock with the tires off the ground.

ta78w72 · « **Reply #1 on:** October 18, 2006, 09:54:23 PM »

Is the engine running when you push the pedal? Otherwise, I can't see why having the rear end off the ground would have any effect on the braking system.

You probably haven't bled the brakes properly. And I'm not saying that because I'm trying to be mean. I know great mechanics that have a hard time bleeding brakes on these cars.

Try bleeding again before you put any money into it.

Edit
Oh, you posted on the other thread about this too.
Do the wheels turn if you set the parking brake?

1onehotTA · « **Reply #2 on:** October 20, 2006, 12:11:49 AM »

My parking brake does lock with the pedal pushed down, in only about four clicks. Also I have my tires off becuase I replaced the wheel cylinders that were leaking fluid. Now upon bleeding the brakes, I noticed that the pedal has to be pumped numerous times before the shoes actually contact the drum. This is with the parking brake off. I only noticed this since the tires were off the car when bleeding them, I noticed the pedal being pumped like 7 times makes the shoes finally contact the drum. But if my thinking is correct, the shoes should contact the drums, or make the brakes work even when the pedal is pressed only once, correct? As what if the car stalled while moving, with the pedal pressed once the brakes should work right? Im still a little confused, I read also that there is a 10 residual valve for drum brakes? Is this a serparate component than the combination valve? Or is it built into it?

ta78w72 · « **Reply #3 on:** October 20, 2006, 02:13:43 PM »

OK, if you can stop the drums from turning with the parking brake set, I believe you've got everything together correctly. If you can pump the brakes and make them contact the drums, then you've got air in the line.
The brake booster works off vacuum. If the car stalls, you've got enough vacuum to stop it before you lose the power assist.

Have you checked out the links on this site for brakes? Brett has documented how to do a brake job, including bleeding the brakes? He also gives a lot of information about the combination valve.

Try reading the link. Then think about the process you went through. Then read the link again and try bleeding the brakes one more time. It sure sounds like you've got air in the line.

You should be able to push the brake pedal and it should be firm. If it feels soft, you've got air in the line.

Edit:
I just reread the other link you've posted. No doubt about it, you've got air in the lines. Did you bench bleed the master cyclinder? You've basically replaced everything but the lines.....so naturally you've got a lot of opportunity for air in there. You may want to take the master cyclinder off and bench bleed it if you haven't already. Then follow what Brett has documented in on this site. You'll need to bleed them several times to get them air free.

Hitman · « **Reply #4 on:** October 20, 2006, 06:31:41 PM »

I have alos had one case to where the new master cylinder that I purchased and installed on the car was bad from the get go. So yes, after you make sure you bench bleed the master cylinder and bleed all of the lines, then it might be a bad master cylinder. Is your brake booster new?

1onehotTA · « **Reply #5 on:** October 20, 2006, 10:30:46 PM »

My brake booster is not new, but if im not mistaken shouldnt I bleed the brakes with the engine off? In which case the power boost would have no affect on its performance, in other words if my car stalls the brakes would still work, just harder right? So I dont start the car before bleeding my brakes do I? One more question also, that combination valve what exactly do I press, mine had a rubber cap on it, is that round what looks like brass piece that sticks out of the end supposed to go into the valve body, or is it just that little pin in the center of that round brass piece that gets pressed in. Im making progress with this I think, you should see my garage floor, looks like a lake of brake fluid, I havent got it on my paint yet though. I bench bled my master cylinder by the letter of the instructions, gonna try again tomorrow, but if you can, please get back to me about that combination valve and what exactly gets pressed in to bleed. Thanks alot for any and all help already.

Tin Indians Rule · « **Reply #6 on:** October 20, 2006, 11:06:09 PM »

Not trying to hijack the thread here but you didn't mention anything about adjusting the slack adjusters on the rear brakes once you installed the new shoes? What method did you use.

What kind of brake fluid pressure do you have at the rear wheel cylinders? You should be able to have someone pump the brakes about 4-5 times and hold the pedal down. While they are holding the pedal down if you open one of the rear wheel cylinders bleeder valves with an open end line wrench and the person in the car pushes firmly down on the brake pedal you should have enough pressure to squirt brake fluid all the way to the middle of the rear end. Tighten the bleeder valve and then have the person in the car release the pedal.

If you don't have that kind of fluid pressure then you either have your slack adjusters too loose, air in the line or a bad master cylinder most likely.

Your rear brakes should be adjusted just tight enough to drag a little when you spin the drum by hand.

Also, is the long brake shoe facing the front of the car or the rear?

Bench bleeding the master cylinder is great but not worth the effort to remove just to bench bleed it. You can accomplish the same thing with the MC on the car.

1onehotTA · « **Reply #7 on:** October 20, 2006, 11:54:33 PM »

I actually sorta felt the same way about bench bleeding the master cylinder, but I already removed it and bench bled it as I didnt the first time and am now willing to try just about anything. Im still not 100% certain what to press on the combination valve. I once replaced my master cylinder and removed and rebuilt the entire ABS elec. motor system on my Oldsmobile, and didnt have near this kinda trouble with it. My Olds I didnt bench bleed the master and had no problems with it, I was still learning then though, as I am now. Also though in my Olds the master wasnt sitting at an upward angle where air could get trapped in it, kinda made sense so I pulled my TA's and bled it good. I am getting good fluid flow out of it I believe, it is blowing the hose off my bleeder bottle when I really really pumped it and cracked the bleeder. That combo I think is my problem, I didnt have the right part pressed, but still if anyone knows, I need to know if its that center pin, or that whole brass piece should slide into the valve body. Mine had a rubber cap on the brass piece.

Tin Indians Rule · « **Reply #8 on:** October 21, 2006, 01:45:25 AM »

If memory serves me correctly all the valve does is separate the front brake system from the rear. Simply meaning that if you blow a line on the front 1/2 of the system the rear 1/2 will still function normally. And vice versa. It should be self centering once pressure builds. You should not have to mess with the pin.

Once you replaced the rear wheel cylinders did you install new shoes? Did you adjust them to where you can hear the shoe dragging against the drum when you spin the drum over by hand? Which way is the long shoe facing? Or, are the shoes the same length?