Binary Brakes
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7th Gear
Joined: May 2023
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Binary Brakes
1994 F350 V8 Gas
When applying the brakes the wheels will lock after the brake pedal moves a small amount, as can be seen in the video with rear lifted off of the ground. I replaced the master cylinder, the booster (observing clearance between master and booster rod) and ABS sensor on the rear differential (no sensors on front tires). Any suggestions as to next steps? Is this indicative of a bad ABS controller?
Thanks in advance,
glebis
When applying the brakes the wheels will lock after the brake pedal moves a small amount, as can be seen in the video with rear lifted off of the ground. I replaced the master cylinder, the booster (observing clearance between master and booster rod) and ABS sensor on the rear differential (no sensors on front tires). Any suggestions as to next steps? Is this indicative of a bad ABS controller?
Thanks in advance,
glebis
Lead Driver
Joined: Sep 2003
Posts: 7,017
Likes: 209
From: SoCal
Did this start happening after you changed the MC?
This happened to me a long time ago when I did that, and dropped the little rubber cap that sat between the pushrod going into the MC and the vacuum diaphragm. That little cap acts as a cushion between the diaphragm and the pushrod, and losing it changes the distance between the two, so it throws off the power assist curve. On my rod, there is a threaded length adjuster, and setting it helped, but without the rubber cap, the boost activation was still abrupt.
In my case, I dropped the cap into the vacuum housing; it was way too easy to do if you're not careful pulling out the pushrod. It required pulling the booster off the firewall to shake it out. I could never figure out where to buy one of those things.
I'm not sure if newer brake boosters and MC still use the same arrangement.
This happened to me a long time ago when I did that, and dropped the little rubber cap that sat between the pushrod going into the MC and the vacuum diaphragm. That little cap acts as a cushion between the diaphragm and the pushrod, and losing it changes the distance between the two, so it throws off the power assist curve. On my rod, there is a threaded length adjuster, and setting it helped, but without the rubber cap, the boost activation was still abrupt.
In my case, I dropped the cap into the vacuum housing; it was way too easy to do if you're not careful pulling out the pushrod. It required pulling the booster off the firewall to shake it out. I could never figure out where to buy one of those things.
I'm not sure if newer brake boosters and MC still use the same arrangement.
i ain't rite
Joined: Mar 2005
Posts: 65,573
Likes: 5,609
From: Marlboro Mental Hospital.
that is normal for a vehicle lifted off the ground. i can lock up all 4 wheels with one finger push on the pedal. once down on the ground and go for a drive you should see no problems with the brakes.
Thread Starter
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7th Gear
Joined: May 2023
Posts: 7
Likes: 3
Did this start happening after you changed the MC?
This happened to me a long time ago when I did that, and dropped the little rubber cap that sat between the pushrod going into the MC and the vacuum diaphragm. That little cap acts as a cushion between the diaphragm and the pushrod, and losing it changes the distance between the two, so it throws off the power assist curve. On my rod, there is a threaded length adjuster, and setting it helped, but without the rubber cap, the boost activation was still abrupt.
In my case, I dropped the cap into the vacuum housing; it was way too easy to do if you're not careful pulling out the pushrod. It required pulling the booster off the firewall to shake it out. I could never figure out where to buy one of those things.
I'm not sure if newer brake boosters and MC still use the same arrangement.
This happened to me a long time ago when I did that, and dropped the little rubber cap that sat between the pushrod going into the MC and the vacuum diaphragm. That little cap acts as a cushion between the diaphragm and the pushrod, and losing it changes the distance between the two, so it throws off the power assist curve. On my rod, there is a threaded length adjuster, and setting it helped, but without the rubber cap, the boost activation was still abrupt.
In my case, I dropped the cap into the vacuum housing; it was way too easy to do if you're not careful pulling out the pushrod. It required pulling the booster off the firewall to shake it out. I could never figure out where to buy one of those things.
I'm not sure if newer brake boosters and MC still use the same arrangement.
Thread Starter
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7th Gear
Joined: May 2023
Posts: 7
Likes: 3
Thank you for your response, the truck behaves the same when on the ground, if I push the brakes more than a little bit they go into a hard lock. After replacing the MC, booster, and ABS sensor it seems that I can push the pedal further farther without locking up. Last night it occurred to me that I should remove the fuse to the ABS controller to eliminate that as a potential cause, I will do so today.
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