What do you mean you "upgraded the master cylinder"?!?!?!?!?!?
The truck was built with a hydro-vac and there was a reason for it!!! A truck that size/weight with brakes the size it has it's
almost a no brainer why they use hydro-vacs.
Also the stock MC is matched to the particular HV unit so they work as a "team",this should
not be changed!!! They also correspond to the bore(s) of the wheel cylinders.
In some systems the HV has a residual check valve whilst the MC does not,in other's the MC has the RCV and the HV does not. They
cannot be "mixed and matched",one or the other
must have a RCV but
never both.
The control valve is
not a check valve,it controls the vacuum actuation,the RCV is located in the end cap on the slave cylinder (end cap is where the hydraulic output line connects).
I can't look up the HV or MC at GangstarIH because the section with them is missing.
I have a list with many MC's I've crossed to aftermarket pn's plus the rebuild kits but not for the K/KB5. I'd like to add them if anyone can provide the IH's pn's or copies of the pages in the book.
Other things to know...
There should also be a vacuum check valve somewhere in the supply line from the intake manifold to the HV unit,usually mounted to the firewall.
If the vacuum system has any hose connecting the steel tubing,it is special hose and
must be replaced with same.Not hard to find,all trucks with HV's used it in either 1/2" or 3/4" ID.
If you have the IH parts manual (MT-52D) for the truck you can find the illustrations for the HV unit,the vacuum hosing & piping in Group 12.
Forget about rebuilding it yourself,you won't find the parts,I've tried and they are NLA.
The piston type units also require periodic "lubrication" as they have leather seals inside that must be kept pliable,
neatsfoot oil is the most popular.
This link has a lot of useful info.
http://www.bepco.biz/Catalogs/vacuums_&_hydraulics.htmI use "Section III - Bendix Brake Boosters" all the time for reference and identification.
I also have a few links for rebuilders if needed. They usually go for around $300 w/exchange from what I've found.