Update....
Check and retorque caliper bolts. Nothing out of ordinary.
Checked steering assembly, all seems tight.
Checked pads. Lots of life remains. Fit seems "normal". No Hugh movement play.
What I did do is take the spacers off the front. The spacers are minimal @ 8mm.
Nonetheless, went for a quick drive. Got to engin temp and then performed light pressure and threshold braking. NO shuddering. Now I recognise that the is not a complete heat soak cycle so tomorrow I'll go for a drive at speed and brake.
Makes me think there is a high/low spot on the spacer which causes the shuddering at braking. Gotta think it thru. Feed back is alway needed/welcomed.

 

The residue doesn't show itself in the brake fluid; it corruupts brake system components. Nevertheless, it sounds like you may have found the cause of the problem in your car's suspension.

 

Could def be the spacers ... If they're not true.
Also, how much track vs road of late?

 

I have this issue when I have driven the car in the rain without enough braking to get the rotors hot (like 5 minute a trip to the corner store) and then parked the car for a few days. The rotors will rust under the brake pads due to the water collected there and for the first couple of trips afterward the uneven surface will cause this grabbing, shuddering sensation. This will continue until enough heavy braking has been done to smooth out the rotors again.

May be your problem?

Jim G.

 

Assuming that the rotors were brand new and you cleaned them VERY thoroughly with brake cleaner before installation, exactly how did you bed the pads?

Did you clean the caliper spring plates at each end to get all the brake dust out?

Jim G also raises a good point; embedded rust particles in the pads completely change the pads' characteristics. Its critical to drive the car after washing to get the rotors hot enough to shed all the water and dry them. For cars that are driven in the rain and then parked, different compound pads may be needed to keep this from happening since some are more affected than others.

 

From my experience it turned out that brand new rotors may not give the effect of being true after mounting. They are fine on a flat surface, but after mounting and measuring with a guage they wouldn't be true relative to the caliper. (Don't ask how, I didn't believe it either.)

This was with a clean, otherwise fine functioning brake system.

I went down the path of changing: rotors, pads (more than once), tires, wheels, spacers. In the end it went away after using a pro-cut lathe. Instantly the car felt fixed.

My car was exhibiting the same symptoms. I had the issue with genuine parts and OEM. Luckily all were wear parts and some are awaiting their turn.

 

Follow up:
Shudder problem solved after skimmed my pagid brake discs at front.
The discs are new. Not sure this is discs quality problem or like some say brake pad deposit on discs problem. Anyway, the problem solved.