front brake problem

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  #1  
Old 02-29-08, 12:38 PM
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front brake problem

I have had the front rotors replaced on my 1996 Buick Le Sabre 4 times. After 2-3 weeks they are warped can anyone tell me what is or could be causeing this problem.
Help! I'm frustrated and nearly Broke$$$$
 
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  #2  
Old 02-29-08, 12:44 PM
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Cool warped rotors

i have had trouble on a ford with warpage when the rotors are hot and you run through a water puddle. it seems to cool the rotors so fast they warp. now when i drive through a puddle i apply gentle brake pressure to keep the pads in contact with the rotor until after i exit the puddle. maybe this helps?
 
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Old 02-29-08, 03:32 PM
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Originally Posted by stephers View Post
can anyone tell me what is or could be causeing this problem.
Help! I'm frustrated and nearly Broke$$$$

1. you drive like you are in the Daytona 500

2. you are buying cheap rotors

3. you have a bad brake hose that retains too much pressure in the caliper and the brakes are always applied to some extent.

4. (and I believe the most likely cause)----- the rear brakes are not working properly.
 
  #4  
Old 03-01-08, 08:05 AM
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dont skimp

Buy good quality. Rotars from overseas are the pits. Get made in USA or Canada. Not from Mexico,China or any other country.Spend a few extra dollars. I recommend NAPA parts.
 
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Old 03-01-08, 01:33 PM
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Originally Posted by nap View Post
4. (and I believe the most likely cause)----- the rear brakes are not working properly.
Absolutely agree. And if you live in snow country, you can find this out in a hurry if you apply brakes hard in snow and look out the door and see fronts lock up and rear wheels keep turning. Makes things rather testy when driving down city thoroughfares that allow 45 mph and it has that slime layer of snow on the road and the light turns yellow on you. Makes it so you don't know whether to attempt to stop, and maybe go (slide) through a red light or keep going.

Lacking properly working back brakes can be a fooler when the pavement is dry. My car does the above in the snow, but on dry pavement, I would not have a clue.
 
  #6  
Old 03-02-08, 07:11 AM
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have you checked to see if your rear brakes are working properly...could be over-working your front brakes due to malfunctioning rear brakes, causing the front brakes to be over worked, and therefore overheated, therefore warping...just a thought
 
  #7  
Old 03-02-08, 08:14 AM
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The real cause of Brake Pedal Pulsation

The following is from the GM Publication "TECH Link" that is sent to GM dealers once a month. Mentioned are tools and other service equipment available at GM dealers but may not be readily available elswhere. This information, if performed correctly, will correct the cause of thickness variation which is what you feel as brake pulsation.

BRAKE PULSATION
Pulsation is caused by thickness variation. Thickness variation is caused by corrosion or rotor lateral run-out.

Remember, a caliper floats in the steering knuckle. Parallel surfaces (no thickness variation) WILL NOT produce brake pulsation even with 0.010 inch (0.25 mm) or more lateral run-out.

Wear-induced thickness variation usually occurs 2,000-10,000 (3,200-16,000 km) after miles after rotor service. Lateral run-out can be cut into the rotor with an improperly maintained brake lathe.

On brake apply, a rotor with thickness variation will push the brake pads apart resulting in hydraulic movement through brake piping to the master cylinder and to the brake pedal.

CRITICAL DIMENSIONS OF A ROTOR
Here are some details about measuring a rotor.

TIP: Thickness measurements should be done with a brake micrometer, which has a pointed anvil and a deep throat.

Brake Rotor Thickness
SI provides three dimensions:
- New (original)
- Minimum after machining
- Discard
TIP: If you subtract the minimum thickness after refinishing from the new thickness, the result is the amount of useful rotor life left.

TIP: Brake rotor thickness should be checked a final time just before you put the wheel back on the vehicle.

Rotor Thickness Variation

TIP: This measurement is used when addressing brake pulsation concerns.

The rotor should be measured in at least four places in the pad contact surface area.

The Service Manual calls for correction if the thickness variation exceeds 0.001 inch (0.025 mm).


MEASURING AND CORRECTING LATERAL RUN-OUT

TIP: Before installing the rotor to the hub, be sure there is no debris on the rotor or hub mating surfaces.

TIP: When installing a rotor on a hub, hold the rotor at the 5 o’clock and 8 o’clock positions to avoid dropping any residue from inside the rotor cooling vanes into the hub/rotor interface area.

Hold the rotor flat to the hub. Install J 45101-100 conical washers (A) and lug nuts (B) and finger tighten (fig. 5). Torque the lug nuts to SI specifications using a star pattern.



A Conical washer

B Lug nut

TIP: Conical washers simulate the clamping load of the wheel on the rotor/hub interface to make an accurate LRO measurement.

TIP: Print the brake specifications from SI as handy reference during the repair. Attach it to the repair order as a permanent part of the vehicle history file to substantiate the specifications you were working with.

LATERAL RUNOUT (LRO) CORRECTION

IMPORTANT: Over time, excessive LRO causes thickness variation which causes brake pulsation. See the December 2004 TechLink as well as 00-05-22-002F.

This procedure involves placing a machined, tapered correction plate between the rotor and hub.

Install a dial indicator J 45101 (or equivalent) to the steering knuckle and position the indicator button so it contacts the brake rotor friction surface at a 90° angle, approximately 0.5 inch (13 mm) from the outer edge of the rotor (fig. 6).



With the dial indicator installed, rotate the rotor until the lowest reading is displayed on the indicator dial and set the dial to zero. Rotate the rotor until the highest reading is displayed on the dial. Mark the location of the high spot relative to the nearest wheel stud, or studs. Mark the studs and rotor (fig. 7) to allow you to reinstall the rotor to the hub in the same index location. Record the amount of measured LRO on the repair order for the corner of the vehicle you are working on.



Refer to LRO measurement procedures in SI. On most passenger cars, if LRO is greater than 0.002 inch (0.055 mm), correction is required. P-90/N-car specification is 0.0015 inch (0.038 mm). Always consult SI for the specifications for the model/year vehicle your are working on.

Select and document the appropriate correction plate. Use the Brake-Align application chart supplied with the plates. Brake-Align plates are numbered XXX-XX, where the first three numbers represent the type of hub they fit and the last two numbers represent the correction value in thousandths of an inch (03 gives 0.003-inch correction, 06 gives 0.006-inch correction and 09 gives 0.009-inch correction). Brake-Align plates come in only these three thicknesses. Select the appropriate correction plate as indicated below.

You are trying to get the total LRO as close to zero as possible. Because you are compensating a rotating device, it doesn’t matter if the values go positive or negative.

EXAMPLE: If the runout is 0.005-inch, the 0.006-inch plate would give you -0.001-inch LRO after installation. The 0.003-inch plate would bring you to +0.002-inch (which might be within spec) but the 0.006-inch plate minimizes the total LRO and gives a better repair.

With the rotor removed, install the plate (A) on the hub with the V-notch (B) at the high point previously marked (C) (fig. 8).



A Plate

B V-notch

C High point mark

TIP: Brake-Align plates have a double wheel lug pattern of mounting holes to allow positioning the V-notch at a lug location or in between lugs, depending on the location of the high spot mark.

Install the rotor, observing the index marks you made earlier.

Hold the rotor flat to the hub, add a conical washer and finger-tighten the first lug nut. Repeat with the other lug nuts. Tighten to the specified torque, in a star pattern.

Confirm that LRO is within specification using the measurement procedure above.

Measure the final rotor thickness for that rotor in that position on that vehicle and record on the repair order.

Install the caliper and pads. Pad inspection and replacement guidelines were covered in part 1 and bulletin 00-05-22-002F.

Remove the lug nuts and conical washers; re-install the wheels, using the recommended lug torque and procedure.

Depress the brake pedal several times to take up changes in component clearance due to rotor refinishing and to secure the rotor in place.

Verify and adjust the brake fluid level in the master cylinder reservoir.

Brake-Align Tips

Brake-Align plates save you time. Using them is an approved repair procedure and they should be used to correct brake rotor LRO when it exceeds the specification. Brake-Align plates, properly used, give you repeatable, exact LRO correction results quickly.

TIP: The LRO Indexing Correction procedure in SI is valid to correct minor LRO variation. But you may need to bolt and un-bolt the rotor from the hub 4 or 5 times to get the lowest LRO measurement, which still may or may not be within the vehicle’s maximum LRO specification.

The most commonly used plates are the 0.003-inch and 0.006-inch. If rotor LRO measurements indicate the need for a 0.009-inch plate, determine EXACTLY where that LRO is coming from. First, remove the marked/indexed rotor from the hub and check the hub lateral surface for LRO with a dial indicator in the same method as above for checking the rotor. Place the indicator tip just outboard of the lug circle. Generally, most hub outer edges are approximately half the distance from the centerline of the axle to the area you were checking on the rotor. Using some geometry, it would be logical to expect this value to be approximately half of what you were seeing at the rotor, if 100% of the runout is in the hub.

EXAMPLE: You measured 0.011-inch LRO on the rotor. You disassembled the rotor from the hub and measured the outer edge of the hub and found 0.001-inch LRO. This would indicate that approximately 0.002-inch of your 0.011-inch total LRO is due to hub LRO.The rest is LRO in the rotor itself. If you have just cut that rotor, you need to take a very close look at your cleaning process and your lathe equipment.

TIP: Never re-use a Brake-Align correction plate. Never stack more than one Brake-Align correction plate on an individual hub.
 
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Old 03-02-08, 08:51 AM
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just a note slj, OP is not experiencing problems when first installing the rotors, it is a problem that preents itself after some use. They are also new rotors.

That would indicate that the rotors are within tolerance when installed but are being warped by something later.

and yes dodger, that is a thought, that two posters previously had recommended as probable cause.
 
  #9  
Old 03-02-08, 09:15 AM
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Originally Posted by nap View Post
just a note slj, OP is not experiencing problems when first installing the rotors, it is a problem that preents itself after some use. They are also new rotors.

That would indicate that the rotors are within tolerance when installed but are being warped by something later.

and yes dodger, that is a thought, that two posters previously had recommended as probable cause.
If perfectly machined rotors are installed with incorrect/inconsistant wheel nut torque, dirt or rust between the rotor and hub interface or on a hub that has run out, the rotors will not run true. This lateral run out will in a short time cause thickness variation that causes brake pulse. My testing showed it may happen in as little as 2000 miles. What happens is as the rotor turns, the so called (warped) area of the rotor will rub on the pads. This same part of the rotor as it is rubbed many many thousands of times will wear that spot thinner and that thin spot (thickness Variation) is what causes feed back into the brake pedal. Most vehicles are fixed for a short period of time but if the cause of run out is not fixed, the problem will return.
 
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Old 03-02-08, 09:52 AM
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sorry steve, been fixin' cars for too many years to see that as a reality.

If there is runout at installation, there is typically some indication that there is a problem. In todays world where a pad slap is all to common, the slides are not cleaned and lubricated as they should be and lateral runout WILL be felt as thickness variations. Even when the calipers slide freely, lateral runout does present itself in a manner most drivers will notice.

and to your argument:

Parallel surfaces (no thickness variation) WILL NOT produce brake pulsation even with 0.010 inch (0.25 mm) or more lateral run-out.
Not neccessarily true. IF the calipers do not slide freely, that runout will be felt exactly as thickness variations will be because that runout and a "sticking caliper mount" will cause the same action on the caliper; it will cause the piston to be pushed back into its' bore and then allowed to extend repeatedly. If the calipers slides offer absolutely no resistance, then I can accept your statement but that it generally not the situation.

as well, in your claim, if the rotor is in fact contacting the pad enough to be worn down enough in 2k miles that it would result in a measurable amount, that "bumping" is going to be felt as well. Obviously not in the pedal as the brakes ar not being applied with the foot but they are effectively being applied by the car and the conditions so the braking action would be felt at very low speeds. (idling through a parking lot for example)

Since the OP is apprently aware of his brakes and what is happening, I would suggest this would not go unnoticed. To a totally ignorant person, it may escape them.

and your use of shims is really a bad idea. If there is ever any need for them, it would be to correct HUB runout only, not rotor runout. If you install them on a hub that is true to correct some rotor runout, you are causing the tire to now have runout, which due to the differences in diameter of the 2 parts, will be much greater on the outer surface of the tire. Why would you knowingly and willingly cause the tire to not track true? This will cause increased tire wear and reduced fuel mileage. If you have rotor runout, you machine or replace the rotor as needed. If you have hub runout, the proper thing to do would be to replace it but if you want to shim it, I can see no harm.

To properly correct for hub caused rotor runout, you would machine the rotor in situ so it would then compensate for the hub variances and always remember to mark the relative rotational installation of the rotor on the hub and always place it in the same position.

oh, and;

used to be ASE/ NIASE certified but let it lapse as I changed careers.
 
  #11  
Old 03-02-08, 11:22 AM
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You do make some valid points. The procedure which I only partially quoted has been fixing repeat brake pulsation for about 10 years now. If I have runout in a hub I would prefer to offset the runout with a shim than spend alot of money replacing a hub. You could always have the rotor machined "on car" and then any runout in the hub is compensated for, of course the rotor must then always be returned to that specific location and indexing. The shims, in most cases, are for hub runout that would then cause rotor runout. Some cars require correction of the total rotor runout if the runout is over .0015". With the runout that you will find in many hubs and the degree of inaccuracy found in many rotor machining tools, including operator error, shimming is necessary. As far as causing the tire and wheel not to run true, as I said you are mostly shimming for runout in the hub so you will be causing the tire and wheel to run truer that if not shimmed. All I can add to this is I have a hard time argueing with success. This process does permanently fix cars and not only GM endorses the process but other manufacturers use this procedure.
 
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Old 03-02-08, 03:06 PM
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you stick with yours and I'll stick with mine. I do not have problems with my repairs and I have done literally thousands of brake jobs.

just for clarification though:

You could always have the rotor machined "on car" and then any runout in the hub is compensated for, of course the rotor must then always be returned to that specific location and indexing. The shims, in most cases, are for hub runout that would then cause rotor runout.
machining a rotor in situ is machining on the car. If you use shims, you will always have to make sure the shim is placed correctly when removing the rotor as well. I would rather mark the rotor than worry about a shim falling out and having to figure out where it goes.
 
  #13  
Old 04-22-08, 09:40 PM
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Listen to Steve on this one, he knows what he's talking about.

In layman's terms, if you are replacing rotors only to have a brake vibration within a few thousand miles consistently, then you probably have lateral runout in your hub. The way to fix this is to have your *BRAND NEW* rotors turned with an on-car brake lathe the minute you put them on. They will match your rotors to the runout in your hub....problem solved. Make sure of course that you replace your pads at the same time as they will also have uneven wear.

I know it sounds crazy, but this is exactly why GM, Ford, Nissan, Subaru, Chrysler, Honda, Toyota, etc. have all mandated the use of on-car lathes in their shops. All dealerships above obviously have on-car lathes, but so do all corporately owned Firestones, Carmax's, etc.

Statistically, many brand-new rotors don't even come 100% "true." On-car lathes are not a bad idea on any vehicle that has had a history of brake vibration issues.
 
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