Vibration when braking

[hutch85]

I have noticed that when braking at speeds over 60 m.p.h in my 02 Legacy Wagon that the steering wheel shudders back and forth. I notice it more when there are more people in the car also. It is a manual if that matters. Any thoughts or is this just normal behavior?

[GLCraig]

You may have a warped brake rotor.

[brus brother]

Brake rotor "warped". Some say the warpage is actually just brake pad material deposited on the rotor but regardless the end result is high spots on the rotor that become more noticeable when braking at highway speeds where the rotor is cooled down. Have the rotors ever been resurfaced with a brake pad replacement? I've been advised against numerous resurfacings as the rotors become thinner and more subject to thermal stresses that more easily cook the pad material onto the rotor. Sometimes it's better to just replace rotors if you are doing the job yourself than driving the rotors around town to be resurfaced. There are some scholarly posts on the subject if you use the search function.

[amk]

I have noticed that when braking at speeds over 60 m.p.h in my 02 Legacy Wagon that the steering wheel shudders back and forth. I notice it more when there are more people in the car also. It is a manual if that matters. Any thoughts or is this just normal behavior?

 

It could be your discs are not even that was my prob i took it to some engineers to make it even a lath machine was used if im not mistaken and i changed the stablilzer bushes, rackend bushes. First check your discs.

Hope this helps.

[johnceggleston]

late 90's outbacks have vented (looks like 2 discs with walls/chambers seperating them) front and rear braked disc. my mechanic says these can be resurfaced. late 90's legacy l has vented front (same as outback) and nonvented rear. my guy says he won't resurface ANY non vented dics. some get fixed some don't .

 

i bougth a 97obw that had vibration when breaking. it was the rear and they had just been turned. i bought new, they were cheap and easy. there is some trick to figuring out if it's front or rear.

 

see correction below.

 

 

 

 

Brake rotor "warped". Some say the warpage is actually just brake pad material deposited on the rotor but regardless the end result is high spots on the rotor that become more noticeable when braking at highway speeds where the rotor is cooled down. Have the rotors ever been resurfaced with a brake pad replacement? I've been advised against numerous resurfacings as the rotors become thinner and more subject to thermal stresses that more easily cook the pad material onto the rotor. Sometimes it's better to just replace rotors if you are doing the job yourself than driving the rotors around town to be resurfaced. There are some scholarly posts on the subject if you use the search function.

[tcspeer]

If you feel it in steering wheel it is most likely the front. I would also suggest replacing instead of turning. New rotors from Auto Zone are only around 30.00 dollars each.

late 90's outbacks have vented (looks like 2 discs with walls/chambers seperating them) front and rear braked disc. my mechanic says these can be resurfaced. late 90's legacy l has vented front (same as outback) and nonvented rear. my guy says he won't resurface ANY non vented dics. some get fixed some don't .

 

i bougth a 97obw that had vibration when breaking. it was the rear and they had just been turned. i bought new, they were cheap and easy. there is some trick to figuring out if it's front or rear.

[johnceggleston]

i need to correct something before i get corrected. the rear dics on outback are the same as legacy. direct swap. the front are different. the front on the outback are bigger, more stopping power? i don't know about the calipers or pads.

 

the legacy front may not be vented. i can't remeber.

 

 

late 90's outbacks have vented (looks like 2 discs with walls/chambers seperating them) front and rear braked disc. my mechanic says these can be resurfaced. late 90's legacy l has vented front (same as outback) and nonvented rear. my guy says he won't resurface ANY non vented dics. some get fixed some don't .

 

i bougth a 97obw that had vibration when breaking. it was the rear and they had just been turned. i bought new, they were cheap and easy. there is some trick to figuring out if it's front or rear.

[hutch85]

Thanks everyone for your help. Sounds like the best idea then is to take it in to my mechanic and have him check out the rotors. I know that nothing has ever been done to them so I wouldn't be surprised if a replacement was in order. Thanks again.

[Setright]

It might be worth looking into some slightly-better-than-stock pads. This will prevent problems in the future.

[Broyer]

Just another thought... I ran into this on my 2000 OBW. Check the wheel balance. If the wheels are not balanced, you may feel the vibration in the steering wheel when you touch the brakes....

[1 Lucky Texan]

Just another thought... I ran into this on my 2000 OBW. Check the wheel balance. If the wheels are not balanced, you may feel the vibration in the steering wheel when you touch the brakes....

 

I once had some tread seperation cause vibration that was worse when braking. But brake rotors are a more likely source of the problem - likely the fronts.

 

the 'technical white papers'/whatever at www.stoptech.com have a section called the myth of warped rotors or something, good reading.

 

 

Carl

[njdrsubaru]

ROTOR RESURFACE AND WHEEL BALANCING :-p

[Wayne Boncyk]

Carl,

That's absolutely the best article I've ever read on the technology of braking. Finally somebody explains exactly why you want to break in a new set of pads, and what will happen if you don't do it the right way. Thanks for the pointer!

[1 Lucky Texan]

Carl,

That's absolutely the best article I've ever read on the technology of braking. Finally somebody explains exactly why you want to break in a new set of pads, and what will happen if you don't do it the right way. Thanks for the pointer!

 

It educated me. I try to recommend it when I can. I'm sure there must be folks that disagree with it, but I feel it is a good mix of experience and 'science'.

 

Carl

[SubaruLove]

.

Edited October 16, 2009 by SubaruLove

[CNY_Dave]

I usually poke fun at reviving long-lost threads, but the tech articles are worth the bump!

 

http://www.stoptech.com/tech_info/tech_white_papers.shtml

 

I had severe 'uneven pad material deposition', and have discussed it here, but now I know the proper phrase!

 

"Regardless of pad composition, if both disc and pad are not properly broken in, material transfer between the two materials can take place in a random fashion - resulting is uneven deposits and vibration under braking. Similarly, even if the brakes are properly broken, if, when they are very hot or following a single long stop from high speed, the brakes are kept applied after the vehicle comes to a complete stop it is possible to leave a telltale deposit behind that looks like the outline of a pad. This kind of deposit is called pad imprinting and looks like the pad was inked for printing like a stamp and then set on the disc face. It is possible to see the perfect outline of the pad on the disc. (FIGURE 5)

 

 

It gets worse. Cast iron is an alloy of iron and silicon in solution interspersed with particles of carbon. At elevated temperatures, inclusions of carbides begin to form in the matrix. In the case of the brake disk, any uneven deposits - standing proud of the disc surface - become hotter than the surrounding metal. Every time that the leading edge of one of the deposits rotates into contact with the pad, the local temperature increases. When this local temperature reaches around 1200 or 1300 degrees F. the cast iron under the deposit begins to transform into cementite (an iron carbide in which three atoms of iron combine with one atom of carbon). Cementite is very hard, very abrasive and is a poor heat sink. If severe use continues the system will enter a self-defeating spiral - the amount and depth of the cementite increases with increasing temperature and so does the brake roughness. Drat!"

 

What's more, later it describes how the cementite forms sub-surface, and cannot be removed by turning the rotor.

 

Dave

Edited October 16, 2009 by CNY_Dave

[Setright]

Agreed. The Stoptech articles really set things straight.

 

Good reading. I still refer people to their pages...

[SubaruLove]

This is an old thread if you look at the date.

 

But if someone else is having the same problem, it could very well be the struts, if it only happens when you break then it might not be it, but if it happens when you are going fast and let off the gas, or when your just at a low speed, have the struts get checked out. Might be worth the try!