Hi,

Did you reset or check the brake booster rods length to fit up into the new master cylinder?

With different master cylinders the piston cup distance may have changed and the rod or pedal has to be pushed farther out to engage the master cylinders piston.
If the rod is too short or long it can cause problems in two different ways.

There only needs to be about .020 of an inch space between the two when the Master Cylinder is bolt up tight to the brake booster.

If you make the rod too long then the piston will not move back far enough to close off the outputs completely to the calipers and will not be able to put more fluid into the lines on the next pump or too short it will not stroke enough to feel normal.
It appears to be the latter.

If you still have the old unit you will have to measure that depth to the piston cups seating spot.
Then you compare that depth to the new units depth or measure the depth to the rod from the face of the booster and do some mathematical subtractions or addition and shoot for some small spacing.

The rod has an adjustment nut to let the ball end move back and forth.

I’m surprised that the instructions of the master cylinder or the shop manual did not run this in with the replacement exchange.

It sounds like you did everything else correctly.


Phil