Mechanics

OVER HEATING BRAKES

2001 Dodge Ram • 114,500 miles

Starting in March the brakes on my Dodge Ram van were binding and actually slowing the van. So I first replaced the Brake Hoses master cyl. And fully loaded posi quiet calipers. Then the combination valve was leaking so I replaced it. The rotors were resurfaced but still have a wobble. Most recently the vacuum brake booster is replaced too. Still after all that the wheels are tight to turn by hand especially the right front which always runs hotter than the left wheel. The van has RWAL brakes only. What else could be wrong if any thing. How free should the wheels spin by hand when every thing is right?
Avatar
Frankiedonnn
June 28, 2013.



When you get the brakes to drag again, open the hydraulic system to see where the brake fluid is being trapped. You already replaced the most common suspects so start with the right front bleeder screw. If the brake still doesn't release, suspect that caliper or a lack of high-temperature brake grease on its mounting slides. If it does release, next time loosen the steel line at the master cylinder. If that lets it release, the master cylinder is blocked, and if that is the second one to do that, it is due to the brake fluid being contaminated with a petroleum product. It would take a few days for the new master cylinder to develop the same problem.

Caradiodoc
Jun 28, 2013.
Hello caradiodoc: I thank you for your response.I did grease the mounting slides of the calipers but your other suggestion about the petroleum contamination sounds very good because it's something I have'nt thought of. Only I don't have the slightest idea how it got contaminated.I benched-bled the master cylinder but I suppose it could have had some thing in it from the factory or I got something in it some how. I bled the system a number of times. However, I will try what you suggest and I suppose it means I will have to flush the system all over again. Thanks again and I will let you know how it turns out.

Tiny
Frankiedonnn
Jun 29, 2013.
Hello, Caradiodoc, I don't have enough fluid to flush the whole system today, but I did the things you suggested : what I find is when I open the caliper bleeder or the master cyl. Union fluid does not come flowing out on its own which I think is strange. Nor does the caliper free up the rotor. But when the banjo-bolt is opened fluid comes out. So I disconnected the brake line to the right caliper on both ends and blew the air line through it into a clean container. What came out looked a little cloudy.I also blew through the brake hose and the caliper bleed hole and banjo-bolt hole separately to clean it. After reconnecting everything and bleeding the system the rotors on both wheels were spinning freely until the engine is started and the vacuum booster operated. Then the rotors became extremely tight again and hard to turn. It alwa ys seem to come right back to the same thing. Although the new calipers say O.E on the box they look a little bit different from the old ones. The new ones are Kelsey Hayes while the old ones only has a part number and I'm guessing they are Mopar or Chrysler. Are these parts interchangeable? I wonder. .

Tiny
Frankiedonnn
Jun 30, 2013.
Hello again, Just to be sure that I'm not missing anything important I want to let you know that I am using Valvoline Synthetic Dot 3 and 4 brake fluid.

Tiny
Frankiedonnn
Jun 30, 2013.
Sorry to leave you hanging. Been out for a week fighting a kidney stone. Your reply was one of the last ones I read but I was in way too much pain to care at the time.

I don't think you have a brake fluid contamination problem, at least I really hope so. That is serious. There won't be any contamination in the new master cylinder from the manufacturer. They take great care to avoid that. The common consumer-caused things include engine oil, power steering fluid, automatic transmission fluid, and axle grease. Some people pour those things in not realizing they're putting the products in the wrong place, but other things that have happened are mechanics will wipe out a funnel used for engine oil, then use it to pour a five-gallon pail of new brake fluid into a pressurized brake bleeder ball. The oil residue that remains on the funnel is more than enough to contaminate a dozen brake systems. Another common cause on older cars was when we had to remove, clean, and pack wheel bearings with grease. We'd do that by hand, then when we were ready to fill the master cylinder with brake fluid and bleed the system, we found the rubber bladder seal under the reservoir cap pulled down from the normal vacuum built up over time as the brake fluid got pulled out. We used our finger tip to push the seal back into place, and even after wiping our hands on a rag, that was plenty of grease residue to cause a problem. To avoid any chance of that, most experienced mechanics wash their hands with soap and water before working on hydraulic system parts so they don't risk getting fingerprint oil mixed in.

Brake fluid is a glycol product and all the rubber parts in the hydraulic system are compatible with that. When they come in contact with any hint of petroleum product that causes the rubber to swell and get mushy. Mainly two problems result. The first is the tapered lip seals in the master cylinder grow past the fluid return ports and trap the fluid you pushed down to the wheels. That's like driving with the brake pedal pressed down an inch or two. The first clue is the trapped fluid will release right at the master cylinder when you loosen a steel line. The second clue is that rubber bladder seal will be blown up and mushy and you often won't be able to reseat it in the cap and make it stay in place.

The second less common symptom is the square-cut seal in the caliper swells so much it won't retract the piston when you release the brake pedal. It works by sticking to the piston and bending or deforming slightly when you apply the brakes. When you release the pedal it bends back to its normal shape and pulls the piston back with it, perhaps as little as the thickness of a couple of sheets of paper, but that's all that's needed to prevent brake drag. There are other physical things that very commonly happen in calipers to cause the same symptoms so those should be expected first, but I always worry about fluid contamination too since I have no first-hand knowledge of the vehicle's recent history.

There is a third place a problem can show up with a rubber flex hose, especially on those vehicles that have a metal support bracket crimped around the middle of the hose. That applies to a lot of Chrysler products, and it has happened to one hose on my '88 Grand Caravan and on my '89 Grand Voyager. One sat in storage all winter, then the problem developed, and it occurred on my '88 daily driver about two months ago. Rust builds up inside that crimp that constricts the hose. You can force brake fluid through it with the pedal but it won't release from that wimpy square-cut seal. (The fix is to simply open that crimp up a little with a flat-blade screwdriver or large pliers). It takes way longer to crawl under the vehicle than to actually do the repair. Where brake fluid contamination becomes an issue with hoses is if that problem is close to occurring anyway, the rubber will expand inside and block that hose sooner, so there's really two things working together to cause the problem.

What is hard to convince people of is there is only one proper fix for brake fluid contamination. All rubber parts that contact the fluid must be replaced at the same time, all the steel lines must be flushed and dried, THEN the new rubber parts can be installed and system can be filled and bled. Those parts include obviously the calipers, master cylinder, and front hoses, but often forgotten are the rear wheel cylinders, rear hose(s), combination valve, height-sensing proportioning valve typically used on pickup trucks and minivans near a rear wheel, and any RWAL or four-wheel anti-lock brake hydraulic controller.

You can buy rebuilding kits for wheel cylinders and calipers but they aren't a good economic option. Professionally-rebuilt units today are a lot less expensive than they were in the '80s. Also, most rebuild kits for master cylinders cost more than the rebuilt master cylinder already done, with a warranty. My additional concern is those parts are usually made from cast iron which is porous. The contamination can get into the casting, then work its way out again later recontaminating the entire system again. That is when you hear about cars that have non-stop continuing brake problems after just a few parts were replaced. The only proper fix is to replace all rubber parts at the same time. When even one contaminated part is left on the vehicle, the contamination will leach out and start the problem all over again.

Now that that's out of the way, I think you've identified a potential cause that I never stopped to think about. That's the power booster. That will not be part of a brake fluid contamination repair because brake fluid doesn't contact the rubber diaphragm, but if you notice the front brakes start to drag when you start the engine, that is the only explanation unless you have a four-wheel anti-lock brake controller. Those have three states controlled by a set of valves for each wheel. They BLOCK additional fluid flow to a wheel when the computer sees it about to lock up, then they BLEED fluid pressure off if the locking appears to be continuing, then they APPLY fluid under pressure from a small storage container called an accumulator. That cycle occurs from 15 to 30 times per second. It's very rarely heard of but if the "apply" valve were to leak, pressurized brake fluid would go to one wheel, (or commonly the two rear wheels together, especially on GM cars), and start to apply that brake. Pressure shouldn't build anyway because the "block" valve is always open to allow normal fluid flow when no wheel lockup is taking place. The normal complaint to expect is the high-pressure accumulator pump cycles on and off too often to keep the stored pressure built up.

That self-applying is not a concern if you have rear-wheel anti-lock brakes, (RWAL), which most Dodge trucks had. There is no brake fluid stored under pressure. All that system does is block fluid flow to the rear wheels, then bleed some pressure off if the wheels are still slowing down too quickly. Once the wheels get back up to speed to match the front wheels additional brake fluid comes from you pushing the pedal a little further. A concern is you could run out of brake pedal but I've never heard of that happening. Even if the pedal did go all the way to the floor, you'd just release it and push again and start the process all over. That would probably only happen if you were driving down a long, steep mountain road.

There's a couple of things you can do to identify if the power booster is the cause of the problem. First, disconnect the large rubber vacuum hose at the booster and plug it. There will be no more self-applying of the brakes. Second, with the hose connected, the booster stores enough vacuum when the engine is stopped for at least two pedal applications so you can stop the vehicle safely. After the engine has been off for a minute or more, you should feel the power assist help you push the brake pedal once or twice, and maybe even three times. I have some cars that will hold that vacuum for days but that is not necessary. If you find there is no vacuum just a few seconds after stopping the engine, it is bleeding off through the valve that is leaking and applying the brakes. That is not a common condition but it is cause to replace the booster.

Caradiodoc
Jul 4, 2013.
Caradiodoc: Sorry about the kidney stone, I've heard how painful they can be. I read the information you sent twice and it's most interesting: Even though the booster is new I took your suggestion and disconnected the hose anyway and astonishingly the calipers released.I still can't believe it, every few secs i'm out there turning the wheels to see if they're still turning.I also took it for a short spin in the neighborhood and the brakes are not holding too good, but maybe it's just that I've gotten used to having the booster. Now the important question is why would a new booster do that.I understand that the push-rod adjustment is done at the factory but I did srew it in a little anyway and still it was a problem. So I would have to wait and hear what your assesment of that is.I'm not sure if I should drive it generally without the booster. Thank you for your time and experience.

Tiny
Frankiedonnn
Jul 5, 2013.
Power boosters give such little trouble that I haven't had cause to investigate many problems. I'll have to defer to theory of operation rather than training and experience. Most push rods aren't even adjustable. When they are you really shouldn't need to change the adjustment. That is set by the rebuilder. When installing a used booster it is not normally necessary to vary the adjustment between two different vehicles.

Engine vacuum tugs on the diaphragm that pulls that push rod forward. The back-side of the diaphragm is a sealed chamber so vacuum builds up in that too when the diaphragm tries to move. That vacuum in the sealed chamber is what prevents the diaphragm from moving and applying the brakes. When you press the brake pedal all you're doing is pushing open a spring-loaded valve that lets air rush into that sealed chamber. Then the vacuum in front pulls the diaphragm to move the push rod, and it moves the second part of that valve to close it again to the entry of more air. That stops the brakes from applying harder and harder when you're holding the pedal steady. If you want to apply the brakes harder you push the pedal some more, the valve opens, more air comes into the back chamber, the diaphragm and push rod move some more, and the valve gets pulled closed again.

There is no need to have the huge metal bar going from the pedal to the booster under normal conditions. When the system is operating properly you aren't doing any mechanical work with the pedal. You're just opening that valve. It's when the engine stalls, the booster fails, or for some other reason the booster isn't working, that then there is a mechanical connection as a safety backup to apply the brakes. The pedal push rod butts up to the master cylinder push rod and one pushes the other. You have regular manual brakes instead of power brakes, but in this case the pedal will be harder to push than if the vehicle had just manual brakes. Two reasons for that. First of all you are the one who is still pushing that really beefy diaphragm in the booster in addition to pushing the master cylinder, so you're moving more stuff. Second, since the manufacturer knows the power assist is so effective and helpful, they can design the brake system to be a lot more responsive. That is a factor of the ratio of the surface areas of the pistons in the master cylinder to the surface areas of the caliper pistons and wheel cylinder pistons. Bigger diameter pistons in the master cylinder move more brake fluid by volume but that translates to less pressure per square inch acting on each piston at the wheels. That means you have to push harder on the pedal to stop the vehicle. Power assist overcomes that having to push harder.

Since they took advantage of the power assist and increased the size of the master cylinder pistons, when there's a failure you have to push a lot harder on the pedal to stop the vehicle. Add to that the diaphragm you're moving and that's why it's so hard to stop with power brakes that aren't working. Some cars and trucks aren't so bad. Some are real hard to stop.

I would have to unbolt a master cylinder from the booster and move it forward to see the push rod to see what "normal" operation is. I think that push rod should not move at all when you start the engine but it would not surprise me if it moved as much as perhaps an eight of an inch. What I DO know is if it does move a little it must not make contact with the piston in the master cylinder. Pushing that piston 1/16" can be enough to block the fluid return ports and cause brake drag. That means if the push rod moves 1/8", (for example), when you start the engine, there had better be 1/8" gap between the piston and push rod when the engine is off.

An easy way to identify if a simple misadjustment of the push rod is the cause of the problem is to loosen the two mounting nuts for the master cylinder about one complete turn, then pull the master cylinder away from the booster. That will let the pistons fully release and any dragging brake will release.

If that valve in the booster is leaking I suspect the push rod would just keep on extending as far as possible unless there was something in the booster that suddenly caused that valve to seal again. This is where watching it with the master cylinder pulled forward would give the clue. If you start the engine and that push rod doesn't move even a hair, any problem would have to be due to its adjustment. If it does move a little, the same could be true or that could be a sign of a defect. If it keeps on extending a lot, that is cause to replace the booster because the valve is not sealing.

Caradiodoc
Jul 5, 2013.
I started the engine with the master cyl. Off and the push-rod did not move at all, but would it move with the master cylinder disconnected? I can hear the vacuum from the engine in it.I feel sure that the booster has something to do with it, although it's a new booster only installed 2 weeks ago. With the engine running I reconnected the master cyl. And the calipers just locked up tight. What I have been doing is retracting the calipers with a srewdriver and as long as I don't start the engine the rotors would spin freely. As soon as the engine is started and the pedal applied the rotors are locked again. I'm going to ask a question which may sound silly but is it possible at all that the pressure alone in the booster could move the master cyl. Piston because I adjusted the push-rod extremely short just for the test and the condition still exist. The booster is a Bosch brand and it came from Jerry Ulm Dodge.I don't thik it's a reconditioned, I believe it to be a new one judging by the price. The other parts are reconditioned from J.C. Whitney on line. The calipers have phenolic pistons. Another thing is I dismantled one of the calipers a day ago and the fluid in there was a little black. The system has been bled so many times that by now it should be clean.

Tiny
Frankiedonnn
Jul 6, 2013.
I didn't stop to consider that there could be vacuum held in by the master cylinder. I think that's a secondary symptom of the problem. They wouldn't make the master cylinder seal in the vacuum at that point because that would put a lot of stress on the rear seal which simply holds brake fluid in so it doesn't run into the booster. Also, they would have used a gasket between the two parts, and I've never seen that. What you might try is with the master cylinder pulled forward, spraying some water in that area with the engine running and watching if it gets sucked in. If it does, have the booster replaced.

Normally boosters are very low failure items so I would be fine with a used one from a salvage yard. In a conversation a few years ago with a fellow who worked at a booster rebuilder, some boosters have two diaphragms and an unusual valve design that can fall apart if the booster is transported improperly. That mainly applies to some GM car models but it's worth repeating. With those the power assist appears to work fine, (as did the one I was involved with), but owners familiar with their cars are certain too much pedal effort is required. They are right. That's caused by that valve falling apart. In my case it happened after the owner's wife went in a ditch after hitting a deer, but it more commonly happens when a used booster is tossed in the trunk and hauled home. You need the master cylinder bolted on to hold that valve together, or you need a special plastic tube inserted to do the same thing. Rebuilt boosters come with the sleeve. You're not supposed to remove that sleeve until the booster is installed on the firewall. If neither the master cylinder nor the sleeve are in place, you have to keep the booster standing up in its normal orientation to keep that valve together, and hope you don't hit any big bumps.

As to your question about the booster being strong enough to move the master cylinder's pistons, yes; in fact, that's all that moves them. There is no mechanical connection between the pedal and the master cylinder. The master cylinder is applied 100 percent by engine vacuum. All you're doing with the pedal is opening a valve to let air in the backside of the diaphragm so vacuum on the other side can pull it. There is a backup mechanical connection in the booster in case the engine stalls but that isn't even close to coming into play under normal conditions.

Caradiodoc
Jul 6, 2013.
Hi caradiodoc: Although I read about the operation of boosters and saw diagrams I still did'nt understand how they worked until you explained. So you're saying that the push-rod is only there for manual operation if the booster fails. As it happens I still have the old booster, so I could try reusing it and see if this problem changes. Unfortunately, I'm not in the U.S, so it's not that easy for me to exchange the new one or even find a salvage one.I'm all the way in Barbados and we only have a few Dodges on the road here.I lived in Florida for 22yrs, and two years ago we returned to Barbados and I shipped the van here. I was not aware of the sensitvity of the valve problem you explained and the booster came all the way from Florida by mail so it must have gotten some good jerking. Now the old one might have the same problem but I'll give a try and see what happens. The only sleeve mine has is a yellow plastic tapered sleeve but it does'nt come off even after installation. There's a green sponge inside with a pink dot and one of the mounting bolts has blue marker. The pink dot seems to be aligned with the blue mounting bolt. No instuctions came with it so I don't know what it means. Thanks for your time and all the good information.

Tiny
Frankiedonnn
Jul 6, 2013.
Page 1 of 2