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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 06-05-2017
79Ranger 79Ranger is offline
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Default Brake pots

I've seen some threads here asking why Bluebird put the 30/36 maxis on the PT's and replies of "just put a 30/30 in there"

I don't like arbitrary answers so I asked a good buddy that helps me out on my Bird as he is a heavy duty mechanic.

The first number is the service brake and the second number is the parking brake.

When we apply the service brakes (the pedal), all chambers work....when the parking brake is applied, the only brake is the maxi....hence the larger diaphragm

Simple answer actually....the PT's with a typical 23k drive and a 10k tag only have one parking brake...which is the maxi on the drive...30/30 is fine for a GVW of say 33k....not so much with another 15k put on it.

So the parking brake chamber must be sized to accomodate for the entire weight of both axles.

If that has been discussed here before, then please ignore.....but I did search and came up with results I was not happy with.
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Last edited by 79Ranger; 06-05-2017 at 03:07 AM.
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  #2  
Old 06-05-2017
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gcyeaw gcyeaw is offline
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I had wondered if a smaller pot on the tag would help prevent locking up under heavy braking situations. I suppose it would not be a good idea as an accident investigation would result in big trouble. But a locked up wheel is significantly less effective at stopping a vehicle. Oh well, it was a thought
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  #3  
Old 06-05-2017
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I have only once in 25 years locked up a tag brake during hard braking,and i may have locked up the drives at the same time,i just don't remember,
I was braking because of a deer that ran out of the woods.
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  #4  
Old 06-05-2017
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Quote:
Originally Posted by 79Ranger View Post
I've seen some threads here asking why Bluebird put the 30/36 maxis on the PT's and replies of "just put a 30/30 in there"

I don't like arbitrary answers so I asked a good buddy that helps me out on my Bird as he is a heavy duty mechanic.

The first number is the service brake and the second number is the parking brake.

When we apply the service brakes (the pedal), all chambers work....when the parking brake is applied, the only brake is the maxi....hence the larger diaphragm

Simple answer actually....the PT's with a typical 23k drive and a 10k tag only have one parking brake...which is the maxi on the drive...30/30 is fine for a GVW of say 33k....not so much with another 15k put on it.

So the parking brake chamber must be sized to accomodate for the entire weight of both axles.

If that has been discussed here before, then please ignore.....but I did search and came up with results I was not happy with.
The diaphragm does not hold the coach at all,it releases the spring that holds the coach,so the size of the diaphragm does not help braking,now if you had a 36 on the service barke,that will help,and we have a member here thats done that,he says it helps.
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  #5  
Old 06-05-2017
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Quote:
Originally Posted by 79Ranger View Post
I've seen some threads here asking why Bluebird put the 30/36 maxis on the PT's and replies of "just put a 30/30 in there"

I don't like arbitrary answers so I asked a good buddy that helps me out on my Bird as he is a heavy duty mechanic.

The first number is the service brake and the second number is the parking brake.

When we apply the service brakes (the pedal), all chambers work....when the parking brake is applied, the only brake is the maxi....hence the larger diaphragm

Simple answer actually....the PT's with a typical 23k drive and a 10k tag only have one parking brake...which is the maxi on the drive...30/30 is fine for a GVW of say 33k....not so much with another 15k put on it.

So the parking brake chamber must be sized to accomodate for the entire weight of both axles.

If that has been discussed here before, then please ignore.....but I did search and came up with results I was not happy with.

A 30 36 chamber could be better if your emergency/parking brake needs more help. the 36 side of the chamber is just holding a big spring that is the emergency side of the braking. When that knob is pulled or you loose air pressure the diaphragm can not hold the spring back and it pushes the rod that that applies the brake. Now if the chamber is 20 percent larger does that mean you have more emergency/parking brake? Bet you would. Don't expect better service braking with the 30/36 pod.
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Old 06-05-2017
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Quote:
Originally Posted by Rick View Post
A 30 36 chamber could be better if your emergency/parking brake needs more help. the 36 side of the chamber is just holding a big spring that is the emergency side of the braking. When that knob is pulled or you loose air pressure the diaphragm can not hold the spring back and it pushes the rod that that applies the brake. Now if the chamber is 20 percent larger does that mean you have more emergency/parking brake? Bet you would. Don't expect better service braking with the 30/36 pod.
The only way you will have more parking brake with a 36 chamber is if the spring is bigger too,right?
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  #7  
Old 06-05-2017
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Quote:
Originally Posted by Randy Dupree View Post
The only way you will have more parking brake with a 36 chamber is if the spring is bigger too,right?
That's right Randy. All the emergency and parking brake pressure is applied by a very strong spring inside that 36 side of the pod. When you push the Parking Brake Knob you can hear all the air rush from the brake system.
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  #8  
Old 06-05-2017
LarryKehler LarryKehler is offline
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So does the 30/36 have a bigger spring or the same spring as a 30/30?
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  #9  
Old 06-05-2017
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Originally Posted by LarryKehler View Post
So does the 30/36 have a bigger spring or the same spring as a 30/30?

I would say "who the heck knows"?
I doubt anybody will tell you one way or the other,and most of the aftermarket parts are made in,well,you know.
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  #10  
Old 06-05-2017
wtom24 wtom24 is offline
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It would seem that the 36 would have a bigger spring-what other reason would there be for a larger emergency diaphragm?
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