I just had new rear drums put on, my front brake pads are new, my rotors are good…but there is still a pulsating when I brake. When I am just about slowed down you can definitely feel a surging coming from somewhere. The steering wheel does not shake, and I don’t feel more than a vibration from the brake pedal. I have taken it to 3 mechanics and replacing the drums was given as a solution. But since I have already done that, the problem is obviously not resolved. I know I need new tires as 2 of them are really cupped and loud…could that be it?
If you need new tires anyway, try that first. You might luck out. Pulsation on a front disc/rear drum car when braking is usually due to warped front rotors or (less frequently) warped rear drums. Unless you are certain this is coming from the rear drums, first suspect the front rotors. They may have been warped by overtightening during the install process. Warped disc rotors usually cannot be successfully machined. They have to be replaced.
If non-oem brake pads were installed on the front recently, that could be a cause of the rotors warping. Some of the inexpensive aftermarket brake pads don’t transfer heat effectively, and can lead to rotor warping.
I had both rear drums replaced just a few days ago because they were warped. So that is ruled out. I can have the front rotors checked, but they have been checked 3 times in the last month and all have said the same…they are “true”. So irritating not knowing what’s causing this.
Did this pulsing sensation start right after the rear drums were replaced? i.e. that there was no pulsing sensation before? If so, is that the only other work that was done on the car at that time?
It is warped rotors could be caused by improper lug tightening or a sticking caliper is my guess.
The pulsing was there before. Two of the mechanics pulled on the parking brake lightly to make sure that it was the rear brakes and both said the same…it was the rear. Unless it is my imagination, the pulsing seems a little worse now than before. I did just recently have the struts replaced in my car. Other than that, no additional work has been done.
Its the fronts, not the rears. Residue builds up on the rotors from the pads, this is worse with people who use their brakes lightly. The rotors still turn true, but you can’t see the residue so it is undetected. The steering wheel doesn’t shake because the rotors are not warped, its just uneven gripping of the brake pads as the rotors go round.
The cure, a couple of hard stops from about 60 mph. apply the brakes hard, but not to the point of wheel lockup, just short of that. Also don’t come to a complete stop, 60 to 10 is about right. Do this where it is safe to do.
The hard application will heat up the rotors and burn off the residues, and its cheaper to do than going to the mechanics. and it works.
@keith we missed the obvious." I know I need new tires as 2 of them are really cupped and loud…could that be it?"
Re considered, alignment strut, balance problem.
The park brake test is valid and warped rear drums are a real possibility if the lugs are overtightened. The best thing to do at this point if the drums are warped is to machine the drums with the wheels mounted to the drums and lugs torqued.
In some cases as strange as it seems, I’ve actually seen warped wheel rims distort the drums. When the lugs are tightened, properly or not, the drum distorts to the wheel. In those cases it required new wheel rims.
The latter is an oddity but it’s something for consideration, especially if the car has steel wheels.
What Ford?
What year?
What brake setup?
It kind of sounds like an unwanted ABS activation. Bad wheel speed sensors and/or dirty tone rings can cause those strange things to happen. I’ve run into it a few times.
Rear drums are always warped, or slightly out of round, its the nature of how they work. The rear brake shoes actually distort the drum when the brakes are applied so the trick of lightly applying the parking brake will always give a slight pulsation. That test was pure bogosity and the drums were replaced unnecessarily. They do not get warped because of improper torque of the lug nuts either.
I did not miss the tires either, but they are not the problem if the pulsing only occurs while braking. That is another issue altogether. All smile13 has to do is a couple of hard stops and this problem goes away. The cupped tires, not so easy to fix.
Because the rotors are “true”, and I assume they checked them for not only lateral runout but also miced them for consistancy in thickness (?), does not mean that the friction surfaces are consistant in their frictional coefficients. You may want to change the rotors…being sure to clean the proective coating off the new ones with brake cleaner…even though a shop has deemed them “true”. And try some good rotors. The parts store will have different grades, and it’s worth the extra bucks. I just changed mine yesterday, and wouldn’t even bother tryong to save money by getting cheap ones.
Keith commented on the residue, and I’ll add that this is often due to improper rottor cleaning before installation. Rotors are shipped with a rust-preventive coating, and if they aren’te cleaned you’ll end up with an uneven smear on the rotors.
And yeah. it absolutely could be your rear brakes.
One way to find the source of problems like this is to get a friend, jack up one wheel at a time (tranny in neutral), and spin each wheel by hand while the friend slowly and lightly applies the brakes. You’ll feel the uneven friction on the wheel(s) that are causing the problem. It’s the simplest and best way I know of to isolate the problem, and it really does work.
That park brake test is also recommended by many car manufacturers at their service schools.
@keith I understand what you’re getting at. However, I’m not sure I entirely agree with you.
I’ve driven plenty of trucks that needed to have the rear drums machined because they were so out of round that the rear brakes were locking up under very light braking.
One easy thing to try is to swap the front and rear tires. Shouldn’t take much more than 15 minutes. If it changes the symptom, you know it is related to the cupped tires. At least you’d be able to get that issue off the shelf one way or the other.
If it is actually the new rear drums doing it, getting them turned for trueness should be no problem. Any good tire and wheel shop should be able to do that without much expense. Sometimes the drums will be affected by the wheel, so truing them with the wheel on the drum – I’ve never seen it done that way, but I suppose it possible – as suggested by the poster above makes sense.
OK, I guess that those manufacturers and their service schools did not work on brakes prior to the self adjusters. adjusting brakes was a periodic chore and anyone who did that for awhile knows that as you spin the wheels, the drums will drag during certain parts of the rotation.
Maybe the OP will try my recommendation and report back.
@keith … my 70’s Ford truck requires manual adjument of the rear brakes, and you are right, there is always a little dragging at certain point in the rotation, easily noted during the adjustment process. But this doesn’t cause any noticeable pulsation, at least in my Ford truck. For there to be noticeable pulsation on braking, the problem would seem to be to have to be worse than just the normal imperfections in any drum brake system.
But your recommendation to try a couple of hard stops and see if it helps? Works for me, and it’s easier than changing the tires around. OP should definitely consider it.
If you replaced the drums did you change the shoes? It’s possible.
A broken belt in a tire can the issue also.
Any brake malfunction that becomes an irritant or worse to the driver denotes a malfunction that needs to be remedied whether it’s front, rear, or both.
As to the service instructions, I’m just relating what they’ve stated in service schools about narrowing a shudder or pulsation down to front or rear.
My opinion on this is based on machining a ton of drums to cure problems like this; not necessarily by anything a service school instructor has stated.
have the rotors and drums rechecked for trueness. I have bought rotors before brand new that were not true. That has happened even when i had them machined. if you have a dial indicator you can do this your self very easily and fast. And when you check the rotors with the indicator dont just check one side of the rotor check both sides. good luck!