Which Master cylinder......mismatched parts

[73 cheySuper]

'73 K20, rear out of a C20 with 11 inch brakes. Hydroboost and Dana 60 out of a '89 V3500.

So, the calipers are much larger capacity than a Dana 44 out of a typical K20....so that means I'd have to order the master for a K30 or V3500 to accomodate the front discs. The 1 tons never came with 11 inch rear brakes, so there's that.
Now, toss in the hydroboost I added from the V3500.....and I've been boning up on the master cylinder differences......but RockAuto only lists 1 version of the master for a V3500. Do I just buy that?
I already bought new brake lines to the master, and they're slated for a '73 K20, so the fittings may or may not be correct, but I can fix that on my end.
This is frustrating, but hopefully there's a master that'll work without going adjustable prop valve. I have one but hopefully can get around that.

 

[ali_c20]

The right proportioning valve gives the right brake bias.
Master cylinders just puts out the pressure, proportioning valve reduces the pressure to the rear.
What was the drum size on the original K20 axle?
Is your proportioning valve working?
Do you have the proportioning valve of the donor axle truck?

 

[Ricko1966]

And combination valve controls,proportioning,brake standoff,and has the shuttle valve. So if I were to use an adjustable proportioning valve I would use it in addition to a factory combination valve. I'd also probably investigate eliminating the proportioning portion of the factory combination valve.

 

[73 cheySuper]

I've been bit by an improper master before. The reservoir capacity needs to be sized to displace the fluid required when the piston is moved, bigger piston, more fluid. The calipers on the D60 are quite a bit bigger than the D44 caliper. This system is all new except the prop valve, which came off my '73 C20. It's all dry right now, just buying parts and sorting stuff out. Waiting for all the fluid lines from RockAuto for the hydroboost. I'm probably going to just buy the '89 master for a V3500 for now.

 

[ali_c20]

Brake pedal is for the hydroboost? Forgot to ask this in my first post

I would put everything together and test it on a remote stretch of street or a big parking lot. Or go to a shop that has brake testing system.
You can add an adjustable prop valve additional to the existing proportioning valve if needed. The line in line out valves are cheap, Wilwood less than 50$.

 

[Hunter79764]

I just did some digging on brakes for mine. For reference, it looks like your 11" drums got a 1" wheel cylinder which is 1.57 in^2. 13 drums available on K20 and K30 was 1.0625 for 1.77in2. Big K30 13's were 1.1875 bore for 2.22 in2. I also saw that according to RockAuto, both K30 options got the same master cylinder. If your existing braking is relatively adequate, see if you can swap your front caliper from the D44 to the D60? I know there is some amount of interchange on calipers, but I have not tried to physically swap the smaller calipers to the D60 housing. Rotor on the D60 is thicker, but if the caliper fits and you can retract the pads far enough, you should be good.

 

[bucket]

I just did some digging on brakes for mine. For reference, it looks like your 11" drums got a 1" wheel cylinder which is 1.57 in^2. 13 drums available on K20 and K30 was 1.0625 for 1.77in2. Big K30 13's were 1.1875 bore for 2.22 in2. I also saw that according to RockAuto, both K30 options got the same master cylinder. If your existing braking is relatively adequate, see if you can swap your front caliper from the D44 to the D60? I know there is some amount of interchange on calipers, but I have not tried to physically swap the smaller calipers to the D60 housing. Rotor on the D60 is thicker, but if the caliper fits and you can retract the pads far enough, you should be good.

The C/K 30 calipers mount completely different than the C/K 10/20 and many other GM vehicles.

 

[73 cheySuper]

Not at all possible....I remembered doing a similar swap, but on a '72 vega of all things. I swapped the front brakes and hubs from a S10, and this is where the master needed to be upgraded to a 2nd gen camaro version, advice came from the vega gurus. Everything worked very well. Same theory, and the rear brakes were much smaller than a 2nd gen camaro.....so all thinigs kinda relative, it should work going with the V3500 master.

 

[jcperformance]

'73 K20, rear out of a C20 with 11 inch brakes. Hydroboost and Dana 60 out of a '89 V3500.

So, the calipers are much larger capacity than a Dana 44 out of a typical K20....so that means I'd have to order the master for a K30 or V3500 to accomodate the front discs. The 1 tons never came with 11 inch rear brakes, so there's that.
Now, toss in the hydroboost I added from the V3500.....and I've been boning up on the master cylinder differences......but RockAuto only lists 1 version of the master for a V3500. Do I just buy that?
I already bought new brake lines to the master, and they're slated for a '73 K20, so the fittings may or may not be correct, but I can fix that on my end.
This is frustrating, but hopefully there's a master that'll work without going adjustable prop valve. I have one but hopefully can get around that.

Since you're running those massive V3500 front calipers and the hydroboost setup, going with the V3500 master cylinder is definitely the right move to move enough fluid. The single version listed on RockAuto should work fine as it's designed for that specific high-capacity front disc setup. Dealing with the mismatched line fittings is a small price to pay to avoid the headache of an adjustable proportioning valve if you can get the bias right.