4kcsq braking/chassis behavior problem

[Veetesse]

Hello all...

My 86 4kcsq (with 170k) recently has been performing strangely under braking.  At speeds higher than 40 mph, I apply the brakes firmly and it feels like the chassis is flexing in the rear.  It's not exactly a shudder or a shimy, but rather a floating movement from side to side.  

The car doesn't really seem to pull harshly to one side and it doesn't do it 100% of the time.  Some days are better than others.  It seems to be coming from the driver's rear side, so I suspected that it was that rear caliper not performing up to snuff.  

My theory was that since it wasn't braking like the other wheels, that corner of the car was 
making the car flex or torque since the wheel would be under less stress than the others.  

I looked through the wheel and it appears that the braking surface on the rotor is not uniformly shiny from the center to the edge as compared to the other side.  Side note:  I had this uneven wear problem once on my ghia coupe and it turned out that the calipers were not actuating all the way.  The pads on both rear wheels seem to be worn evenly (plenty of life left), although I haven't measured...

Then, just the other day, I had a friend of mine (retired Audi mechanic) drive the car and he said that if felt more like a rear control arm bushing than the brakes.  Would a worn bushing make the car behave this way only under braking?  I don't notice any noise or roughness from the back under normal conditions.  I haven't had the chance to get the car up in the air or inspect the brakes or bushings fully ... PO says the front control arm bushings were replaced not long ago. 

I was just wondering whether anyone had any advice, BTDT's has "felt" this problem before.

I've read in the archives that suspension bushings fail regularly on the 4kq's and I checked and found that calipers are about $90, but I don't want to go and replace something that's not the problem.  It doesn't make the car undriveable, but it's a little unsettling to say the least. Any ideas?

Thanks in advance...sorry about the long post...I wanted to give full details.

Elliott Bavely

86 4000CS Quattro
83 GTI FSP Racey car
83 GTI 16V
90 VW Cabriolet
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