Friday, May 06, 2016

Park Brake Not Releasing C2 School Bus

Park Brake Not Releasing C2 School Bus from John Whelan on Vimeo.
The park brake on a Thomas C2 school bus has an interlock that requires the service brake to be applied before the park brake releases. Most of the issues we had was the stop lamp module and park brake module located at the air management unit depending on the year of the bus the bank of modules are at the very back in front of the differential housing or behind the transmission.

There was a recall years ago regarding the stop lamp switch located on the right side of the AMU looking towards the back end. The problem was the internal switch wasn't contacting properly so Thomas revised the design and there have been very few problems since then. If you go into  accessfreightliner you can bring up the AMU layout for the VIN you're working on.

The park brake light on the dash is a warning to the driver not to drive away with the park brake on, When a driver pulls out the park brake valve the modules sense this and through the J1939 messaging system air pressure changes trigger a signal that is sent back to the dash illuminating the park brake light. When you come to a stop and shut down the engine if the park brake valve is not activated this triggers an alarm until the park brakes are applied.

Unless there's an air leak most of the trouble with AMU modules is the switch contacts. The first check is to see if the brake lights are working if not the stop lamp switch in the module can be tested by jumping the signal to the bulk head module bypassing the internal switch in the module. If the brake lights work there is a problem internally with the stop lamp module.

The same test can be done with the park brake module. In the video the two terminals that sends signals to the BHM are jumped and if the park brake indicator light comes on then there is an internal problem in the module itself. There are only two wires to this module so it's a straight forward test. Most of our troubles have been with these 2 modules.

Also you can not rule out opens and resistance in the wiring harnesses. This is another possibility that you might have to deal with. If you have a Freightliner dealer in your city you need to get a user and  password to the accessfreightliner website. Here you will find the schematics and troubleshooting required to fix an electrical problem. Without this information it's very difficult to blindly find an electrical fault especially with multiplexing that's here to stay for a long time.

Wednesday, March 02, 2016

Hard Start DT466E

DT 466 ENGINE OIL PUMP from John Whelan on Vimeo.
The regular engine oil pump supplies the HEUI high pressure pump so since the supply wasn't meeting the demand we had a hard start situation. The engine oil pressure regulator appeared to be scored so we attributed the lower oil pressure to that defect.

The oil pump drive and gears had looked alright but who knows what a little wear will do. It could be thousands of an inch causing problems. So after replacing the pump and regulator and using 0W40 oil for the cold start season starting improved drastically. Once we pulled the engine hood off of this bus which was a conventional international 4300 getting at the parts was a breeze.

There was no laying on our backs except for removing the oil pan. One characteristic with all of our DT466E diesel engines was they ran like crap when they were cold. It took some time for the oil pressure in the high pressure side to regulate itself and provide the oil pressure to the injectors. A lot of injector problems were with the injector o-rings that separate the oil from the fuel. They would deteriorate and create an engine miss.

The last of these buses got sold to a church group who took them down to Guatemala. They shipped them by boat the second time around because of an incident while travelling through Mexico. Those road blocks cost a lot of money and you have to watch your back at all times. I talked to a Mechanic who just left to go down there and so some repairs. I hope he has all of the tools and parts he needs. The technology down there is not up to speed so if something breaks it gets fixed in what ever way possible.

The DT466E being electronic needs diagnostic software to analyze faults so I hope the 2 engines stationed down there last for a long time and don't give them grief. I donated a few old parts sitting on the shelf for the air dryer. The mechanic said the air compressor isn't building up very fast. The air dryer most likely needs servicing since it takes out all of the \moisture and oil from the system. Leave it too long and a restriction will build up slowly but surely.

Wednesday, January 20, 2016

Mercedes MBE 900 Parked Regen

Using Mercedes Software To Perform a Regen from John Whelan on Vimeo.

In 2007 everything changed for diesel engines. The newly integrated emission systems were now the most important cog in the wheel. They had to meet certain parameters according to the onboard computer programming and if they did not an engine code would appear and stare you in the face until the fault was repaired. At first it was frustrating since we had not worked extensively on these emission controlled MBE 900 models.

The Mercedes dealer become regular aquaintances and saw our buses many times over the 5 year warranty period. Engine codes appeared then went away and popped back up again a couple of days later and so on. Once warranty expired we knew it was time to get into these engines more than ever. The online resources called DDSCN was very helpful along with the Detroit Diesel engine software we had loaded up on our laptop.

There was a lot to absorb since everything was monitored by the MCM (motor control module). Turbo boost, EGR and diesel particulate filter cleanliness determined how well these engines were going to run. Once there was a restriction in the DPF a regular code 'dpf out of range high' would pop up until we did a parked regen or repaired a sensor or plugged up sensor air line. Without the diagnostic software we could not do a thing to get these engines back in shape.

The DPF section in the software allows you to watch all of the temperatures in the DPF and DOC. The differential pressure indicated if there was a restriction (3 psi max). The video goes into a parked regen where the temperatures go as high as 1,000 degrees cooking out the DPF. This half hour process does the job and most times it makes a huge difference in driveability.

Another option to troubleshooting was an over the road regeneration where you could monitor the regen process while on a road test and record the data. The Detroit Diesel software is very good for narrowing down a problem. Once there is a code the software can troubleshoot the code step by step which really made life easier for the techs.

The filter cartridge in the DPF is replaceable which we had to do a few times because the regen process was not working. It's similar to an air filter that you clean out and stick back in the cannister. Eventually it's not going to clean up properly over time due to the compounded accumulation of debris. Soot and ash are a never ending problem throughout an emission controlled diesel engine and the MBE had lots of that with sensors plugging up and EGR valves sticking.

They are definitely not the perfect engine when combined with emissions but working on them and gaining experience helped our shop know what steps to take whenever a fault occurred.

Saturday, November 28, 2015

Air Brake Job Using Machining Tools

Machining School Bus Brake Shoes from John Whelan on Vimeo.
The lathe in the video makes a complete cut on the brake shoe allowing 100% contact. This is necessary when a chatter or brake pulsation is occurring with brakes applied. We used to machine all of our brake shoes on all brake jobs but found it to be time consuming. Now we replace the drum and shoes plus hardware.

There have been some cases where the contact is not favorable and machining was necessary. Our buses use all sizes of brake shoes from 6 inch on the steering axle to 8.5 inches on the drive axle. All air brakes come standard with automatic slack adjusters. I talked to a sales rep from Canadian Brake and he says there are still customers who purchase manual slack adjusters. I haven't seen one of those for years.

Since we run a fleet of school buses it's policy to replace the auto slacks every brake job. There is only one drive axle so 200.00 for a couple of slacks is nothing. Spring brake pots get replace every 5 years. Our choice is to use MGM piggy back pots because of their superior quality. For an extra 50.00 that's great insurance.

A few months ago I attended a trade show in town and talked to the Haldex slack rep and he informed me to not grease them too often. This will disable the mechanism with the hydraulic effects of the grease. We have auto grease systems installed on our S cam tubes and slack adjusters. That has caused grease leakage on to the brake shoes from over greasing which is picked up by the government vehicle inspectors.

If it's bad enough the wheel has to be removed and shoes cleaned up. This is a procedure we want to avoid so now we advise the auto grease system installers to avoid hooking up to those areas including the steering box bearing. That's another spot the DOT makes notes on during their fleet inspection thinking it's a seal leak.

Getting back to the brake lathe it does wonders on pesky brake problems that the operator experiences. There was one time when we just kept machining down the shoe material until there was a total 100% contact to fix a pulsation. The drums had to be machined as well. There was a lot of material removed to accomplish this but the front brakes last twice as long as the drive axle brake so it was worth the labor to do so.

Sunday, October 04, 2015

Cat 3116 Tune Up Tools and Procedures

CAT 3116 Diesel Engine Tune Up from John Whelan on Vimeo.

Cat 3116 Injector Adjustment

The video shows how the Cat Tuneup Tool Kit works on a 3116 diesel engine. When the injector is installed I find it's easier to place the dial contact on the injector by feel and then having a look to make sure it's seated properly. In the Cat tune up kit you need the dial indicator, contact point, timing gauge block and magnetic base.

On top of the valve cover is a data plate that has the factory timing spec. This is the reading that you need to stick to when the timing tool is all set up. First of all you need to preset the dial indicator on the timing gauge block and set it exactly to 62.00 mm.

Rotate the engine so cylinder #1 is on the compression stroke. Both valves will be closed and cylinder #6 will be on the exhaust stroke. Injectors 3 5 6 can be set in this position along with 1 2 4 intake and 1 3 5 exhaust valves. (Intake .015 in exhaust .025 in) The injector spec on the valve cover can vary plus or minus .020 mm.

Rotate the engine 360 degrees and adjust the remaining valves and injectors. The Cat tool kit comes with a manual and gives you a detailed step by step procedure for these adjustments. It's a fussy operation but once everything is set these engines run very nicely. Keep the valve adjustment on a regular schedule because of a weakness in the exhaust valve stems that blow apart if there running at high temperature and rpms.

I hope the video gives you a better idea what's involved with injector set up on the 3116. The entire tune up kit is pricey and the last time I checked it was up around $4000.00 Canadian. We had to purchase it however that was in the mid 1990s and we paid much less than that. You can not get away with setting up these engines (except valve adjustment) without the kit.

Thursday, September 24, 2015

Cummins ISC Diesel Engine Turbocharger Failure

Cummins ISC Turbocharger Replacement from John Whelan on Vimeo.

This failure occurred without any notice. In the video you can see the nut that loosened off and backed right off of the turbo shaft. Once this happened it caused seizure and a large amount of oil started pumping through the intake system. The turbo bearings are lubricated with pressure engine oil so there's a big mess when this type of failure happens.

The oil did help in a way flowing into the charge air cooler and leaking out a crack in the cooler core. So replacing the charge air cooler was added to the list. Once the turbocharger was replaced with a re-manufactured unit along with the charge air cooler this engine was back in business. It's important to flush out the air piping in case debris got trapped. The steam cleaner does wonders for this type of task.

Preventing this failure would be hard to do since normal preventive maintenance does not involve removing air intake and boost piping for inspection during a service. This would take too much time so the only other clue would be poor boost performance or turbocharger noise audible to the mechanic or driver.

I hope you find this video informative as food for thought. A failure of this kind will happen again undoubtedly somewhere...somehow. It falls under the "how the hell did that happen" category. If you have a comment please state it below. I like to get feedback form readers who have gone through something similar.


Monday, September 21, 2015

School Bus Pusher Radiator Removal Shortcut

Changing the radiator or removing it for repair at the local radiator repair shop is a big operation on the pusher school bus. The charge air cooler, oil cooler and radiator are sandwiched on top of each other making it hard to get the radiator out of the chassis.

The objective in this video is to show you a short cut that all mechanics love to do saving time and some frustration. The way we do it is to support the upper components and loosen off the radiator mounts. The frame supports have to be loosened as well to allow space so the the rad core can be removed freely.

The cooling fan which is a Parker system is braced to the main frame around the radiator so it needs to be chained up out of the way. In most cases if the radiator is original and has a leak the chances of repairing it is remote I'm sorry to report.

This rad core is over 12 years old and has gone through a lot of weather and road debris kicking up into and around the core area on a daily basis. There are cores out there but we had to get one from Thomas buses. I hope this video helps you bus mechanics out there.

I would appreciate it if you shared or commented on this post. It's great to get some feedback from others who have had similar problems and found a faster way to get them done. Time is a precious commodity in a fleet garage and with that said I'll continue to share videos on repairs that will help out fellow mechanics.

Watch the video below on what our shop did to remove the radiator on a pusher school bus:

Radiator Repair Thomas Pusher School Bus from John Whelan on Vimeo.

Thursday, August 13, 2015

A Common School Bus No Start Problem

Thomas School Bus Vandalock

This a common no start problem with all school buses and will continue to be since Vandalocks are standard equipment. The Vandalock as the name states locks out the start circuit and locks the access entries to the inside of the bus. The Thomas pusher in the video does not have any lock out for the entrance doors just the side door and rear emergency exit window.

However there's a cheap and easy solution which is to purchase a metal bike lock (u shaped) and install a couple pieces of angle iron to the entrance door leafs. We only do this with our sports run buses which do a lot of out of town trips. Just recently one of our sports run pusher buses were in Vancouver and the batteries got ripped off.

This is the first time this has ever happened to us perhaps because of the high return for lead at the scrap yard or someone with a truck needed a good set of batteries? Who knows but it's the sign of the times so a lock will be going on both of our sports run battery doors. The service call cost $800.00 in total so a couple of $20.00 hinge locks is a solid investment.

Getting back to the Vandalock system...when we talk to our drivers over the radio we can usually run them through the steps to check all of the exits to see if the latches are either locked or unlocked. One of the students could have very well kicked the latch closed since it's in the perfect spot on the side exit door as seen on the video.

The buzzer will stay on with the ignition key on with no engine crank until the latches are disabled. Vandalock systems are great to have as long as everybody is trained properly.

International School Bus Vandalock 


The International school bus vandalock is the same principle as Thomas buses but designed totally different. The conventional models have the entrance door and the rear door set up to lock out access and the engine start system. The video demonstrates how it works but the there is a minor flaw with the lever that activates the micro switch above the entrance door.

This micro switch has to be activated for the bus to start. Every year we have no start problems because of the lever dropping down while the bus is enroute. A rough road condition will cause this and the lever will drop down deactivating the switch causing an engine no start ... alarms will stay on while the ignition is turned on. One solution is to tighten the lever fastener to increase resistance but ever so slightly so the activating rod has enough push to move the lever.