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Tractor Talk Discussion Forum

Big truck parking brakes

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Roy Suomi

08-10-2007 20:22:45




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I've got a small problem with a '03 International/Navistar 7400 single axle dump truck..Truck has only 13,000 miles on it ..I've adjusted the rear slack adjusters , were out of adjustment quite a bit..still won't hold on a hill..I'm not so sure the brake chambers are junk at this low mileage..Any thoughts ??




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Roy Suomi

08-11-2007 08:48:32




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 Re: Big truck parking brakes in reply to Roy Suomi, 08-10-2007 20:22:45  
First off , I changed the automatic slack adjusters to manuals..[ I had done this on a '97 RD-690P S/A Mack dump..Wouldn't hold adjustment after a complete brake job..Cams , bushings , shoes , springs , drums ..] Snugged the adjusters till tight to the drums..Saw them contact the drums thru the inspection holes in backing plates..Then I backed them off 2 flats and the locking sleeve popped out to lock the adjuster..Is what I did legal ??Or do I have to install OEM automatic slacks??

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RodInNS

08-12-2007 08:21:42




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 Re: Big truck parking brakes in reply to Roy Suomi, 08-11-2007 08:48:32  
I dunno about where you're at. Here, I think it's technically legal to install the old manual slacks, but I think everythign else better be right bang on... They do not like to see the manual slacks going on in place of automatic slacks here, or so I've been told.

Rod



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David in TN

08-11-2007 07:54:04




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 Re: Big truck parking brakes in reply to Roy Suomi, 08-10-2007 20:22:45  
This is off topic, but...I have a semi trailer that I use for storage and I want to move it forward a few feet. There are two air fittings on the front of it, one says service and I think the other says emergency, best I remember. I can get an air line to it from my shop compressor. If I tap into the service line and apply air will that release the brakes? It has only been here a month so they shouldn't be stuck.

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RodInNS

08-11-2007 07:33:09




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 Re: Big truck parking brakes in reply to Roy Suomi, 08-10-2007 20:22:45  
I think Wayne cover about everything. I hadn't heard of using feeler gauges on the shoes, but I don't take these courses either.... I can say for certain that the old style adjustment of run it tight and back off a 1/4-1/2 turn doesn't work all that well on Rockwell automatics... I basically ran them up as tight as I dared, and went for a drive. Find the hot ones and back them off a hair... That's not a precise method by any means, but it got them working better. Haven't smoked any red lights lately anyway.

As far as Maxi's taking 90 PSI to release.... I never heard of that. Maxi's start to release at 45 psi and are fully released at 60 psi. As far as I know that's pretty much an industry standard. The service chamber can develop nearly twice that force...

Rod

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ohio dick

08-11-2007 15:50:13




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 Re: Big truck parking brakes in reply to Roy Suomi, 08-10-2007 20:22:45  
you could have a broken maxi spring.Look in hole for caging bolt if plate is off center or cocked spring is broke.



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Garry Huk

08-11-2007 08:31:35




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 Re: Big truck parking brakes in reply to Roy Suomi, 08-10-2007 20:22:45  
I disagree with NC Wayne on not having as much pressure on your brakes when parked "it is just a spring". It takes close to 90 psi to release the maxi pot, and i've never known anybody to use or be able to use 90 psi application through the foot valve.Not trying to be smart, but don't underestimate the force of that spring in a maxi pot. A lot of injuries have ocurred by people that thought it was just a spring, Garry.

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NC Wayne

08-10-2007 22:48:35




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 Re: Big truck parking brakes in reply to Roy Suomi, 08-10-2007 20:22:45  
Just had to do a complete brake job on my Freightliner that had been having some "stopping issues". In trying to figure out what the problem actually was I talked to a friend that owns a truck repair shop. He and all his guys had just gone through a brake repair course earlier in the week. The old thought on run it out tight and back it off X amount is no longer acceptable with auto style slack adjusters. The new way to do the initial setting is to actually use a feeler guage and run the shoes out til there's .020 clearance between the pad and the drum. He said the instructors told them anymore was doing nothing but causing the brake to be "loose" and created more slippage and therefore more heat when stopping and we all know that means glazing of the pads and drums. When parked all you've got is a spring in the chamber applying the drum with x amount of pressure but when your stopping you've got alot more pressure acting to apply the brakes via the service side of the chamber. If yours has been loose and out of grossly out of adjustment like you said the pads and drums might be glazed and that can effect the holding power of the brakes tremendously when parked, especially on a hill. Once you've got everything adjusted try throwing some bon ami or other abrasive cleanser, or even a handfull of find sand in the drum and do a few slow stops in the drive or somewhere safe. It ought to cut the glaze on the pads and drums and take care of the problem if that's what it is.-----As far as the problem I found with mine, it turned out to be in the slack adjusters. I did a complete brake job including replacing the cams, the cam bushings, and all the other "normal" parts. In 5 years the truck has always stopped Ok but not like I thought it should. With the new parts and everything adjusted per my buddies advice it'll slide the tires now. Idiot was stopped in the middle of the road coming out of a blind curve the other day and I got a chance to really test them...he was lucky, they work great now.... Good luck with yours. Let us know what you find.

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Tim in OR

08-10-2007 22:46:37




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 Re: Big truck parking brakes in reply to Roy Suomi, 08-10-2007 20:22:45  
Try tapping the brake drum to make sure you have the slack adjuster tight before you back off that magic 1/4 to 1/2 turn. I have been know to turn the adjuster the wrong way, and have the adjustment WAY off. The drum won't ring if the brakes are tight.
good luck,
Tim in OR



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johndeeregene

08-10-2007 20:41:08




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 Re: Big truck parking brakes in reply to Roy Suomi, 08-10-2007 20:22:45  
what adjustment did you do?



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Joe in Ne

08-10-2007 20:36:43




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 Re: Big truck parking brakes in reply to Roy Suomi, 08-10-2007 20:22:45  
Tighten up tight and back off 1/4 to 1/2 turn. Thats how I do on mine.



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