The information in this article came from a technical symposium attended by trainers from General Motors, Ford & Chrysler, also Firestone, Goodyear, Big O Tire, Car-X, Merlin, Midas, Monro, Sears, Tuffy, Pep Boys, ProCare and others. The event, was sponsored by Pro-Cut International, a manufacturer of on-car brake lathes.
The purpose of this event was to allow aftermarket tech trainers to quiz OEM brake engineers about their recommend brake service procedures, new brake designs and any problems they are experiencing in their shops.
Keep in mind that the responses given by the OEM engineers reflect their opinions towards new car dealer warranty service procedures and fixes, not necessary repairs that work for the aftermarket.
Also keep in mind that the responses given by the individual engineers are not necessarily the "official" policy of the vehicle manufacturer they represent. In some cases, they expressed their own personal opinions rather than an "approved" service policy (no lawyers were present).
It's also interesting to note that the engineers from Ford, General Motors and Chrysler expressed opposite views on several important issues, including procedures for correcting brake pulsation problems caused by rotor lateral runout (GM approves the use of tapered alignment shims behind the rotors, but Ford and Chrysler do not.), the use of a lubricant or anti-corrosion treatment between the brake rotor and hub (Ford said yes, GM said never), and the use of brake pads that contain ceramic fibers (Ford and GM use them but Chrysler does not).
Here are my notes from the seminar:
Presented by Russ Dobson - GM Service Operations, Warren Tech Center
BRAKE PULSATION & RUNOUT PROBLEMS
Brake pulsation has been a high warranty issue for GM.
GM added four new categories to service manual procedures to cover brake rotor replacement (went from 1 page to 16). Is also paying increased labor rate to cover time needed to make measurements and corrections (a few extra tenths of an hour labor). New manual section covers basics of measuring and correcting Lateral Runout (LRO) Correction.
NOTE Very important to clean any rust/dirt/corrosion from hub anytime rotor is removed from hub. Cleaning is critical!
Must measure assembled lateral runout to see if correction is needed. Must be less than .002 in. If more than .002 runout, may not create a brake pulsation right away but it will appear within few thousand miles.
If a customer has a brake pulsation, you know you have variation so rotors will have to be resurfaced or replaced. GM says measuring rotor thickness variation is very hard to do accurately in the shop, so why waste time trying to measure it? GM spec for maximum allowable thickness variation in rotors is 0.025 mm (0.001 in.).
In the real world, the only things you can measure accurately are rotor thickness and flatness. You can't measure rotor thickness with a high degree of accuracy unless you measure about every couple inches all the way around the rotor. If the rotor pulsates, it has thickness variation and is bad.
To measure lateral runout, mount rotor on hub, install special conical washers (J45101-100) on lugs, then install and torque lug nuts to specs. This simulates wheel load on the rotor. Then you can accurately measure runout. Maximum runout will vary according to the vehicle, but on Chevy Malibu should only be 0.04 mm (0.0015 in.) max.
Major cause of rotor runout is rust & corrosion between hub and rotor, and improper lug nut torque loading. That's why it is so important to inspect and clean mounting area between hub and rotor.
GM has had major runout problems with Malibu ("Warranty problems though the roof"). The car uses small, composite rotors. GM has had difficulty building hub/rotor to .0015 in. or less tolerance at plant. GM has switched to softer pads (number 1417 on pad edge), and tried to tighten hub build tolerances. They are also using a "correction plate" (shim) between the rotor and hub to correct excessive lateral runout in factory and in the field.
To correct a rotor runout problem, first try indexing rotor position on hub to reduce total runout. If that doesn't work, can install thin tapered shim (correction plates) between rotor and hub -- or turn rotor with on-car lathe.
Correction plates: GM says don't reuse old plates, and don't stack plates (one only!). If you install a new rotor, remove and discard the old shim. A new shims should not be needed unless the hub has runout problem or the rotor has been incorrectly machined.
After marking high spot on rotor, install shim with notch opposite high spot. GM admits using correction plates does change wheel alignment slightly. GM approves correction plates for cars only (not trucks), and only for problem cars (like the Malibu).
Lug nut torque is very important. GM guy says leaving only a single lug nut loose or undertorqued may create as much as .003 in. of lateral runout in the rotor!
On-car lathe: GM says turning rotors on the car takes about the same time as measuring/correcting rotor runout with shim procedure. GM does recommend on-car resurfacing to correct runout, but is an expensive technique because of equipment cost. Dealers can decide for themselves whether or not to buy an on-car lathe (not a required tool).
GM says it is not necessary to resurface rotors every time pads are replaced. Do not reface new rotors. Latest GM warranty bulletin says .002 in. is maximum lateral runout for rotors.
Never use grease or lubricant on lugs, nuts or between mounting surfaces. Dry and clean only.
For 2003 model year, GM has changed to a new wheel design with a "flat" hub surface that mounts flush against the rotor and hub. Most GM OEM wheels have a slightly conical mounting surface that helps clamp the rotor against the hub (spring back effect) -- but on the Malibu this increases rotor distortion due to design of rotors and hub. By changing to a flat wheel, rotor distortion is reduced -- but it also requires very accurate torquing of lug nuts.
Technicians must use a torque wrench or torx sticks.
GM says RA finish on rotors should be 40 RA after turning and sanding. GM says to use sanding block and 150 grit aluminum oxide sandpaper. Sanding enhances surface finish and initial brake performance. Smoother is always better.
GM rotor rusting is currently a BIG problem. GM removed chromium from rotor alloy to reduce cost -- but this has increased rotor rusting in field. GM looking at nitrate coated rotors and gray iron rotor to improve rust resistance. GM has also looked at ceramic rotors but they are way too expensive now.
GM says it has not completely evaluated effects of replacing composite rotors with solid rotors. Current advice is to replace same with same.
GM says NEVER! Risk of damaging hose too great.
GM recommends using a positive rake bit in lathe because it requires less pressure, enhances flatness and surface finish. Old Ammco 4000 lathe had negative rake. GM did not approve it until Ammco gave them a positive rake. GM also says to use OE bits. Some round bits may not
give as good a finish.
GM moving toward one minimum rotor thickness spec. Not happened yet, but heading in this direction. GM currently has three different specs. Is too confusing now. Minimum machine to thickness spec should include enough thickness to allow for a certain service life after resurfacing. Question is, how much? Discard spec is thickness at which rotor is unsafe and must be replaced.
To reduce rotor runout, GM improving plate assembly procedures to tighten tolerances. Goal is .002 in. or less. GM is starting to attach rotors to hubs with fasteners instead of just slipping them on hub. Fasteners hold rotor in plate when wheel is removed and reduce risk of anything getting between rotor and hub.
Going to larger rotors and pads (needed to meet new FMVSS 135 braking standards). GM won't repeat Malibu "mistake."
GM says fluid changes are unnecessary - except for some offshore models that do have a specified change interval. For 2004, new GTO Monaro (Holden) from Australia will have a fluid change recommendation. GM is, however, currently reviewing the FASCAR drip strip method of checking brake fluid.
GM says is okay and has a product of their own for this purpose.
Rotor fin configuration? Some aftermarket rotors use different fin pattern than OEM? Is this okay or not? May affect cooling and heat management. May also affect rotor noise dampening characteristics.
Presented by Bill Fedelem, Jerry Balogh & Mike Wiacek
FUTURE OF ELECTRONIC BRAKE CONTROLS
Will see "giant leaps" in new brake technology. Bosch, TRW (Kelsey-Hayes) and Continental Teves developing lot of new hardware.
ABS currently available on most Chrysler products.
Traction control available on all cars, coming to trucks & SUVs now.
Next is stability control (ESP is DaimlerChrysler acronym). Is standard on all Mercedes now. ESP makes a real improvement in vehicle handling and stability for safer driving. Drivers appreciate it more than ABS.
Electro-Hydraulic Braking (EHB) will be available in 2003 on some luxury cars. Will replace vacuum booster. Will have accumulator for backup to apply brakes if electronics fail. Booster and master cylinder replaced with pedal simulator and failsafe hydraulic manifold. Electronic brake controls replaced by EHB unit.
Will likely require special OEM dealer tools and training to service and fix. By end of decade may see full brake-by-wire systems with electronic calipers.
CHRYSLER WHEEL SPEED SENSORS
Old tech: variable reluctant magnetic wheel speed sensors
New tech: Hall effect "active" speed sensors with integrated circuit.
Diagnosis is more complicated. Hard to bench test good or bad. Diagnostics are built into the PCM. A speed sensor code usually means the sensor has to be replaced. Tone wheel rarely go bad or are damaged.
Main warranty issue with new wheel speed sensors is shorting out electrically, sometimes due to moisture and corrosion.
All Chrysler platforms going to new active wheel speed sensors. Trucks there now, and cars going there too. LH will get in 2004.
Chrysler DRB III scan tool with ABS diagnostics has been available thru OTC since June.
Premature pad or rotor wear out has always been a significant customer issue. Chrysler is moving towards bigger, more massive brakes. New RAM truck has very large front rotors and calipers. Brake pads lasting over 50,000 miles on the new RAM truck.
Larger brakes require larger wheels. Most trucks now have 17-inch wheels. Can go up to 20 inches with optional wheels.
DaimlerChrysler does NOT recommend installing aftermarket ceramic pads. They say these pads are highly abrasive to rotors and will accelerate wear and magnify roughness. If used on a typical SAE G3000 gray cast iron rotor, they will wear rapidly and create variations in thickness. This will cause a pad vibration (brake judder). Engineers call this "variable brake torque input." Jeep Grand Cherokee has had this kind of problem (see fix below).
Chrysler uses NAO and low-met pads on their vehicles. They want consistent performance. Ceramics are less predictable, so Chrysler is still evaluating ceramic materials.
How Chrysler tests cars: Uses city driving tests - 4000 to 5000 miles with 400 lb. cargo load. Then measures pad & rotor wear and extrapolates data to estimate pad and rotor life. Trucks are tested at full rated GVW. Jeep test target is 25,000 mile life for the front pads and 50,000 for the rear brakes in city traffic driving. Objective is to replace rear brakes
every other front brake replacement.
Will probably see target for Jeep brake life increase to 30,000 miles soon.
Past European brake system designs used vented master cylinder caps and poor materials which resulted in relatively quick moisture absorption into the fluid. Not necessarily true for newer European vehicles.
NOTE: Brake fluid first developed in 1920s. Was originally caster oil. Then became glycol.
Chrysler says no recommended service interval for brake fluid because today's brake systems are much tighter and don't allow as much moisture penetration. Contamination is a non-issue.
Fluid discoloration can be caused by assembly oils and breakdown of seal compounds -- but does not affect fluid performance.
Chrysler uses DOT 3 brake fluid. Chrysler uses DOW 1000 fluid which exceeds DOT 3 requirements. The EPDM seal compounds are very compatible with the DOW DOT 3 fluid. Others may cause squeaks due to difference in lubricity characteristics.
Why not DOT4? Because DOT 4 absorbs moisture at a faster rate then DOT 3.
Chrysler's DOT 3.550 is same as DOW 1000.
Inspect hoses when servicing brakes. When larger calipers and rotors are used, it lowers the pressure in the brake lines. Is easier on the hoses. Today's hose materials are much longer lived. The weakest link is the crimped fitting.
"You'd blow off the hose before the hose itself failed."
"Hose should last the product life of the vehicle and go with it to the boneyard."
When servicing brakes, do not allow calipers to hang unsupported by their hoses. Some calipers weight up to 18 lbs. and can strain/weaken hose if allowed to hang by hose alone.
Chrysler has gotten away from pad wear indicators because of too many problems with them. Government rules require OEM to provide tools to check pads, so Chrysler includes a jack and lug wrench in every vehicle so the wheels can be removed to check the pads (duh!). Also, using wear indicators limits size of pad that will fit.
Someone in audience said his customers like vehicles with pad wear indicators because it saves them the cost of having to have their rotors replaced when the pads wear down. They don't have to wait until the pads wear down to bare metal and ruin the rotors.
Water gets into rear drums and causes corrosion. From 1996 to 2003. Cure is a new backing plate that keeps out water. Is also a cyclic rubbing problem. Requires relubing rear shoes so they don't stick.
GRAND CHEROKEE 1999-2002 BRAKE ROUGHNESS/JUDDER PROBLEM
Problem is excessive rotor thickness variation generated by poor caliper centering. Causes steering wheel shake. Grand Cherokee brakes up to this year was designed by Teves. Same brakes used on BMW & Ford Expedition. But Grand Cherokee was first to use twin piston caliper design. Chrysler wanted twin piston because vehicle is heavy. Caliper spring causes inboard pad to drag.
Takes a LOT of heat (cherry red) to warp rotors, so main cause of rotor variation is not heat but uneven wear. New calipers now available through Chrysler dealers to solve problem.
See TSB 05-003-02. New calipers are boxed in pairs with hardware P/N 05093174AA. Should replace both rotors, too.
SEBRING/STRATUS COUPE 2001-2003 BRAKE SQUEAL PROBLEM
Change caliper support/anchor.
Chrysler uses damped cast iron. Is better than standard gray iron. But is softer and wears more when aggressive aftermarket pads are installed. Rotor quality and noise characteristics vary a great deal with quality of iron alloy & cooling process. If make rotor alloy harder to extend rotor life, it reduces the rotor's ability to handle heat without heat cracking.
Chrysler only uses phenolic pistons. Very smooth and won't rust. Only way can damage piston is if boot seal is damaged and dirt gets inside. Pistons should go 150,000 miles. Chrome plated steel pistons not as smooth, plating wears away and pistons rust. Steel also transmits heat to brake fluid, increases risk of fluid boil.
Not a problem with Chrysler. Hub runout in 15 micron range. Very tight build and assembly tolerances. Human hair 90 microns thick. So if somebody uses a grease between the rotor and hub and any dirt or grit gets into joint, will cock rotor and cause runout.
Average runout on most Chryslers is only 25 microns on hubs/rotors, Jeep Liberty is 30 microns. Lateral runout spec is 25 microns. (0.001 inch).
Presented by Garrett Van Camp & Chris Oakwood
BRAKE FLUID FLUSHING?
Ford does not recommend brake fluid change intervals here in the U.S.
In Europe, Ford does recommend changing the fluid every two years. Ford in Europe may follow U.S. lead and change their recommendation to reduce maintenance requirements. Auto makers are looking to commonize world standards.
Main reason to flush is moisture contamination (lowers boiling temperature and increases risk of fluid boil). Ford evaluates brakes on 18 mile long hill in Arizona. Engineers ride brakes down the hill. Temperature of DOT 3 fluid must not exceed 284 degrees F (at 3% moisture contamination). In Europe, they use a different hill and test procedure -- so they get different results. Europe requires DOT 4 fluids as a rule (DOT 4 has higher temperature spec, but DOT 4 boiling temperature drops more quickly as a result of moisture contamination than DOT 3). DOT 4 is more hygroscopic than DOT 3.
Ford says flushing brake fluid may increase risk of causing other brake problems (such as getting air or dirt into system). Brake fluid is also not environmentally friendly (creates disposal problem), so shops should not change it unnecessarily.
NOTE: Different DOT 3 fluids absorb moisture at different rates depending on what additives are in fluid.
Ford says need to flush and change fluid varies depending on the area of the country (no moisture problem in Arizona but there is in Florida), and also on the robustness (corrosion resistance) of the parts in the brake system.
Ford's service life for brake fluid is 10 years, 150,000 miles (has been this for past four or five years). Ford says if there is a reliable way to test fluid and the fluid tests bad, then it should be changed. Otherwise, leave it alone.
WHAT'S NEW IN ABS?
Stability control on Lincoln LS in 2000, Focus in 2001, Expedition and Navigator in 2002, and Lincoln Aviator in 2003. System uses lateral acceleramometer, yaw rate sensor and steering angle sensor, plus brake booster is modified so that the brakes can be applied electronically when stability control is needed.
Ford ABS suppliers are Bosch, Kelsey-Hayes, Teves and Sumitomo.
Ford policy is to NOT offer ABS as standard equipment but to offer it as an extra cost option for those who want it.
Wheel speed sensors on Lincoln LS are like Chrysler and use a Hall effect sensor because it generates a stronger signal at low speed than magnetic sensor. Question is how durable the Hall effect sensors will be over the long haul. The Hall effect sensor only uses two wires instead of three as it uses the chassis as ground. Technicians may not realize these vehicles have a different type of sensor and that they require different test procedures to diagnose.
Ford has used ceramic (potassium titanite) since 1993. Ceramic fibers improve durability.
"Ceramics" is hard to define. It's like baking cookies. A lot of ingredients go into a friction material and the manufacturer may choose to call it almost anything they want. Calling it a "ceramic" does not define how much ceramic is actually in the pads. It could only be a very small amount or a lot. Pad performance depends on all the ingredients that are in the pads. Same pads could be called NAO, low-metallic, semi-metallic, ceramic, carbon-metallic, you-name-it. It's all how the pad manufacturer wants to market their product. There are no standard industry definitions.
Semi-met pads are improving, and have less tendency to wear rotors and create runout and pedal pulsations.
Someone in audience said a certain brand of aftermarket ceramic pads are running hot, warping rotors. These are "ceramic" pads. They have a higher coefficient of friction which reduces stopping distance, but the wear problems they are creating may more than offset the other advantages these particular pads offer. Ford uses ceramic pads made by Akebono and have NOT experienced similar problems with the Akebono friction materials.
FMVSS 135 requires less pedal effort to stop a vehicle if brake booster fails, so brakes must be more aggressive to meet the new standard. Ford said most OEMS using pads with a higher coefficient of friction. But this is increasing rotor wear and noise. OEM can also change tire size and aspect ratios, rotor size, etc.
"Brakes don't stop vehicles, tires do." If tires are larger, therefore, it increases the mechanical leverage and load on the brakes, and the amount of pedal force required to stop the vehicle.
FORD FOCUS REAR DRUM REPLACEMENT?
Drum has bearing assembly. Buy Ford YS47-1A049-AA replacement rear bearing if rear drum as to be replaced. It is a new improved bearing. Requires 175 lb./ft. of torque on drum retaining hub nut.
Someone in audience said he is seeing a lot of rear disc brake rotor wear on Ford Taurus & Mercury Sable 1998 & up with OEM brakes (news to Ford guys). Another person said he sees the same thing due to corrosion on caliper pins that binds up caliper & causes pads to drag.
SANDING ROTORS AFTER MACHINING?
Ford endorses on-car rotor resurfacing. Sanding should not be necessary if job is done right. The rotor finish with good, sharp tools should be under 60 RA, so Ford sees no need to sand afterwards. The existing Ford rotor service spec is 100 RA or less. Ford may reduce this to 60 RA or less in the future.
Rotors should be cleaned with brake solvent and wiped after machining.
Ford also says there should be no need to resurface rotors unless they have pulsation or severe rusting. Is best to leave rotors alone.
SHIMMING TO CORRECT ROTOR RUNOUT?
Bosch study conducted for Ford says using shim moves rotor out and may create pad retention problem when pads wear. It may also adversely affect lug nut torque retention. Measuring rotor runout and correcting it with a shim is too complex a service procedure for average technician. A shim may also create wheel runout. Most runout that is present will be in the rotor anyway, not the hub.
TRW study of shims was also negative. So Ford does NOT recommend using rotor shims at this time. If rotor runout is a problem, cut rotor on car with on-car lathe or replace rotor.
New OEM rotors are manufactured to within .001 to .0005 in. runout. Ford recommends using a nickel antiseize compound between the rotor and hub when new rotors are installed. The nickel antiseize provides corrosion protection and will not cause loss of lug nut torque over time as some other products will. Rust growth between the rotor and hub can push the rotor out and create runout, uneven wear and pedal pulsation.
Crown Victoria has had runout problems. Ford is using nickel antiseize treatment between rotor and hub at the factory to protect against corrosion that can cause future problems.
WARNING: DO NOT USE OIL, GREASE, ANTI-SEIZE OR LUBRICANTS OF ANY KIND WHEN TIGHTENING LUG NUTS!
Proper torque on lug nuts is very important for three reasons. One is to keep the lug nuts from loosening up and the wheel coming loose, another is to prevent distortion of the brake rotor behind the wheel, and a third is to prevent broken studs. A torque wrench should be used for final tightening of the lug nuts, and the nuts should always be torqued to the recommended specifications.
CAUTION: Torque specifications for lug nuts are always for CLEANand DRY studs and lug nuts. That means no oil, no grease, no anti-seize and no lubricants of any kind. Any of these products will reduce the friction between the threads. This may seem like a good thing to prevent rust and frozen lug nuts, but the reduction in friction means a much higher percentage of the applied torque (up to 25% or more) will go toward loading the lug nuts. The end result may be brake rotor distortion or broken studs!
Wheel studs should be cleaned with a wire brush to remove rust and dirt BEFORE the wheels are mounted. If the lug nuts are heavily rusted or have damaged threads and won't turn easily on the studs, replace the lug nuts. The same goes for any wheel studs with damaged or badly corroded threads. And remember to mount the wheels DRY with nothing on the threads.
Ford no longer uses composite rotors because they had too many runout and corrosion problems with composite rotors. Ford now uses full cast rotors. Ford says okay to replace composite with full cast rotors.
Heat and time dry out caliper seals and reduce the amount of piston pull-back as seal ages. New seal will pull back piston about .015 in. Old seal may only be .010 or less. May allow pads to drag.
BRAKE BY WIRE?
Makes most sense for rear brakes. Brake-by-wire allows rear brakes to be reduced in size, weight and cost. Rear brakes don't do as much work as front brakes.
CLAMPING BRAKE HOSES?
Ford does not recommend clamping hoses during service procedures. This may damage the hose and increase the risk of hose failure. Better to bleed system afterwards to remove air.
BRAKE LATHE BITS?
Ford says they have not found much difference in rotor finish between round bits and OEM lathe bits. Okay to use either. Someone in audience said he is getting better results with round lathe bits.