Mystery : 1 Thunk from Brakes When Almost Stopped

[bruce.g.cameron]

Hi Peach Parts

I've been mystified by a braking phenomena I haven't been able to solve on my 1989 190D with 96k miles.

When I am slowing down, about 2-4 feet before the final stop (i.e. going very slow), I get a single "thunk". I feel it through the brake pedal, and increasingly I can hear it.

When I get the pulse through the brake pedal, it sort of endures a little - not instantaneous, but sort of feels like there was a dirty spot on the disc that I ride through. However, discs are quite clean, and I only get this thunk once per slow down.

I had the wheels off recently to inspect - all four rotors look good, and seemed I had plenty of pad on all corners. Front rotors pads and rebuilt calipers done 6k miles ago, rears done 30k miles ago.


I have a couple of thoughts, but have not been able to figure it out:

- Could this be something in the Master Cylinder?
- Could this be one of the Calipers - like a rust spot in the bore?
- Could this be a loose control arm or sway bar?
- I haven't gone back to check that all 8 caliper bolts are torqued. Could this be a caliper rotating about one of the bolts?