Hello all, This past weekend I finally swapped the rear drums on my 58 Dodge for a set of discs. I already had discs up front and they worked fine but the rears were causing issues and frankly, working on the tapered axles is a pain. Now things are a lot easier. I had to swap out the MC as well because the previous one was a disc/drum set up. So I got a new disc/disc MC from Master Power Brakes. The current set up is as follows, new MC, 1 year old disc brakes, Wilwood proportioning valve on the rear line by the MC, then the rear disc brakes. All lines are either brand new or about a year old. I bleed the brakes, no issues, got all the air out, topped off the MC and went for a drive. Car stops fine going around the block, great! Well not really. I get the car in the driveway, give it a quick wash and decide to fill the tank. The gas station is two miles from the house and it was about 80 degrees out. I get to the station no problem. I leave and about 2 blocks away I feel a drag, the drag gets worse and now my nice pedal is becoming a rock. The brakes start getting hot and the engine is racing to get the car up to 15 mph. I get it home, and the brakes are smoking, all 4. I let the car site for about 30 minute but the brakes are locked up. I do three things at the same time and I don't know if any or all helped. I took the top of the MC, I let the car site for a couple hours and I opened the bleeder on the front left wheel. And now the wheels spin, the brakes aren't locked and I can at least work on the car. My question is this, if you have too much fluid in the MC, can that cause what I experienced? My plan this weekend is to flush out the fluid again, bleed all the brakes and reduce the amount of fluid in the MC. Then go for a few trips around the block to see if I can reproduce the problem, or confirm I fixed it. What I'm thinking is I put too much Dot 3 in there, it got hot from driving, expanded but had no where to go except to the calipers and pushed them. Just a few more details, it's a manual brake car, the rod has about 1/8" play between that and the MC. Before all this happened the fronts worked fine, the rears, well the drums were more oval then round so not so much there. The new MC is basically the same as the old except for disc/disc the ratio is the same. The new MC has a 1" bore. And sorry for the long post, just wanted to capture everything. Thank you, Sam
Power brakes or manual ? only things I can think of is push rod on the pedal or the one between the booster and master are to long causing the master not to return fully. prop valve not adjusted correctly causing tears to drag causing fluid to heat up. the cap is it vented ? master should have a bit of space between the fluid and top but not a whole lot 1/4” or so is enough. bleed the brakes. Double check your push rods Also is there a return spring on the brake pedal so it’s not leaving a bit of pressure on the master? Put the correct amount of fluid in the master and check that the cap is vented.
Too long of a pushrod is the most common issue. But, Do you have any idea what the MC bore sizes are? How about front and rear piston diameters? This is must have info. You can't just bolt random parts on and hope they work. I use the Wagner Brake bible to confirm and compare to factory combinations.
When a new problem shows up go back to the last thing you fixed, ( Or changed or fucked around with Or to the area you did it in) Sounds like you got a pretty good plan ! Where all four wheels locked? did releasing just one bleeder free up all the brakes?
Thanks all Bore size is 1" Manual brakes Pushrod is adjusted correctly with 1/8" play. I believe my MC cap is non vented, attached is a picture. Caliper size, Fronts are off a 76 Monte Carlo, rears are off a 78-88 Monte Carlo, Both front and rear kits along with the MC are part of the AAJ brake kit designed for a 58 Dodge Coronet. So nothing was thrown together, this was designed specifically to work together. Is the prop valve adjusted properly? I fully reduced the pressure so they should be good. All 4 brakes locked, not just the rear. I only cracked up one bleeder but I also removed the cap from the MC and let the car cool down.
If you have a good positive pedal return spring, 1/16" push rod clearance is all you need. Anymore just increases pedal travel. Your cap should be vented to the top of the gasket. If nothing obvious on top, look around the cap edge for a relief.
The master cylinder should release pressure when the piston returns fully. If the pushrod does not have free play, it can't return fully. You said that's not the problem. So there must be a problem in the master cylinder, with the little holes that get uncovered when it returns. That style cap should have a bump somewhere on the gasket surface, this is where are moves in and out, above the diaphragm.
Thanks all. I think this is why I'm a little confused, the first 2 miles I had no issues, pedal wasn't hard, brakes weren't dragging, etc. The problem happened over time, not a lot of time but at least 2 miles. If the rod was too far in wouldn't I have the problem from the start? And the return spring is good, plenty of tension.
I hate to say this, but both the SAE and Metric rear calipers, with integral parking brake, suck, and rebuilding them can make them worse. I have had them jam up, in this fashion. I have found rebuilt units pre-jammed, in the box, at the parts store. Now, if all 4 are indeed locked, then the problem is at the head-end, which either mean pedal, or master cylinder.
Your master looks like a typical late '60s-'80s disc/drum master, not a disc/disc. Make sure you don't have an internal drum brake residual in the front portion (secondary) of your master. Keep the fluid level 1/4" from the top on that style master.
A little drag causes a just little heat. just a little heat causes more drag sometimes and more drag causes bigger heat. Get it??
Did you bleed the MC before installing? Yes, MC can be overfilled, which doesn't allow much room for fluid expansion. Phil
Ummmmm THIS !! it’s a very common issue with pushrod length. I see it alllllllllllllllll the time on heavy equipment. Guys do a brake job and want a nice firm pedal. Adjust the brakes correctly ?? Naw !! Lift the floor board and crank the push rod and brake pedal stop a bit get that pedal up. Sometimes it will take a few hours before you get the call of smoking brakes or unit stuck in the yard with “ transmission issues” Heat makes things expand which causes more heat which cause more expansion.
1978-1988 calipers are of the Metric Series. Rear disc brake equipped cars with these calipers would have had a 36mm/24mm stepped bore master cylinder, and a power brake booster in all applications. 1977 and older are the SAE series. Disc/drum cars would have had a 1" bore master cylinder with manual brakes, and a 1-1/8" bore master cylinder with power brakes. The master cylinder in your picture is a disc/drum master cylinder, not a disc/disc master cylinder. Being that it has 4-bolt holes, it appears to be Mopar in origin. I cannot say that this is a guaranteed issue here, but none of the listed components are "designed specifically to work together".
I would bet a dollar to a doughnut, it is rod length. I have had the exact same symptoms. Push rod length.
I read that, After shaking my head ,,, I was thinking all the stuff gimpy just said. Brake fluid is smart
If overfilling was the issue, the amount of pressure required to apply the brakes to the point of locking them would also be easily lifting the cap on the MC enough to push fluid out of it.
So one thing to mention about this, the rears don't have parking brakes. The kit was designed for these older Mopars that had the parking brake on the transmission so the calipers in the rear are actually calipers for the front wheels of a Monte Carlo.
Again, the MC was set up by MPB specifically for disc/disc. This is also the same MC suggested/required by AAJ So when I stated that the parts were not thrown together, I meant that the person who designed the kit for the car did the testing and created the parts list. I didn't go down to NAPA and randomly purchase parts. I followed the instructions from AAJ. I will check the push rod again, seems that most people are leaning towards that. Thanks!
No. I had that happen too. Works fine at first, then starts to drag. Recheck your pushrod to piston clearance. Sent from my iPad using The H.A.M.B. mobile app
Definitely a push rod issue, give it another 1/8" of clearance or count the turns if you know the thread pitch.
In order for the brake fluid to the transfer out of the reservoir and into the cylinder either air must be allowed into the reservoir or a diaphragm flexes into the reservoir when the fluid level goes down . I see no way you can cause the brake to lock with an overfilled reservoir. As has been stated pushrods being too long can cause this or the return port that should be just in front of the piston when it returns to the released position being plugged or improperly drilled can cause this. A properly functioning dual reservoir master cylinder will have 2 small " geysers" for want of a better term shoot up from the reservoir when he pedal is pressed then released quickly....this occurs from the pressure relaxing back into the reservoir.if you have this occur in both reservoirs then your problem lies elsewhere.
So what do these people have to say about your problem? MPB, the person, AAJ? I’d be asking them since these HAMB guys can’t out smart some brake fluid.
So it's pretty safe to say the fluid is not returning back to the master cylinder and the more times you apply the brakes the worse it gets. Try loosing the bolts holding the master cylinder to the booster if the brakes release you have push rod or booster problem. If not I would look at the master cylinder.
I don't see where you said if it was just fronts or rears or both, but either the little check valve in the master is in backwards or rubber lines have collapsed, if you have a little play in the push rod and the cylinder is retracting all the way that would be out of the equation, next time it happens take a line off the master and see if that bleeds them off if it doesn't there is a problem further down the line.
Is your MC for a disk/disk system? A drum brake MC puts residual pressure on to keep the shoes against drum. Disk brakes do not, that little residual pressure will lock the brakes up as they get warm. Just one I’d say it was a seizes caliper, but not all 4... Sent from my iPhone using H.A.M.B.
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