Skip to main content ↑ ↓
Topic: Air governor failure (Read 3620 times) previous topic - next topic

Re: Air governor failure

Reply #25 –
Quote from: wolfe10 –
YES, brake pedal uses all 4 brakes. 

But if falling air pressure, do NOT FAN, as that uses up what little air you have.  Just apply steady pressure.

The "fan to test" is to deplete air pressure-- the exact opposite of what you want to do if you are loosing air pressure while driving.
So.  It takes 60# air pressure to release the spring loaded brakes in the rear.  I always understood that to mean that I needed more than 60 PSI to apply the rear brakes.  Or am I missing something?

PS Trust me on this.  If I ever "fanned' the brakes my dearly departed father would still be screaming in my ear "What Do You Think You're doing?  Do you want to kill us?"
1992 Foretravel Grand Villa
U225 SBID Build No. 4134
1986 Rockwood Driftwood
1968 S.I.A.T.A. Spring
1962 Studebaker Lark
1986 Honda VF700C
1983 Honda VF750C
Charlie, the Dog was broken out of jail 24 Oct 2023
N1RPN
AA1OH (H)e who must be obeyed.

Re: Air governor failure

Reply #26 –
On rear brakes the pressure has to build up to release the brakes.  When brakes are applied the air is released from rear brake and the spring is what applies the brakes.  So when you have no air the back brakes are fully engaged.
If this isn't right I'm sure someone will correct me!!!
Chris
1999 U 320 DGFE
Build Number 5523
Chris & Elka Lang
In the field, Lonoke AR

Re: Air governor failure

Reply #27 –
Quote from: Chris m lang –
1.  On rear brakes the pressure has to build up to release the brakes.
2.  When brakes are applied the air is released from rear brake and the spring is what applies the brakes.
3.  when you have no air the back brakes are fully engaged.
Chris,

Your first sentence is correct, IF you are referring to the parking brakes (spring brakes).

The second sentence, however, is only correct if you are referring to applying the parking brake.

The third sentence is correct in all cases.

For a somewhat wordy but simple explanation of the air brake system, check out the video below:

https://www.youtube.com/watch?v=ZFi957GaxpU&frags=pl%2Cwn
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Air governor failure

Reply #28 –
To follow up on Chuck's accurate post:

Front brakes-- air applied ONLY

Rear brakes-- two DIFFERENT cans/methods of application:  Regular service brakes are air applied just like fronts.
The second "can" is spring applied/air released (emergency/parking brake).
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Air governor failure

Reply #29 –
Quote from: wolfe10 –
To follow up on Chuck's accurate post:

Front brakes-- air applied ONLY

Rear brakes-- two DIFFERENT cans/methods of application:  Regular service brakes are air applied just like fronts.
The second "can" is spring applied/air released (emergency/parking brake).
OK!  Now I have a better idea of what is going on in the rear.  I had been thinking that the air pressure needed to overcome the air pressure holding the spring brake at bay.  My bad.  The spring brake only pushes the service piston.  So as long as I have some air pressure I have some brakes, and one prolonged application is the best technique for coming to a controlled stop after air failure.
Thanks for the conversation.  It really helped me understand.

https://www.anythingtruck.com/product/780-72A3030LS.html

FWIW I watched the YouTube video, nothing new there but I think "evacuate" is the wrong word to use for venting the rear circuit.  Wirth and Grufat loves those quick dump valves for releasing spring loaded air cylinders, I'd rather retract the air cylinder with opposing air pressure and have a sensor to tell the system that the cylinder is fully retracted.
1992 Foretravel Grand Villa
U225 SBID Build No. 4134
1986 Rockwood Driftwood
1968 S.I.A.T.A. Spring
1962 Studebaker Lark
1986 Honda VF700C
1983 Honda VF750C
Charlie, the Dog was broken out of jail 24 Oct 2023
N1RPN
AA1OH (H)e who must be obeyed.

Re: Air governor failure

Reply #30 –
The "wedge drum brakes" used on your coach (unrelated to those found on most Foretravels) were very widely used in Europe on MDT's.

I know, at 170,000 miles on our coach with the same brakes (and proper use of exhaust brake) the were less than 50% worn.  And, that included a lot of mountain driving SOB (South Of the Border).
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Air governor failure

Reply #31 –
Quote from: wolfe10 –
The "wedge drum brakes" used on your coach (unrelated to those found on most Foretravels) were very widely used in Europe on MDT's.

I know, at 170,000 miles on our coach with the same brakes (and proper use of exhaust brake) the were less than 50% worn.  And, that included a lot of mountain driving SOB (South Of the Border).
We're knee deep in linings here and all four corners seem to pull evenly especially during one in-town highway speed traffic light stop down grade with car in tow.

Sometimes I get so tightly focused that I can't see the forest.  Happy to know that I have four wheel brakes even as the air pressure goes down.  Over the 33 years we had the 1950 Chrysler I had two brake failures.  Luckily that car had a powerful parking brake on the drive shaft.
1992 Foretravel Grand Villa
U225 SBID Build No. 4134
1986 Rockwood Driftwood
1968 S.I.A.T.A. Spring
1962 Studebaker Lark
1986 Honda VF700C
1983 Honda VF750C
Charlie, the Dog was broken out of jail 24 Oct 2023
N1RPN
AA1OH (H)e who must be obeyed.

Re: Air governor failure

Reply #32 –
Quote from: Old Toolmaker –
  Happy to know that I have four wheel brakes even as the air pressure goes down. 

Actually, the sequence will be:

Diminished braking as air pressure drops, as PSI to the four wheel positions drops.

When it drops low enough to engage the parking/emergency brakes, you will have ONLY the rear brakes-- a poor substitute for all wheels braking.

If air pressure is dropping (actually, if it drops at all below "cut in PSI"), find a place to safely stop! Find and fix the issue before getting back on the road.


Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Air governor failure

Reply #33 –
Quote from: wolfe10 –
Actually, the sequence will be:

When it drops low enough to engage the parking/emergency brakes, you will have ONLY the rear brakes-- a poor substitute for all wheels braking.

If air pressure is dropping (actually, if it drops at all below "cut in PSI"), find a place to safely stop! Find and fix the issue before getting back on the road.


Merry Christmas Brett.  Please grant me the common sense to know that as the air pressure goes down, the available force to operate the brakes also goes down.  And I've slid down a hill on a gravel road in both a 1911 Stanley and my 1926 Ford T Speedster.  Both cars with rear wheel only brakes although the Stanley had the good grace to have external contracting brakes on both rear wheels, while the Ford's transmission brake cold clamp the drive shaft tight and leave the rear wheels spinning in opposite directions.

Rear wheel braking force with air pressure from 60# to 0 would make an interesting spread sheet graph.
1992 Foretravel Grand Villa
U225 SBID Build No. 4134
1986 Rockwood Driftwood
1968 S.I.A.T.A. Spring
1962 Studebaker Lark
1986 Honda VF700C
1983 Honda VF750C
Charlie, the Dog was broken out of jail 24 Oct 2023
N1RPN
AA1OH (H)e who must be obeyed.

Re: Air governor failure

Reply #34 –
The spring section presses the shoe cam or wedge when the pressure drops under 60 ish psi. You don't have control over the situation . No pressure = no move
If pressure is over 60 ish the spring / park brake may be released and brakes are controlled by the pedal  . The buzzer should stay on until around 80psi.

Newer d 2 seem to run at more pressure. Mine likes the 125 target psi. Oe was 105 

Re: Air governor failure

Reply #35 –
Quote from: Protech Racing –
Newer D2 seem to run at more pressure. Mine likes the 125 target psi. Oe was 105
Most D2 are adjustable.  Set the pressure where you want it.

http://www.plazafleetparts.com/uploads/2/1/9/0/2190100/d-2_governor_maintenance.pdf
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"