Brakes pulsating

[BodybyFisher]

Add this thought to the equation (interesting thread):

http://www.nsxprime.com/forums/showthread.php?t=2372

Summary:

This has been a subject of extended discussion and debate. As you already are aware, when rotors are warped, they usually shudder all the time, not just when they get hot.

The best guess is that the brake shudder occurs only when hot, due to the development of "hot spots" on the rotors. These are areas that expand at different rates when they are heated, so that the rotor is not a uniform thickness; hence the shudder.

They cite three types of rotor warpage:

1) One type is what I call "cold warpage" and the other is "hot ghost warpage". Cold warpage is a permanent warpage which you will feel at all speeds and temperatures - it is typically the result of poor casting and quality control.

2) "Hot ghost warpage" becomes evident only when the rotors reach a certain temperature, such as when they become hot after hard braking; it results from uneven heating and cooling during the heat tempering process and/or the final cryogenic treatment of the rotor. This type of warpage in the rotor is NOT evident when they are cold - you can literally put the rotor on a lathe with a feeler gauge at room temperature, and it will spin true...but heat it up to some arbitrary temperature, say, 500deg, and the warping becomes evident.

3) Now, there is a third cause of brake shudder, which is NOT caused by a warped rotor, but can often lead many to believe that their rotors are warped. This third cause is "friction material film transfer", which is essentially the irregular, non-uniform deposition/transfer of brake friction material onto the rotor surface. All high-performance compounds exhibit this phenomenon to a certain extent at various temperatures, with some compounds being very hard offenders, indeed. When the brake friction material is deposited or smeared onto the rotor surface in an irregular pattern, upon application of the brakes, the brake pad will "grab-and-release" on the film transfers due to chemical adhesion, resulting in a brake shudder, and thus simulating what is often assumed to be a warped rotor.

Veddy Interesting......

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Here is more information for our on-going discussion base by Dave Zeckhousen:

http://www.zeckhausen.com/avoiding_brake_judder.htm

Avoiding Brake Judder at the Track

by Dave Zeckhausen

If you have taken your car to the track on weekends, changing between racing brake pads and street pads, you've probably experienced brake judder. Brake judder, also known as "brake shimmy," is the feedback through the steering wheel and suspension when you apply the brakes at certain speeds and pressures. The steering wheel can shake back and forth, ranging from a faint, barely noticeable vibration to a violent shudder that feels like it could rip itself from your hands.

Judder can occur on the street or track and, in both cases, is caused by uneven build-up of pad material on the surfaces of the rotors. It is aggravated by the high temperatures experienced at the track and by switching back and forth between two incompatible friction materials.

Despite the popular myth, brake judder is not caused by warped rotors. http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml Judder is the result of a thickness variation in pad buildup on the rotors' surfaces.

To understand why this is happening, you first need to understand the concept of bedding brakes. Click here for bedding instructions>> http://www.zeckhausen.com/bedding_in_brakes.htm . In order to maximize the performance of your brakes, you must transfer a thin layer of pad material onto the surfaces of your brake rotors. This "transfer layer" forms molecular bonds to the pads when you apply the brakes. As the rotors rotate underneath the pads, these bonds are torn apart. The resistance of the bonds to being broken yields additional friction above and beyond the abrasive action of the pads and rotors scraping against each other. This additional friction is called "adherent mode." You must bed your brakes in order to benefit from adherent mode friction.

When you install race pads, you would like to remove the street pad transfer layer from your rotors before you bed them in. Conversely, when your track event is over and you reinstall your street pads, you would like to remove the race pad transfer layer before bedding in your street pads. How do you do this?

Some drivers swap pads and rotors at the same time, keeping one set of rotors dedicated for the track and the other set dedicated for the street. This works by keeping the transfer layer pure and not piling up incompatible layers of pad material on top of each other. But it's a lot of extra work. The last thing you feel like doing, after a long track event, is to swap hot rotors. There is a better way.

Street pads exhibit a mixture of abrasive and adherent friction almost immediately without extensive warm up. Race pads don't get into their adherent mode unless they are several hundred degrees, a temperature rarely seen on the street. Under normal street driving conditions, a race pad will operate almost purely in abrasive mode.

Use Race Pads as a Tool to Remove Deposits from Rotors

If you install race pads before your track event and drive around normally, the race pads will polish away the transfer layer left behind by your street pads. This leaves you with nice, clean rotors which may be bedded with your race pads when you are at or near the track.

After the track event is over, you should not switch back to street pads right away. Instead, drive home from the event using your race pads. As they cool down, the race pads will once again go into pure abrasive mode and polish away their own transfer layer from your race weekend. Cold race pads will even cure judder problems from pad deposits accumulated during the track event. By the time you get home, the rotors are polished clean and ready for you to install and bed your street pads.

In essence, you are using your race pads as portable brake lathes. The race pads are a tool for removing unwanted transfer layer before and after your track event.

Avoid Pad Imprinting on your Rotors

After a fast lap on the race track or a high speed stop from over 120 mph, your brake rotors may be literally glowing red hot. If you keep your foot planted firmly on the brake pedal after coming to a complete stop, you may find your brake pads bonded firmly to the rotors. The extreme heat melts the surface of the pads and forms an imprint on the rotors. This imprint is a few ten thousandths of an inch thick and can result in a noticeable shimmy. If it happens on unbedded rotors, you will also end up with a significant difference in the coefficient of friction between the imprint and the rest of the rotor, further aggravating the situation. In addition, the heat transfer through your brake pads can boil your brake fluid, resulting in a spongy pedal feel.

To avoid this problem, try to take advantage of the cool down lap before entering the pits at the end of your track session. Use the brakes as little as possible during your last lap. If you must enter the pits directly after a hot lap, make sure to roll to a stop and place the car in gear (or park) to keep it in place, rather than leaving your foot on the brake pedal. If your parking brake is incorporated into the rear calipers (e.g., many VW and Ford models), then avoid using it. Use a wheel chock, if necessary, to keep the car from rolling.

In the excitement of a track event, it's easy to forget all of this. As adrenalin courses through your body, your hands will be firmly clamped to the steering wheel and your foot on the brake pedal. Try to relax and keep that foot off the brake pedal! By following these techniques, you can forever banish the brake judder demons from your car.

[epricedright]

If the shudder reappears, I'd say #2 is probably my problem. I still think the warpage can appear and disappear as metal will expand and contract, when the rotor is heated then cooled. Hopefully, since the sticking slider bolt issue has been fixed, the shudder will be gone for good.

[BodybyFisher]

I think you are correct, at least the mystery of your HOT shudder is solved... Mike

[GreenMachine]

I've been going threw a back and forth brake problem. I'll take it in for service, the guys at the shop try this or that, the squeak or squeel will go away for a few days (or this last time just a few small trips to the store/around town).

The sqeak/squeel has reappered faster and faster these last couple times and now after my trip I get what sounds like a bird chirping on my left side even when I DON"T hit the brakes.

They are cermic pads so my understanding is they really shouldn't make any sounds since there isn't any metal to rub against each other, any ideas on my problem would be a good help, I'll try the "bedding" procedure again, that seemed to help alitltle, and the sounds that happen when I apply the brakes seem to go away when I get the brakes hot.

Also after washing the brakes wheels they brakes feel 10 times better but then a day or so later they feel grabby, and the pedal at a stop lights "drops" slightly once in awhile.

other than that they work great and stop the car fine The problem only seemed to get worse AFTER they replaced the rotors for a squeek I was getting on the right front.

[KHE]

Check to make sure the air deflector is not bent and touching the rotor. That will make a squeal while the brakes are not applied.

[BodybyFisher]

Check to make sure the air deflector is not bent and touching the rotor. That will make a squeal while the brakes are not applied.

I have actually had this happen...

[epricedright]

If it's not the air deflector, and I'm not sure if this would apply to your car, but some older brake pads sometimes needed an anti-squeal lubricant applied to the back of the pads to prevent squeaking. I've done a few older cars where that helped. My Raybestos ceramic pads didn't require it though. I'm assuming your pads aren't worn down to squeakers?

The pedal dropping sounds like either there's air in your brake lines - bleeding would help that, or a caliper going bad that is leaking brake fluid. Look on each caliper and see if you have any wet spots. Look at your master cylinder and brake booster as well. I had to replace a booster once with somewhat similiar symptoms, but the pedal would drop much more.

Good Luck!

[GreenMachine]

If it's not the air deflector, and I'm not sure if this would apply to your car, but some older brake pads sometimes needed an anti-squeal lubricant applied to the back of the pads to prevent squeaking. I've done a few older cars where that helped. My Raybestos ceramic pads didn't require it though. I'm assuming your pads aren't worn down to squeakers?

The pedal dropping sounds like either there's air in your brake lines - bleeding would help that, or a caliper going bad that is leaking brake fluid. Look on each caliper and see if you have any wet spots. Look at your master cylinder and brake booster as well. I had to replace a booster once with somewhat similiar symptoms, but the pedal would drop much more.

Good Luck!

I'll check the air deflector and see if the anti-sqeak is requested. The "bird chirping" constant sqeak that I mentioned goes away once I hit the brakes.

Also I did have one of the rear calipers replaced and when I think about it I don't believe I had that happen since them.

Thanks for the suggestions, i'll let you know how I make out.

[Ranger]

If it's not the air deflector, and I'm not sure if this would apply to your car, but some older brake pads sometimes needed an anti-squeal lubricant applied to the back of the pads to prevent squeaking. I've done a few older cars where that helped. My Raybestos ceramic pads didn't require it though. I'm assuming your pads aren't worn down to squeakers?

The pedal dropping sounds like either there's air in your brake lines - bleeding would help that, or a caliper going bad that is leaking brake fluid. Look on each caliper and see if you have any wet spots. Look at your master cylinder and brake booster as well. I had to replace a booster once with somewhat similiar symptoms, but the pedal would drop much more.

Good Luck!

I'll check the air deflector and see if the anti-sqeak is requested. The "bird chirping" constant sqeak that I mentioned goes away once I hit the brakes.

Also I did have one of the rear calipers replaced and when I think about it I don't believe I had that happen since them.

Thanks for the suggestions, i'll let you know how I make out.

That is a dead give away for the brake ware indicator (metal tab) just begining to make contact with the rotor.

[BodybyFisher]

Very True, here is a photo of the wear indicator, mine are chirping right now, I need front brakes ASAP...before I need ROTORS

[GreenMachine]

geez these were just replaced under warranty this winter, something not right if the wear indicator is already squeaking (I didn't look at that because I figured it couldn't be that). Is it possible that is bent and going off "early"?

[BodybyFisher]

Unlikely, pull the wheel that is squeeling and take a look at the pad thickness, they will begin to squeel at about 1/8" thickness or so... It is possible that you need brakes if your rears are not doing the job or need bleeding or you are heavy on your brakes...

My cousin has a 96 Deville and she says that she goes through brakes often.

It is also possible that you have a bad caliper or sticking sliders.. if the improper grease was used or if the sliders were not serviced at all.

[epricedright]

I assumed by the statement "I'm assuming your pads aren't worn down to squeakers?" that I wrote above, that the squeakers (wear indicators) were not the problem, being you've had the car in and out of the shop as much as you have. That should have been the first thing they checked - the condition of your pads. When I heard "bird chirping", that was the first thing that came to my mind, but I assumed they certainly looked at that! If they didn't, you ought to maybe find another shop.

[BodybyFisher]

Good catch Kim, I didn't see that you caught that above..

[Ranger]

I agree. Not likely that it is a false indication. My money is on a caliper hanging up. Slide pins like Mike said. If that is the case, the shop that did them, did a poor job. I'd ask them to correct their mistake, at their cost. If they refuse, go elseware as they are not very compitent.

[epricedright]

My crystal ball says when EGreen takes it back to the shop, they find the pads worn down to the squeakers, when asked why so soon, they reply he needs a new caliper and brake hardware (slider bolts and boots), then they say he will need to pay for the new pads, as well as the cost for the caliper and hardware. At that point, I would find another shop to do the work.

If they would have done the job right the first time, he may have had to pay for a new caliper and hardware at that time, but atleast he wouldn't have had the frustration, time lost (having to take it there several times), and costs of work done so far, and never getting it fixed right.

I had a jack-leg mechanic helping me with problems I didn't want to handle myself, and was very reasonable price wise. Problem was, he never got it right the first time. After getting frustrated to no end, I told myself never again. I've decided to do all the work myself, that I can handle - so I know it's done right, and whatever I can't handle, I will take it to the shop that did my AC work (a very reputable shop that does high quality work for a fair price). No more jack-legs for me!

EGreen, If your pads wore out that soon, I agree with what BBF and Ranger wrote, there is definately a problem that wasn't addressed earlier; either a sticking caliper, rusted slider bolts, sliding contact points not cleaned, boots worn or wrong grease used. Who ever does the work, I would have them bleed the system as well with all new fluid, front and rear, being the system has been opened up, maybe twice now.

Good Luck!

[BodybyFisher]

For what its worth, I have never had to replace a caliper....

[Ranger]

For what its worth, I have never had to replace a caliper....

Same here. As I said before, my money is on the slide pins.

I also think Epriced's crystal ball is pretty clear. I'd also put money on them denying any fault or offering to fix it. At that point I'd be waiting with baited breath for them to ask if I'd like them to do another brake job at my expense. Ah, no thank you, I think I'll find a competent shop for this one.

[epricedright]

I'm not saying he has a bad caliper, but I've relaced 3 or 4 in my life. They were leaking...not on a Caddy though. It's possible the boot in his caliper was mishandled when the caliper was compressed while replacing the pads. Care must be taken the folds on the boot are nice, neat and clean, and the rust/debris is cleaned off. The piston wall can rust as well causing it to stick. But then again, my money is on seized/sticky slider bolts.

[GreenMachine]

^thanks for the addition of the above info, the car is going in to finally get the driver seat situation fixed, and then this brake job is getting done right.

This time I'm "armed" with more knowledge on the subject and its getting beyond frustrating having this cadillac sqeaking and squeeling. My father is almost to point of saying "well if the windows up, radios on, ACs on, I don't hear it so we can live with it". I always tell him, yeah but somethings wrong and the brakes are one place you don't want to mess around.

I know I could change the brakes myself, but I'm one of the guys who knows how to fix things....but has no idea what the "thinger majiggies" are called The last couple times (i can't believe i can say couple meaning I'm not sure how many now) they haven't charged us to look at it and try and fix it. But this is getting redicoulous, they have one new guy there, and another guy we don't know to well, and since them arriving its been problem after problem and we've been going their for years never with this kind of hangup, beginning to wonder if that rear caliper that was replaced really needed to be....

[epricedright]

Get a copy of your factory service manual...look on eBay for a good deal maybe, and with the help of the board here, you'll be able to fix more things than you think. Besides, you'll have peace of mind knowing it was done right, and save a bundle in the process. Good luck with your brakes issue. I agree, brakes are too important to neglect - get them done right!

[GreenMachine]

Searching the forums I've found alot of instances of a "bushing kit" needing to be replaced when the front brake hardware is changed.

So far on my "check list" to make sure of what they have done I have:

-Check Air Deflector

-Wear Indicator= if worn why so soon-----

---Caliper Hanging up

-------Siezed Sticky Slider/bolt or Slide Pins

-Bushing "kit" (came across this in several posts)

I've also come across many posts takling about some sort of electronic wear indictor for the pads...I'm guessing thats a dealer only thing and the average shop isn't going to reset/replace the sensors, or the OEM pads are the only ones that have the sensors...my guess that is an expensive way to avoid haveing "sqeakers" to indicate wear.

[epricedright]

The rubber bushings are so inexpensive, I'd recommend replacing them every time the pads are replaced. There will be 2 of them that go into each caliper (total 4 rubber bushings for the front). The slider pins (bolts) slide inside of the bushings. There is also a metal bushing that your bolts go through, that goes into the rubber bushing as well. When you buy new bolts, the new metal bushings come with them. The bushing "kit" is just the 4 rubber bushings that you'll need for the front brakes.

I would add to your list to verify that SILICONE grease was used to lubricate your slider bolts and bushings, and NOT petroleum grease. The Mgr. of the Pepboys close to me had no idea that petroleum grease was not allowed on Caddy brakes. I bought my grease from them when I originally did my brakes, and they sold me high temp petroleum grease....I later learned that's a BIG no no! Petroleum grease will make your rubber boots swell and will seize your pins in the boots.

You'll be able to replace your own brakes next time! Pretty easy job.

I hope all this applies to your '98 Deville. The above applies to my '94 Deville, and most likely yours as well. Hopefully someone will verify that?

[Ranger]

The electronic wear indicators cannot be "reset". They are sacrificail. There is a small notch cut in the top of the inner pad. The wear indicator is just a wire (probably two) that are embedded in a small plastic square that fits into said notch. As the brakes wear, they eventually wear into the plastic and the wires come apart opening the circuit and tripping the service brakes message. I don't know if aftermarket pads have this notch cut into them. It would not be terribly difficult to add it with a dremel or such. The wear indicators can be had from Rockauto for $20-$25.

[epricedright]

If he has electronic wear indicators, then he shouldn't be getting a sqeak from the metal "old school" type squeakers (wear indicators), right? If that's the case, then maybe his pads are not worn down, and the squeak is something else.