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Old 12-09-2004, 11:17 PM
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brake issue

hi. i own a 63 sedan deville. i just converted my front end to disc brakes. i used the assemblies off the 69. everything is about finished, i wanted to know if anyone knows about the braking system on a 69 cadillac. on the proportioning valve, (brass box with little nipple on it for brake warning plug) anyway on that valve i have two lines that obviously go to the master.. on that same box i have two ports.. one is a 1/4 in female, and the other is bigger,,,, female plug. im curious which one trials to the front brakes, and which goes to rear? also on the master which port is front, which port is rear? and i think last but not least, once i have my lines all plugged and ready, is there a trick to bleeding this brake system? do i really need to bench bleed, im using anew 69 booster, and a 69 eldo master. and if anyone is the authority on the 69, am i correct in saying that the brass box im talking about is for sure the proportionvalve for this car or is it just a safety switch.

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Old 12-10-2004, 05:01 AM
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Proportioning valve...............the larger line goes to the front. I thought that there should be 2 lines to the front, One to each wheel from the valve...............maybe not in 69.

Master. The larger resevoir goes to the front brakes. If they are the same size, the one closest to the firewall, which is always the larger one.
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Old 12-10-2004, 09:22 AM
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The brass block on a '69 is likely just a distributor and warning switch. GM as a rule did not change to combo valves until '71. Before that, they had a separate hold-off (metering) valve for the front, and many models also got a separate proportioning valve for the rear.

You can easily tell if it is a combo valve or just the dist/switch. If it has a rubber button and a big nut, it is a combo valve. Otherwise you need the separate valving for a balanced system.

The 1/4" master line goes to the rear brakes. It is 1/4" from the master to the switch/valve, and to the rear hose, where it Ts off to 3/16" across the rear axle.

The 3/16" master line(s) go to the front. Single 3/16" line from master, then two 3/16"lines coming from switch.. one to each front wheel.

If the master has resivoirs of the same size, GM usually put the front brakes on the front resivoir back then, but it could be either way. If one resivoir is larger, it goes to the front.

You may be able to tell by the brass seat inside the master ports. One might have a larger flare, and goes to the rear. You cant tell by the fitting size, as the line fittings were all different sizes for ease of assembly. If you have the OE lines and master, you may be able to tell from that because the fittings do not interchange from port to port. They may also be the same fitting size for the master and valve on the same circuit though. (hope that made sense)

Yes you need to bench bleed... Always.
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Old 12-10-2004, 10:23 AM
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Here is a typical GM master with what appears to be the same size resivoirs. The front is for the front brakes. This is actually a drum/drum master, but their disc/drum were similar at first.

note that although they appear to be the same size, they are not. I just learned something too

This one is a typical distribution block with no valving. GM used the same one for disc and drum cars. This one I think is a Chrysler, but GM was very similar, save for the large weight:

note it is 5 port, with warning switch, with no button, or large nut to hold the prop spring/piston.

Here is a typical pre-71 GM prop valve used with the above valve, to reduce pressure to the rear brakes:

This one is a GM valve which holds fluid away from the front discs, allowing rear drums to catch up. It is used in the front circuit with the above:

you cant see it in the pic, but it also has a button to assist with bleeding.

Now here is a later brass combination valve for disc/drum. Note the button on the front, and the large nut on the back. Sometimes there is a nut under the button too.

and a diagram of above:

Here is a disc/disc valve. Note the lack of metering button:

GM has always used 1/4" line for the rear brakes until the axle, and 3/16" line for the front on RWD cars for as long as I can remember.

Some of their early combo valves were cast iron, and they later switched back to brass.
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Old 12-10-2004, 11:34 AM
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I'm right in the middle of doing a power front disc swap on my 57 Buick. Yesgo , your explanations and pics are great, but have raised some more questions.I'm using a GM pickup master and prop. valve.The car is3/16 to the rear drums right from the old distributer. The line is in excellent condition, so was wondering if it is a problem with smaller line, and also if there is an adapter fitting made to go from the 1/4 out of prop. valve to the existing 3/16 line?
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Old 12-10-2004, 01:50 PM
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You can get adapters or different thread size line fittings. If the combo valve was made for 1/4" you should probably use an adapter. NAPA sells them.

I doubt you would have a problem with the smaller line. Let me know if you do though.

I have seen a lot of vehicles with 3/16" rear line. The above info I should have specified was for 67+ GM RWD drum/drum and disc/drum dual circuit, with which I am the most familiar.

I don't know why some manufacturers went to 1/4" for the front to rear line. Sounds like it is for volume, although I'm not sure that makes lots of sense, hydraulically, considering the rest of the system. I have been trying to figure that one out myself. I also have no idea why some had the front circuit of the master for the front, and some for the rear.

One note on the combo valves... the sections are designed with specific vehicles in mind. The truck one is likely a good choice for your Buick, as the weight transfer vs. cylinder sizing may be very similar. There are ways to tweak the balance if you need to. If the rears dont seem to do much work, the first thing I'd do is switch to the larger line though.....

Last edited by yesgo; 12-10-2004 at 03:37 PM.
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Old 12-11-2004, 11:49 PM
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so i know you prolly explained it but im still a little hazy on some stuff ... so now im decided that the front reservior(farthest from booster) is def front(disc) port. and of course the other is rear. the front has a 1/4 in line that runs to the "proportioning valve" the rear ports plug is a bastard size or something, i got a 5/16s plug to plug it cause its the next size up from 1/4, and it was to big??? im not sure why that is. anyway that line also comes out of the master and goes to the "prop valve" so im good till point. now the prop valve is in question. its a brass junction looking box that is obviously meant to be mounted to the frame. it looks alot like the Chrysler picture you showed. it has the warning light post right btween the two incoming lines from the master. its a rectangle shape, and those lines from the master go in the top side(longer side) then out of both of the 2 short sides of the rectangle are the outlets that go to both disc and drum. front and rear. i know which outlet goes to which set of brakes. so basically im good to go right? plug it in and everythings finished?
the only thing that doest make sense is that there no "metering" or the rubber button you mentioned. and appearently thats there to help me bleed the system. so if there isnt a button then does this mean that it isnt a proportion valve, or equalizer, and that my car wont disperse the fluid properly and my brakes wont work right? i called the junk yard i got my spindles and stuff from and he said it doesnt have that i guess. so im confused.. i guess i need to maybe buy a 69 book unless of course you can tell what it is i should look for or have. again thanx for your help thus far. you are extremely informative, i am thankful for the time you took to post all those pics.. blackbeard
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Old 12-12-2004, 09:12 AM
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If there is no button, it is not a problem. It will bleed fine.

What you have is the distribution block with a warning sensor.

All it does is basically 'T' off the lines from the master, and provide a warning switch to trip the brake light if there is failure.

The different valves are not necessary for the system to function.
They are primarily for slippery conditions, better pad life, and panic stops. (it makes it more safe)

I still think the 1/4" line goes to the rear brakes, but I cant always be right.

Make sure you know which resivoir goes to which brakes.

You wont be able to tell by the fitting sizes because masters dont always take the standard store-bought sizes that come on the tubes.

Here are some common fitting sizes: (diameter X thread count for tube size)

3/8x24 for 3/16 tube (standard; comes on store-bought tube)
7/16x24 for 3/16 tube
1/2x20 for 3/16 tube
9/16x18 for 3/16 tube
7/16x24 for 1/4" tube (standard; comes on storebought tube)
1/2x20 for 1/4" tube
9/16x18 for 1/4" tube
1/2x20 for 5/16" tube (standard)

you can see pictures of these fittings and some other quasi-accurate info @

You can just use adapters if you get the right ones.

Don't worry about the valves for now. You could even just get a 'T' off the master for the front brakes, and run the rear straigfht to the master, eliminating the block completely.

Last edited by yesgo; 12-12-2004 at 09:17 AM.
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Old 12-13-2004, 10:11 PM
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its in and bleed

ok so i got everything together, i went ahead and used that prop valve i have. so it goes master, prop valve, trails to front junction box on frame that aplits it into LEFT AND RIGHT, then from prop valve to rear junction, that also splits. so ya i guess i might not need that prop/safety/dummy light valve. but i made it work, and it never hurts to have everything off the original setup i guess. which brings me to my next problem its all done and bleed. the only issue now is my rims.. as you know im putting a 69 set up on a 63. im trying to use my 63 rims but they rub on the caliper body. i used a 5/16 spacer and still a bit of rub. i spaced it with some washers as well and now i think all i hear is the pads on the rotors. (is that ok to ride that way? will that nose go away) anyway. so its approx 3/8s spaced right now, which now gives me alot less lug stud to bholt to.. NOT so SAFE. i really want to keep my hub caps cause i just love the 63 cap style. so i guess my main question would be,, can i use a 69 rim(bigger offset or depth to clear caliper) and still be able to put my 63 caps on those? then i wouldnt have to go and change the lug studs on each rotor.. real pain. i blieve both wheels are 15s.. i guess it would be a matter of how deep is the lip where the cap fits? if it is possible to do what it is im talking about ill be extra excited cause i have afeeling my rims are not true, so this might solve some vib. problems. anyway thank you for your time and concern. blackbeard
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Old 12-14-2004, 07:35 AM
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Use the disc brake rims. The hubcaps very well may fit. If they do, it's a bonus on top of being safe.
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