power brake problem

[RShaips]

My brakes don't seem to work correctly, when I mash on the pedal the truck stops but it takes longer than it should. I have a 67 SB on a 71 frame with disc brakes up front, the power booster came off of a 72 4 x 4 truck, do I need to put a different portioning unit on it ,since it came off a 4 x 4 ? The brakes feel like they have air in them, but I have bled them and also have installed new wheel cylinders. Thanks for the help

[Stepsides 4Ever]

When you say the brakes feel like they have air in them, does that mean they feel spongey? Or does the pedal slowly sink toward the floor when you have your foot on the brake?

I would buy or rebuild the master cylinder before changing out the proportioning valve myself...the disk brakes work off high pressure/low volume, while the drum brakes work off low pressure/high volume, relatively speaking. The front brakes do about 70% of the stopping, so if you have a leak in the front chamber of your master cylinder you will have the effect of poor braking.

[RShaips]

I put a new master cylinder on it already, the brakes feel like they should when you are driving it but if you need to stop quickly it goes all the way to the floor and slowly stops the truck. The only thing that I have not replaced are the front whell cylinders, but they are not leaking and seem to be working fine. Thanks

[krue]

Have you tried adjusting the rod between the booster and master cylinder? Sounds like you may need to lengthen it a little bit.

[RShaips]

That sounds like a good idea ! I will try it. Thanks