the disc the brake pads have been replaced every time i brake hard i get a juddering can anybody help

 

When my 07 was new, it took about a year and a few track days to stop that.

It's probably the glue in the pads which can be rubbed off the dics somewhat with laquer thinner or gas.

On some cars the rotors can heat spot and do that, but the RX8 brakes are very good, and mine don't heat spot.

So what you need to do is bed the new pads in by driving on a deserted road up to 60-70mph and brake real hard several times, then go driving around very gently to let them cool off.

They might smell like solvent, but that means they need bedding, and the next day you drive the pulsing should stop.

In a rare instance depending on what you mean, the abs could be going off, but the bedding in is still necessary.

 

Were the discs sanded down before the new pads were put on? Could just be old grunge on them. If the discs were replaced or resurfaced, were they checked for lateral run-out?

I've had juddering from both of those on other cars. Personally, I'd take a look at that stuff before trying the bedding in. YMMV.

Ken

 

Even though you replaced the rotors (discs?) make sure you had them turned first. I put a fresh set on my 8 when I had it and still had juddering until I had them turned and then hard braking was very smooth.

 

before putting the new discs on i cleaned them off and i rubbed the protective stuff of the pads ! it does not seem to be coming from the brakes or the disc and as got me baffled ? any ideas anyone? and thanks for previous replies

 

If it's not the brakes you need to look for worn suspension parts, or maybe something like bad alignment and munged tires. But since it was OK before you changed the brakes, I would really suspect the brakes.

Since you cleaned the rotors, you might check for run-out. Take off a wheel, rig some kind of pointer that just touches the rotor, then turn it. If it's not true, it could be a bad rotor that can be fixed by turning or returning. Also possible for it to not be seated squarely on the hub due to some crud on the back side.

I had a couple of instances of brake juddering on my Honda. Once it was because of a misaligned replacement wheel bearing, and once because of an out-of-true new rotor.

If the run-out is OK, then do the bedding that 40w8 suggested. And accept my apology for distracting you with other possibilities.

Ken

 

The "Warped" Brake Disc and Other Myths of the Braking System
(by Carroll Smith)

http://www.stoptech.com/tech_info/wp...akedisk.shtml#

 

Forgot to mention the most obvious possibility...although this might be an insult to the OP.

Unevenly torqued lugs. That will warp a rotor. I've had that happen a number of times on safety inspections. Bubba pulls a wheel, then runs the lug nuts back on one at a time tightening each all the way on the first shot. Fixed by loosening them and tightening properly.

Carroll Smith has never seen this because he's not Bubba. Not by a long shot.

Be careful about the myth that what happens with race cars, and competent mechanics, always applies to street cars.

Ken

 

Here's a good link, take an hour or two to read this very informative post: BRAKE FAQ. I have the same problem and it's because of an air bubble in the lines. It's not bothersome that's why I haven't taken care mine. I should because it may potentially cause an uneven wear on either the brake pads or my tires.

 

I think you'll find that one of the pins that the caliper slides on is frozen due to corrosion. I have been told that it is difficult, but not impossible, to get it off, clean it up and put brake grease on those pins. If the boot is broken, there is a caliper rebuild kit that comes with new boots.

 

Yes, that could be a cause, as well. I had that problem too, and if I can remember I think it's a 12 mm and a 13 mm wrench is used to remove the bolt and the floating pin, respectively. I also used a flat head and rubber mallet to remove mine.

 

Thanks for all your info I have cleaned the sliders and greased them I have completly stripped the calipers and brakes still no change

 

Bubbles within the fluid in the brake lines or resurface your rotors

 

Do you ever use wheel acid to clean your wheels? I have found that some of the wheel cleaners will alter the surface of the rotors enough to cause a shudder even though the brake pad and rotors are new or next to new.

 

After 3 weeks of trial and error, I still say to bed them in, and then, come back and tell us if they're smoother or not.

 

But, isn't it the same as having the rotors resurfaced?

 

It might sound like it, but go read up, and you'll see that the heat changes the iron rotors into a material with different characteristics.

The stock brakes are so good that I drove around hard for a year without bedding my brakes in, and you could smell them on my first track day.

I've driven all my cars without using brakes much ( gets better mileage and speeds through corners).

I used to have Ford F150 calipers that ran too tight, and would eat on the rotors, so I just put new pads on, and let the pads clean up the surface of the rotors.

Like I said earlier: My 07 GT 8 had all that gummy glue pulsing for about a year, but at 27k miles and approx 12 track days, they are smooth as glass, and barely worn.