Braking works but gets Super strong

Tiny
JBUCO315
  • MEMBER
  • 1995 BUICK ROADMASTER
  • 5.7L
  • V8
  • RWD
  • AUTOMATIC
  • 68,000 MILES
Hello, have replaced: front calipers and pads, rear cylinders, shoes, brake spring kit installed, and new drums. Problem is when braking, if at a slower speed, let us say thirty, and slowly slowing to a stop, if I give it just a hair more peddle, it is like the brakes go into super stop now emergency mode, not locking up or causing anti-lock to engage. However if I am at a high speed and stomp on the brake, it brakes just fine like it should, anti-lock kicking in out with road condition (I used to be a police officer, I really know what anti-lock is supposed to feel like and this is doing it). I just cannot comfortable come to a slow stop. It has been doing this for a while and has recently gotten worse, that is why I did all the work. I have further noticed that it seems like, the right rear especially, may be dragging a little when I release peddle and start to go. All four wheels were bleed, repeatedly, I wanted to cycle new fluid into system. Please help, I am getting to where I hate driving this car, but I love my car!
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Tuesday, July 26th, 2016 AT 8:08 PM

16 Replies

Tiny
JBUCO315
  • MEMBER
Wanted to add more information; I have yet to notice any rear wheel lock up or skidding, and the brake peddle feels good and correct, not spongy or soft at any point.
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Tuesday, July 26th, 2016 AT 8:28 PM
Tiny
CARADIODOC
  • EXPERT
There are a few things to look at. The most likely suspect is a rear parking brake cable that is rusted in the partially-applied position. Remove the drum, then look at the two shoes where they hit the large anchor pin at the top. If the parking brake cable is not fully released, one of the shoes may not be hitting that pin. Even if both of them are resting on the anchor, look at the parking brake strut bar between the middle of the two shoes. You should be able to push that forward 1/8" against the anti-rattle spring pressure, with your thumb. If there is no free play, the parking brake is partially applied. That will hold the front shoe out and make it grab the drum very aggressively under light brake pedal pressure.

Compare the length of the linings on the front and rear shoes on each rear wheel. The front one, (toward the front of the car), must be shorter than the the rear lining. If they are reversed, that can also cause that brake to apply harder than it is supposed to. The shorter front lining is only supposed to try to grab the drum and rotate with it. Doing so pushes on the lower link, the adjuster in this case, which pushes on the bottom of the rear shoe to apply it. The rear piston in the wheel cylinder pushes on the top of the rear shoe. This is called a "duo-servo" brake because two forces are acting on the rear shoe. The rear one is longer because it is the one that does most of the stopping.

Rear gear lube leaking onto the rear shoes will make the shoes grab real hard. Once they have been hot from normal braking, there is no way to get that grease out. The shoes and drum have to be replaced. Both are porous, and that grease will soak into the cast iron drum, then leach out later to recontaminate the new shoes.

Same goes for axle / bearing grease. There cannot be any contamination on the friction surfaces. If there is, it can be washed off with brake parts cleaner as long as the parts have not gone through their first heat cycle yet. Professionals even wash their hands first with soap and water to prevent getting fingerprint grease on brake parts.

A drum brake can apply too hard if the drum was not machined or replaced. No two linings ever ride in exactly the same place, so the new one could hit a rust ridge on either side of the drum's friction surface.

There are six "lands", or raised spots, on the backing plate that the shoes slide on. Those must be lubricated with a special high-temperature brake grease. GM has a design issue with their shoes where just a thin edge of the frames slide on the backing plate. That promotes the formation of grooves in those lands. Those can cause a shoe to stick and not apply under light pedal pressure, and it can cause a shoe to not release right away. Other manufacturers have bent-over tabs on their shoes to distribute the wear. The grease is still used to prevent an annoying squeak when the shoes retract. On GM vehicles it is also important to reduce the formation of those grooves.

As long as we are discussing brake jobs, if an old drum is machined, look at the hub it mounts on and you will see at least one access hole, and sometimes three. Water can get through those holes and form a circle of rust on the inside of the drum's mounting face. Those must be scraped off before a drum is machined so it sits squarely on the brake lathe, to prevent machining a warp into it. When a used drum isn't machined, if it is reinstalled in a different orientation, those rust spots will be trapped between the hub and drum and prevent the drum from sitting squarely. You may feel that as a vibration when braking.

Be aware too that a real lot of research goes into making the brake system balanced front-to-rear. Any time a friction part is replaced or machined, the linings will not make one hundred percent contact until they have as much as one hundred miles of use. Until then, you have to apply harder pressure to the brake pedal to stop the car, and that will cause the linings to get hotter than normal, leading to one type of brake fade. Once they cool down they will be fine, but you can have one brake working more effectively than the rest making it appear to be locking up. That problem would have started after you replaced parts, not before.
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Tuesday, July 26th, 2016 AT 10:36 PM
Tiny
JBUCO315
  • MEMBER
Alright, very very interesting, I will get into this tonight, weather permitting, and post what I find. Thank you so much for your assistance.
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Wednesday, July 27th, 2016 AT 1:21 PM
Tiny
RIVERMIKERAT
  • MEMBER
What have you found out JBUC?
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Saturday, July 30th, 2016 AT 9:25 AM
Tiny
JBUCO315
  • MEMBER
As of July 30 @1700, I have not been able to get to it. I don't have a garage and it keeps raining!
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Saturday, July 30th, 2016 AT 1:58 PM
Tiny
JBUCO315
  • MEMBER
Ok, it finally stopped raining for a bit. Jacked up car and first thing I noticed taking off rear right hub is a lot of brake dust in the drum! It is the second brand new one and only has about 20 miles on it. Next inspected for leaks, all is dry. Both shoes are pulled up nicely against top pin, and yes there is some slack in that E-brake cross bar, rattle spring nice and solid and seated good. Had helper press parking brake and then release. Was interesting to watch, all worked and released. Now I pulled it apart and the rub points all appear to have been making contact, initially and now regreased with CRC brake grease. I also moved the brake cables in and out by hand with out any issues noted, felt free and smooth. FYI, for first 17 years car was a garage queen and only accumulated 32k miles. When I was doing the bleeding, fluid was very clear, slight gold tint to it and came out nice and strong.
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Sunday, July 31st, 2016 AT 2:15 PM
Tiny
JBUCO315
  • MEMBER
Starting to rain again, so here are some pics, maybe a "pic CAN be worth a 1000 words". 1-4 are left rear, 5-8 RR, and 9 is amount of brake dust from less than 20 miles, both sides are like this.
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Sunday, July 31st, 2016 AT 3:00 PM
Tiny
CARADIODOC
  • EXPERT
I don't see anything obvious. There's only two other things I can think of. The first is since you replaced the wheel cylinders, did you buy the correct diameter? Did you look at one of the old ones or go by what the person looked up at the auto parts store? On the old one the diameter is molded onto the inside of each rubber lip seal.

The other thing is if there's a height-sensing proportioning valve. Those are used at the rear axle on most pickup trucks and minivans because there can be such a wide variation in weight distribution based on loading and number of passengers. As the rear is loaded more heavily, more braking power goes to the rear brakes. Reducing braking power to the rear when lightly loaded reduces the tendency for the rear brakes to lock up during hard braking.

Cars don't normally use a height-sensing proportioning valve, but you should check to be sure. In the late '80s, Chrysler minivans had an irritating characteristic where the rear brakes would lock up very easily when the road was wet. That was due to slightly sagged rear springs making it falsely appear that the rear was more heavily-loaded. The adjustment for that valve took less than ten seconds, and I carried a 5/16" wrench with me on all my alignment test-drives in case I ran into one doing that.

The springs on all vehicles sag with age, and if your car has this valve, it is almost surely the cause of this problem. The valve is almost always above the left rear axle, bolted to the body, with a linkage connected to the axle housing.
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Sunday, July 31st, 2016 AT 8:56 PM
Tiny
JBUCO315
  • MEMBER
Unfortunately no, I did not physically check the cylinders. I did a side by side and all looked okay, but that was a very quick look.
Will have to check into the height valve, not sure about that. It does have automatic rear air leveling, but I suspect thats a totally different system.
Since there has not been any peddle issues I am suspecting the booster is okay, but what do you think about the master cylinder or that proportion valve thats right under it? On this second time of replacing the drums, I adjusted the shoes way in so that they could adjust on their own. Until they adjusted out, I could feel the fronts doing all the work and although kinda weak feeling (because only 2 wheels instead of all 4), they were smooth and consistent. As the rears adjusted out it got grabby again, I could feel the rears pulling me down! It is like the system has reversed its self, rears stronger than front.
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Monday, August 1st, 2016 AT 6:10 AM
Tiny
CARADIODOC
  • EXPERT
This isn't a symptom I run into very often, other than the sticking parking brake cables, so I don't know if the proportioning valve will cause this. If you have it in the combination valve under the master cylinder, you likely don't have a height-sensing valve in the rear. That combination valve also has a metering valve, aka "hold-off" valve that delays the application of the front disc brakes to give the rear shoes time to expand and contact the drums. That makes all four brakes apply at the same time. On some older Fords, that valve had to be manually held open to gravity-bleed the front brakes. There was a small tool made for that, and if you'd forget it and leave it on the car, the front brakes would apply too soon and they'd apply too aggressively under very light pedal pressure.

I can share an unusual story related to wheel cylinder diameters. I worked at a Sears Auto Center in the '80s, specializing in Brakes and Suspension and Alignment. Most of our brake jobs included rebuilding wheel cylinders and calipers. I liked to team up with a friend because we had similar work habits. Also, rebuilding one front brake was okay, but the second one got boring, so we would each do one front and one rear. On one Chevy in particular, our brake kits included the correct shoes to cover a number of vehicles, and three or four sizes of wheel cylinder seal and boot kits. You were supposed to use the kit that fit your car and throw the rest away.

Once I had the wheel cylinder honed out and washed, I grabbed the 7/8" kit to replace the seals and boots, but I noticed my friend had already opened the 15/16" bag. Upon closer inspection, we found out there were two different size wheel cylinders on the rear, ... From the factory. The owner said the car had a brake pull to the right ever since it was new. This was its second rear brake job. No one caught the difference up to that point. I don't remember, but I suspect the wheel cylinders weren't rebuilt during the first brake job.

Goes to show that 1/16" difference on a big, heavy car can cause a brake pull, so you can see how much effect wheel cylinder diameter can make.

Let me share another story. Front disc brakes are expected to need to be replaced twice as often as rear shoes. Dodge had a problem with their trucks in the mid '90s where the fronts were wearing out four-to-one, ... Much too quickly. This was only on those that regularly carried a heavy load. There was a factory service bulletin to address this issue. It called for replacing the wheel cylinders with a pair that were 1/16" larger in diameter. In most cases that solved the problem by making the rear brakes work harder. If you had a truck that was always fully-loaded, (we had two that were seriously overloaded all the time), you could go a full 1/8" larger in diameter, but the clinker was that size wasn't available from Chrysler. We had to buy them from the Chevy dealer. This problem was mainly on the 3500 diesels because of the higher weight on the front end.
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Monday, August 1st, 2016 AT 8:21 PM
Tiny
JBUCO315
  • MEMBER
Great, thanks for all the info, I will get into figuring the diameter out and see what I have! Whatever it turns out to be I will let all know. Thanks again.
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Monday, August 1st, 2016 AT 8:36 PM
Tiny
JBUCO315
  • MEMBER
Fixed; I did have the original pistons to compare to however the two replacements are the same diameter. With that said, looking at the new shoes that I had just put on, both L and R sides seem to be falling apart as well as destroying the drums! Best I can describe it is, have you ever seen a board drug across smooth dirt, but when it hits a rock, it creates a gouge that gets progressively worse until something gives. Well this was happening all over these shoes. Took them back and went with a different store and brand as well as another spring kit (although there was nothing wrong with the tension of the these ones I had just put on! Lol). These new shoes do not have as much material on them and kind of resemble several layers of stacked hard pressed gray cardboard but, its been three days now, they have adjusted out and all is fine again.
I hate to throw names out there but the bad ones were: O'Reilly's BrakeBest Select Brake Shoes #462. The replacements are from Advance Auto, Wearever Brake Shoe #S462.
Thought this was funny, when returning them I showed the guy and he said "oh yea, they are shredding on you". I asked if this was a common thing, "no, never seen that before". Okay, never seen that before but you know what it is and you have a name for it, hummm.
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Friday, August 5th, 2016 AT 2:09 PM
Tiny
JBUCO315
  • MEMBER
Oops, first line should read, "I did NOT have."
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Friday, August 5th, 2016 AT 2:10 PM
Tiny
CARADIODOC
  • EXPERT
Dandy. Lets hope this solves the problem.
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Friday, August 5th, 2016 AT 3:01 PM
Tiny
JBUCO315
  • MEMBER
A follow up with closure; it's been almost two weeks and several hundred miles, and no problems what-so-ever.
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Monday, August 15th, 2016 AT 8:12 PM
Tiny
CARADIODOC
  • EXPERT
Dandy. Come back again when you need my wondrous wisdom!
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Monday, August 15th, 2016 AT 10:36 PM

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