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  #1  
Old 11-28-2007, 04:20 PM
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vibration when braking hard

Noob question, but when I brake from higher speeds (like 45-55) and a good amount of pressure on the pedal I get some pretty bad vibration throughout the car.

I got new front brake pads almost a year ago, put on by a local shop here, but they didn't mention the rotors needing replaced.

I have just had a lot of work done recently so I want to not take it back, but can I assume I have a warped rotor, or worn down rotor... is there any other thing that it could be....

when I softly apply the brakes I get no vibration...

I can get the rotors for about $50 shipped, but is this a job a novice can handle. I have only done brakes once with my Dad, but I have a friend who is more experienced than I am....

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Old 11-28-2007, 04:29 PM
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Sounds like rotors to me. They are quite easy to replace.
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  #3  
Old 11-28-2007, 06:37 PM
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I would also check the brake calipers. I have the same symptom and it is caused by the caliper on the driver front. It has a corroded piston and a torn boot. Thus the piston is not functioning properly causing the shimmy. I have a rebuild kit and will repair this weekend.
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Old 11-29-2007, 10:34 AM
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Thanks

With the wheel off, can I visually see a problem if it is the rotors warped, or worn out, or do I have to take them off and have them measured, machined, etc...

Honestly for $50 in parts, if I can do it myself I will probably change them, and if it is not the problem, look at the calipers, right?
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Old 11-29-2007, 11:24 AM
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well- the way to check your rotors is w/ a ball ended caliper(measuring device) and check for disc thickness variation. the rotor will wear thinner in some areas than others, causing the shudder. they really dont "warp"

could also be worn bushings. worn tie rod. worn ball joint, etc.

get the front end up on good jackstands and push,pry,pull the front steering/ suspension bits. look at the stay rod bushings that are on the bottom of the firewall. they have a rod going out to the lower control arm.

there are many things that will give a shimmy while braking. dont just start throwing parts at it, your brakes could be fine.
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Old 11-29-2007, 11:27 AM
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Originally Posted by johntksr View Post
I would also check the brake calipers. I have the same symptom and it is caused by the caliper on the driver front. It has a corroded piston and a torn boot. Thus the piston is not functioning properly causing the shimmy. I have a rebuild kit and will repair this weekend.
I'm not following how the lack of proper piston function can cause any vibration on the front end? The loss of a piston will cause a severe pull away from the side of the frozen piston, however, I don't see any scenario that will cause front end vibration.
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Old 11-29-2007, 11:34 AM
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I had a similar problem with a sticky caliper. The brakes would shudder after driving a while a speed. Apprently the rotor would get wavy once it was hot. Jack up the wheel(s) and see how hard they are to turn by hand after applying the brakes and releasing. The same symptoms can be caused by a collapsed rubber brake line, but there the brake is released by opening the bleeder screw.
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  #8  
Old 11-29-2007, 12:32 PM
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Originally Posted by mobetta View Post
could also be worn bushings. worn tie rod. worn ball joint, etc.

get the front end up on good jackstands and push,pry,pull the front steering/ suspension bits. look at the stay rod bushings that are on the bottom of the firewall. they have a rod going out to the lower control arm.

there are many things that will give a shimmy while braking. dont just start throwing parts at it, your brakes could be fine.
While worn suspension components can possibly cause a shimmy on braking, it would be more likely to observe such a shimmy at higher speeds when not braking. The act of braking loads the components on the front end and prevents oscillation in most cases. However, when the disc is loaded, it will immediately display a vibration at most speeds above 40 mph if it's got any runout in it's faces.
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Old 11-29-2007, 05:22 PM
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Originally Posted by Brian Carlton View Post
I'm not following how the lack of proper piston function can cause any vibration on the front end? The loss of a piston will cause a severe pull away from the side of the frozen piston, however, I don't see any scenario that will cause front end vibration.
I will confirm the results following the caliper repair this weekend.
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  #10  
Old 11-29-2007, 07:40 PM
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Originally Posted by spugeddy View Post
With the wheel off, can I visually see a problem if it is the rotors warped, or worn out, or do I have to take them off and have them measured, machined, etc...

Honestly for $50 in parts, if I can do it myself I will probably change them, and if it is not the problem, look at the calipers, right?
Often times it is cheaper to replace the rotors, as you have found out, a bit involved replacing the fronts, new/and or repacked bearings. Yet a DIY. MB requests not turning. See if there is any rust spots on the caliper cylinder walls.
You can use the old pads, as long as they measure 2mm, might as well, just swapping those out, very simple. If you replace, get new sensors too, only on front.
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Old 11-29-2007, 08:46 PM
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Originally Posted by Brian Carlton View Post
While worn suspension components can possibly cause a shimmy on braking, it would be more likely to observe such a shimmy at higher speeds when not braking. The act of braking loads the components on the front end and prevents oscillation in most cases. However, when the disc is loaded, it will immediately display a vibration at most speeds above 40 mph if it's got any runout in it's faces.
Check the bushings I showed in this picture. I had both these bearing ware out on me and when they are warn they will feel solid while driving, but when you step on the breaks if puts force directly on that rod. and if the bushings on ether end are warn out the whole assembly will vibrate.
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  #12  
Old 11-29-2007, 09:44 PM
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Check the bushings I showed in this picture. I had both these bearing ware out on me and when they are warn they will feel solid while driving, but when you step on the breaks if puts force directly on that rod. and if the bushings on ether end are warn out the whole assembly will vibrate.
I don't disagree that such a condition can exist. It's simply far more common for the rotor to have runout than for the guide rod bushings to be worn to just the level where there is oscillation in the rod on braking.
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  #13  
Old 11-30-2007, 01:58 PM
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Vibration on braking!

Your rotors are warped. That's where the vibration comes in. If they are too thin to turn, it's time to replace them!
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  #14  
Old 11-30-2007, 02:09 PM
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FWIW, youy can get rotors from checker/shucks/kragen for $18. turning is prolly $15.
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Old 11-30-2007, 03:15 PM
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Originally Posted by mobetta View Post
FWIW, youy can get rotors from checker/shucks/kragen for $18. turning is prolly $15.
Yes, but turning has a effect you dont often find in new rotors.
Braking performance is enhanced by turning those rotors!
Those rotors from checker/schucks/kragen are made in CHINA and reliability with chinese made auto parts keeps them off ANY of my vehicles!
Chinese parts use weaker and less costly pot metals in their castings! With something as important as brakes, I'm going to get what should be on their in the first place, Febi, Lemforder or Goetts rotors!! Genuine MB parts, that's where it's at! Turning is $10.00.

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