Hello gents!

The car is a 2004 SS Non-supercharged.

I'm experiencing pulsating braking while in smooth, light decelerations at all speeds. Emergency braking is good and solid. No vibration in the steering column during braking. IT IS NOT THE ROTORS. I did spin checks on all wheels and replaced my rears which had some burn issues, but were engaging properly and the rotors were not warped.

Any ideas on what could cause this issue? Anything you can supply would be greatly appreciated!

Best regards,

Andrew

 

Curious how you are ruling out the rotors?

 

ABS acting up?

 

I've seen rotors (cheap Chinese rotors) where the outward facing part of the rotor looked great, you could spin the wheel by hand and all was fine.... Take the rotors off, back side had large flakes/chunks missing (that was the pulsing).

Also, a rotor has to be REALLY bad to see warp issues. Example:

My wife's Impala made a strange noise on both front wheels (you could jack the car up, spin them and hear it). It was in the same spot of the wheel travel. By eye-ball, no signs of damage or issues. That was the year I had the Monte calipers powder coated. Since I had the front rotors off my Monte (I was not 100% sure if they had an issue or not, the looked fine but the brake pedal felt some "pulsing"). To test the noise issue, I put the Monte rotors on her Impala. Good news, the noise went away. Bad news.... The Monte rotors are bad as now the Impala has the pedal pulsing feel. Again, nake eye, the rotors looked 100% fine.

My guess, change your front rotors. Or at least have them checked out. Odds are, they are out of spec somewhere and you'll never see it....

Now, if the ABS is causing the pulsing, could be something completely different (like a bad speed sensor).....

 

blacksheep: I took off all rotors to visually inspect, found no abnormal wear patterns or burn spots, reassembled and did wheel spin checks, all passed with no issues. I replaced the rears because I did find burn spots on one, but the issue still hasn't been solved.

nighthawk: Yes, my ABS and traction control have had issues since I've had the car. Traction activates when accelerating from a stop with the wheel turned (getting out of a parking spot) and occasionally, I will turn on the car in the morning and the "Check ABS" light comes on, and traction control is forced off.

Maniac: That could be the issue. Like I said, I visually inspected and spun all and they seemed good. Could I get the rotor face machined to solve the problem, or is replacement necessary? Any more info on the ABS issues?

 

A visual inspection cannot reveal warpage unless it is extreme. The rotor needs to either be mounted on the vehicle or chucked up in a resurfacing machine. Then a dial indicator needs to be placed on the rotor and zeroed out. Then the rotor needs to be rotated and the reading on the dial indicator observed. Readings should be taken in a minimum of 3 locations (outer edge/middle/inner edge). Even run-out as little as .003" can be felt as pulsing in the pedal.

 

Especially since you are saying you only feel it during light braking, I would suspect it's a very fine warpage

 

As far as an ABS issue, you can tell when pulsing is AMB related (you have a "mechanic" feel to it for lack of a better term and in some cars you will hear the ABS pump activate). With a good scan tool that can read the ABS speed sensors and record data, you can record some stops and review the data frame by frame. Typically if it's a bad speed sensor that is not throwing a engine code you will find in the last couple of frames of coming to a stop one wheel hit's zero before the rest. If that's the case, you replace the speed sensor (on the Monte, it's in the hub) and that resolves the problem in the cases I ran across (granted, that assumes no issues with a hung caliper or something else interfering).

If it's the rotors, honestly, for the cost of new rotors and pads, I would not bother having them turned. You can get good quality rotors for an inexpensive price. Right now I have AC Delco Advantage rotors (for performance driving) and they were like $20-$30 a rotor at the time from RockAuto.

Most cars today don't have rotors with enough material to re-surface and if they "need" resurfaced, the material is usually borderline on if there is enough to do the job.