Electrical Fire/Brake Warning Switch
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
Bleeding the brakes is what can cause the value to not be centered. You need to apply enough pressure to the opposite side to center the valve. If you get it centered there is tool to lock the valve while bleeding so this doesn't happen. On the off chance the valve is stuck I'm not sure if it can be un stuck
I let me cylinder self bleed by opening it an let it flow keeping the MC full.
It take awhile when your working by ones self.
Orich
Lead Driver
Joined: Apr 2011
Posts: 6,399
Likes: 40
From: El Dorado, Arkansas
If the brake warning light was not staying on prior to this event, chances are the spool isn't stuck, just shifted.
With a '68-up model, the warning light will momentarily illuminate when the key is turned to the Start position. When the key moves to the Run position, the warning light should go out. If it stays lit, the spool is shifted off-center.
'67 models have a one wire pressure warning switch (instead of a two-wire switch) and don't have this prove out circuit going back to the ignition switch.
'68-up brake pressure warning light circuit.
http://www.fordification.com/tech/wi...rninglight.jpg
With a '68-up model, the warning light will momentarily illuminate when the key is turned to the Start position. When the key moves to the Run position, the warning light should go out. If it stays lit, the spool is shifted off-center.
'67 models have a one wire pressure warning switch (instead of a two-wire switch) and don't have this prove out circuit going back to the ignition switch.
'68-up brake pressure warning light circuit.
http://www.fordification.com/tech/wi...rninglight.jpg
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
I'm at a lost as to the web site to where, I got the parts but bought what they had as a rebuild kit which was very few parts. They all seem to have 0-rings but are flat on the outer face on the one's, I 've pulled apart.
I used the pistol bore brush to help clean the inner bore out an brake cleaner soaked it for a while.
Orich
Lead Driver
Joined: Apr 2011
Posts: 6,399
Likes: 40
From: El Dorado, Arkansas
This is very similar to the pressure differential valve found on the Bumpsides and shows the steps of how to clean and reseal the valve. A seal kit is available from Muscle Car Research --a pressure differential valve lock tool is also available from them.
https://www.musclecarresearch.com/va...atherhead-drum
https://www.musclecarresearch.com/va...atherhead-drum
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
Instead of bleeding the brakes to center it, follow the instructions Ultraranger posted in post #26.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Thread Starter
|
New User
Joined: Oct 2014
Posts: 13
Likes: 0
From: San Diego
I tried bleeding the brakes with slow pressure on the petal with no luck. The light is still on.
I'll go ahead and try loosening the outlet port tube nut on differential valve and see if that will get it to re-center.
Thanks for the suggestions.
I'll go ahead and try loosening the outlet port tube nut on differential valve and see if that will get it to re-center.
Thanks for the suggestions.
Posting Guru
Joined: Mar 2016
Posts: 1,412
Likes: 1
From: Barre Mass
Could you loosen both lines at the same time and let the pressure balance itself while pressing slowly on the pedal?
Lead Driver
Joined: Apr 2011
Posts: 6,399
Likes: 40
From: El Dorado, Arkansas
The problem is there was low pressure even created on one side of the spool --bleeder open and bleeding out the system, failed seal, blown brake line/hose. These are all things that will shift the spool.
The closed (good) side of the system is going to be at a higher pressure potential than the lower pressure/failed side of the circuit. The higher pressure is going to act on the end of the valve spool and push it over to the lower pressure/failed side of the brake system.
In order to get the spool back to the center, pressure is going to have to be built up and be greater than the side that was originally good. This means you have to create a pressure drop (open bleeder or crack open a fitting) on what was the high pressure side and make what was the bad side the high pressure side to push the spool back over.
Thread Starter
|
New User
Joined: Oct 2014
Posts: 13
Likes: 0
From: San Diego
I was finally able to get the differential valve re-centered.
On my truck the differential valve also splits the left and right front brake lines. When I was trying to re-center the valve I only opened one of the front bleeders. I figured that with one closed it may be providing some back pressure on the valve and that's why it wasn't moving. After opening both left and right front bleeders the light on the dash went out on the second pump of the pedal.
Thanks for everyone's help.
Greg
On my truck the differential valve also splits the left and right front brake lines. When I was trying to re-center the valve I only opened one of the front bleeders. I figured that with one closed it may be providing some back pressure on the valve and that's why it wasn't moving. After opening both left and right front bleeders the light on the dash went out on the second pump of the pedal.
Thanks for everyone's help.
Greg
Lead Driver
Joined: Apr 2011
Posts: 6,399
Likes: 40
From: El Dorado, Arkansas
The two lines coming off the brake valve, out to the front wheels, are at the same pressure potential. If you open the bleeder on one front wheel, you create the same pressure drop on the other.
The only way there would not be the same pressure drop (or pressure applied, with the bleeders closed) would be if there was a blockage in one of the valve ports or in the line out to one of the front wheel cylinders/front calipers.
A bad brake hose on one wheel could create a blockage (act like a check valve) to either restrict fluid/pressure from either getting to the wheel cylinder/caliper or, resticting the fluid from releasing the wheel cylinder/caliper after you take your foot off the brake pedal.
Assuming there are no blockages in the brake circuit and the brake hoses are good, internally, the pressure will be the same on both front wheels and opening a bleeder on one front wheel will lower the pressure of the other front wheel by the same amount.
The only way there would not be the same pressure drop (or pressure applied, with the bleeders closed) would be if there was a blockage in one of the valve ports or in the line out to one of the front wheel cylinders/front calipers.
A bad brake hose on one wheel could create a blockage (act like a check valve) to either restrict fluid/pressure from either getting to the wheel cylinder/caliper or, resticting the fluid from releasing the wheel cylinder/caliper after you take your foot off the brake pedal.
Assuming there are no blockages in the brake circuit and the brake hoses are good, internally, the pressure will be the same on both front wheels and opening a bleeder on one front wheel will lower the pressure of the other front wheel by the same amount.
Thread
Thread Starter
Forum
Replies
Last Post