Breaks or Tires?

[jgirard2]

[99ContourLX]

Hi Jeff,

 

I'll add my 2 cents but would recommend waiting for Terry's reply.

 

Firstly, if the dealer did a brake rebuild, he should be responsible for figuring this out so I would take it back to him.

 

It's possible that the lug nuts have not been tightened to spec. You may want to loosen the lug nuts a bit and re-tighten them with a torque wrench. I had the same problem a few years ago after a tire rotation and it turned out that the lug nuts were over-tightened.

 

If the vibration happens while driving (and not only during braking), your tires need to be re-balanced.

[SVTDEMON]

Hi Jeff,

 

I'll add my 2 cents but would recommend waiting for Terry's reply.

 

Firstly, if the dealer did a brake rebuild, he should be responsible for figuring this out so I would take it back to him.

 

It's possible that the lug nuts have not been tightened to spec. You may want to loosen the lug nuts a bit and re-tighten them with a torque wrench. I had the same problem a few years ago after a tire rotation and it turned out that the lug nuts were over-tightened.

 

If the vibration happens while driving (and not only during braking), your tires need to be re-balanced.

Damaged or worn front caliper retaining clips!

[CrewChiefPro]

Damaged or worn front caliper retaining clips!

 

 

Were the front rotors turned on your "brakes" ( notice correct spelling ). English is tough, both words sound the same but you "break" things while you need "brakes" to stop.

Edited April 9, 2010 by CrewChiefPro

[Gar]

Jeff,

 

I keep discovering incomplete service work on brake jobs. It is important to assure that the centering mechanism is also addressed when doing service. The caliper only squeezes from one side. To allow the squeeze to apply to both sides of the rotor, the caliper must be able to center itself. This is done by letting it slide on two pins anchored to the bracket and in turn, the spindle knuckle. Rubber bellows boots keep crud and wet out. These can dry and tear over time, and the worse... a tech may not take the time to secure them back tight on both ends. The problem is either gummy old lube, or rusty pins develop. Now the caliper doesn't center, and you get several symptoms.

 

It is pretty painless to look at this. Jack, remove wheel, loosen the smaller pair of bolts (they are the pins) (careful not to stress or dangle the caliper by the flexible brake hose) coax off the boot, and see how well they slide, and how shiny they still are. Fixing is also pretty easy. Run both pins against the wire wheel, clean the bore they slide into well (I say sandpaper is NOT the answer in the bores), and lube with high temp grease meant for the task (small packets like catsup at the parts store counter usually) then make sure you get the boot lip in its groove on both ends going back together to keep out the crud.

 

I would check this for your symptoms.

While you're there you can also look for an edge that formed on the rotor that should have been knocked down before new pads, cocked pads (not loaded in the caliper true) or missing/mangled springs, and sloppiness of the centering pins. Depending on how grooved the rotor face is, use a straight edge to see if there's warpage. Also wooble the spindle bearing. I bought a Subaru with a ruined bearing that flopped all over and the previous driver didn't have a clue.... apparently it wasn't noisy, but I

ll bet it made stopping peculiar.

 

You didn't mention symptoms before the brake job, but you must have had a reason to get it done. So it's not certain where the cause is, but you stand a fair chance of locating it if you look instead of just changing parts yet.... and more cost effective.

 

Gar

[jgirard2]

[jgirard2]

[jgirard2]

[Gar]

Jeff,

 

After driving, put your hand near (and slowly) (don't touch initially), the wheel rim near the lug nuts to see how warm or hot they are. Unless you just stopped from 60, you shouldn't feel very much heat. If you do, then the pads are dragging, and the cause is still likely due to stiff pins. Gotta ask... what originally generated so much heat that the rotors warped in the first place? If you don't race or pull high G stops 20 times in a row in 5 minutes, your rotors shouldn't be hot.

 

Gar

[jgirard2]

Hi Gar,

 

Well dragging pads are never good so I will unquestionably check this out.

 

While I tend to stop (on occasion) a bit quicker than a little old lady, I definitely am not abusive of my car or its brakes.

 

Thanks for the useful tip!

 

Jeff

[Viking22190]

Before i Read What Was Said About The Problem Being Resolved, i Was Going To Suggest The Brake disks Were Warped. The Same Thing Happened To My Sebring Under Hard Stopping scenarios.

[jgirard2]

[Terry Haines]

First off, rotors do not 'warp' as most think..the usual problem is that they have crud/rust between the rotor/hub that will mess up runout..You should all also not that most car makers now match rotors to hubs etc when a car is built and mark the hub/rotor with a paint dot or mark..which tells you to fit the rotor back on the hub in the same position..As for turning rotors..only ONE way to have them 100% true...turned 'on the car'...

[Terry Haines]

..this is worth a read,written by Dave Mann, it explains why most who fit new rotors still have vibration!!

 

..AUTOMOTIVE BRAKING SYSTEMS- ROUGHNESS AND VIBRATION

 

One of the most common brake system customer vehicle performance complaints is brake

roughness, pulsation and vibration. As common as this complaint is very few people, including

many service technicians, actually understand the true cause of it and what to do to correct it

permanently. This leads to misdiagnosis, unnecessary repairs and parts replaced and the likely

re-occurrence of the problem a short time later. Brake roughness can be defined as vibration that

is felt in the steering wheel, brake pedal and/or seat during vehicle braking. This does not

include the normal pulsation that occurs when anti-lock brakes are activated during a panic stop

or when on wet, snow or ice covered roads, which can activate the anti-lock brakes.

What typically happens is the customer experiences this type of vibration and pulsation and

thinks something is wrong with their brakes and then takes their vehicle into a repair facility.

The customer explains the problem and the repair facility technician or service writer either takes

the vehicle out for a test drive to confirm the symptoms or pulls it into the shop and starts right in

on the brakes. Then they come out to the customer and inform them that their brake rotors are

"warped" and they need new rotors and pads (and sometimes hubs), or they can machine the

rotors on their bench lathe if there is enough rotor material remaining to meet the manufacturers

minimum thickness requirements.

The problem with this diagnosis and repair procedure is that first of all is that brake rotors do

not warp. The second problem is that replacing a brake rotor with a new brake rotor or

machining the rotor on a bench lathe will only fix the problem temporary. The problem will

almost always re-occur after a period of time, thus necessitating further repairs. Brake rotor disc

thickness variation or excessive lateral runout, as well as drums that are out of round can cause

vibrations and pulsations in the brake pedal and/or steering wheel. Brake lining material transfer

onto the rotor can also have an effect on this as well.

 

Here's what really occurs: all brake rotors and hubs have an associated Lateral Runout (LRO).

LRO occurs when two axes are not parallel to each other, such as the axes of the rotor and the

hub or the spindle and the rotor/hub. LRO may be caused by manufacturing tolerances,

improperly torqued wheel nuts (uneven or excessive torque), corrosion between the brake rotor

and the hub, hub with excessive runout, worn or improperly adjusted wheel bearings or any

damage or wear. This is what is commonly referred to as "warped" rotors. These so called

"warped" rotors do not in and of themselves cause the vibrations and pulsations. Any machined

component, such as brake rotors and hubs, are going to have manufacturing tolerances, which

include runout. Typical original equipment new rotor runout specifications are in the range of

0.0015-0.002 in. while low quality aftermarket rotors can be significantly higher. In addition to

excessive manufacturing tolerances, cheap, low quality aftermarket rotors can have increased

impurities and porosity in the metallurgy. I recommend using either the OEM rotors or a high

quality aftermarket rotor.

New rotors and hubs are machined to precision tolerances from the auto manufacturers.

Aftermarket rotors and hubs are usually not machined to the same tolerances, as the aftermarket

manufacturers do not know the OEM specifications, although some are much better than others.

 

 

 

Auto manufacturers will either match mount the rotor and hubs or machine the rotor on the hub

unit as an assembly. Match mounting is matching up the low spot on the brake rotor with the

high spot on the hub. This match mounting process minimizes the runout ofthe assembled

components, but is only a production process. A service technician cannot effectively determine

where the high and low spots are in order to match' mount the components. Machining the rotor

on the hub (and/or spindle) with the proper on-vehicle machining equipment is the very best

method and almost completely eliminates runout. But, if they do not effectively prevent rust and

corrosion in the joint, over a period of time it will induce runout and eventually brake roughness.

What can occur over a period of time is that whatever runout is in the system coupled with

improperly torqued wheel nuts and/or misadjusted or loose wheel bearings and rust and

corrosion forming between the rotor and hub surface leads to increases in runout. As you drive

your vehicle without using the brakes, such as on the highway, every rotation of the rotor high

spot or multiple high spots contacts your brake linings in the caliper, even when you are not

using the brakes and wears the high spot or multiple high spots offthe rotor which causes a thin

spot or multiple thin spots. Over a period of time this repeated process causes what is called

Disc Thickness Variation (DTV). DTV is when the rotor thickness is not the same all the way

around the rotor. DTV is typically caused by lateral runout. DTV can only be measured with

very specialized laboratory testing equipment or with special on vehicle capacitance probes.

When you apply your brakes, and a brake rotor has DTV, the thick and thin spots on the rotor

cause the brake pads to move in and out. This in-and-out pad motion causes increases and

decreases in brake system pressure, which the driver can feel in the brake pedal. This in-and-out

pad motion causes a varying brake force, which is passed to the steering wheel. As the rotor gets

hot, it is much more likely to increase thickness variation, thus increasing pedal pulsations as

well as steering wheel and other vehicle vibrations. This phenomenon is what many technicians

refer to as "warping", however they actually think the rotor warped and needs replacement.

Typical acceptable values for DTV are around 0.0004 in. That's 4 ten thousandth\9! an inch! As

DTV increases beyond 0.0004 in., brake pedal, steering wheel and vehicle vibrations and

pulsations will almost always occur.

Replacing a rotor with excessive DTV with another new rotor will only correct the problem

temporarily, because eventually the associated LRO with the new rotor will lead to DTV over a

period of time, and the problem repeats itself all over again. Machining a rotor with excessive

DTV on a bench lathe will only temporarily correct the problem because the rotor is being

machined true to the bench lathes spindle and not the spindle on the car, plus the spindle on the

bench lathe has its own runout.

The correct method is to machine the brake rotor on the vehicle using an on-vehicle brake lathe.

For applications where the rotor is separate from the hub (loose rotor) make certain that both

surfaces are free of rust and corrosion and be sure to put a thin layer of nickel anti-seize on the

mating surfaces. This will prevent rust induced increases in LRO over a period of time. Rust can

form in-between the mating surfaces and exert tremendous forces which will cause increases in I

tension of the wheel studs and resulting clamp load variation which creates LRO. The LRO will

then eventually lead to DTV, brake roughness and vibration. For vehicles with adjustable wheel

bearings, be certain to properly adjust the bearing preload prior to machining the rotor.