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Discussion Starter #1 (Edited)
I have a fairly severe shaking when braking gently to slow down at high speeds ( 70 mph+). If I brake hard the shaking does not happen but the car obviously stops "too abruptly". The brake pads, front and rear, were replaced but it made no difference. I have not resurfaced on installed a new set of rotors at the front, where the vibration seems to be coming from. Are my rotors " too thin" or warped, or is there another problems ?
I am hoping to avoid trial and error replacement of parts.

The brakes work fine and the fluid was changed some 10,000 miles ago.:frown
 

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easy to check for both warped rotors and wheel bearing play, just lift and spin.

if there's an uneven drag, there's your warp. grab the wheel at 9/3 o'clock and 12/6 o'clock and try to wiggle, any play and there's your bearing.

i'd add that play in the suspension bushings and/or tie rods could allow the front wheels to deflect (toe out) under braking, also causing shaking.

my w210's been exhibiting such behavior...
 

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There are two possible brake rotor conditions that can cause a problem - warpage and hard spots.

Warped rotors can cause pulsating, usually more with easy braking than hard braking. With easy braking, the "stickiness" in the calipers cause uneven braking as the non-moving pads rub harder, then softer as the warped spot passes the caliper. On hard braking, the effect is often less noticeable, as the increased clamping force makes the pads follow the warped area.

Warped rotors also often cause "pad knock-back" (as can loose wheel bearings). The brake pads normally run barely touching the rotor, since the only thing pulling them back is the flexing of the rubber seals on the caliper pistons. As you drive with warped rotors, the warped areas gradually knock the pads back in the caliper bores, so there is as much clearance between pad and rotor as the rotors are warped. When you next apply the brakes, the pedal will go down further - a little if the warpage isn't bad, a lot if it is bad.

The other (and more common) rotor problem is hard spots. If you park the car with very hot rotors, the rotor area inside the pads stays hot much longer. This differential cooling can cause hard spots in the rotor iron. These hard spots wear less than the rest of the rotor surface, and it only takes a very few thousandths of an inch of additional thickness at the hard spot to cause very noticeable pulsation of the pedal. Hard braking usually makes the pulsation worse. The small thickness differential usually doesn't cause pad knock-back.

Rotors are wear item. Some vehicles wear out a set of rotors with every set of pads, some with every second or third set of pads, and a few vehicles wear the rotors very little. The rotors usually have the wear limits stamped into the edges or hats (hubs) of the rotors. You can get a rough estimate of wear by feeling of the little ridge on the outer edge of the rotors.

You can have rotors "turned" at a garage or brake shop. Whether you should or not is usually an economic decision. If the rotors are near the wear limits (or will be after they are turned), it might make more sense to just replace them along with the pads.
 

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I swapped front rotors and pads a few months back and braking was smooth for a while until the pulsating came back after about a month. Turns out the rear rotors were well, swapped those out with new pads and braking has been silky smooth ever since.
 

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Another thing to to do is to torque the nuts to the correct specs. After using a impact gun for years i always had issues with warping. The uneven torque will warp the rotor over time every time it heats up. I always torque with a torque wrench and have had no more issues on any of my cars.
 

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I have a fairly severe shaking when braking gently to slow down at high speeds ( 70 mph+). If I brake hard the shaking does not happen but the car obviously stops "too abruptly". The brake pads, front and rear, were replaced but it made no difference. I have not resurfaced on installed a new set of rotors at the front, where the vibration seems to be coming from. Are my rotors " too thin" or warped, or is there another problems ?
I am hoping to avoid trial and error replacement of parts.

The brakes work fine and the fluid was changed some 10,000 miles ago.:frown
Had the same issue was a warped rotor, worst part was the rotors looked new and pads had a ton of meat. I even know exactly when I wrapped them
 

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Can you tell me what you did to cause the warpage, so I can avoid it please ?
With me it was stop and go traffic for a fairly long stretch then there was a break in the traffic so I got up to highway speed for a very short time. Traffic came to a sudden stop so I had to hit the brakes very hard. So hot rotors very hard stop makes for a warped rotor.

Generally it is hot rotors and panic stops that wreck the rotors, there are of reasons but this is the most common. One of the main reasons you should not ride your brakes down a steep hill brakes overheat then when you do have to stop they warp.
 
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