Crenwelge,
I stopped at my local part store and per your idea purchased a diaphragm for a brake assy.It is the right diameter but is somewhat thicker than the original part and also stiffer . I am going to try and assemble it in place of the original.What I am afraid of is the truck may not have enough vacuum to make the unit function.By the way the part no. was a no-go at my local Chevy dealer.He said it should contain eight numbers? Oh well thanks anyway. I will let you know how it goes.Almost forgot to tell you my unit is complete minus the diaphragm.
Thanks,
JMH
