4 wheel disc brake master cyl. which one?

Jeff B

Jeff B

Thanos was right
Joined
Dec 23, 2006
Location
Lincolnton N.C.
did the gm caliper brake swap on the d70. Now the brakes are dragging in the rear due to the disc/drum type master cyl.

I am running a GM hydro-boost. Need to know what year model master cyl. to by that would be set up for 4 wheel disc & bolt up to the gm hydro-boost.

Thanks
 
I had one from a '60s or 70's corvette in the cj5 and with no help it worked pretty well. I've got it around here somewhere if you want to try it out first. But either way, let me see what year it's from.
 
ChrisM said:
I had one from a '60s or 70's corvette in the cj5 and with no help it worked pretty well. I've got it around here somewhere if you want to try it out first. But either way, let me see what year it's from.
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That would be great thanks.
 
It might be your proportioning valve, I had to modify my valve. If I ever go back into messing with my brakes again I'm gon'na use an adjutable one. I'm using a corvette MC also with wilwood calipers but no hydro boost.
 
I'm running the 78 Mercury Marquis MC for four wheel disc brakes on my cab truck. This is a popular one to use when swapping ton axles under a rig. It works good, and I have 42's on the truck. I am running a booster off an early 90's F350.
 
SSWaters said:
It might be your proportioning valve, I had to modify my valve. If I ever go back into messing with my brakes again I'm gon'na use an adjutable one. I'm using a corvette MC also with wilwood calipers but no hydro boost.
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I am using the wilwood adjustable valve.

drkelly said:
I'm running the 78 Mercury Marquis MC for four wheel disc brakes on my cab truck. This is a popular one to use when swapping ton axles under a rig. It works good, and I have 42's on the truck. I am running a booster off an early 90's F350.
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Do you know if that MC will bolt up to a chevy hydro-boost?
 
Jeff B said:
I am using the wilwood adjustable valve.
Do you know if that MC will bolt up to a chevy hydro-boost?
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No, I sure don't, but I can take any measurements off of it that you want. I don't know anything about hydroboost. Maybe try a search on pbb?
 
drkelly said:
No, I sure don't, but I can take any measurements off of it that you want. I don't know anything about hydroboost. Maybe try a search on pbb?
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Don't take measurements just yet, I'm gonna try the corvet master cyl.

Hopfully somebody will chime in that has experiance with the hydro-boost.

thank you.
 
I've done several and never had a problem with the rear brakes "dragging". I would assume you are saying they are not fully releasing? Look for a crimp in the line somewhere not allowing proper flow without pressure. If you don't find anything it may be a soft line. Simply converting to disc wouldn't cause it to drag.

Are the caliper new? If not it may be time to replace them.
 
GubNi said:
I've done several and never had a problem with the rear brakes "dragging". I would assume you are saying they are not fully releasing? Look for a crimp in the line somewhere not allowing proper flow without pressure. If you don't find anything it may be a soft line. Simply converting to disc wouldn't cause it to drag.
Are the caliper new? If not it may be time to replace them.
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Yes, they are dragging.

Calipers are new, so are all the brake lines.

Maybe as sswaters suggested I need to fool around with the proportional valve more.
 
I've never had to mess with the valve. The valve in theory just restricts flow to the rear. You might want to bypass it completely.
 
Sounds like your brake rod may not be fully releasing the piston in the MC, unless the MC has a built-in residual valve? (I'm assuming you've bypassed any kind of large junction blocks on the chassis)
 
Rich said:
Sounds like your brake rod may not be fully releasing the piston in the MC, unless the MC has a built-in residual valve? (I'm assuming you've bypassed any kind of large junction blocks on the chassis)
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Thats correct, I think there is a built-in residual valve in the master cyl. The booster & master cyl. are matched from GM.

I will pull them apart tonight to make sure, I had to replace the hydro boost.

The rear end of the truck that they came off of was a dually 14 bolt with drum breaks.

I ran all the break lines, the only block is the proportional valve.

Is master cyl. mounting point of a vacuum brake booster the same as a hydro-boost?
 
Well hell, got home from work & started taking stuff apart & found a stuck caliper. damn auto zone crap.


Thanks for all the replies guys.
 
Glad it was just a stuck caliper for you, less mess and bleeding.

The problem I had with my prop valve is it wouldn't let enough flow to the rear calipers. The frt was doing almost 100% of the braking, even with the corvette master cylinder, the rear was barely knocking the rust off the disc. Thought maybe yours was restricting flow back like the residual valve does. I know some older vehicles don't even have a prop valve in them.
 
Damn, I completely forgot about getting that info for you. Glad you got it worked out though.
 
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