juddering when braking

[Gary Waugh]

I just fitted the pads, am not aware of any bedding procedure? Also did not touch the proportioning valve, but the pads were new along with the disks. Why would we touch the proportioning valve? what is the correct bedding procedure? I usually push the brake pistons back into the calipers, remove the old pads and spring plates, fit the new pads and spring plates, refit the calipers, then pump the brakes until the pads have touched the rotors and the pedal becomes stiff and then I go and test drive the car by performing a couple of gentle stops and then a few more harder stops and that is it. Would love to hear/learn more.

 

[GlennSullivan]

Brake Bedding Instructions​

The break-in process for new brakes is called “bedding.” It consists of heating up and cooling down the brakes in a controlled way.
The bedding process transfers an even layer of Brake Pad material to the new Brake Rotors. This improves the braking performance. It can also release any gas in the pad material to prevent future Brake Fade.

How is it done?​

Many brake manufacturers have a specific bedding procedure. If so, follow those instructions. If not, follow the instructions below.
First, find a safe place. This could be a track or an open stretch of flat road. Be sure that you are able to speed up and slow down multiple times, away from other vehicles.

1. Speed up to 35 mph.
2. Use moderate brake pressure to slow down to 5 mph.
   1. Do not come to a complete stop.
3. Repeat 2-3 times.
4. Speed up to 55 mph.
5. Use strong brake pressure to slow down to 5 mph.
   1. Do not brake so hard that the ABS activates or the wheels lock up.
   2. Do not come to a complete stop.
6. Repeat 4-5 times.
7. Drive for 5-10 minutes to allow the brakes to slowly cool down.
   1. Use light brake pressure when needed.
   2. Try not to come to a complete stop.
8. Park the vehicle and let the brakes cool for an hour.

Notes​

• During the bedding process, try not to come to a complete stop.
  • Squeezing the pads against the hot rotors can cause uneven material transfer.
  • This can result in squeaking, pulsating and reduced performance.
• Performance brakes have a higher temperature tolerance.
  • This means you may need to perform more rounds of speeding up and slowing down.

 

[GlennSullivan]

Every front shaking / vibrating issue during braking (as opposed to pulling left or right) on my 3 Gen 3 Expys was resolved by cutting the rotors.

Thinking out loud, you could remove the wheels, put hollow lug nuts on the rotors to securely hold them in place, mount a dial indicator and rotate to see if there is any rotor runout when mounted in place.