sudden onset of pulsing brakes

[thirdman]

Today I put on a new muffler and added thin (1/8") spacers to my rear wheels (more about that in a different thread).

Now my brakes pulse! I am feeling it through the brake pedal only. I did not touch the front wheels, I did not touch the brakes, brake lines, etc., I tightened the rear lugs carefully (like I always do). Tires, rims, lugs are all unchanged. The muffler bolted on easily with no cutting, bending or other violence.

What did I screw up?

Could I have screwed up the rear drums by torquing unevenly or something?

Oh, and it does not pull to one side or the other when braking. Parking brake works and does not drag. Using the parking brake only while driving straight does not pulse, vibrate or pull.

I am going out now to recheck everything I just did while I wait for y'all's wisdom...

[thirdman]

Update: I lied, it is definitely the rear brakes (or something closely related). It will pulse when using only the handbrake.

Also, there is a very quiet shicka-shicka sound coming from the back when it pulses. I can't tell which side it is coming from, though.

Any ideas?

[hawkdoc60]

All you would need is an incidence of brake fade (and you may not even be aware it has happened) and the heat generated could be enough to distort your drums. I would recommend taking the drums off and after checking the brake shoes for wear, etc., take the drums in to be turned. Most places I have dealt with will turn a drum for about $10 each. Just a thought.

[GenevaDirt]

would almost bet that the pulsing has been there for a little while but as you said it is barely there so you just have not noticed it. And now that you added the spacers you have been paying attention just waiting to see if anything is wrong with what you did. So now that you are really paying attention to it you noticed it.

[FestYboy]

check your bearings (mostly outer) and have your drums turned

[thirdman]

Phooey. Would there be any benefit to replacing my bearings if I have my drums turned? That is, could I kill two birds with one stone, or is there not enough overlap in labor to make it worthwhile?

In my searches regarding this problem, I found this website:
http://home.att.net/~m.prendergast-a...l/BRAKCHRT.htm
which has some pretty interesting brake diagnosis info. Pulsing brake drums show up about 2/3 of the way down.

[hawkdoc60]

If it has been a couple years since you last changed the rear bearings, then by all means, it would not hurt to change them. I remember when I drove Silver Bullet 20 years ago that I was replacing the rear bearings on average every two to three years anyway. They were wearing out on me that quickly.

[thirdman]

Update: At long last I took it into the shop that I semi-trust. I ended up replacing rotors, pads, drums and shoes and flushing the brake system. They were all pretty ancient, so I didn't mind too much. BUT: I still have pulsing. Definitely not as bad as it was, and the brakes themselves are much more responsive.

The mechanic claimed that the pulsing would be gone when I talked to him over the phone, but when I picked it up he said that the real cause of the pulse is that my rack is shot and my front right wheel is shaking on deceleration. They would be happy to replace the rack for a zillion dollars.

This smells strongly of BS as I get no vibration in the steering wheel ever... accelerating, coasting, decelerating, turning, etc. If I use the handbrake to --gently-- slow the car while in motion, I get bad vibes.

So did I get screwed? Is my mechanic fully of baloney or is this actually possible? How does one check to see if their rack is hosed? What are other possible causes of pulsing during braking?

[Dave G]

I vote "full of baloney".

[lessersivad]

^ x2

[FB71]

weapons-grade Balonieum...

[FestYboy]

you're still shaking? have the drums turned (yes i know they're NEW, but they can still be warped especially if they were standing on edge for a long time. same for the rotors.

[thirdman]

weapons-grade Balonieum...

Truly, you are a prophet. My rack was well and truly screwed, so I ordered one from "that guy" on ebay, and had a new semi-trustworthy mech install it. My handling and steering are MUCH tighter, and several gnarly clunks and rattles went away... but... (wait for it)... the brakes still pulse like mad.

Gonna see a brake dude this weekend... wish me luck...

[FestYboy]

turn 'em!

[Mike McKown]

Have you tried removing the spacers to see if the pulsation goes away?

Sometimes, brake pulsing is caused by lining material transferred from the pad/shoe to the rotor/drum. That happens after the brakes get hot and then the car stops rolling with the friction materials in contact with one another. Everytime that spot on the rotor/drum passes the lining material as the drum rotates, it'll drag and create a pusle. It usually won't go away on it's own.