cars shakes applying brakes at speed

I just got a used legacy today, a 2001 GT wagon ( JDM ) and around 80+ kph when I hit the brakes there is a bit of shake, feels like warped rotors. Would getting the rotors machined help? I'm taking it in to the shop on Saturday but the local mechs here are not normally that great and parts for subies are hard to come by here

You'd need to see if there's anything left to shave- if there is, take them off and have them done- if not, you need new ones. Might want to make sure the pads haven't been affected as well.

Thanks! there's a bit left to work with on the rotors, they only have 30,000 km on them, I've just found out that the trip across the two ponds cause lots of brake problems having the car sit exposed to salt and not moved for 4 weeks. I'll probably put new pads on to be safe, I'm hoping this works since the last time I had a car with warped rotors I needed new ones and here thats gonna take a while.

This is most likely "pad transfer", not a warped rotor.

 

Do the bedding procedure found here and it might go away.

 

http://www.stoptech.com/technical/

Also check the amount of torque on the lug nuts. Overtightened or uneven tightened lug nuts can contribute to rotor warp.

Paul H

This is most likely "pad transfer", not a warped rotor.

 

Do the bedding procedure found here and it might go away.

 

http://www.stoptech.com/technical/

 

I second that. Warping a rotor is extremely hard to do on a street car, but the myth still runs rampant.

 

You can try cleaning the rotors yourself with some emery cloth moving in circles to expose fresh metal. Scuff the pads too. Or switch over to some new pads. Follow the bedding procedures from Stoptech.

Warping a rotor is extremely hard to do on a street car, but the myth still runs rampant.

 

Are you kidding? I've done it lots of times. You must be a very judicious driver!

I probably don't use my brakes as much as some on the street, and I do normally get a little runout when turning rotors on a lathe, but actually warping them has been a rare case for me. This was a huge issue for the Evo crowd, blaming warped rotors, but time after time if I got some steering shake a few hot and hard runs would clear things right up. But, true warping is not out of the question.

I would like to know why several people with less than 3000mi on there LGT's have, brake induced, steering shake???

Are you kidding? I've done it lots of times. You must be a very judicious driver!

 

Nope

 

9 out of 10 times you have got pad transfer that puts deposits of pad material in the rotor. This changes the ceffiecient of friction locally as well as putting a slight high spot on the rotor.

 

The rotor is not "warped" but it feals like it. About the only time you can get a warped rotor is if it's worn so much that the structural integrity has been comprimised or the rotor was thermally shocked. (see stoptech bed procedure...)

 

Please read the stoptech technical sections.

 

This happens for a few reasons:

1. Not bedding in the rotors (reference Stoptech)

2. Getting the brakes hot then standing on them at a stop.

3. Geting the brakes hot then letting the rotor cool without rotating the wheels.

 

Disk brakes don't actually loose contact between the rotor and the pad, there is always some contact. Other wise you get pad knockback and need to double pump the brake pedal. BTW, this is why drag racers still like brake drums - they actually do fully release from the drum.

SO, possibly we are experiencing this shake because our pads have not seated yet @ 2000miles? Hmmmmmm

 

Dont like it!

Possible - but I think the user manual might say to use the brakes gently for a few 1000 miles or so - that does an OK job of breaking them in. (not sure though)

 

If you want to do it properly.... you need to break them in actively. If you are an enthusiast in any fasion, it shouldn't be a problem

 

Your brakes will get better after the process; more consistent and a more predictable initial grab. The only real problem is that you might boil the fluid if you have the crappy stock stuff in there. A flush with ATE Super Blue is a good idea.

 

Besides, the process will teach you the threshold limits of your car's brakes.

 

It could be a pad selection problem from SOA, but if you just get new rotors under warrenty, you'll just get the same problem again.

 

This happen in a couple of common situations:

1. Stopping hard from freeway speeds then standing on the hot brakes at the bottom of the ramp.

2. driving hard then parking the car with hot brakes.

 

Both will put enough heat in them to create this problem.

It has like 20000 miles on them warranty doesn't do brakes after time. I'm geting them machined saturday and putting new pads on. I also ordered new rotors that I'll have slotted ( maybe drilled to ) and treated, here it's cheap.

 

UPDATE

 

The shake is gone with the machine rotors, I'll try bedding the new pads in to make sure it doesn't come back.