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Tires, Wheels, Brakes, Steering and Suspensions Discussion of preventative/corrective maintenance and other technical issues regarding your coach's Tires, Wheels, Brakes, Steering and Suspensions and related components.

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  #1  
Old 03-24-2018
rshrimp rshrimp is online now
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Default Air Brakes and Air Pressure questions

I have been having what I feel is a brake issue with my Bird. I have driven big trucks for 20 plus years and the Bird just doesn't stop like I think it should.
I know it's not going to stop like a car but it should stop as good as a loaded semi, shouldn't it??

I had a conversation with Monti, from M&G brake systems at the FMCA Rally. My question was about the system on my TOAD no seeming to work as good as it should and could it be adjusted???

He said they are designed to operate at 90psi max brake application pressure and that I should check that first.

I ran the tanks up to 120psi+ and then put a guage in the TOAD connection. When I stomp on the brakes the max pressure is 60psi

Knowing that the low pressure alarm is set to 60psi, my thought is that 60psi, would be correct for maximum braking, but is it???

Does anyone have a truck with an application pressure gauge?
What is the design max pressure for a brake chamber?

Can someone with an M&G system (or other air system tapped into the rear brakes) do a pressure check please??
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  #2  
Old 03-25-2018
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For what it's worth, I get well over 90 psi at the Toad connection when the brake treadle is pushed hard.

I think that 100 psi is considered the "minimum" full application pressure for my MGM service brake chambers.
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1991 40' WLWB-WTB
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1991 40' WB ...From 2008 - Present
1984 ½ PT-36 .From 2000 - 2008
1973 FC-31 .....From 1991 - 2001
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  #3  
Old 03-25-2018
SAFCO SAFCO is offline
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I'm guessing the Toad brakes do not work like Bus air brakes. That being they will be full on with no air as a safety. That being said, low air = less brakes perhaps? or - if they do work the same, by air overcoming a spring, then perhaps they are dragging in your case from low air pressure and heated up and not working.

In either case I'm thinking my bus would still stop on a dime hauling a Toad of almost any size with no brakes on the Toad.

Better look into those brakes on the bus, every slack adjuster, every lining, drum, etc. One corner may very well be not working
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  #4  
Old 03-25-2018
rshrimp rshrimp is online now
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Quote:
Originally Posted by Dieselbird01 View Post
For what it's worth, I get well over 90 psi at the Toad connection when the brake treadle is pushed hard.

I think that 100 psi is considered the "minimum" full application pressure for my MGM service brake chambers.
Good to know and Thank you!
So, any ideas on what to check as to why I only get 60psi to the rear brake chambers? Does the air relay also regulate pressure??

I know there is a relay valve in the system. I guess I need to plumb in some more temporary gauge ports.

FYI, All my brakes except the tag axle have been fully serviced with new shoes and drums and related parts and are working, but apparently at 60psi max.

I have only checked one wheel (Right Drive) at this point but will be checking further as soon as I get a second test case back.
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Birdless for now.
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  #5  
Old 03-25-2018
rshrimp rshrimp is online now
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HMMMM! There is also a limiting valve somewhere that limits the brake pressure at the drives when the parking brake is applied so it doesnt over torque the s-cam with the spring + air. I wonder if that valve could be bad and limiting drive axle brake pressure all the time??? More testing to follow....
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  #6  
Old 03-25-2018
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Quote:
Originally Posted by rshrimp View Post
HMMMM! There is also a limiting valve somewhere that limits the brake pressure at the drives when the parking brake is applied so it doesnt over torque the s-cam with the spring + air. I wonder if that valve could be bad and limiting drive axle brake pressure all the time??? More testing to follow....
Thats interesting.
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  #7  
Old 03-25-2018
Friday1 Friday1 is offline
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Back in the 80's we got ten new fire engines and they had some brake issues. Technician came from Wagner and he had a suitcase with eight or ten pressure gauges and another with braided lines and T fittings. He said pressure at the brake chambers during a full application should be same as tank or supply pressure minus a few pounds. We put T fittings at the tank and all the brake chambers and they were very close when reading a full application. Final determination was the brake shoe composition was wrong. A ton of work went into getting to that point diagnosing the problem and every other part of the system got blamed before the culprit was found.

Rick in Ohio
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  #8  
Old 03-25-2018
Flyfisher Flyfisher is offline
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100 psi at the brake line port on the bumper.
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Dakota (our Aussie traveling buddy)
Beverly Hills, FL
1996 WB42 (SOLD)
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  #9  
Old 03-25-2018
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John Wyatt – Administrator/Moderator
 
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Quote:
Originally Posted by rshrimp View Post
Good to know and Thank you!
So, any ideas on what to check as to why I only get 60psi to the rear brake chambers? Does the air relay also regulate pressure??

I know there is a relay valve in the system. I guess I need to plumb in some more temporary gauge ports.

FYI, All my brakes except the tag axle have been fully serviced with new shoes and drums and related parts and are working, but apparently at 60psi max.

I have only checked one wheel (Right Drive) at this point but will be checking further as soon as I get a second test case back.
The air for my Toad brakes comes from one of the Tag Axle brake chambers.
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John Wyatt
Titusville, Florida
1991 40' WLWB-WTB
Body Number F095567
My Location: http://www.bbirdmaps.com/user1.cfm?user=4

1991 40' WB ...From 2008 - Present
1984 ½ PT-36 .From 2000 - 2008
1973 FC-31 .....From 1991 - 2001
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  #10  
Old 03-25-2018
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giderich giderich is online now
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Default you.tube anti-compounding video

Anti-compounding brake video.


https://www.youtube.com/watch?v=LmrP_BxMfOI


http://www.gonefcon.com/trucktcom/br...ompounding.htm


Quote:
Originally Posted by rshrimp View Post
HMMMM! There is also a limiting valve somewhere that limits the brake pressure at the drives when the parking brake is applied so it doesnt over torque the s-cam with the spring + air. I wonder if that valve could be bad and limiting drive axle brake pressure all the time??? More testing to follow....
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Dick & Patsy Gideon
1999 43 LXI Single Slide Body # F124510
2005 JEEP Liberty Limited CRD (diesel Toad)
SOLD 89 FC in 2012; SOLD 88 WB in 2016
Rolla, MO 65401
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