I just installed a power brake booster kit in my 1966 mustang with drum brakes. When I apply the brakes they partially depress without any noticeable brake engagement and then the booster seems to kick in and they depress the rest of the way (almost to the floor) and brake the car. When I am driving very slow, the car jerks to a stop when the booster appears to engage. There is not the smooth movement and braking action that I expected. It also seems like I still have to apply a lot of pressure on the brake pedal to slow the car when it is at speed.
I have checked the vacuum and it is providing 16-17 inches at idle. The booster kit included a new single bowl master cylinder and I drained all the lines and replaced the wheel cylinders at the time of conversion.
Does anyone have any recommendations?

 

Did you check the headspace between the booster and cylinder?

Did you use the OEM style booster?

 

Have you adjusted the drums yet? This has an enormous effect on brake pedal feel.

 

The oem booster kit came with the new master cylinder already attached to the booster, so I didn't make any adjustments to that. I adjusted and bled the brakes when I reassembled everything. Note that the kit said I could reuse my existing pedal, which I did. It does depress closer to the floor now, then it did with the manual system. Any other ideas?

 

Yeah, my prior question-

Did you really use the OEM style booster?