Expert: Brad Sears - 4/28/2011

Question
QUESTION: we have a 1954 chevy 4100 truck with 14000 gvw. The problem we are having is no brake pedal when you 1ST hit the brakes.You can pump the pedal and get builds pressure and has brakes. when you let off the brake pedal after pumpimp up then releasing fluid is forced out the m/cylinder cap. 1st question is why cant we get a firm pedal when you first hit the brakes. 2nd why is the fluid forced back out the cap?
we have replaced the brakes all the way around, we have replaced the m/cylinder 2 times. we have replaced all the wheel cylinders and brake lines, both steel and rubber lines. please see what you come up with.
from: run over by a truck
THANKS AND HAVE A GREAT DAY

ANSWER: Ok, lets start off with a question or two. First, there is an adjustment on the brake pedal linkage. The adjustment should be made so that there is about an inch of pedal movement before the push rod actually puts pressure on the piston in the cylinder. The can really only be felt by actuating the brake pedal with your hand. Do you have that free play? Does the truck have a brake booster such as hydro vac? Let me know and we will go from there.

---------- FOLLOW-UP ----------

QUESTION: we do not have a brake booster on this system. and there is 1-1/2" of pedal travel.
thanks again: RUN OVER BY A TRUCK

Answer
OK, a few thoughts here. First, is the fluid spilling out of the master cylinder with the cap in place or with the cap off? When you let your foot off the brake pedal there is a pretty good rush of fluid returning from the wheel cylinders into the master cylinder bore and then up through the port into the master cylinder reservoir. This looks like a fountain and is normal. With the cover off this will splash out of the cylinder. Inside the cover for you master cylinder there should be a stamped steel splash guard pressed into the under side of the cap. This prevents that fountain from spraying the fluid out of the breather hole in the cap. Now as far as the low pedal on the first pump goes there are two most likely causes. The first is of course air in the system. Have you been bleeding the brakes starting with the brake furthermost away from the master cylinder? That would be the right rear and then working towards the closest? Have you checked to make sure that all of the brake shoe ends are contacting the pressure points on the wheel cylinders correctly? The next most common cause is a miss adjusted brake shoe. If I am right the wheel cylinder end caps on your truck have notches for adjusting with a brake spoon. If so make sure that you adjust both side, in other words there are two adjustments on each wheel. Tighten the brake until the wheel will not turn and then back of the adjuster 10 to 14 notches. The wheel should turn. Adjust each end of each wheel cylinder. Then bleed the brakes. I like to adjust first then bleed as there is not so much movement in each cylinder that the job gets quicker with less fluid used. Let me know if this works, if it does not get back to me and we will go deeper.