40 mm master mods hydroboost adapter and changing stops

40 MM internals on top P30 below for size comparison.

Fabricated two piece spring retainer to allow more stroke on primary

   Recessed stop for more primary stroke, far as it could go without spring bind.

                               Before modification

                          Two piece retainer installed, original below.

                                       Two piece on the rod

            Primary spring not binding when on the stop.
   I wanted a 3.2 to 1 ratio but that would require new pistons. 3 to 1 worked OK.

 The bottom of the bore is not flat. Spacer makes up the difference that was put on the primary side.

               grooves go to the bottom to let any air out

Hydroboost being installed has an output stroke of 1.708"

 This is the 40mm master shown and it fits:

2001

Chevrolet

C3500HD

Base Cab & Chassis 4-Door

8.1L 496Cu. In. V8 GAS OHV Naturally Aspirated

Doorman M630028
 http://www.dormanproducts.com/itemdetail.aspx?ProductID=6760&SEName=m630028

Ours came from Rock Auto and I see them on Ebay too.