My low brake pedal issues resolved.
11-13-2016, 08:53 PM
#1
Junior Member
Thread Starter
My low brake pedal issues resolved.
This topic has had its share of postings so I'll try to keep this brief. The typical issue of a low and spongy brake pedal was something I noticed when I bought my truck used back in 2010.
Its a 2005 F150 XLT super cab model with the 4.6 litre engine, I'm mentioning this just so you will know what year and type of truck I'm working on.
The first thing I replaced was the brake booster, simply because it was making a grinding sound when you pushed on the pedal. The same issue remained after that replacement.
The fluid in the master cylinder was really dark and sludgy so I replaced the cylinder and bled the brakes through a few times. And as you would expect the same issue remained after that work.
So I took the calipers off and drained them to check for residue, made sure the pistons were moving freely, and the seals were not weeping. Then I lubed all the pins, refitting the parts and bleeding the system again. And yes as expected the issue remained.
The thing is the pedal was always low on first application, but if you double pumped it quickly the pedal came up, so its a vacuum travel issue from the brake booster and not a fluid related issue.
My next plan of attack was to check the push rod free clearance setting in the brake booster; a quick measuring of the clearances showed it was about a 1/4 inch off the master cylinder piston which is way too much.
What I did was measure the depth from the master cylinders flange down into the master cylinder pistons cup with a vernier caliper to get that distance, then transferred it to the brake booster face to push rod end to see just where the tip of the push rod was when its assembled.
Holding the rods outer serrated part, I then rotated the inner adjustable push rod with a 7mm wrench bringing it outwards to close in the wide gap it had.
So you dont have to do all the measuring I did, the end result I found acceptable is to have the push rods tip no closer than 1.5mm inside the face of the brake booster if you hold a straight edge across the face and measure down onto the push rods tip.
Now the brakes work as they should, a high pedal with good feel and feedback while braking. You need a small clearance between the push rods tip and where it will contact the back of the piston cup to allow for some expansion of the parts as they heat up when the system is working.
If you have it too close, the brakes will be very high but they will begin to bind as the parts heat up while driving. If its too wide you have simply low spongy brakes. This fix worked for me and the results are excellent brakes with no low spongy pedal feel.
Please be aware that you do this alteration at your own risk and you stand fully responsible for the outcome of your own repair work.
Its a 2005 F150 XLT super cab model with the 4.6 litre engine, I'm mentioning this just so you will know what year and type of truck I'm working on.
The first thing I replaced was the brake booster, simply because it was making a grinding sound when you pushed on the pedal. The same issue remained after that replacement.
The fluid in the master cylinder was really dark and sludgy so I replaced the cylinder and bled the brakes through a few times. And as you would expect the same issue remained after that work.
So I took the calipers off and drained them to check for residue, made sure the pistons were moving freely, and the seals were not weeping. Then I lubed all the pins, refitting the parts and bleeding the system again. And yes as expected the issue remained.
The thing is the pedal was always low on first application, but if you double pumped it quickly the pedal came up, so its a vacuum travel issue from the brake booster and not a fluid related issue.
My next plan of attack was to check the push rod free clearance setting in the brake booster; a quick measuring of the clearances showed it was about a 1/4 inch off the master cylinder piston which is way too much.
What I did was measure the depth from the master cylinders flange down into the master cylinder pistons cup with a vernier caliper to get that distance, then transferred it to the brake booster face to push rod end to see just where the tip of the push rod was when its assembled.
Holding the rods outer serrated part, I then rotated the inner adjustable push rod with a 7mm wrench bringing it outwards to close in the wide gap it had.
So you dont have to do all the measuring I did, the end result I found acceptable is to have the push rods tip no closer than 1.5mm inside the face of the brake booster if you hold a straight edge across the face and measure down onto the push rods tip.
Now the brakes work as they should, a high pedal with good feel and feedback while braking. You need a small clearance between the push rods tip and where it will contact the back of the piston cup to allow for some expansion of the parts as they heat up when the system is working.
If you have it too close, the brakes will be very high but they will begin to bind as the parts heat up while driving. If its too wide you have simply low spongy brakes. This fix worked for me and the results are excellent brakes with no low spongy pedal feel.
Please be aware that you do this alteration at your own risk and you stand fully responsible for the outcome of your own repair work.
Last edited by F150 XLT; 11-13-2016 at 08:57 PM.
11-14-2016, 10:26 AM
#3
I'm gonna do this soon, I've complained from the day I bought my truck (used) about the brakes. They never had a rock solid feeling. I've replaced calipers (sticking) and flushed fluid, this is next thanks
11-14-2016, 03:27 PM
#4
I will update, I did this, researched a little more, saw a video on YouTube, read the other forums on this. It's simple, I took the measurements, and turned mine 1 full turn, and tried it. I like it, I think it's much much better. I didn't want to over do it and drag the brakes, and I can confirm everything is all good. Thanks, you just fixed my biggest irritation with this truck!
04-01-2017, 06:53 PM
#6
Junior Member
Thread Starter
Remove the nuts holding the brake master to the booster housing and have a look. It may be tight to remove due to vacuum pressure holding it in position.