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joeheb
Senior Member
121 Posts |
 Posted - 09/28/2012 : 06:44:08 AM
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I have a 2002 International Blue Bird mid size bus, problem with the braking. When the brakes are applied, the rear end dog tracks to the right. I've performed the following repairs:
1. Replaced all s-cam bushings. Wore out.
2. Checked psi. at all 4 corners. Same psi. all the way around.
3. Replace front spring bushings. Wore out.
4. Replace both rear slack adjusters,one was bad.
5. Replaced both rear brake chambers.
6. Cut all drums to ensure roundness. Brakes all the way around are like new. Rear drums like new.
7. Replaced rear ABS vavles from sister bus. Didn't make a difference.
8. Replaced rear torsion rods.
Any suggestions why the rear end dog tracks when brakes are applied? I just joined this forum today,hopefully someone can help. Thanks in advance. |
Edited by - joeheb on 09/28/2012 06:46:46 AM
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pmorris
Active Member
15 Posts |
Posted - 09/28/2012 : 12:02:45 PM
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| did u check rear tie bolts |
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joeheb
Senior Member
121 Posts |
Posted - 09/28/2012 : 12:16:30 PM
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| Do you mean U bolts? It's air ride. |
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eicsbus
Senior Member
Canada
126 Posts |
Posted - 09/28/2012 : 12:36:40 PM
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| just a thought chk your r side spring center bolt and for loose u-bolts |
I.C. NO FUTURE
formally ,,,,wright11 |
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joeheb
Senior Member
121 Posts |
Posted - 09/28/2012 : 12:51:02 PM
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| The spring is only a helper spring, it's mounted to the rear axle with U bolts. It's actualy a Z spring, no shackles to the frame like on the front spring. It's air ride. I've never seen this happen before, 24 years turning wrenches. |
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Thomasbus24
Administrator
USA
3169 Posts |
Posted - 09/28/2012 : 1:14:28 PM
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| Did it start after a brake job? (You say the brakes are like new, made me wonder) Are you certain all the shoes are the same hardness? I could see a mislabeled shoe ruining your day! |
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joeheb
Senior Member
121 Posts |
Posted - 09/28/2012 : 1:24:22 PM
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| Shoes were replaced 6 months ago, may have been doin it then but driver didn't say anything about it. It's a different driver in it now and he wrote it up for that problem. |
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Fastback
Top Member
720 Posts |
Posted - 09/28/2012 : 2:12:32 PM
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| Check the rear air suspension axle u bolts, they support the weight of the bus on the air ride supension and can stretch allowing axle to shift. A give away indicator that the u bolts have stretched is air bags that don't appear plumb. |
Why yes, the ORIGinal CHARGER is a Fastback |
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joeheb
Senior Member
121 Posts |
Posted - 09/28/2012 : 2:39:41 PM
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| You may be on to something Fastback. I noticed this week that one of the airbags isn't quite plum. I'm gonna give it a shot and replace those rear U bolts on Monday. |
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tigger2
Advanced Member
USA
230 Posts |
Posted - 10/01/2012 : 05:27:34 AM
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| The u bolts come loose and the pin in the top of the axle housing gets sheared off and the axle has no way of staying in place no matter how tight you get the u bolts. Very common on road tractors with navistar corporate air ride. not so much on school buses but it will still happen, the hole in the bottom of the pad on top of the diff housing is quite a bit larger than the diff housing pin. When you replace u bolts do all of them and push the diff housing all the way to the rear tight against the pins so when the driver hits the big chuck hole the diff will already be back there. |
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joeheb
Senior Member
121 Posts |
Posted - 10/01/2012 : 06:12:25 AM
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It's difficult to explain, but the Z spring is not mounted at all to the frame like the front end spring is mounted with shackles. The only thing that keeps the rear end inline is the 2 torsion arms that mount to the rear axle, then to the frame. But I'm still replacing all U bolts to see if that cures the problem. At this point I'm fishing. I'll keep y'all posted if that fixes the problem.
Yeah I'm from Texas y'all. |
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slippert
Advanced Member
USA
308 Posts |
Posted - 10/01/2012 : 10:41:02 AM
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Maybe I'm lost here, but if the bus dog tracks when you hit the brakes. I assume it still dog tracks after brake application? I would think it has to have a loose/broken component somewhere in the rear suspension and seems like it would be pretty obvious , be it a u-bolt or z-leaf, 1 of the 3 torque arms.
You said you replaced torsion arms is the axle square or was an alignment done? after replacement. you are saying there are 2 arms
You should have a third arm going from the axle to the frame, bushings do wear out in those also |
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joeheb
Senior Member
121 Posts |
Posted - 10/01/2012 : 11:21:33 AM
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| Torsion arms keep the rear end in line, doesn't dog track after braking, it goes strait as an arrow. That's what's got me puzzled, you would think it's something obvious, nothing is broke or loose on or near the rear end. Axle is square. |
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wocobus
Active Member
United States
15 Posts |
Posted - 10/02/2012 : 06:06:07 AM
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try disconnecting the front brakes and see if it still dog tracks .
thin try disconnecting the rear brakes.
you could aply the parking brake and pull on the bus and look for movemet. |
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joeheb
Senior Member
121 Posts |
Posted - 10/02/2012 : 06:12:57 AM
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| Waiting on the nuts for the U bolts they brought the wrong nuts. I'll try that out if U bolts don't fix it. Thanks for the response wocobus, will keep y'all posted. |
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wrenchmen
Senior Member
USA
115 Posts |
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joeheb
Senior Member
121 Posts |
Posted - 10/03/2012 : 09:22:52 AM
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| Well guys I replaced the back U bolts and still doing the same thing, I hate to do it but I'm going to send it to the experts for this one. All rear end parts are present, nothing is missing. Thanks to everyone who chimed in on this. I will keep you posted on the fix. |
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joeheb
Senior Member
121 Posts |
Posted - 10/18/2012 : 08:38:38 AM
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| Well after sending it to the experts for two weeks, they themselves could not fix the problem. They said that every part I replaced , they would've replaced also. So I'm now starting to think it's someting in the front end. I'm gonna totally disable the front brakes as someone had mention before to do and see if it makes any differnce. |
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Thomasbus24
Administrator
USA
3169 Posts |
Posted - 10/18/2012 : 11:23:07 AM
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| What a nightmare. |
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Offroadwolf
Active Member
41 Posts |
Posted - 10/23/2012 : 08:25:42 AM
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| Don't know if your have found the cure or not yet. A couple other things, is the alignment correct on the front and rear axle? Does the bus lean in the direction of the pull? Are all the steering components good, king pins, bearings, etc? Another thing lift the front end of the bus off the ground and start the bus. Does the steering float to one side on its own with the bus running? |
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eddo
Senior Member
USA
62 Posts |
Posted - 10/23/2012 : 2:37:39 PM
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ok, this might sound a bit off, but how new are the rear tires?
My IH trucks are all mid size, and if I put new tires on the rear, they will dog walk all over the place. Mine has never been a braking only issue, but it took forever for me to pinpoint that it was the new tires.
Tires with greater than 18/32nd's tread depth are bad until they get broken in. I can put new ones on with fewer than 18/32nd's and all is good (Dunlop, Continental used to,) but even one side new over 18/32nds and the drivers are screaming that they cannot keep control.
This may or may not help you out, but I hope it does. :) |
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slippert
Advanced Member
USA
308 Posts |
Posted - 10/24/2012 : 08:03:12 AM
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quote:
Originally posted by eddo
ok, this might sound a bit off, but how new are the rear tires?
My IH trucks are all mid size, and if I put new tires on the rear, they will dog walk all over the place. Mine has never been a braking only issue, but it took forever for me to pinpoint that it was the new tires.
Tires with greater than 18/32nd's tread depth are bad until they get broken in. I can put new ones on with fewer than 18/32nd's and all is good (Dunlop, Continental used to,) but even one side new over 18/32nds and the drivers are screaming that they cannot keep control.
This may or may not help you out, but I hope it does. :)
Eddo may be on to something, I have had similar complaints after new recaps installed. also found in the caps I have, that if I run more than 90 psi the drivers complain about rear end feeling loose or walking around on them.
after the tires are worn down some I can increase pressure if I want but actually seem to get as good or better wear on caps at 90psi.so i generally leave it there for life of tire. |
Edited by - slippert on 10/24/2012 08:03:56 AM |
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joeheb
Senior Member
121 Posts |
Posted - 10/25/2012 : 2:19:23 PM
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@ eddo, I know exactly what you are talking about when you put tires with tread greater than 18/32. We have one bus with Dunlop tires on it and it feels like you're driving on ice with it. We buy only new tires no recaps.
@ Offraodwolf, front end king pins were replaced 1 year ago, just replaced spring bushings,bearings are good, tie rods look good but that don't mean nothing. Haven't had the alignment checked.
By the way , I did totally disable the front brakes and it still dog tracks slightly to the right, not as bad as when the front brakes are enabled. Still not sure what it could be, front end? The alignment? That's where I'm at. Keep feeding me some more ideas and past experiences PLEASE!!!
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Offroadwolf
Active Member
41 Posts |
Posted - 10/25/2012 : 3:42:21 PM
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OK, let's start with the front end parts, something replaced a year ago doesn't mean its good now. Raise the front end off the ground and use a prybar to lift up on each wheel. Is there any play from either the king pin or wheel bearing? Also remember if you don't have a lift you can grease king pins on the ground, you have to take the wieght off this tires. While you have it jacked up sping the tires and check the brake shoe gap to the drum, does it change like the drums are out of round? Also swap the front tires to see if you have a radial tire pull, the pull will change when you switch the front tires left to right, if it's the problem.
Reading back through the thread you were saying it does wierd stuff when your brakeing and its fine driving. Have you checked the front springs to see if you have a sheered center bolt? Your going to have to raise the spring off the axle and look at it. You can buy replacement center bolts.
At that point if all this is good, take it for an alignment. Make sure they can straighten the front axle, this does mean bending it. They need to be able to align the rear end. And a very important note, the front axle caster is set with shims, do NOT let them use aluminum shims on your bus. They must be brass. Believe or not the aluminum shims will crush and break and fall out. If you have a good alignment shop explain all the problems you've been having and the things you have done. This whole thing just seems like an alignment issue. Let me know what you find. |
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joeheb
Senior Member
121 Posts |
Posted - 10/26/2012 : 05:21:49 AM
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quote:
Originally posted by Offroadwolf
OK, let's start with the front end parts, something replaced a year ago doesn't mean its good now. Raise the front end off the ground and use a prybar to lift up on each wheel. Is there any play from either the king pin or wheel bearing? Also remember if you don't have a lift you can grease king pins on the ground, you have to take the wieght off this tires. While you have it jacked up sping the tires and check the brake shoe gap to the drum, does it change like the drums are out of round? Also swap the front tires to see if you have a radial tire pull, the pull will change when you switch the front tires left to right, if it's the problem.
Reading back through the thread you were saying it does wierd stuff when your brakeing and its fine driving. Have you checked the front springs to see if you have a sheered center bolt? Your going to have to raise the spring off the axle and look at it. You can buy replacement center bolts.
At that point if all this is good, take it for an alignment. Make sure they can straighten the front axle, this does mean bending it. They need to be able to align the rear end. And a very important note, the front axle caster is set with shims, do NOT let them use aluminum shims on your bus. They must be brass. Believe or not the aluminum shims will crush and break and fall out. If you have a good alignment shop explain all the problems you've been having and the things you have done. This whole thing just seems like an alignment issue. Let me know what you find.
I checked the whole front end, king pins are good, bearings are good, I replaced front spring bushings and checked the front spring center bolts at that time, bolts are good. You make a good point about the front tires though, I'm goint to swap them around left to right... and see if that makes a difference in the pull. I'll keep you posted.
Thanks. |
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joeheb
Senior Member
121 Posts |
Posted - 11/06/2012 : 09:19:53 AM
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It's FIXED!!!!
It ended up being the front brakes and drums. They were replaced back in Feb. 2012. We're in the process of changing over to a new fleet system management and the work orders are in a mess, so when i looked back at the work orders, they were out of sequence. So long story short, the driver complained about the bus pulling to the left 2 weeks after the front brake job was done. So after this nightmare of a bus. It's FIXED!!! Someone had mentioned that if the problem started after the brake job was done. Thanks to everyone for all the help, this forum is awesome! |
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Thomasbus24
Administrator
USA
3169 Posts |
Posted - 11/06/2012 : 09:24:39 AM
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| Thank goodness it is fixed! Thanks for coming back to let us know the end result...all too often we never get to hear what the issue ended up being. |
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joeheb
Senior Member
121 Posts |
Posted - 11/06/2012 : 09:37:00 AM
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| @ Thomasbus24 absolutely. The bus rides like a Caddilac now, driver's happy. Yeah that made all the difference in the world replacing the shoes and drums even though they were new, that's why I dismissed it in the beginning that the front brakes were the problem. |
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Topic |
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Rear end dog tracks when brakes applied
