'89 K1500 Master Cylinder Upgrade

[TruckNorris89]

We've fought a VERY soft brake pedal on my son's '89 K1500.  I previously had a '97 C1500 and I remembered it also had the soft pedal problem.

 

We ordered a Dorman M630031 Brake Master Cylinder and the necessary adapter for the larger thread fittings.  The lines were in a different place than the original so we made new ones and it all seemed to be fine.  I used a power brake bleeder to flush the system and thought everything was all set.

 

The issue is the brake pedal feels extremely hard.  We have better braking but it feels like you have to stand on the pedal, almost like old non-power brakes.  On the original master cylinder your foot would almost go to the floor but with the new one you get about halfway down and it won't depress any further.

 

Before I spend money on replacing the vacuum booster I'd like to know if anyone experienced this after upgrading to a GMT800 master cylinder?  If so, is this normal or did you have to make other changes to get good braking?  I"m pretty certain the feel of our pedal is not normal and I'd like to fix it soon so the truck is safe to drive.

 

Thanks,

Kevin

[flyingfool]

need matching proportioning valve