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Frame/Suspension/Brake... Talk & Q&A All things... Frame/Suspension/Brake

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  #1  
Old 05-13-2019, 05:56 PM
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Default Drum brake problem!

I'm to the point of bleeding the brakes and seeing what I've got. So far the front discs are working but the back drums aren't.

There is a small amount of fluid coming out of the wheel cylinders but not enough to move the cylinders. I've bled them several times and I'm not getting any air.

I've checked all connections for leaks and fixed them. The vacuum is not hooked up engine isn't running yet. That shouldn't be an issue but I could be wrong. Wrong master and valve?? I'm stumped any suggestions please. Thanks guys!

This is what I have. GM disc/drum master cylinder with 7" dual power assist. Front brakes hooked up to the front reservoir and rear drums to rear. Hope that's right?



GM proportioning valve hopefully it's a disc/drum.


9 1/2" GM brakes new wheel cylinders and shoes
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Old 05-13-2019, 06:24 PM
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Even if the lines were reversed, which I don't think they are, I'd expect you would still get pressure to the rear brakes...
When you bled them how much pressure did you get back there?
wondering if maybe that proportioning valve might be shifted over to the block off the rears and isn't centering again.... ? if that isn't it then I'm thinking that there is something wrong with the master cylinder... maybe an internal bleed back?
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Old 05-13-2019, 07:19 PM
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HUGE PICTURES.



Are you getting fluid consistently and steady at the rear?

A common problem is lack of free play at the MC pushrod... if the piston and rod can't fully return with adequate free play, the piston never exposes the "return" orifice... if that's the case, the cylinder cannot refill, nor add fluid to the circuit...

.
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Old 05-13-2019, 07:22 PM
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Did you bench bleed the MC?

Toad
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Old 05-13-2019, 09:23 PM
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[QUOTE=Dr Crankenstein;513239]HUGE PICTURES.



I didn't want to mention the HUGE PICTURES but since you did yes they are HUGE!!
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Old 05-14-2019, 07:34 AM
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I'm thinking the front reservoir goes to the rear drum brakes and rear reservoir goes to the front discs...
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Old 05-14-2019, 07:43 AM
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If the reservoirs are two different sizes then the large one is for the disc brakes and the small one is for the drum brakes.
If the reservoirs are the same size then, it doesn't matter.
The reason for the large bowl is because the calipers hold more fluid as the pads wear. Drum wheel cylinders always return to their original position pushing the fluid back into the reservoir.
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Old 05-14-2019, 08:00 AM
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Can't see pix...the large reservoir is in the rear on mine and several others in my barn...don't know what MC dmw56 has here...
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Old 05-14-2019, 09:32 AM
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Sorry about the huge pictures! Don't know how that happened. Both reservoirs are the same size do I figured it didn't matter.
I did a little more digging and found a combination valve bleeder that is screwed in the warning light fitting. I guess to keep the valve centered. Anyone know anything about that. I've never bled a new combination valve.
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Old 05-14-2019, 09:34 AM
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Quote:
Originally Posted by Toad View Post
Did you bench bleed the MC?

Toad
Yes I did. I was getting good flow too. I'm thinking something up with the valve.
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