Bumpy stopping when applying brakes


#1

I have a 1987 Olds Ferenza (Federated) with 225,000 miles. Runs great but when I apply the breaks I get this bumping that seems like I’m on a bumpy road…But I’m not. Any suggestions to this problem? I put new pads and rotors a few months ago.



Thanks for any help you can relay.





bklahr

rklahr@sbcglobal.net


#2

Possibly warped rotors. Even if you did replace them recently all it takes is driving through a puddle when the brakes are warm.


#3

Agreed. If the rate of wheel vibration depends on your speed, suspect warped disc rotors (especially since you don’t have ABS).


#4

Did you clean the rotor surfaces before installing them? If not, the protective coating on new rotors can cause pulsating.

And, yup, warpage is another possibility. But cleaning teh surfaces with a good brake cleaning solvent is worth a try.


#5

I posted this very question about a week ago (will driving through a puddle with warm brakes warp your rotors) 3 of the regulars responded all said “no-way” you cannot warp your rotors this way. One said them most common way rotors get warped is from over-tourque on the lugs. I always wondered about this as so many people believe it is true thats why I posted the question. Its like a urban myth. I think the tag is “warped brake rotors” or sometning similar. Iam not trying to start a fight here like some posted about my postings concerning transmission service. I do think the OPs problem could be warped brake rotors


#6

So, what do you do to check for warped rotors??

Thanks everyone.


#7

Can you fix warped rotors or do you have to get new ones.?


#8

Put the front of the car up on jack stands, put the transmission in neutral. With the engine off, rotate the wheels by hand, and have an assistant press slowly on the brake pedal. If the rotors are warped, you will begin to notice the sound of the pads rubbing at one point in their rotation, then becoming free as you pass that point. The person applying the brake must push the pedal down SLOWLY.

If that doesn?t give definitive results, remove the wheel and looki at the rotor surfaces, inside and out. You should be able to see the high and low spots on the rotor.

Let us know what you find.


#9

You could do it the book way with a magnetic base dial indicator Zero the dial indicator and rotate the rotor watch the needle swing note the swing check against allowable spec. Place the plunger of the dial indicator against the rotor then zero


#10

This is really a very common problem with new brake pads. There are a LOT of posts exactly like yours here. There is a bedding process that should eliminate the pulsing, but very few mechanics take the time to explain the process to their customers. Sometimes the process will vary according to the materials used in the pads.

For now, your best bet is to find a relatively unused road and make some moderately hard stops from 50 to 5 mph. Don’t “lock em up” but do apply more than normal pressure. Don’t come to a complete stop either as this can trap heat against the rotors in one spot and lead to warping. Two or three of these moderately hard almost stops with at least a minute between each at moderate speed should clear up the problem.

It may return after a few thousand miles, just repeat the procedure. This may happen three or four times before it finally stops and the brakes remain smooth until the next brake job.