School Bus Fleet Magazine Forums
Home | Profile | Register | Active Topics | Members | Search | FAQ
 All Forums
 Professional Garage
 Enter Forum: Professional Garage
 Meritor Wabco 4 wheel disc brake system #2
 New Topic  Reply to Topic
 Printer Friendly
Author Previous Topic Topic Next Topic  

CISDbusman
Advanced Member

305 Posts

Posted - 03/01/2016 :  07:34:05 AM  Show Profile  Reply with Quote
I bummed the thread title as I don't feel we can have enough info on these things.

I posted earlier about loosing prime to the pump for the e-brake. After lots of reading I found that its the front pump that controls the e-brake and if I remember correctly the brakes on the front axle. I cut the e-brake cable connector and got the bus in a stall. Brakes felt spongy so the entire system must share pressure from both pumps somehow??

Anyway.... I pulled the one 30 amp mega fuse on the fire wall and couldn't bleed the pressure off the accumulators as one pump still ran as needed. UGH!! I pulled all the relays and fuses I could find and still couldn't bleed down the system. I finally decided to pull all the connectors off the brake unit under the bus. This quieted both pumps and let me bleed the accumulators off.

After reconnecting the wires both pumps came on and sounds as they should upon shutoff. P-brake releashed and everything seemed fine. front pumped reprimed!!

Fast forward about a week. I take bus out on the am route and all seems fine until the brake pressure light comes on briefly then the service e-brake light comes on then the entire dash lights up. Golden triangle and all....... Video below. Sorry for the orientation of the video!! I have no idea why it uploaded like that.

https://youtu.be/HZusg52RMEQ

I feel I need to be chasing a bad/high resistance ground. This is my next plan of action. Any thoughts as to where to start?

Thanks all!!

Edited by - CISDbusman on 03/01/2016 2:28:37 PM

krmvcs
Advanced Member

362 Posts

Posted - 03/01/2016 :  08:33:58 AM  Show Profile  Reply with Quote
that is crazy. i wonder if youve got some odd electrical issues related to the brake switch on the pedal. just for kicks what would happen if you unplug the switch?

-Ken-
Go to Top of Page

exmod110
Senior Member

150 Posts

Posted - 03/01/2016 :  2:19:02 PM  Show Profile  Visit exmod110's Homepage  Reply with Quote
Check for data link wire damage at the HCU connector, they are the yellow and green wires at the forward most end of the connector and are susceptible to damage. I had one that did some truly weird things like what you have going on. I also had the cruise switches inop and the exhaust brake switch light flashing at times with mine... I can't remember for sure but the wabco software would communicate no prob with only one of the 2 data link wires intact.
Go to Top of Page

CISDbusman
Advanced Member

305 Posts

Posted - 03/01/2016 :  2:24:57 PM  Show Profile  Reply with Quote
quote:
Originally posted by krmvcs

that is crazy. i wonder if youve got some odd electrical issues related to the brake switch on the pedal. just for kicks what would happen if you unplug the switch?



I'll do just that once I get it in the shop. It was in the storage barn when I shot that video.
Go to Top of Page

CISDbusman
Advanced Member

305 Posts

Posted - 03/01/2016 :  2:27:02 PM  Show Profile  Reply with Quote
quote:
Originally posted by exmod110

Check for data link wire damage at the HCU connector, they are the yellow and green wires at the forward most end of the connector and are susceptible to damage. I had one that did some truly weird things like what you have going on. I also had the cruise switches inop and the exhaust brake switch light flashing at times with mine... I can't remember for sure but the wabco software would communicate no prob with only one of the 2 data link wires intact.



I'll test out the wires you mentioned. Come to think of it my cruise wasn't working either. Seems like the fast idle worked that morning though!? Crazyness!!!
Go to Top of Page

torque
Advanced Member

Canada
358 Posts

Posted - 03/02/2016 :  1:09:30 PM  Show Profile  Reply with Quote
Remove the brake switch on the underside of the master. Check for brake fluid contamination. If so you will need to replace the brake switch, BUT you may need to replace the complete master cylinder. On early models you cannot replace just the switch, and if you do, the clearance is not enough and your brake lights will flicker going down the road, loose cruise etc.
If it is a later master that you can replace just the switch, sometimes the fluid is present over time and the master is not necessarily defective. Check with your dealer to see if you can try just the switch or have to buy the complete master.
This switch could be causing the loss of cruise and warning lights, but the master may be part of you spongy pedal feel.

Keep in mind when diagnosing this system, there is NO DIRECT link between the master cylinder and the calipers. The pressure from the master goes to sensors in the brake module, then the module does all the work applying the brakes.

So if the pedal feels spongy, you would bleed where the lines from the master go into the module.
Make sure when the accumulators are freshly filled there is not a vacuum when you remove the master cap. It must be able to breath to allow for the large volume of fluid moving to fill the accumulators or it wont be able to build pressure.

This is a complex system, but once you sit with it for a while, and it definitely helps with the tool box software to see what it sees, it isn't as bad to troubleshoot.

Hard to tell, but you may have a couple of problems going on here by the problems you are having. But you gotta start somewhere :)
Go to Top of Page

CISDbusman
Advanced Member

305 Posts

Posted - 11/17/2017 :  04:21:57 AM  Show Profile  Reply with Quote
Time to revisit this issue. Bus has 'sat" for an extended period of time. We get a new Admin and fleet questions arose. Bus ends up on a hook to a nearby shop. They had no clue busses even had this system... I am asked to DRIVE it now 75 miles to our local IH dealer. Dash went crazy for about a minute at start up, then never made a peep the whole trip. Local dealer keeps it about 3 weeks, could not "replicate" issue. Changed the positive multi fuse battery cable in the battery box and said come get it. $500 FOR HOOK, 2K at dealer. Bus doesnt act up for almost 2 months. It is giving the same lights and buzzer as it did in the video above. E-brake locked up on me during route and after about 3 minutes of fighting with it, everything went back to normal. "Boss" is ready to sell it, but I feel its to good a bus to give away and have been pleading for its life.

I have it in the shop now and can replicate all the lights/buzzers by moving around the harness connector/wiring to the brake ECU under the bus. Wonderful place for a ECU and a 31 pin connector!!!! Grr!

I guess now I need to know is a complete harness connector available with short pigtails on it to splice in or do I need to order up some connector tools and terminals and do exploratory surgery on the connector?
If the later what release tools are recommended for the terminals in the connector?

Help me save this bus and my pride!! :-)

Edited by - CISDbusman on 11/17/2017 04:28:07 AM
Go to Top of Page

Thomasbus24
Administrator

USA
4544 Posts

Posted - 11/17/2017 :  05:01:09 AM  Show Profile  Reply with Quote
Look on the bright side...if you are still ordering IC and hydraulic brakes, this nightmare system has been placed into history's dumpster (where it belonged on day 1).
Go to Top of Page

CISDbusman
Advanced Member

305 Posts

Posted - 11/17/2017 :  06:05:31 AM  Show Profile  Reply with Quote
quote:
Originally posted by Thomasbus24

Look on the bright side...if you are still ordering IC and hydraulic brakes, this nightmare system has been placed into history's dumpster (where it belonged on day 1).



Really? What have they gone to insted of the train wreck we have now?
Going all air brakes from here out if I can get my drivers to complete their air brake certs. Getting tough!!
Go to Top of Page

Thomasbus24
Administrator

USA
4544 Posts

Posted - 11/17/2017 :  08:35:52 AM  Show Profile  Reply with Quote
They tell me it's the old-school system with hyrdomax type setup. Park brake is a foot pedal like Bird and Thomas use.

I will stick with my air brakes though.
Go to Top of Page

drp53188
Senior Member

89 Posts

Posted - 11/17/2017 :  10:30:11 AM  Show Profile  Reply with Quote
You can get a pigtail for that connector from navistar or you can replace the front or rear harness assy.
as stated before this system is not that hard you just have to understand and work with the system to learn it.
The front pump did not shut off because the fuse for that is in the battery box.
Go to Top of Page

CISDbusman
Advanced Member

305 Posts

Posted - 11/21/2017 :  04:29:49 AM  Show Profile  Reply with Quote
quote:
Originally posted by Thomasbus24

They tell me it's the old-school system with hyrdomax type setup. Park brake is a foot pedal like Bird and Thomas use.

I will stick with my air brakes though.



Sounds about right! Thanks.
Go to Top of Page

CISDbusman
Advanced Member

305 Posts

Posted - 11/21/2017 :  04:35:37 AM  Show Profile  Reply with Quote
quote:
Originally posted by drp53188

You can get a pigtail for that connector from navistar or you can replace the front or rear harness assy.
as stated before this system is not that hard you just have to understand and work with the system to learn it.
The front pump did not shut off because the fuse for that is in the battery box.



The mechanical side of the system isn't bad. Understanding the electrical side is what separates the techs from the nut twisters!!

I found a PDF for International tech training on the system when it first came out and I learned a lot from it. Added link to PDF below.



Mine is all wiring issues!! I have known that from the beginning but tracking down the problem without a scan tool has been a real bear. I'm hunting parts now.

Anybody messed with the 31 pin connector on one of these things?? What does a person need to release the pins if I decide to fix what is in place.

Thanks all!!!

http://www.navistarlearning.com/dotnet/application/downloadcontent2.aspx?flag=&content_id=12379

Edited by - CISDbusman on 01/23/2018 04:40:07 AM
Go to Top of Page

namao
Senior Member

Canada
89 Posts

Posted - 11/21/2017 :  06:05:25 AM  Show Profile  Visit namao's Homepage  Reply with Quote
Had to replace two of thoughts connectors over time because of rock damage, not fun. I ended up buying this kit https://www.summitracing.com/int/parts/wmr-w89732/overview/ seemed to have tools required for removing the terminals. not sure on the exact one but it has been helpful over the years on other connectors as well.
Go to Top of Page

TerryH
New Member

Canada
4 Posts

Posted - 11/21/2017 :  10:37:22 AM  Show Profile  Reply with Quote
sounds like the same issue i had on 2 of my bus's, all light s would come on,no cruise, exhaust brake & trac control switchs flashing, dash read out would say electrical fault, both times turned out to be Brake module.
Go to Top of Page

Donotpass
Active Member

14 Posts

Posted - 11/28/2017 :  06:30:47 AM  Show Profile  Visit Donotpass's Homepage  Reply with Quote
there is another brake fuse located in the battery box, with the clean power cables. id replace the clean power cables and check to see brake operation after.
Go to Top of Page

valleybusman
Top Member

USA
799 Posts

Posted - 12/02/2017 :  10:27:59 PM  Show Profile  Send valleybusman an AOL message  Reply with Quote
Awhile back I had issues with the same system .What mine did was while bus was running we filled the master to the full mark . Then it was turned off the fluid would climb and ruined the main power that works the brakes . We didn't know at the time that was the problem . So we bought a Meritor Wabco program . That's what steered us in the right direction . The program also has tests to check the system and re program things
Go to Top of Page

CISDbusman
Advanced Member

305 Posts

Posted - 01/23/2018 :  04:37:01 AM  Show Profile  Reply with Quote
I pulled my bus in and changed just the connector assy at the ECU. So far so good. I found my old connector to be in pretty bad shape. Both of the slide in connector retainers on the side were broken along with a couple of the clips that keep the two halves together. I also found corrosion on about four of the smaller reward wires (#'s 1-5). One being the 'IGN 12 VOLT" that I thought I had a intermittent lose of connection with. I assume from my studies that if the ecu senses a loss of 12 volts that it goes into panic mode and flashes the lights then locks the e-brake once the bus gets below 2 mph. A cycle of the ignition switch would bring everything back to working order when it last acted up. The corrosion on the wires I found, wasn't at the end where they make contact with the ECU pins it was in the area of the slide in side locks which is also the area where the terminal is crimped on. Any I found corroded in that area got a cleaning up and a dab of silver solder applied. All connectors were cleaned at the contact area with fine sand paper and I also hit the ECU pins.

Also to the dash showed "Electrical Fault" when I started it up to bring it into the shop for theses repairs.

Time will tell if I got a scald on it or not but I am feeling better about the repairs each trip out.

So I HIGHLY recommend a very good once or twice over of the bulk connector if you are having issues, especially the "Electrical Fault" showing up on dash.

I have a video of how that dash was acting Ill have to scrounge up and attach to this thread also.

Hope this helps someone else down the road.
Go to Top of Page
  Previous Topic Topic Next Topic  
 New Topic  Reply to Topic
 Printer Friendly
Jump To:
 


School Bus Fleet Magazine Forums © 2022 School Bus Fleet Magazine Go To Top Of Page
This page was generated in 0.2 seconds. Snitz Forums 2000