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muddywater
Senior Member

USA
50 Posts

Posted - 06/20/2018 :  11:18:42 AM  Show Profile  Send muddywater a Yahoo! Message  Reply with Quote
Hey guy's, I have a theoretical question. A friend of mine that is working on an old school bus he purchased and needs to replace a brake can on the rear axle. His question, ( and mine also ) "If the travel limit on the slack adjuster rod is 2", to be legal, and you have a 3" travel brake can that needs to be replaced, is it legal to put a brake can on it that travels 2.5" ?
What are your thoughts?

Mechan1c
Top Member

USA
853 Posts

Posted - 06/21/2018 :  3:31:17 PM  Show Profile  Reply with Quote
"...a brake can?" Old bus probably has standard stroke cans. Don't mix in extended stroke on one side only.We only replace brake components in pairs.

He'll also need to know how to set up the cans to the slacks.

Does he know if the extended out of spec travel is due to a bad can, or a bad slack? Auto slacks?
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muddywater
Senior Member

USA
50 Posts

Posted - 06/21/2018 :  3:57:21 PM  Show Profile  Send muddywater a Yahoo! Message  Reply with Quote
This is a 07 c2. The ones on it have the 3" stroke. He had a set of 2.5" stroked can, but didn't know if it would be "legal", to put one on, well you have answered the one question about mixing the two lengths on the same axle. I have never mixed them, but, we got into the question about length of stroke for legal needs, (2"), compared to actual stroke length of can, so I thought I'd ask the body of knowledge that we have here in this forum. The bus is running auto-slack. The bus was actually leaking air out of one can when you had the park brake depressed, but was actually stroking 1.5" with full application pressure. After he blocked the tires and rolling under bus you could hear and feel a slight air leak on the one side. I told him I'd set the slacks to the cans after he got them put on.
Thank you for your reply.
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Mechan1c
Top Member

USA
853 Posts

Posted - 06/21/2018 :  6:51:00 PM  Show Profile  Reply with Quote
I would stay with extended stroke cans if that's what came on my bus OE.

1.5" of stroke is good.

I thought you were talking about a real old bus...

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RonF
Top Member

867 Posts

Posted - 06/25/2018 :  08:56:15 AM  Show Profile  Reply with Quote
2.5" is short stroke, 3" is long stroke. NEVER mix them. You should always replace them with what they were built with.

Here's just one search.
https://www.todaystrucking.com/mixing-standard-and-long-stroke-chambers/

US Army retired CMBT
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muddywater
Senior Member

USA
50 Posts

Posted - 06/26/2018 :  07:09:11 AM  Show Profile  Send muddywater a Yahoo! Message  Reply with Quote
Thanks Ron, I thought there could be a very good reason for staying with the 3" can but I didn't understand all the dynamics of the situation, your forwarded article makes perfect sense. Thank you, and I thank the collective here that helps me understand our world better.
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kummins
Active Member

41 Posts

Posted - 06/26/2018 :  10:48:02 AM  Show Profile  Visit kummins's Homepage  Reply with Quote
the long stroke chambers also require matching slack adjusters, mismatching them creates all sorts of adjustment & wear issues, as well as violating DOT regs.

modifying the brake system on any vehicle is a big NO NO.

keep in mind, every truck/bus built from 1994 to present must have auto slack adjusters.

Edited by - kummins on 06/26/2018 10:51:57 AM
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BigPapa
Advanced Member

215 Posts

Posted - 07/16/2018 :  05:39:26 AM  Show Profile  Visit BigPapa's Homepage  Reply with Quote
It's easy to tell them apart. The 2.5" have round ports where the hoses screw in and the 3.0" have square shaped ports.

All of our 2000-2014 Thomas and Bluebird buses use 2.5". Our 2016-2016 IC's use 3.0". I'm sure it depends on how you order them.
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Thomasbus24
Administrator

USA
4544 Posts

Posted - 07/17/2018 :  07:02:13 AM  Show Profile  Reply with Quote
quote:
Originally posted by BigPapa

It's easy to tell them apart. The 2.5" have round ports where the hoses screw in and the 3.0" have square shaped ports.



I'd not recommend using this method anymore. I've held in my hand a standard stroke with square ports. Welcome to the age of parts from God-knows-where.
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Torquey
New Member

2 Posts

Posted - 07/18/2018 :  06:25:44 AM  Show Profile  Reply with Quote
hello everyone. Im new ! I feel like i should stand and admit that I've beed a mechanicaholic for 30 plus years but now have moved into a bus garage position.
Q: 04 BB pusher 8.3L cummins just replaced the rear 30/30 cans .ajusted the brakes and now the park brake doesn't seem to hold as strong , is the 8.3L powerful enough to over ride the brake ?? i never power braked the bus before replacing the cans so not sure if it held at full throttle or not thanks Ken
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40ngone
Senior Member

USA
166 Posts

Posted - 07/18/2018 :  06:43:17 AM  Show Profile  Reply with Quote
Welcome. I would first question if the rod lengths were cut correctly, if they were not welded units. Check to see if you are going past 90 degrees.

Hope that helps with a place to start.
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Torquey
New Member

2 Posts

Posted - 07/18/2018 :  07:11:45 AM  Show Profile  Reply with Quote
they were welded so i got 2 clevis measured cut remeasured installed , have not checked for the 90
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aaronwilmoth80911
Top Member

538 Posts

Posted - 07/19/2018 :  12:18:34 PM  Show Profile  Visit aaronwilmoth80911's Homepage  Reply with Quote
At full throttle I'm sure that 8.3 can overpower those cans. I find on most ours with the ISB, if you start getting above about 1700-1800 rpm, they will start to break away a bit, so an 8.3 at full throttle will probably make it move.
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Rich Michels
Active Member

12 Posts

Posted - 07/19/2018 :  8:07:02 PM  Show Profile  Reply with Quote
FYI: If you have MGM brake chambers don't replace them with Bendix chambers. MGM uses a heavier spring.
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