Master Cylinder Search for Rear Disc Conversion

[bigdawgcje]

Evening folks. I am seeking your wisdom. I am rebuilding 2 Suburbans. The first is a 1984 2WD C30. The second is a 1990 K2500, 4WD. The 2wd has the full floating rear end. The 4wd has the semi floating rear end. I have completed a rear disc conversion on the 1990, and am nearly complete in completing the 2wd.

After changing out the 1990, I did not get the pedal height that I thought I should have. In speaking to a fellow gear head, and searching various web sites, it appears that I need a master cylinder with a bigger bore diameter. I looked at a master cylinder for a 4wd dually, with rear disc, but the bore diameter is only 1.456". The master cylinder on the truck has a bore diameter of 1.575". I read on one site that a MC for a C3500HD would improve the performance, but the bore diameter is 40mm, or 1.575", so no fix there.

My question is, do any of you folks know what master cylinder would fit these trucks with a larger bore diameter? Anybody out there that has done on of these conversions and run into the same issue?

Thanks in advance.....

[Irish_Alley]

pedal height? as in the pedal didnt fully return when you released the brakes?

[bigdawgcje]

No. The pedal goes too far down to fully engage the brakes. This system has been bled 3 times. When you pump the brakes you get  a higher pedal.....

[bigdawgcje]

I also replaced all of the brake lines with braided stainless.

[Captkaos]

Are you still running the combination valve for the disc/drum?  I would talk to the kit designer.
As for bigger master cylinders there is a Tech article on all the MC's in the Technical forum.

[werewolfx13]

On my 76 k20, I'm running a master cylinder for a 77 c30 w/ hydroboost. Bore diameter was a bit bigger. That said, I know both are under 1.5" bore, I think the one I used is 1.3, the one my truck had on it was under 1.2. I'm using 4 new stock calipers for a 76 k20.