On my 87 MC9, when I apply the brakes sometimes, it seems more like flipping a switch then operating a valve. Ill apply the brakes and all of the suudden they will "come on". Once they come on, they work like any other air brake Ive used and I can apply more or less brake. When I let off its the same thing. This happens as soon as I apply the brakes and they operate normally other than that. All my pads and drums are "like new" and they are adjusted correctly. Im thinking possably a valve issue ?
Maybe a treadle valve issue? Which treadle valve do you have? Is there anything around/under the pedal to the valve?
A brake expert will chime in soon, I'm curious as to why this is happening to you.
Good Luck,
Paul
Dreamscape is more likely right!
First thing first...recheck the brake adjustment. Make sure the camshaft is fully re-tracked before adjustment. If you done that before then go to the next step. It probably is OK with new linings already installed.
Have some one watch the brake can-lever movement just as soon as the foot pedal is press down. If it don't respond quickly...then you may have relay valve problem...leaking relay diaphragm or dry-up foot valve need to taken apart for cleaning and re-lube with white lithium grease to the spool & bore hole.. It could be that the floating spool valve is hanging up due to dry-up grease or none.
Or take your bus to a heavy truck shop and them tell you what the problem in a few minutes. It only required the brake mechanic to watch what is the problem...no testing equipment to hook up to find out (usually).
Let us know the results if you will, thanks.
FWIW
Sojourn for Christ, Gerald
I think it is safe to assume your mechanical bits are ok.
You will probably have sticking valving.
The brake pedal has no option on application, as you are applying a mechanical pressure to it via the pedal linkage. It has to open in relation to your foot movement. The relay valve that applies the rear brakes remotely via an air signal however....
Air pressure makes its internals apply, and lack of air pressure make them release. If the valve's internal lube is dried out or otherwise the valve is resisting an absolutely smooth as a baby's bottom movement, the effect is grabbing on application and hanging on release brakes from the driver's seat. It won't move until the pressure builds up and then snaps on, and sticks on release and then the springs snap it closed.
All of the valving on our buses are consumable products, when you consider the millions of miles involved in chassis life. A busnut would be well served to systematically replace all valving at some point, and then enjoy the reliability for years and years to come.
Change out the rear relay valve, justify it as preventive maintenance, it might be bleeding air pressure out the exhaust anyway... and see what happens.
Remember, our coaches were in the hands of second or third tier companies who rode them hard, put them away wet, and may not have had a clue how to properly maintain them, if they were willing to spend the cash in the first place. And which business person puts money into a vehicle they plan to sell...?
happy coaching!
buswarrior
Whereabouts in the system is the rear relay valve located ? Im of to look in my manual also..
travelingfools....Relay valve is above rear axle housing assembly with 2 air hose connected to brake cans.
I add a text to gumpy's photo...open photo link below of the post.
Great website "gumpydog" (Craig) http://www.gumpydog.com/bus/MC9_WIP/Mechanical/Drive_Axle/drive_axle.htm
FWIW
Sojourn for Christ, Gerald
Try some WD40 on the pedal pins. Sometimes they hang. Work the brake pedal full on and off repeatedly (50 times with full air pressure) to put some air through the system, sometimes they just need to be used. Are you running cold weather? Sticking valves respond favorably to air brake alcohol. The trick is to get it into the system after the air dryer and that means finding a plug in the wet tank, removing the plug and pouring at least a pint of air brake alcohol in that tank, then pumping it through the system with your foot pedal over a period of days.
pedal pins ?
Travelingfools...about the "pin" to cause hang up or binding from non-lube pin. Click the following titles:
TROUBLESHOOTING BRAKE PROBLEMS - TREADLE/PEDAL TIPS (http://www.bendixvrc.com/itemDisplay.asp?documentID=3218)
BRAKE VALVE TREADLE REPLACEMENT – COACH APPLICATIONS (http://www.bendixvrc.com/itemDisplay.asp?documentID=3220)
BTW here a link to foot control:
E-9 and E-10 Brake Valves (http://www.bendixvrc.com/itemDisplay.asp?documentID=3462)
Primary piston need to be freely to move under spring pressure under depressed pedal... I use "Aero" Lubriplate white Lithium grease.
A neutral lithium base lubricant, manufactured with a light viscosity mineral oil that remains plastic down to -70°F, has an ASTM Dropping Point
of over 350°F and is an NLGI No. 1 consistency.
FWIW
Sojourn for Christ, Gerald
Thanks for all the info..Ill start with the pedal and work my way back..