Hello all, Ive got a tech question for you all. I put in a disc brake conversion in my50 chevy with one of those ebay kits that come with everything. the problem is that my brakes do not seem to retract and continue to grab until the pads are smoking. why is this? is it air in the system? Ive got a rebuilt 50 chevy master cylinder that is rated for the powerglide tranny. any help would realy be helpful. thanks all! "universal parts are known not to fit anything universally"
If you're using the stock master cylinder made for use with drums there's probably a built in residual pressure valve installed in it. Disk brakes don't normally require a residual valve. The residual pressure may be preventing the pistons from retracting. If you find that to be the cause, the valve can be removed from the master cylinder, but you'll likely need to install one in line to the rear drum brakes. Bob
X2 and if the master is under the floor a 2# front, 10# rear and maybe even a proportioning valve to the rear as well.
I think bobscogin nailed it with the residual valve issue. But I wonder if it might be almost as easy to just upgrade to a later model drum/disc, dual channel master cylinder? You won't have to splice in a seperate residual valve for the rear drums and there will be a little extra safety built into the system compared to the old single master cylinder.
i've always thought the master cylinder had to be changed to a dual due to the fact that wheel cylinders and calipers require different pressures/volume. did the kit recommend the original master?
In the interest of keeping my response directed at the cause of the problem, I didn't elaborate enough to suggest that, but I agree. I'd definitely upgrade to a modern dual piston master from a car with front disk / rear drum. Bob
Thanks for the quick help guys! The kit said the stock master cylinder would work, but I do plan in the future to upgrade to a modern dual channel type. In the quote: Disk brakes don't normally require a residual valve. The residual pressure may be preventing the pistons from retracting. If you find that to be the cause, the valve can be removed from the master cylinder. Where is this valve located?
It's in the end of the master cylinder where the line attaches. I'm not sure of the details of your master, but it probably has to be disassembled to remove it. If you take it apart, you can push it out by sticking a rod in the outlet port and pushing toward the open end. Bob
Some are under the brass seat where the line connects. The seat is brass and can be removed by pulling it out with a self tapping screw. Never tried it myself though. I'd check a manual for an assembly diagram.
Thanks for the info guys! I'm going to climb under it tomorrow to try and solve this issue. thanks again, Nick.
FIXED!!! Thanks a TON guys!!!!!!!!!!! i was able to take her out on the maiden voyage today. I would have never figured it out on my own. thanks again. Nick.
Good for you. If you keep the stock master for long, make sure you keep tabs on the fluid level. For one, Disc calipers displace more fluid as they wear.
Well, I'm back to having drag issues again in the front disc brakes. Here is my problem. when the car is cold its rolls easy but as you drive the car for a few miles it starts to feel like you have the brakes on. and when you drive it for about 5-6 mile as you apply the brake pedal it catches higher than when its cold and the brakes really drag allmost like you have applied the brakes to the point that its starts smelling and brake dust all over the front rims. here is the funny part if you stop and let it cool down it all go's away until you move a few miles and it starts all over again. it seems like the brakes have pressure in the line. has this happen to anyone on this forum?
Is it possible that you twisted a brake hose when you put the calipers on? I say this because I'v done it...once. Master cyl pressure will allow the brakes to apply, but slows bleed back into the master through the kink so the brakes stayed applied.
Thanks for the quick reply guys! I don't think the hoses are twisted, but I will check. I do have a little play in my brake pedal. I am using the stock master cylinder as well. Im starting to fear that I may have to put the drums back on. uhhgg.
I would go to your local parts store and get a $20 master for a car with disc/drum brakes. Is your master still under the floor? or did you move it? Is it a single line master?
im doing a disc swap on my olds and using my original mc. i read from a donwow post that u have to lose the check valve from inside the mc or the brakes wont retract. mine was the last thing i pulled out of the mc when i rebuilt it.
I pulled out the check valve on my ms as well. but for some reason they are still not retracting fully. I thought it might be because I have new rotors as well as calipers and that it just needed to wear in for a while, but I guess not.
Are they a single piston floating caliper? If so make sure that the calipers can move freely on their guide pins. Also possible that a piston is sticking in the caliper and not returning, but kind of unusual if it's doing it on both sides. With the master cylinder under the floor, I'm wondering if any of your exhaust is routed near it or any of the brake lines. Maybe enough heat to expand the fluid and partially apply the brakes even without any pedal pressure.
they are single piston floating caliper. I didn't know that it should be able to freely move back and fourth on its guide pins. So if I have the tire off with it jacked up,should I be able to move the caliper? I do have custom 2 inch true dual exhaust, so I will check to see if they are by the brake line. I really am grateful for all the help guys!
Bottom line is that you can't successfully run a disk/drum brake set-up with a stock 50 chevy master cylinder. Now I know someone or two will say I'm full of shit, but ask any respectable disk brake kit shops, Mor Power (MP Brakes) Fat Man, SSBC etc. If you bought it on E-bay and it was a kit that uses a stock 50 chevy master the person shorted you a correct master for your application. It was probably very inexpensive compared to a reputable manufacturer. Sorry to rain on your parade but these are the facts. Pat
The pushrod in the master might be held in place with a snap ring. Make sure it's not twisted. If it is, it will apply pressure to the brakes and as the pads heat up, the fluid boils in the caliper and then more pressure closes the pads. Happened to me with a jeep master...bitch to discover the issue.
hello Pat. My buddy has a 52 chevy with the same set up as mine ( and parts) and it has run fine for 5 years. but thanks for your colorful opinion regardless!
Yep! You're not going to move them with one finger, but the caliper can't be sticking on the guide pins. Study the layout of the caliper and rotor and you'll fugure it out. When the brakes are applied the piston only moves one of the pads into contact with one side of the rotor. After that the caliper has to move freely enough in the opposite direction to move the other pad into contact with the other side of the rotor. When the brake is released the caliper has to be able to move back just slightly to allow for an air gap between the pads and the rotor.
Well I jacked it up and I cant get the calipers to slide at all with any force whatsoever. Is there a way to adjust this so it will? thanks.
are the sliders there for the calipers? there should basically be a pair of tubes that goes thru the caliper, and the bolts that hold the caliper on goes thru these tubes. The tubes can slide in the caliper, and they will usually have a rubber boot.
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