Pulsating in brake pedal, despite new brakes and rotors, good caliper.

[SamC777]

94 Ranger, 4x4. Felt pulsating in my brake pedal this last week. Nothing in the steering wheel, nothing in the seat. Brake pistons extended and retracted on their own. Examined my rotors, had some visible grooving but nothing incredible. Still felt smooth to the touch, albeit the lip on the outside. Brakes were recently replaced, had some slight grooving as well. Chose to replace the rotors and brakes, as the rotors were over three years old and had plenty of miles burned into them.

Alas, even after replacing the brakes, rotors, and bearings, the pulsating continues. I've yet to check my drums and shoes, but I replaced both of them within the last year. What could still be causing this?

 

[Bgunner]

It is common for the drums to go out of round in the rear causing the pulsation in the pedal.

Mine were fine and new till both my calipers seized and left me with only rear brakes which over heated the drums causing them to go out of round. Now I have the pulsation again but I know why in my case. You have the option of finding someone who has the brake lathe to have them turned down (depending on if there is enough meat there to get them round again and stay in spec) or replace the drums. You should replace the brake shoes and hardware while you are there but not necessary. If you don't replace them you take the chance that the shoes will ware the drums unevenly though. Like pad slapping a grooved rotor, eventually the pad will end up having high spots from the grooves. If the shoes are worn uneven or have high spots in them you will not have as good of a braking system.

 

[Uncle Gump]

I've never seen a drum brake cause a pulsating pedal... and I've done a lot brake work. I won't go as far to say it couldn't... but in my experience it would be pretty rare.

Disc brakes are a different story. A warped rotor or one with a high spot will directly force the caliper piston in and the fluid gets dissipated back to the master lifting the pedal. Once the high spot clears the brake pads... the fluid is again applied to force the caliper piston out and the pedal falls.

With drum brakes and the way the brake shoes self energize... brake fluid gets dissipated from the secondary brake shoe to the primary shoe through the wheel cylinder just under normal operation. So it would work the opposite way if there was an irregularity in the drum. Like I said above... I've never seen it.

I would be more apt to believe one of your new rotors might be out of spec. It happens. You will have to check rotor run out to know for sure.

 

[Bgunner]

I've never seen a drum brake cause a pulsating pedal... and I've done a lot brake work. I won't go as far to say it couldn't... but in my experience it would be pretty rare.

Come to MA. I'd love to show you one that has it just to be the first one you've seen. Rear drums will cause a pulsation. I have it now with new rotors and calipers and out of round drums. The pulsation is light but there.

Even though the fluid can flow/pressure between the wheel cylinders the change in pressure between the rear drums the force putting the pressure there, your foot, will feel it.

You must have never driven a 4 wheel drum brake vehicle before as pulsation was a common issue when all 4 wheels had drum brakes.

 

[Uncle Gump]

My first 5 vehicles were 4 wheel drum. I started wrenching as a career in the later 70's. Close to half the vehicles on the road still had 4 wheel drum brakes. I honestly never seen a brake pedal pulsate until those damn new fangled disc brakes ruined my life.

 

[Bgunner]

To check if the drums are out of round is easy enough. Lift the rear end so both wheels are off the ground, use jack stands for safety, and spin one side at a time and feel if the drag is even throughout the whole rotation of the wheel. If it gets stiff in one spot then easy again the that drum is usually out of round. Now you may also hear it drag in one spot but not in others this to a sign that the drum could be out of round.



When front rotors go out of round, I use out of round but it's more like wavy, you will feel it in the steering, pedal and in the seat/motion of the truck but with drums you only feel a slight pulsation in the pedal. I've only ever felt it with both rear drums out of round though, it may be a coincidence but that is my experience.


Now days people see drum brakes and send them to the garage to be changed because they don't understand them and see all the springs and run. Many don't realize that if you remove the drum from the other side you have a mirror image of what it should be like, as long as the last person that did the job did it correctly that is, and to do one side at a time so you can use the other as a reference if you need to.

Brake tools are another example I have seen why someone was going to send it to a garage because they didn't realize that a few different size flat heads, an assortment of plyer and a wire brush can get the job done easy enough.

The way I look at drum brakes is if they can stop 80K+ lbs they work plenty fine for everyday use. Propper adjustment is key though as they can cause a pull to one side or the other when not adjusted properly, meaning tighter on one side than the other.

 

[Jazzer]

Many times pulsating in the brake pedal is due to an uneven coating of brake pad material on the mating surface of the rotor, rather than warpage of the rotor itself.

Here’s a description of the proper bedding in procedure for disc brakes;

Bedding In Brake Rotors

 

[Ranger850]

I'm with @Bgunner . In my experience ( which often gets raked over the coals here, but i turned drums and rotors for over 2 years ) warped front rotors can cause the steering wheel to wiggle, while warped rear drums can cause the pedal to pulse. I've seen new drums leave the shop straight and come back a week or month later warped as shit. Sometimes we would turn them, others we would just replace them under warranty. It's as easy as Bgunner said it was to check for warped drums, I usually pull the wheels off to spin the drums by hand, and its easier to get to the adjuster that way.

 

[Uncle Gump]

The only comment I'll make is...

Refer back to post #3

I have nothing more to add here.

 

[sgtsandman]

I've heard of warped drums causing the pulsing issue but never experienced it myself. So, it is possible.

 

[RonD]

I agree with Uncle Gump, because it makes me seem smart


Only effect in drum brakes, in the front or rear, I have experienced myself is "grabbing", over braking, never pulsing

The Rear ABS valve could be pulsing, but long shot
May want to unplug it and see if pulsing goes away
Its in the drivers side frame under the firewall area, looks like this: https://m.media-amazon.com/images/I/61x1cLq2wVL.jpg
3 or 4 wire plug

Could be faulty rear axle sensor causing ABS module to "think" a rear wheel is locking up when brakes are applied

Other that that, rotor is warped, new or not

 

[bobbywalter]

My first 5 vehicles were 4 wheel drum. I started wrenching as a career in the later 70's. Close to half the vehicles on the road still had 4 wheel drum brakes. I honestly never seen a brake pedal pulsate until those damn new fangled disc brakes ruined my life.

color me amazed. i still drive a 4 wheel drum.......and a 6 axle drum.

 

[Josh B]

I more attributed uneven wear on drums to be in the shoes

 

[bobbywalter]

of course.....qualified this way GUMP. i have seen more severely out of round drums the past 10 years then in the 30 before it.....

BRAND NEW. chinesium.....or overseasium.... brand new. rotors too. nothing like turning brand new shit true.

 

[bobbywalter]

dont even get me started on heavy duty moog parts.