2002 3.4 non/abs wobble at first from speed

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.

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.

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

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...

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.

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

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

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?

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.

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....

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?

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

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

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.

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

I don't have a way to do that, I don't have access to a lift. I am going to jack it up take rear pass tire off but spin it first see if I can see anything. I think I can find out of round and may be able to see sidewalls in/out as well. I'll have help available then. Supposed to rain and if it does, my next chance is Tuesday the 6th. I'll post asap. Thanks for the ideas Maxwedge & Tech II.

AS Max says, jack up the rear end, and have someone manually spin the wheels fast,,,,,watch for flat spots, cupping, shifting of belt, concentrating on the bottom edge of the tire....

I had this problem on a 93 Century a couple times. Rear drum, not 4 wheel disc. First time it was hot spots in the rotors. They were from Federated. Second time it was bad drums from Autozone. Turns out there was .020 run out in one of the drums I bought. Both instances were from cheap, poorly manufactured auto parts. I don't skimp on parts anymore and I ALWAYS check the run out of the rotors when I install them. I also check the thickness to make sure they are within .0005. It takes longer but it's worth the time. Your vehicle has a run out spec you can look up. Personally, I always try for .002 max.

Most DIY'ers don't have the gauge set up to check this....but I agree, cheap aftermarket products, especially those made in China, do not last long before problems show up....

Most DIY'ers don't have the gauge set up to check this....but I agree, cheap aftermarket products, especially those made in China, do not last long before problems show up....

Good point Tech II. I'm so used to having the gauges around that I forget that most people don't.

Tech II & Maxwedge, you will be happy to know I could find nothing wrong with the bearings either side...as with the tires as well evenly worn across tread 3/32 depth above tread ware indicator, both rear tires.

I did however discover that the rotors, both sides were a bit out due to spin resistance at a section on pass side, a little worse than driver side. Not enough to feel a pulsating pedal at speeds lower than 60. I do hear the rub or whatever as the rotors turn through the pads. Might also be time to check tire balance.

Parts stores and shops here close at noon. Ergo, next week I will perhaps just get new rotors, getting these turned requires drop off and next day pick up. Do either of you have a preferred mfg/brand. Have a NAPA, home town parts and a Chevy dealer. All others 30 miles.

Before you buy new rotors, there are a couple things that you might try to reduce the run out if that is what you have and not thickness variation. Clean all dirt and rust off the hub and the inside of the rotor where it mounts. You can also mount the rotor in 5 different positions on the hub. Most likely there is some run out in both the hub and rotor and you can find the best condition which might be good enough to solve your problem. Make sure the calipers move freely too.

Thanks Jerryg2112, funny you should mention thickness variation, I didn't check for that. Also did not consider the five position thought. Did clean surfaces though. Think the calipers were fine but I may take them apart to check more. I did both wheels today and that really did me in, I don't think I could myself do the five position switching, to labor intensive for me.

I agree with you on that being a lot of labor. Doing a lot of extra work for nothing isn't any fun:crying:. Without a dial indicator you'd probably be wasting your time. Even with one I don't go that far unless I have a problem. I just suggested it in case you wanted to really be thorough before buying new parts so soon after the last brake job.

I will admit these rotors were pretty cheap $41.90 for the pair. I think the Chevy dealer price was $169.00 ea.

Well guys, I had the rotors turned and one was pretty well out of true, this did not however solve my issue. I also tried to replace the hub bearing but was unable to do so because I could not get the parking brake cable unhooked. Since the backing plate must be removed with the hub.

I then took it to the garage that does most of my work I can't do. They told me that my tire was cupped on the inside tread. I could not feel this cupping and he basically told me to live with it and not worry about it. Driver side rear tire.

I still feel that the driver side bearing is bad for this reason: The passenger side the bearing (sans rotor) feels good and turns like a new one. The driver side is far easier to turn (read turns freely) though I cannot feel any 3-9 or 12-6 play, w/o dial indicator it not the best test procedure.

You don't need a dial indicator.......you would "feel" it if it was bad....

Cupping is not caused by bad bearings, usually it's lack of rotation or worn suspension parts.....

Thanks Tech II, I did perhaps not rotate them properly the first time. I put the back tires straight to front and vice-versa. I had forgotten the back were to crossover and front straight back. Only did this twice in the 36k miles. Last time I did it correctly I did not keep track of mileage at rotation. My mistake.

Hello automotive forum friends. I thought it a good idea to bring you up to date nearly a month after my original post on this thread. Thanks to all whom have read my posts and a special thanks to those of you responding with your thoughts and recommendations.

After a full re-inspection of drive line components I found a faulty left drive axle and had that replaced. This did not however clear my issue with the repetitive rubbing coming from the rear. I decided to buy a dial gauge set-up from Harbor (Fright)! Anyway I checked R rear and it was out of plane by 14 deg. the left was out of plane by 10 deg.

So I made the decision to change out the rear bearings and went and got a hammer slide puller from Pep Boys (67.50 rental dep.) 67.50 on return. They give you four days, so a shout out to Pep Boys...thanks! I could not have done this without this tool. These were extremely difficult to separate from the knuckles. The pass side took about 15 whacks and the driver side around 30 whacks.
The corrosion inside the knuckles in the bearing bore seat was incredible, 1/4 inch build-up. This must have been pushing the hub out of plane over time. Installation was a bit troublesome getting the parking brake actuator together but I learned a few things with the second one I did not figure out from the first. One has to do with removing the cable from the actuator lever...right at the end of the cable housing by the actuator lever there is a slotted cable stay with a white button type nylon rivet pressed through the stay (bracket). You can us a 1/8 punch or a thin flat blade screwdriver to get this apart releasing the actuator lever.
I cleaned out the corrosion with a 3" wide cone rotary wire brush and 1/2" electric drill and several different scraping tools...you really need to get all of the crud out as the bearing hub fit is a tight tolerance to the inner seat lip. I coated this area with anti-seize lubricant and also the flat mating surface + the four 10MM bolts.

I started this project when I got back from P Boy's at 8:30 AM and returned the tool at 4:30 PM. I would recommend if possible to do this job on a rack or at least jacked and supported as high as you are able. I am too old to be a contortionist and this really beat my feathers.

This seems to have solved my problem as I have been driving it since June 5 and can't hear the sound anymore. I have a few other issues to address so I will return soon and post a new thread when I get a better idea of what to ask.

Thanks all. David K.