Looking for tips on how to get smooth (no surge) motion from a tracking dolly - especially for truck and pan shots.

I wish the motion to be very slow and I find it difficult to maintain a constant velocity at very slow speeds without some jerkiness.

Would fitting brakes help to reduce the jerkiness since the dolly could be pushed harder?

I wouldn't recommend brakes or drag, they will make it harder to achieve the results you desire (imagine operating a tripod head with the locks partially engaged).

The more inertia, the smoother the ride. Try piling extra weight onto the dolly, like sandbags etc. Or adding another rider.

A lot depends on the dolly you are using (and track if applicable). The bearings and the wheels need to be smooth, as does the track (try talcum powder or Lemon Pledge if the track is sticky or squeaky)

Good luck...