Brake Problems!! Need Help Please!
Thread Starter
|
New User
Joined: Dec 2003
Posts: 4
Likes: 0
Brake Problems!! Need Help Please!
Brake problems: I have a 1993 Ford F350XLT Diesel 7.3 Intl, 1 ton dully crew cab. I have not been able to get a full brake pedal. Have bled the brakes correctly, replaced master cylinder three times, booster, and equalizer. The master cylinder when plugged, you get a full solid pedal, with NO bypass, but when lines are hooked up, you get a bypass, and the brakes slowly sink to the floor. I have had more than three shops look at this, and they are all dumb founded.Any help please!!!!
Cargo Master
Joined: Nov 2003
Posts: 2,585
Likes: 1
From: Duluth, Mn.
This is a strange one.
I take it, there's no fluid leaking? Does the resivoir stay at the same level?
Is your ABS light on?
93' has RAB's and there's a control valve on the frame rail right under the drivers seat.
I take it, there's no fluid leaking? Does the resivoir stay at the same level?
Is your ABS light on?
93' has RAB's and there's a control valve on the frame rail right under the drivers seat.
Thread Starter
|
New User
Joined: Dec 2003
Posts: 4
Likes: 0
Yes, there is NO fluid leaking, and the ABS light does not stay on. I think it only comes on when the truck is first started. The Reservoir stays full. What is really strange is that if the truck is not running, the pedal is full and solid, but once you start the truck, the pedal drops slowly to the floor, bypassing the all pressure. I have even replaced the booster.
Senior User
Joined: Feb 2003
Posts: 315
Likes: 1
From: Alabama Gulf Coast
Ed2004,
Have the shops checked all the vacuum lines for leaks, and the vacuum pump for output? Here is a quote from the 1992 Ford tech CD (principles should be the same for your year model):
".....For example, after braking to a hard stop, the vacuum in a diesel booster may be significantly reduced. If the driver continues to apply the brakes at the stop, the vacuum will start to build again, and the pedal will sink as the increasing boost moves the diaphragm forward. This doesn't mean there is a leak or a malfunction in the system. Always inspect the vacuum supply on a diesel before suspecting other defects when the complaint is pedal drop."
Perhaps, because you have a vacuum leak in the system, once the engine is started, the vacuum pump is always attempting to catch up.
Hope this helps, R.A.
Have the shops checked all the vacuum lines for leaks, and the vacuum pump for output? Here is a quote from the 1992 Ford tech CD (principles should be the same for your year model):
".....For example, after braking to a hard stop, the vacuum in a diesel booster may be significantly reduced. If the driver continues to apply the brakes at the stop, the vacuum will start to build again, and the pedal will sink as the increasing boost moves the diaphragm forward. This doesn't mean there is a leak or a malfunction in the system. Always inspect the vacuum supply on a diesel before suspecting other defects when the complaint is pedal drop."
Perhaps, because you have a vacuum leak in the system, once the engine is started, the vacuum pump is always attempting to catch up.
Hope this helps, R.A.
Posting Guru
Joined: Oct 2003
Posts: 2,438
Likes: 0
From: Monroe, WA
We've gone through this before at our shop. We went through two master cylinders and replaced the RABS valve on the frame. We finally decided there was nothing wrong with it. They have so much power on the pedal with the motor running, it was actually bypassing the anti-lock valve and leaking off pressure. We finally took it on a test drive and it felt completely normal. As long as you've got all the air out of it, there's not much else you can do.
Senior User
Joined: May 2003
Posts: 455
Likes: 0
From: Alaska
I have found that replacing the RABS valve usually cures a falling pedal condition even if it does not trigger a light or code.
Trending Topics
Senior User
Joined: Feb 2003
Posts: 315
Likes: 1
From: Alabama Gulf Coast
Ed2004,
You say you've gone over the hydraulic system through three shops and they've not found anything wrong with that aspect. Seems to me it's worth hooking a vacuum gauge up to the pump to see what kind of vacuum you're getting off it ( respective, of course to whatever elevation you happen to be at) and also to inspect the major(if not all) vac lines for splits, holes, bad connections.
I think that if you have a problem and you've checked the hydraulic system thoroughly and have not checked the vac system which directly influences it, it's worth looking into. R.A.
You say you've gone over the hydraulic system through three shops and they've not found anything wrong with that aspect. Seems to me it's worth hooking a vacuum gauge up to the pump to see what kind of vacuum you're getting off it ( respective, of course to whatever elevation you happen to be at) and also to inspect the major(if not all) vac lines for splits, holes, bad connections.
I think that if you have a problem and you've checked the hydraulic system thoroughly and have not checked the vac system which directly influences it, it's worth looking into. R.A.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Top 10 Fords at 2026 Carlisle Ford Nationals
Joe Kucinski
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski