GM Brake Pulsation Due To Lateral Runout

[Music] [Applause] [Music] hello i'm lynn mccall and i'd like to welcome you to this general motors service know-how release in this presentation and the accompanying reference booklet we're going to thoroughly review the topic of brake pulsation due to lateral run out or lro it's no secret that vehicle complexity is ever increasing advancements are being made at the corners as well hubs calipers rotors although mechanical and operation are becoming more sophisticated and subject to tighter tolerances and precise assembly break pulsation has been and continues to be a significant customer satisfaction issue unfortunately it often reoccurs after a service visit but can take as many as ten thousand miles to develop the bottom line is that rotor lateral runout or lro is often misread and directly contributes to the pulsation issue attention to detail and machining accuracy while performing procedures are essential to avoid comebacks the guesswork of brake pulsation has been eliminated bulletin numbers 0005 and 005222002a are available to establish an accurate procedure and allow the time necessary to do the job correctly while we'll focus on the and carl aero grand dam and malibu due to their tighter tolerances the procedures and practices demonstrated in this presentation apply to all vehicles the intent is to capture the entire brake pulsation service issue in one place and we're specifically going to review these topics we'll begin with caliper operation so we can all begin on the same page then we'll cover inspection of the related components rotor measurement and rotor cutting the brake align system will also be examined then we'll put it all together and cover the complete procedure from start to finish concentrating on the details that are key to successful repair let's begin by reviewing caliper operation [Music] the need to minimize lateral runout should be obvious in view of the tough job the rotor and caliper have to do together when the driver applies the brakes fluid pressure behind the piston presses against the caliper piston and the piston bore the piston movement forces the pad against the inboard rotor surface pressure applied to the piston's bore forces the caliper to move on its slides caliper movement applies pressure against the outboard brake pad forcing the pads against the rotor surface both brake pads press against the rotor surfaces bringing the vehicle to a stop when hydraulic pressure is released the square cut seal retracts the piston this allows the system to reduce brake pad drag improving brake release and fuel economy without any perceived lateral run out the rotor rotates within the caliper's pads when the brakes are applied braking force is even and efficient however operation is affected when the rotor has lateral run out this could be caused by an improperly torqued wheel nut a burr or rust on the hub rotor mounting surface or contamination on the wheel hub mounting surface with excessive lateral run out the rotor wobbles as it rotates uneven rotor wear occurs when the brakes are not applied causing thickness variation over time this variation increases to the point where brake pressure feedback and therefore pedal pulsation is felt at the driver's foot here's the bottom line lateral run out causes rotor wear the resulting rotor thickness variation causes the pulsation the real customer satisfaction issue is that rotor lateral run out may not occur for thousands of miles after an improper repair and furthermore the original repair may have nothing to do with the brake service procedure it may have been an hvac technician that over torqued a wheel after removing it for better access to an ac line or the compressor mounting bracket the entire service department must properly install wheels whenever they're removed it's a simple procedure that's worth reviewing every time a wheel is removed it must be installed with the proper torquing procedure first all wheel nuts are hand tightened using the star pattern then the wheel nuts are tightened to torque specification in two passes a torque wrench is required during the first pass the wheel nuts are tightened to one half the specification using the star pattern on the second pass each nut is then tightened to the full specification again the star pattern must be used a point needs to be made here about impact guns you can not only distort the rotor but create a rust shower as well these particles can get in between components on the mating surfaces possibly contributing to lateral run out to help prevent anything falling in between mounting surfaces always hold the rotor in position during installation on this rotor the wheel nuts have been properly torqued to specification as we just showed you as shown on the dial indicator there is little or no lateral run out falling within the specifications for variation on this rotor we tighten the wheel nuts with an impact gun without the star pattern well beyond specified torque lateral run out is definitely present in this case we allowed rust pieces to fall on the hub's mating surface to the rotor and then installed the rotor and wheel again lateral run out is present in this case we put a burr on the wheel hub mating surface and then installed the wheel again lateral run out is present lateral run out typically results in brake pulsation within three thousand to seven thousand miles after an improper repair in a vehicle's corner by corner we mean the hub brake and wheel however we also have seen cases where it can take as much as 10 000 or even 12 000 miles for the pulsation to be noticed to protect everyone's professional image over-torquing wheelnuts has got to stop pass the word to all the techs in your shop [Music] sometimes the root cause of rotor lateral runout is apparent if you take the time to look just like brake drums brake rotors provide a friction surface for the brake pads to contact for stopping the vehicle when you look at the corner it is important to identify corrosion is it merely cosmetic what many of us refer to as lot rot or is the corrosion severe leaving the metal surfaces pitted obviously severe surface damage must be refinished or replaced several moderate stops in a safe area and manner will clean most cosmetic corrosion on the previous style calipers used on older rear-wheel drive vehicles it's also a good idea to measure caliper to mounting bracket clearance it should be 10 to 24 000 of an inch depending on model make sure the clearance is consistent top to bottom also if you're servicing the caliper don't forget to check caliper slide clearance on any caliper that uses machined guides new rotors on general motors vehicles have a surface finish of 0.25 to 1.27 micrometers or 10 to 50 micro inches with a non-directional swirl pattern although it is not customary to measure the surface finish of rotors check the existing rotors for deep scoring which may require rotor refinishing or replacement a thorough inspection for brake pulsation must always include a look at the mounting surfaces look closely where the hub meets the rotor look for debris corrosion metal chips or lips basically anything that might offset how the rotor and hub mate the same is true for the hub wheel mounting surface anything other than a flat true surface may cause run out when installed the j42450a tool kit is specifically designed to help clean these mounting surfaces while most components can be cleaned with an air driven die grinder and abrasive pads the stud cleaner will do a better job and offer longer tool life if powered by a slower drill motor [Music] before we continue we want to make sure you understand one point about measuring rotor thickness you're not looking for thickness variation if the vehicle came in for brake pulsation you know the rotor has thickness variation due to wear from the lateral run out our only check here is to find out if we have enough rotor to resurface or whether we need a new rotor on this alaro the minimum rotor thickness is 25 millimeters or 98 hundredths of an inch as found on other models this discard specification is cast into the rotor measure thickness in several locations if the rotor is thinner in any location replace it also if a new rotor is required there is no need to resurface it an accurate micrometer reading is critical to disc brake service obtaining a correct micrometer measurement is accomplished by combining three readings on the micrometer the following example will illustrate accurate micrometer reading using an english standard micrometer metric micrometers work similarly when using a micrometer always use the calibrated end of the thimble this end is calibrated to slip when the micrometer is adjusted for the measurement shown here the outer barrel roll to reveal the numeral scale on the stationary barrel which measures in tenths of an inch increments in our case we see the zero which identifies one inch and the first 25 one thousandths of an inch hash mark on the stationary barrel the outer barrel also rolled one thousandths of an inch past as well therefore our rotor has a thickness of 1.026 inches or 1 and twenty six thousands of an inch micrometers that measure in ten thousandths of an inch use a vernier scale to read the scale identify the vernier number that is perfectly aligned with a thimble number and or segment in this case the three on the vernier scale lines up squarely this equals three ten thousandths of an inch when measuring lateral run out on most rear-wheel drive vehicles tighten adjustable wheel bearings slightly to take out any free play before beginning be sure to readjust the wheel bearings correctly after run-out measurements are complete to avoid damaging the bearings for non-adjustable bearings refer to the service information on end play diagnosis with the wheel removed we must install the rotor on the vehicle with the proper torque sequence using the conical washers supplied with the brake align system hold the rotor while securing the wheel nuts finger tight using the star pattern then tighten the nuts to specification with a torque stick attach a dial indicator arm assembly to a fixed part of the suspension this assembly included in the brake align system is specifically designed for this area when the relationship to the rotor is right secure the assembly by engaging the locking lever be sure the indicator tip contacts the rotor face approximately one quarter inch from the outside edge of the rotor also ensure the tip is tight so it does not vibrate during rotation always turn the rotor in the same direction clockwise is best slowly move the rotor through one complete revolution while observing the dial indicator find the low spot and set the dial indicator to zero rotate the rotor again mark the high spot on the rotor and the stud on most gm vehicles the lateral runout spec is typically 55 thousandths of a millimeter or two thousandths of an inch on the end car alaro grand am and malibu the spec is tighter at forty thousandths of a millimeter or fifteen ten thousandths of an inch [Music] we have a sequence on rototurning from the foundation breaks and abs systems service interactive distance learning course number 15045 now most of you should have taken it if not we highly recommend it we're using this footage to stress how important it is to use a lathe correctly in fact we know from visiting dealerships across the country that many lathes are not properly maintained always ensure that the lathe you use is properly maintained and qualified when we say your lathe must be qualified here's what we mean from manufacturers directions and making sure all mating surfaces are clean measure a rotor's lateral run out after machining it use the same method as you would on a vehicle then hold the inside valve clamp in place while you rotate the rotor 180 degrees measure the lateral run out again add the readings together and divide by two to identify the amount of run out the lathe is cutting into the rotor if run out is greater than the manufacturer's specification you probably need to machine the inside of the belt clamp and index it to the arbor we'll have the procedure in the reference booklet be sure to check it out now as we review the rotor turning procedure remember you can only cut the rotor as accurately as your lathe allows resurfacing a rotor is a machining operation so properly practice the procedure because you are the machinist proper brake lathe operation whether on or off vehicle is critical to producing an acceptable rotor surface finish therefore always check for proper operation of all motors switches feed controls and levers also make sure radius cones bell clamps and taper cones are free of all nicks burrs rust and foreign debris check the arbor for run out typically it should have less than two thousandths total indicated runout make sure the bottom of the tool bit holder is also clean as well as the carbide bit seat on the tool bit holder if the surface is not flat install a new tool bit holder always follow the lathe manufacturer's specific operating and maintenance instructions for best results there are three basic conditions that are required for a brake rotor to be effective when stopping a vehicle first both sides of the rotor need to be flat and parallel second the surface finish needs a roughness analysis or ra reading of 50 or lower and third the machined sides of the rotor need to be perpendicular to the center line of the hub with the lathe properly qualified mount the rotor and install the vibration dampener before mounting either a composite or hubless rotor for refinishing clean the hat section of all rust burrs and any foreign matter if any debris is present on this surface the rotor will not properly mount on the lathe hub and cause an inaccurate cut when mounting a composite rotor adapters are used to hold it because composite rotors do not have an integral hub the stamped center must be squeezed just as it would be when the wheel is tightened against it once it is properly mounted the machining process is just like that for hubbed rotors with the rotor mounted and vibration dampener installed bottom the tip of the tool bit in the deepest groove of the rotor then zero the scale and back out the tool bit repeat this for the other side of the rotor move the cutters to the innermost edge of the rotor face adjust the micrometer knobs for approximately two thousandths of an inch more than the original reading and start the resurfacing operation if the groove is extremely deep and the rotor is thick enough you may want to make two cuts after cutting is complete sand both sides of the rotor with 150 grit aluminum oxide sandpaper to produce a non-directional finish use a sanding block and leave the rotor turning at the lathe manufacturer's recommended cutting speed sand for 60 seconds sanding reduces the peak height when finished wipe the rotor clean with brake cleaning solvent and a clean rag be sure to check that the refinished rotor meets all inspection requirements in summary remember to practice good machining techniques know your equipment follow manufacturer's recommendations cutting equipment must be maintained and qualified regularly bell clamp services must be true and clean free of debris corrosion metal chips lips etc never excessively torque lathe collar bolts gradual accurate torque is essential on a related note we need to point out that an on-vehicle lathe offers no inherent advantages over a bench lathe either way you must cut every rotor accurately and precisely the break a line system offers the best path to correcting brake pulsation due to lateral run out the procedure is completely documented in bulletins 0005 23002a specifically for the end cars and bulletin0522202a for our other vehicles the break-a-line system basic kit includes a good selection of correction plates a vice grip dial indicator hub cleaner with additional pads this is an enhanced version of essential tool j42450a conical washers an instructional video two markers a deluxe toolbox to keep all the pieces together and an application chart to help ensure you use the appropriate correction plate on a specific vehicle the brake align system efficiently and effectively identifies the high spot on a rotor with lateral run out based upon the amount of run out a correction plate is selected and indexed on a rotor to compensate for the lateral high spot and bring the installed rotor within the lateral run out specification if for example the rotor has four thousandths of an inch of lateral run out then a three thousandth of an inch correction plate is used to bring the lateral runout down to only one thousandth of an inch this is within the acceptable specification of fifteen ten thousands of an inch or if the rotor has seventy one ten thousands of an inch of lateral run out then a 6 000th correction plate is used to bring the lateral run out down to only 11 10 thousandths of an inch this is also within the acceptable specification of 15 10 thousands of an inch each correction plate has a v-nut so you can index it to the rotor's high spot never attempt to stack two or more correction plates together on one hub also a correction plate should never be reused before we look at a sample service scenario here's a tip some technicians check the correction before installing the wheel in addition to the required check with the wheel installed to proper torque specifications let's now summarize what we've learned here today by walking through a brake pulsation service procedure start to finish whenever servicing a brake pulsation concern road test the vehicle be sure you're dealing with the concern as stated take the time to inspect the front corners are the pads of proper thickness are the caliper mounting gaps good are there any deep grooves in the rotors are there any signs of damage or corrosion make sure the rotors meet the minimum thickness specification before machining them if you're using new rotors don't waste your time by machining them it's unnecessary next make sure all the mating surfaces of the rotor hub and wheel are clean remember to use the special stud cleaner with a drill motor either the rotor can be machined or must be replaced when machining the rotor you must use an approved lathe that is not only maintained but qualified on a regular basis as well with the mounting surfaces clean install the rotor and then the conical washers from the kit tighten all the wheel nuts using the star pattern with a torque stick to the full specification fasten the dial indicator to the steering knuckle and position the indicator needle on the front side of the rotor approximately a quarter inch from the edge if the lateral run out is higher than the specification you'll need to locate the high spot and determine how high it is this will determine which correction plate to use to locate the high spot rotate the rotor clockwise to the lowest reading and then zero the dial indicator next rotate the rotor clockwise again to find the high spot the gauge will provide you with the amount of run out record it and then mark the wheel stud closest to the high spot if the high spot is equally between studs mark both repositioning the rotor on the hub can in some cases be used to reduce the lateral run out if you can get the run out under the specification by indexing the rotor on the hub you won't need to use a correction plate most vehicles require a run out of two thousandths of an inch or less the encar alero grand am and malibu are tighter at fifteen ten thousands of an inch if you're ever in doubt check the specs with the amount of runout recorded and the location marked you can select the appropriate correction plate to bring the run out within specifications for example if you have two and a half thousandths of an inch run out select the three thousandths correction plate also make sure you align the correction plates notch to the marked stud if two studs were marked install the notch between the two as stated before never install more than one plate or reuse a previously installed one also don't bend or drop the plates with one side corrected leave those conical washers and nuts in place and go to the other side before installing the wheels then with both sides corrected and the conical washers still in place install both calipers pump the brake pedal until it's firm before continuing since the specification for run out is rather tight on the end cars we're also concerned with the stack up when you install the brake calipers and wheels so make a final check after assembly to check the run out with the wheels on fasten the dial indicator to the steering knuckle and position the dial needle on the back side of the rotor a quarter inch from the edge perform the measurement by rotating the opposite wheel so the rotor you're checking rotates clockwise this will help prevent causing a false run out reading what if your previous run-out was within specifications and then changed after the wheel was installed it could be caused by incorrect torque contamination between mating surfaces or component damage this is why it is so important to check the wheel hub mating surfaces as part of your initial inspection remember when working on brake systems cleanliness is essential rust or debris between mating components can result in excess run out as we said in the beginning vehicle complexity is ever increasing and advancements are being made at the corners as well hubs calipers rotors although mechanical and operation are becoming more sophisticated and subject to tighter tolerances and precise assembly brake pulsation has been and continues to be a significant customer satisfaction issue unfortunately it often reoccurs after a service visit but can take as many as ten thousand miles or more to develop the bottom line is that rotor lateral run out or lro is often misread and directly contributes to the pulsation issue attention to detail and machining accuracy while performing procedures are essential to avoid comebacks the guesswork of brake pulsation has been eliminated bulletin number 0005230002a and 005 2200 are available to establish an accurate procedure and allow the time necessary to do the job correctly thank you for taking the time to view this presentation be sure to read the accompanying reference booklet and take the online test to certify your participation in this gm service know-how release on brake pulsation due to lateral run out or lro you

Channel: Retro Video Archive

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Rating: 5 out of 5

Keywords: GM, Chevrolet, Chevy, Brake, pulsation, repair, help, service

Id: TAj6--xiSgg

Length: 29min 20sec (1760 seconds)

Published: Wed Dec 09 2020