2002 3.4 non/abs wobble at first from speed

[57chevyragtop]

119,000 miles, replaced brake pads and rotors 112k F&B. I seem to have a slight wobble when braking from speed above 60 MPH. Would this indicate there is a problem equalizing fluid pressure at the master cylinder. I am a bit stumped as I have no pulsating or wobble below that speed at first touch.

Do the front brakes apply before the rear or are they equally applied F to B rather than Left or right...seems the left F begins first. As always your input on this subject is appreciated.

No I have not changed the fluid. New front bearings 2 years ago (Timken). Stabilizer (F) replaced 2 months ago. Have new (Timken) rear bearing hubs to put in when time/weather permits.

[maxwedge]

The brakes are applied ft and rear, not lt to rt. There may be a split second delay in application based on the proportioning valves design. This " wobble" braking only, can be caused by rotor runout, any loose bearing or steering component. You could try lightly applying the parking brake and see if this generates the problem.

[57chevyragtop]

Thanks Maxwedge, I'll try that and I will repost. Run out, I need a dial indicator and time.

[Tech II]

The wobble sounds more like a pulsation......

When coming off the highway at 65 mph, LIGHTLY apply the brakes.....if the steering wheel shakes, front pulsation....if you "feel" it in the lower seat, rear pulsation....

Max, you can't apply the rear e-brake to check for rear pulsation, because this system uses the shoe inside the rotor set up for the e-brake...

[57chevyragtop]

Thanks Tech II, And To Maxwedge Parking brake answer is definitely YES. but almost to total stop though I had to use normal braking to full stop. OK, now back to Tech II, You are correct of course about the inside the disk/drum...but to answer to your thought, I will say in the seat.. This indicates _____________?

Using the disk brakes it smooth's out after the wobble, still in the seat feel to it.

[maxwedge]

Yeah, thought you had the rear caliper type like my Buick, Thanks Tech 11 for the correction, still back to checking the rotor runout.

[57chevyragtop]

Thanks Maxwedge, The only thing I can think of to cause run out is a bad hub bearing.

[Tech II]

If you lightly apply the brakes at 65 and feel the vibration in the seat, it's the rears doing the pulsating......could be rotor run out or improper brake installation techniques.......was the hub and rotor surfaces cleaned before installation? Proper lug torque to the wheels?

[57chevyragtop]

Thanks Tech II, I rotated tires October 13". All were hand torqued to spec 100fp. Clean surface same as when I replaced rotors/pads June 2012. E brake required no maintenance at that time. wire brushed hub surface.

I think your assessment of "pulsation" does describe this problem from a Tech's point of view.

I even think I hear this when no brakes are applied.

[Tech II]

I even think I hear this when no brakes are applied.

Then I would be checking for cupped tires or a shifted belt in a tire....

[57chevyragtop]

Tech II Thanks, I am not sure I know how to check that cupping, or the belt in the tire. I do remember some 15 years ago, I had a tire that was bigger outboard than inboard giving slant across the tread. Is that what you mean?

[maxwedge]

Cupping is a choppy uneven pattern usually on the edges, shifted belt causes the center or sidewall to run off center or wobbly.

[57chevyragtop]

OK Maxwedge, that gives me start point I'll check that tomorrow, in daylight.

[57chevyragtop]

Tech II and Maxwedge, checked all four tires I can not see or feel anything 360 deg. I know that does not mean there isn't something. I will try rotating rear cross to front, front to back not crossed, (per manual). Maybe that will enlighten me plus allow a better look. 36,500 miles on tires May 2009 install date.

[maxwedge]

Did you look at them from behind as you spin them looking for tread separation, and from the side looking for out of round?