03 F-350 Diesel rear brakes self applying
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03 F-350 Diesel rear brakes self applying
Have a 03 f-350 7.3 liter auto.Has hydroboost brakes. The more you drive the truck the rear brakes seem to self apply. All brake hoses and calipers check out? HAs anyone seen the hydroboost unit cause this concern?
FTE Leadership Emeritus
Joined: Sep 2000
Posts: 23,174
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From: Stephensville WI
I would first suspect the parking brakes or axle bearings before I looked at the disc brakes or the hydroboost.
Describe what you feel when you say the rear brakes "self apply".
Describe what you feel when you say the rear brakes "self apply".
Posting Guru
Joined: Mar 2005
Posts: 2,060
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From: Burnsville, MN
In the "old" days, vehicles used to have two redundant braking systems coming out of the master cylinder, one to the front brakes, and one to the rear brakes. Then somewhere along the line the two independant systems came to be one rear, and the diagonally opposite front.
Seems like for a system as new as a 2003, this would be of the diagonal type?, which wouldn't lock up just the rear axle, without involving the front as well...... On the other hand, if these trucks have a "proportioning valve" which is sticking, maybe the let-up pressure gradually builds up with use to the point that it never releases.
Then again, if the '03's have the front/rear split, I'd just siphon the brake fluid out of the rear reservoir then take it for a test drive.
Sorry, I don't know anything about hydro-boost, and maybe shouldn't even be trying to contribute......
Seems like for a system as new as a 2003, this would be of the diagonal type?, which wouldn't lock up just the rear axle, without involving the front as well...... On the other hand, if these trucks have a "proportioning valve" which is sticking, maybe the let-up pressure gradually builds up with use to the point that it never releases.
Then again, if the '03's have the front/rear split, I'd just siphon the brake fluid out of the rear reservoir then take it for a test drive.
Sorry, I don't know anything about hydro-boost, and maybe shouldn't even be trying to contribute......
Cargo Master
Joined: Mar 2007
Posts: 3,103
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From: AB/BC
Sounds to me like the park brake dragging. The more it drags the tighter they get because of heat.
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Cargo Master
Joined: Mar 2007
Posts: 3,103
Likes: 32
From: AB/BC
[QUOTE=BareBones;6849015]In the "old" days, vehicles used to have two redundant braking systems coming out of the master cylinder, one to the front brakes, and one to the rear brakes. Then somewhere along the line the two independant systems came to be one rear, and the diagonally opposite front.
Seems like for a system as new as a 2003, this would be of the diagonal type?, which wouldn't lock up just the rear axle, without involving the front as well...... On the other hand, if these trucks have a "proportioning valve" which is sticking, maybe the let-up pressure gradually builds up with use to the point that it never releases.
Then again, if the '03's have the front/rear split, I'd just siphon the brake fluid out of the rear reservoir then take it for a test drive.
Barebones,The park brake is on the rear wheels only and is on its own cable not the hydraulic system.
Seems like for a system as new as a 2003, this would be of the diagonal type?, which wouldn't lock up just the rear axle, without involving the front as well...... On the other hand, if these trucks have a "proportioning valve" which is sticking, maybe the let-up pressure gradually builds up with use to the point that it never releases.
Then again, if the '03's have the front/rear split, I'd just siphon the brake fluid out of the rear reservoir then take it for a test drive.
Barebones,The park brake is on the rear wheels only and is on its own cable not the hydraulic system.
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Cargo Master
Joined: Mar 2007
Posts: 3,103
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From: AB/BC
Have you had the park brake assembly apart?Have you tried adjusting the park brake?They are totally enclosed,and easily adjusted as you know.If they are binding there is only one way to free them up.
Logistics Pro
Joined: Mar 2002
Posts: 3,881
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From: Wake Forest, NC
Well then, have you pulled the rotors off to inspect the parking brakes? What else have you done to determine the calipers hoses etc are good?
I've never seen a hydroboost self apply. I'm not even sure it's theoretically possible. It wouldn't apply just the rear's anyway.
The superduty doesn't use a dual diagonal setup. It is a front rear split. While the front two brakes have separate lines, they are hydraulically on the same circuit before the ABS module.
I've never seen a hydroboost self apply. I'm not even sure it's theoretically possible. It wouldn't apply just the rear's anyway.
The superduty doesn't use a dual diagonal setup. It is a front rear split. While the front two brakes have separate lines, they are hydraulically on the same circuit before the ABS module.
Senior User
Joined: Aug 2007
Posts: 111
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Only reason I could see the brakes dragging due to the hydro boost would be the return line or something wrong with the booster. This would cause all 4 brakes to drag not just the rear though. Are you sure its just the rear or could they be all grabbing just the rears are more noticable?
Freshman User
Joined: Jan 2007
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Seen this type of problem more than once before when the brake fluid was contaminated. Most other fluids like trans. and power steering fluid have a much lower boiling point than brake fluid. As the fluid heats near the rotors and drums the pressure starts to build slightly but enough to apply the brake in the rear and or front. The more you drive the more the brakes lock-up. If you park and let it cool down the brakes start to release until you heat them up again. It doesnt take much time to heat them up. Usually within 5 to 10 minutes of city driving. Usually the hoses and rubber parts start to swell as well.
This has contamination usually happens when you go to get your oil changed. Some of these places top off you fluids sometimes not knowing what is in the container due to an unreadable or no label or using the little rubber bulb to fill your power steering fluid then using the same one to top off you master cylender.
If this is your problem then the complete brake fluid system needs to be replaced including the steel lines becase you may never get all of the other fluid out and could cause the problem again {been there done that}.
This has contamination usually happens when you go to get your oil changed. Some of these places top off you fluids sometimes not knowing what is in the container due to an unreadable or no label or using the little rubber bulb to fill your power steering fluid then using the same one to top off you master cylender.
If this is your problem then the complete brake fluid system needs to be replaced including the steel lines becase you may never get all of the other fluid out and could cause the problem again {been there done that}.
