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-   -   Rear brakes wont bleed. (http://67-72chevytrucks.com/vboard/showthread.php?t=750297)

WyattTX 11-11-2017 10:09 PM

Rear brakes wont bleed.
 
I have replaced every brake componet except the brake lines. I have also used a tool to hold my metering valve open, during the bleeding process. The front disk brakes bleed really well, but the rear drums do hardly anything. Every source I find tells me it is the metering valve, but as I said earlier, I have ruled that out. If anyone has an idea, what is causing please tell me. I am running out of ideas. Thanks.

mongocanfly 11-11-2017 10:49 PM

Re: Rear brakes wont bleed.
 
you might try bleeding the rear lines at every union and or fitting..checking for fluid movement...have you checked the metering valve at the outlet side to make sure fluid is going thru it?...look for pinched lines as well that might restrict flow...

68c10airstream 11-11-2017 10:55 PM

Re: Rear brakes wont bleed.
 
Obviously the rear shoes need to be adjusted very close to the drums, otherwise all of the fluid motion is being used up just moving the shoes in/out.

A trick that never fails to improve the pedal feel is to jack up the rear of the truck as high as you are comfortable, then do the same up front. If you can get someone to do the jack work while you look at the fluid inside the master cylinder and watch for bubbles to rise up to the top. If you see the bubbles, you are on the right track. Another way to do this is to just unbolt the master cylinder from the booster and tilt it up/down as needed.

The other thing that happens a lot is pumping the brake pedal frantically. This will typically introduce air into the back end of the master cylinder. And if by chance the master is mounted uphill in the front you will frantically be putting air into the master that just gets trapped in the front uphill chamber.

Just move the brake pedal slowly as you bleed the lines. Remember this; as you release the pedal the only thing that keeps the lip of the plunger seal tight to the bore is how much tension is left in the rubber cup. Now throw in a rust pitted bore and you got the idea!

Another tip is never bottom out the brake pedal when bleeding because if the master cylinder has some mileage on it crud will migrate and get pushed forward, and when bottomed out this crud will move through the system. Not ideal!

If you think you have air in the rear another trick is to pinch the flex hose at the rear axle area and if the pedal improves your trouble is in the rear brake area. Pinching the flex hose isn't ideal but if desperate oh well.

68gmsee 11-12-2017 10:48 AM

Re: Rear brakes wont bleed.
 
You didn't mention what vehicle or year you are working on but if it's an old one, you might want to check the rear rubber brake line between the axle brake lines and the frame. It collapses and swells internally with age clogging it up and either restricting or completely blocking fluid from passing through. Could even break some pieces off and clog the line.

The only way to know for sure is to remove it and inspect it. On mine it's above the passenger side rear axle.

WyattTX 11-14-2017 08:13 AM

Re: Rear brakes wont bleed.
 
Thanks for the help guys. Hopefully I will get this sorted out.


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