The previous owner of my '67 had a disk brake conversion done by Scarebird in Seattle. All seemed fine, but during a recent drive I found myself fighting some drag. All four disks were quite hot. I jacked it up and both front and rear disks can be turned by hand, but with some noticable drag.

I disconected the brake pedal to see if the rod adjustment was off... all good there. The booster (11") and the master cylender seem new.

My next guess is the portioning valve... I don't think that I have air in the system as the pedal feels firm.

Any other thoughts?

-Kris

The drum brake distribution valve has a check valve in it that holds pressure on the wheel cylinders to keep the seals pressureized. Make sure they replaced the distribution/proportioning valve with one designed for four wheel disk brakes.

OK... How do I tell what I've got?

I don't know how you can tell, but I think that PMI hit it on the head

The OE distributor was the same part for disc and drum and held no residual pressure or any other balance valving to either the front or rear. A replacement valve could, though I have not heard of one holding pressure to the fronts....

the OE residual valves were held inside the master cylinder. If you are using a 4wl drum master cylinder, that could be it. A disc/drum master might have one in the rear port.

Your first step was a good one. If you disconnected the rod and the brakes still drag, then that is not it.

Your next step is to loosen a fitting at the master and see if the brakes release. Also check to see if someone has installed inline residual check valves.

picture of typical drum brake master

picture of OE distribution block
this block contains a warning switch only.

inline residual valves

residual valve possibly located inside master:

to check for the presence of this valve, you would need the lines away from the master so you could insert a paprerclip or somesuch into the outlet port(s), and feel for something blocking the way, with spring tension.

swelled hoses or seals can also make the brakes drag. make sure no one poured anything in the master which does not belong.

here's a cutaway of a combo valve from MPbrakes. It says it has a residual valve for the rear brakes. This is a disc/drum only valve.


most of the replacement valveblocks will have the two bolt holes like that. Brass ones are shaped like that, Iron ones are a little bigger.

I knew I should have deferred that question to SixStarved. Thanks, again, Scott!

Thanks a TON! Here is what I found out so far...
Scarebird used the following to convert a power drum car to the current 4 wheel disk setup:

Master Cyl = 1981 Trans Am
Booster = 1985 Iroc
Front Calipers = 82-92 Camaro
Rear Calipers = 79-85 Eldorado

Removed the residual pressure valve in the new master cylinder for the front.
Left original distribution block.

I have a Mutt on my hands!

the first thing i would do is loosen one of the bleeder screws.if you see fluid squirt out and the rotor frees up,your problem is probably a hose or a valve.if that dont do it check the calipers.

Well, hey the guy tried. At least you are going to make it right. It does sound like quite the mix and match. I hope the rotors match the calipers? I didn't even know the 82-92 camaro would fit. Just be happy you don't have drums all around!

Now you wanna see a mutt? Come over and take a look at my car :rolleyes:

Scarebird uses those calipers with s10 rotors and brackets he makes to bolt on the drum spindle. I dont know on the rear rotors, but the frnt calipers are the same calipers the s10 uses up front, and the 80-85 eldorado rear calipers are basically the same as the 3rdgen rear calipers.

The kit is balanced but the brackets seem flimsy compared to OE, and the rotors and calipers are smaller too, but it seems to work.
I dont know why a master from an 81 either... an 82+ would be a better size IMO... since you are basically running a 3rdgen brake set up.
BTW those aluminum masters have no residual valves as far as I know.

69FBM is right on the money. You want to start loosening fittings and bleeders to check for restriction. Since it is all 4 wheels, loosen the fittings at the master, and if the brakes release, it is a problem at the master/booster. If not, start at the wheels and work your way up.
Loosen a bleeder screw, and if that brake releases, it is a problem above the calipers (hose, check valve, master, line...)
If the brakes dont release when you loosen the bleeder screw, the problem is at the wheel (caliper, hdwre, bracket...). It would be unusual for all 4 calipers or hoses to go bad at the same time unless there is a contaminant.


You might also try unbolting the master from the booster to see if the brakes release.

i guess there is no sense in installing the correct parts.that would be too easy

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif"> Just be happy you don't have drums all around!
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Not sure what you mean by that I have drums all-around and have not had any problems in over 3 years, and I drive my car alot more that just "weekends". Have made numerous trips from Corpus to Houston(400 miles round trip), with no problems. Just ask that cat that I missed in Houston a couple of weeks ago, those drums saved his *ss

Kelly

Those drums worked great! And the cat never looked back! lol

Here's a poser for you guys:

If my e-brake is holding some pressure on the rears... would it hold some pressureon the fronts too?

I ask this as there is quite a bit more drag on the rear. I assumed that since it was all 4 wheels that it was not the e-brake....

If it turns out to be the Master/Booster set up, do I fix whats there or install a "new" setup like the one from CPP???

the parking brake should have no effect on the front.

on the master/booster, it depends. dont burn the bridge until you cross it

emergency brake is mechanical on rear brakes only, master cylinder hydraulic effort is on all four wheels. E-brake is easy to eliminate by disconnecting the cable at one end or the other (just drop the underdash bracket)

Call me Mr. Turtle... I have a heavy travel schedule so I only get to this in fits and starts..

I cracked the breakline at the master and it released the brakes.

So I have determined that it's either the master cyl. or the booster or the connecting rod in between.

What am I in for to adjust this connection?

get the brakes dragging again and unbolt the master from the booster. If they continue to drag, you will have to check for a residual valve inside the master. If they release, you want to check the pushrod-master relationship.

I'm travelling in L.A. this week... so I'll try that this weekend.

Thanks!

Hello again all-

I just wanted to update you all that I did replace the portioning valve and got the problem solved.

Thanks again for all the help!

-Kris