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Old 10-29-2007, 09:32 AM
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disck/drum to disk/disk

I am going from disk/drum to disk/disk. I have a non power master with the two round circles on the cover. I am pretty sure this will work with disk/disk. Can I use the same valve? I have seen it done in a mag two ways. One the person took out the front nut and spring on the valve with the front cylinder to the back and the back to the front. In another they did not mention taking the nut out but did move the lines master cylinder lines front to back back to front. What to do? Will a dick/disk valve leave the lines from the master front to front back to back?

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Old 10-29-2007, 07:29 PM
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i just did a disc/drum to a disc/disc conversion on a 50 gmc not to long ago.
What i did was kept the 69 camaro master ditched the bad combo valve, installed an adjustable prop valve in the line to the rear with a 2 psi residual
pressure valve in both the front and rear lines. Presto!
I left the lines in the original ports on the master cylinder. Installed the rear RPV in between the master cyl and the APV.
here are some part no.s that i used from Speedway.

Residual Pressue Valve 2 psi..... 835-2601874 $17.95 x2
Adjustable Proportioning Valve... 910-31355 $32.95 x1

Hope this might help.
Tom
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Old 10-29-2007, 08:06 PM
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A disc/ drum master has some different springs in the primary and secondary pistons than in a disc/disc, but you should be ok as long as you have enough volume to run your new rear calipers. You may still need to go up one size, even though you are staying manual.

Check your master cylinder for RPV's in the output ports...many disc/drum masters have a 10# one in the rear port.

They are easy to spot, just probe the port with a blunt peice of paper clip to see if there is a somewhat soft obstruction in the brass inverted flare seat about 1/4" in.


You can remove the rpv by tapping the brass seat with a 6-32 tap , then putting a 6-32 screw with a big washer and winding the seat out. Take out the rubber RPV valve and spring then put the seat back in.


You can disable the stayoff,(metering), valve, and then use the combination valve as a distribution block, but I don't know if the proportioning valve will have the right setting though, being as how the factory setting is for drums rear, which operate at lower pressures than discs..I should add that the combo valves that I have tried to take apart usually have some kind of thread locker on the fittings that make it very hard to dissassemble them with out tearing them up.


In a 4 wheel disc system the magazine guy you refer to, swapping the front outputs onto the rear is probably done to take advantage of the stayoff valve acting like a delay valve, in an effort to try to duplicate an old dirt track trick.

(Lets the fronts come on first, then the rears).. But then he'd have a pressure reduction to the fronts.....DOH!!!

More magazine make believe tech.
Want some blinker fluid with that ?

If it were me, I'd order a disc/disc combination valve from one of the suppliers like Brake Tech Solutions, CPP, or Master Power.

I recently learned from a brake system engineer that the function of those "proportioning valves" is not as advertised, they are really a delay valve. I always wondered why they didn't really do anything unless you stabbed the brakes, as in a panic stop..( I have always said that is the only time they work)

I need to do a bit of testing myself to see.

In any event, don't leave the disc/ drum combination valve with it's stayoff valve in place, the last thing you want to do is have the fronts delayed in a 4 wheel disc system. It won't make any significant difference in normal driving, but the effect of that valving will show up in a big way if you need to do a panic stop...especially in a corner.

You can use the 2# RPVs, they are really only necessary in systems with the master below the floor, but they won't hurt the performance of any system.


Hope this helps.
mikey
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Last edited by powerrodsmike; 10-29-2007 at 08:30 PM. Reason: because I can. Some forums don't let you edit your posts...did you know that?
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Old 10-29-2007, 08:28 PM
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what application are you workuing on?
I should add a little more info. In my particular situation the truck was already built and finished, but had crap for brakes when my customer bought it. He (the seller) claimed it just started having a problem after the rear left line got a hole in it. but the rear caliper pistons would retract all the wayback into the piston cyl. so I didnt have to mess with the master. this truck did have power brakes and the booster and the master were mounted undercab. please dont do any work based on my particular application. cars are like women, the same but all different!
Tom

Last edited by TRLBLAZR60; 10-29-2007 at 08:33 PM.
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Old 10-29-2007, 08:35 PM
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55 chevy

It is a 55 chevy. I have a front disk kit installed in front. I am putting in a 99 ford explorer 8.8 rear end and it has disk. The front disk I think is out of a Monte Carlo 80ish.
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Old 10-29-2007, 08:53 PM
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The manufacturer or supplier of the kit should be able to easily inform you of what all is necessary, once you give him your info and or part numbers. They usually have a toll free tech line. I suggested the kit to my frind but he's kin of a tight *** that way. Guess thats why he has 9 or more hot rods.
what brad of kit do you have?

powerrods mike had some great info.

tom
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