Power brake disc/drum conversion

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65 Valiant Vert

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Got an MBM master cylinder and porportioning valve years ago to convert to a double master cylinder with discs front drums rear. I am trying to bleed the brakes, have the master cylinder bench bleeded but can't get any fluid to the rear brakes as the first to bleed is the right rear brake. The car has all new brake lines. Is their someone out there that could help. Do I need to get a vacuum bleeder to get brake fluid in the lines as they are new and the master cylinder doesn't push enough fluid when everything is new?
I also am going with Silicone brake fluid dot 5 as I don't want to ruin any paint. Thanks in advance for any help.
 
Remove the bleeder screw entirely. It could have something plugging its small port. The fluid should run thru just under gravity, indeed many people bleed that way. I use a vacuum pump, but in concert with a helper on the pedal and a good "down-down" call response (wife is trained). Certainly catch all of that valuable silicone fluid in clean jars. If free of oil, just filter and re-use.

Kind of late, but I would have run a little ethanol thru the new tubing, then blown w/ air to remove any oil or shavings and let it dry. I did that with my old tubes before connecting to the new rubber hoses and wheel cylinders. That also insures there are no restrictions. I also used silicone. People have found brake hoses to degrade internally and get a flap of rubber than blocks the flow, even under pressure, but we assume you used new hoses. The prop valve seems the main suspect.
 
Thanks Bill for the reply, good information. Since posting I am finding a few other problems. One problem is following the directions on my flaring tool. It said to use the inverted flare at the step on the adaptor, wrong wrong wrong. I was making the inverted flare smaller than what it should have been, damn chinese junk. This caused two problems. The flare seat was to small and not sealing properly on the inner seat, also the flare would cut into the brass internal seat and making a ridge so when you used a proper flare it did not seal properly because of the ridge. Please pay attention folks it will save you alot of grief and I never see any posts to be careful of this. You chance ruining your inner brass seat requiring replacement of new parts again. Thanks again Bill for taking the time to give that important reply. Still working trying to get the brakes operational. :eek:ops:
 
With bad flares, the fluid from the MC must have been running out various places. Expensive loss w/ silicone fluid, but at least it won't eat up your paint like glycol does.
 
Hi Bill. Redid all the flares so good there now but need a new proportioning valve as the chinese one supplied by MBM is leaking from every position. Would it make a difference if the inlets to the valve are reversed? It doesn't specify witch bank of the master cylinder supplies fluid to the front or rear brakes of the car through the proportioning valve?
 
It matters, you can't interchange the "in" and "out" ports of the proportioning valve. I suspect it would not flow thru if you did, guessing at how the internals work. You want to plumb the proportioning valve to the MC port "for rear brakes". That is the fwd port on all MC's I have seen. Look for photos of MC/boosters in brake kits from Wilwood, SSBC, and others. Most have a "combo valve" right under the MC and you can see how it is plumbed, though most also plumb the front circuit to it as in 1970's Mopars.

To be exact, most newer cars have an "X-split" pattern (fed mandate? my 1996 Voyager does), meaning a LF-RR circuit and a RF-LR circuit. Even if you use such an MC, use the fwd port for your rear circuit.
 
Bought a new proportioning valve U.S. made SSBC. Plumbed correctly. Still having problems getting fluid to the rear axle even if I remove bleeder completely at the wheel. Not quite sure what the problem is, no kinks in brand new line and all brand new components. I have heard that the MMB master cylinders don't have the same pressure as stock. Do you think that could be the problem? Sure getting frustrated with what I thought would be straight up installation. The SSBC valve looks like a block of aluminum with just a adjustment valve for the rear brakes and five ports, no metering valve that I can see. Larry
 
Car is running great, still got brake problems though. Seem to get pressure to the rear brakes, absouletely no pressure to the fronts. Tryed adjusting the valve in out all over. I am wondering about the chinese MC. Would there be less pressure from the front and rear? Used a hand held vacuum to help bleed front brakes, still no pressure.
 
I am pretty sure that all MC's produce the same pressure at both ports because the "pressure imbalance switch" in the distribution block (or ABS block) looks for that and trips if the 2 circuits don't have the same pressure. If there is a proportioning valve, it is in the rear circuit, after the imbalance switch.

Transiently, there are slight differences in the pressures, such as a "metering valve" halts fluid flow to front calipers until rear drum shoes have had time to move into contact and a "residual valve" holds ~10 psig on the rear wheel cylinders after the pedal is up to prevent leaks. But, those are all low-pressure events (<20 psig) compared to braking pressures (>100 psig) so don't trip the imbalance warning. Much of above changed with the X-pattern of the 2 circuits in ~1990+ cars (no longer a front-rear split).
 
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