11 replies to this topic

[fixxer]

'97 850 sometimes when I put on the brakes the whole car starts shakeing and makes a vibrating noise
happens more often when more people are in the car
any clues?

[Volvo Virgin]

Warped rotors?

[bloc]

anyone that suggests warped rotors as soon as they hear of these symptoms needs to read this article.


http://stoptech.com/tech_info/wp_warped_brakedisk.shtml






fixxer. how many miles on your car? any idea if it has the original brake discs?

can you get similar results by getting the car to 80 or so and really applying the brakes?

[fixxer]

it has about 70k miles, but the brakes are relatively new
ill try to go to 80 and put on the brakes hard

[Patrick.]

okay-- sounds like discs w/ a TV (thickness variation)

I had this same issue, replaced my front rotors, and all was well.

[Volvo Virgin]

okay-- sounds like discs w/ a TV (thickness variation)

+1 Warped may be a misnomer,so if it pleases everyone we'll try and use thickness variation from now on.Or if that upsets anyone.......maybe we can use Excessive Runout. Either way I think most realize when you have a pulse while applying your brakes,it is usually caused by a deviation in the thickness of your rotors.

[bloc]

if you want to know what is likely the real cause, read the article.


most of the time when people think rotors have excessive runout or a thickness variation, it is in fact uneven pad deposits on the surface of the rotors. these can be removed without machining or replacing the rotors.

[Volvo Virgin]

if you want to know what is likely the real cause, read the article.
most of the time when people think rotors have excessive runout or a thickness variation, it is in fact uneven pad deposits on the surface of the rotors. these can be removed without machining or replacing the rotors.

For many years I worked in a shop where we machined rotors regularly.Over that period I machined more rotors than I could possibly count that miked so inconsistently that there was no possible way you could have sanded or grinded them effectively.And even if you had attempted this method by hand,there would be no possible way to attain a true flat braking surface,such as machining does.I can honestly say that the number of times I saw any signs of residual pad deposits were few and far between.That's not to say it never happens,and cetrtainly if it does it must be caught in the very early stages to be rectified by hand.I just don't happen to concur that more times than not the problem with a pulsing brake pedal is excessive pad deposits,and not an actual warped rotor,especially with the number of cheap import rotors flooding the market.Just my humble opinion.

Edited by Volvo Virgin, 21 March 2006 - 01:11 AM.

[fixxer]

are you sure it has nothing to do with the engine mounts because all of the shaking seems to be coming from the front end and only happens sometimes

[Volvo Virgin]

are you sure it has nothing to do with the engine mounts because all of the shaking seems to be coming from the front end and only happens sometimes

Front end vibration would be indicative of front rotors if you can feel it in the steering wheel and brake pedal while braking.Motor mounts wouldn't be the first thing that comes to my mind,but they are easy to check,especially the top one in the back of the engine compartment,which is the most frequently broken mount.Pull the nut and bolt out and see if it is in one piece,or otherwise.Good luck.

Edited by Volvo Virgin, 21 March 2006 - 01:10 AM.

[bloc]

characteristics of broken motor mounts are usually excessive vibration upon acceleration, not braking. it is possible for mounts to be so blown that when you hit a big bump you will feel a thump as the engine flops around, but youd likely know long before it got that bad.







volvovirgin, i'm not talking about doing it by hand.
likelyhood of the car being on the original rotors is pretty high, and they are by no means cheap. they probably do need to be replaced anyway.
i'm not saying the rotors -ARENT- warped, just that pad deposits are the culprit in far more of the pulsation-on-brake-application cases than people realize.

stoptech's preferred method of getting rid of the deposits is to load the caliper with a set of very abrasive pads and go through a specific procedure of hard stops to scrub the rotors.

i really dont mean to sound like a hotdog, but read the article. even if you dont agree with me, there's easily enough good info on their tech section in the white papers about brake systems to make it worth your time.

[Volvo Virgin]

characteristics of broken motor mounts are usually excessive vibration upon acceleration, not braking. it is possible for mounts to be so blown that when you hit a big bump you will feel a thump as the engine flops around, but youd likely know long before it got that bad.
volvovirgin, i'm not talking about doing it by hand.
likelyhood of the car being on the original rotors is pretty high, and they are by no means cheap. they probably do need to be replaced anyway.
i'm not saying the rotors -ARENT- warped, just that pad deposits are the culprit in far more of the pulsation-on-brake-application cases than people realize.

stoptech's preferred method of getting rid of the deposits is to load the caliper with a set of very abrasive pads and go through a specific procedure of hard stops to scrub the rotors.

i really dont mean to sound like a hotdog, but read the article. even if you dont agree with me, there's easily enough good info on their tech section in the white papers about brake systems to make it worth your time.

Hey bloc,I'm all ears to different opinions and things I didn't know or consider before.That's why I did read the article initially,and what I found troubling was his statements that he never saw a warped rotor in all his years,which I thought was misleading due to the context.He was basing his article on his experience,which was 40 years of professional racing.I would assume he was using higher end products specifically for high performane/racing applications,and mostly in a racing arena which are definitely more abusive and much different conditions than the average passenger car ever sees,even with spirited driving.I would agree that smoking your pads early in their life cycle before breaking them in correctly could produce pad deposits and/or premature pad failure.It would also stand to reason that a higher end race-specific rotor would most likely be more resilient to warping,and given the constant attention that race cars are attended to,pads and rotors are constanly being checked and replaced before small problems become big problems.My experience is that most of the time in a passenger car application by the time the rotors are producing a pulsation while braking,unless caught very early if indeed an improperly broken in new set of pads and/or an excessive pad deposit situation,the rotors will be too far gone for a solution other than machining.This would also take into account the differences in the quality of the parts in the specific application.

Again,only my opinion and experiences.

Edited by Volvo Virgin, 21 March 2006 - 05:13 PM.