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I recently ordered a combination power break booster and master brake cylinder from Napa. After all my research I was never able to find new and had to go with factory rebuilt. After installing it on the truck I had minimal to no brake pedal. And I was baffled. I bench bled the master cylinder and bled my brake lines. But still had the same nonexistent pedal pressure. After much research I came upon one post that led me to the culprit. And wanted to share with you what I found hoping that it would simplify your issue.
if you buy a preassembled brake booster and master brake cylinder you're probably just going to install it and assume that it works however there is an adjustment in between the power break booster and master cylinder that you may have to set up. By removing the two bolts holding the master cylinder to the brake booster you will find the push needle that the booster pushes into the master cylinder and for some reason mine was set very low causing me to have to push almost all the way to the floor before it made contact with the master cylinder to push pressure into the brake lines. I physically pulled this pin out of the booster, it's not a permantly imstalled piece and using a pair of vise grips's and a socket I was able to adjust it out to where it now pushes ever so slightly on the master cylinder without the brake booster being engaged. This has given me an almost immediate response on my brake pedal. You may have to remove and reinstall the master brake cylinder several times until you get the needle where you want it. But without adjusting it you will never have the firm brake pedal you were hoping for.
I recently ordered a combination power break booster and master brake cylinder from Napa. After all my research I was never able to find new and had to go with factory rebuilt. After installing it on the truck I had minimal to no brake pedal. And I was baffled. I bench bled the master cylinder and bled my brake lines. But still had the same nonexistent pedal pressure. After much research I came upon one post that led me to the culprit. And wanted to share with you what I found hoping that it would simplify your issue.
if you buy a preassembled brake booster and master brake cylinder you're probably just going to install it and assume that it works however there is an adjustment in between the power break booster and master cylinder that you may have to set up. By removing the two bolts holding the master cylinder to the brake booster you will find the push needle that the booster pushes into the master cylinder and for some reason mine was set very low causing me to have to push almost all the way to the floor before it made contact with the master cylinder to push pressure into the brake lines. I physically pulled this pin out of the booster, it's not a permantly imstalled piece and using a pair of vise grips's and a socket I was able to adjust it out to where it now pushes ever so slightly on the master cylinder without the brake booster being engaged. This has given me an almost immediate response on my brake pedal. You may have to remove and reinstall the master brake cylinder several times until you get the needle where you want it. But without adjusting it you will never have the firm brake pedal you were hoping for.
You will want to check the factory book for this adjustment because if out to far out when you release the brakes the piston will still cover the ports in the master not letting fluid to return to master and keep the brakes applied.
I just did the master & booster on my 81 F100 and the rod was not what the book gave.
I also found that the jamb nut on mine, yours does not have one, was loose and it would have moved if I had not found that.
BTW I found that because I was fighting a low pedal also and someone said to check it but was from air in the system, system was all new, but would not pump up.
I had to pressure bleed the system to get any kind of pedal and may do it again now that I have some miles on the truck but not happy with the pedal level still.
Dave ----
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