rear drums not workin

[chmurphy]

Hello, i got an issue with my rear drum brakes not working. its a 86 silverado 305 700r4 2wd reg cab long bed.

I originally thought the wheel cylinders were bad so i replaced them, re-adjusted the shoes, gravity bled the rear, and when i wedge a 2x4 on the brakes the front brakes are working but the rear drums still rotate in the air. Pedal feels firm , really don't think there's any air left in the lines? Am i missing anything obvious?

Thanks for input in advance.

 

[PrairieDrifter]

Is there resistance on the back wheels or none at all? Have you driven the truck since doing brake work? Was the truck running when you tried the 2x4 test? Have you replaced the rubber line from the frame to the axle at any point or is it original?

 

[Bennyt]

Have you adjusted the shoes correctly? You can pull a drum half off and have someone step on the brakes and look to see if parts are moving.

 

[chmurphy]

Is there resistance on the back wheels or none at all? Have you driven the truck since doing brake work? Was the truck running when you tried the 2x4 test? Have you replaced the rubber line from the frame to the axle at any point or is it original?

Doesn't feel like any resistance at all. Haven't driven it since the cylinders were replaced and brakes bled yesterday, and no the truck wasn't running. Does it need to be running? Some sort of vacuum functionality? Havent replaced the rubber line, I read last night that sometimes they collapse internally, no visual indicator.

Have you adjusted the shoes correctly? You can pull a drum half off and have someone step on the brakes and look to see if parts are moving.

I think they're correct, I get them close enough there's a little resistance pushing the drum back on. I don't think the parts are moving. Is this an issue with the proportioning valve? When I was doing the gravity bleed, it was flowing out at a good rate.

 

[PrairieDrifter]

Doesn't feel like any resistance at all. Haven't driven it since the cylinders were replaced and brakes bled yesterday, and no the truck wasn't running. Does it need to be running? Some sort of vacuum functionality? Havent replaced the rubber line, I read last night that sometimes they collapse internally, no visual indicator.

You won't be able to see a collapsed hose, but if it bled fine and they aren't hanging up, the hose should be good.

The brakes don't work at full capacity without the truck running and supplying vacuum. It's called a brake booster for a reason lol.

To adjust the brakes you need the drum installed and you need to adjust them out till they make contact with the drum and create a slight amount of consistent drag. The brakes also seat themselves fully after some time driving.

Make the brake adjustment like I said just make them snug on the drum, then I would leave it alone until you can drive it, then make sure that it's functioning. Doing brake jobs you should pump the pedal before you put it in gear. Every time you do a brake job, to make sure you have brakes before you put it in gear and crash into something.

 

[chmurphy]

You won't be able to see a collapsed hose, but if it bled fine and they aren't hanging up, the hose should be good.

The brakes don't work at full capacity without the truck running and supplying vacuum. It's called a brake booster for a reason lol.

To adjust the brakes you need the drum installed and you need to adjust them out till they make contact with the drum and create a slight amount of consistent drag. The brakes also seat themselves fully after some time driving.

Make the brake adjustment like I said just make them snug on the drum, then I would leave it alone until you can drive it, then make sure that it's functioning. Doing brake jobs you should pump the pedal before you put it in gear. Every time you do a brake job, to make sure you have brakes before you put it in gear and crash into something.

Thanks for your help, i'll try to come back when i get it on the road and update.

 

[dvdswan]

Why did you replace the wheel cylinders? Were they leaking? Did you think they were just not working?

If they were leaking, then you will want to replace the shoes as well. Brake fluid acts as a lubricant on the shoes so they can not grab the drums. Whereas, gear oil swells the brake shoe causing them to grab and lock up the wheel when braking.

 

[chmurphy]

alright probably made the wife mad but re-adjusted the shoes a little more snug, and started the truck and voila they worked.

 

[Octane]

Always make sure your brakes function before going onto the road. That's easier than crashing and telling the officer your brakes went out...when they're new.I replaced virtually my entire brake system and it took a bit to get adjusted and all air out.

 

[PrairieDrifter]

alright probably made the wife mad but re-adjusted the shoes a little more snug, and started the truck and voila they worked.

A lot of people don't know that drum brakes are supposed to have a constant light drag. Not a lot of drag, but consistent and firm.

 

[MikeB]

Did you use new shoes on drums that have been turned? If so, the arc of the shoes will have a smaller radius than the arc of the drum. That causes only the center 1/3 or less (!) of the linings to make contact with the drum. Back in the day, shops would "arc in" the shoes so the entire lining surface would snug up against a freshly turned drum. These days, all you can do is try to reshape the linings with a very coarse file, or simply buy new brake drums.