June 1-5 Air brake relay

Learning about air brake relays last week got me wondering what one looked like inside. I am a visual learner and could not picture what the text was talking about in regards to how it worked. So naturally, I set out to take one apart so that I could see the inside of it!

The relay valve is used to speed the application and release of the brakes. It gives the same amount of air pressure to the brake chambers as it receives from the foot valve or other source.

BTC hours: 10
Total: 301.5

Month of May. Wheel ends and brakes.

  Here we are at the end of May. Where did the time go? Best catch up what I have learned and done.

  We began to learn the basics of performing wheel end maintenance. Complete dis-assembly started with removal of the wheels and tires (obviously), brake drum, hub, bearings,  seals, s-cam, automatic slack adjusters.

  Inspection during this process is key. Even minor details can give you insight to deeper problems that may be easily missed. Uneven wear on the tires, for example, can indicate not only a misalignment, but worn bearings that need to be replaced. The drum is inspected for odd wear as well, measurements are taken of the interior to ensure it is still in specification.

  Typically I will remove the brakes next and inspect them to insure that they are wearing evenly and are not worn past the specified wear indication mark. We used several specialty spring removal tools, however, one tool in particular I found to be the most useful (pictured to the left). The rollers were also removed and cleaned.

 

  Next, hub and bearings are removed.


  S-cam removed and measured. I ended up replacing the bushings on a few wheel ends as I had more than 5 thousandths of an inch play in the S-cam.



Bearing were removed and cleaned, it is important to note that bearings should NEVER be allowed to sit with no kind of protective oil/lubricant because they will rust. Inner and outer race is to be visually inspected. I also replaced the hub seal on multiple wheel ends. There are two types that we used in class. Hand pressed and seals that require a drive. Hand pressed need to have a light coating of wheel end lubricant on them before installation.



When all said and done and the wheel end is being re-assembled the wheel end must have .001"-.005" free play. This is accomplished by torquing the wheel end nut to proper torque specs. The procedure usually has you torque to aprox. 200 ft.lbs while rotating the hub assembly, backing off a full turn, torque again to 50ft.lbs while rotating, then backing off aprox. a 1/4 turn. In the end you should have between .001"-.005." of free play.

Re-installing the wheels is pretty straight forward. Lugs for the trucks I was working on ranged in torque ratings from 450-500ft.lbs.

This concludes the month of may and my wheel end assignment.

BTC hours for 5/11-5/29: 45hrs.
Total hours: 291.5

4/27-5/8 Wheel Ends

These last two weeks we began focusing on wheel ends and all the nitty gritty that comes with that. We learned the importance of accuracy in torque specifications as we listened to many stories of not only wheels falling off, but breaks failing as well as S cam assemblies falling apart. The most interesting wheel end we worked on was brakes off of a front end heavy duty Cat loader. It had internal hydraulic dis brakes. Unfortunately, the steps to get to these brakes required us to remove components off of the axle that weighed more than Thor's hammer which required us to use the shop crane and some rigging to move. I learned a great deal and gained a base knowledge of wheel ends and air brakes that I believe I will be able to build upon and further as my career progresses.

BTC Hours: 24
Total Running Hours: 216.5

Cat loader axle

 Me and Cody did a little custom work to the shops hand truck, gave it larger hard plastic wheels that would not fit on the old rod so we welded on a longer piece.

 Taking the S cam and components apart

Checking inner drum diameter 

Some disc brakes off of the freightliner

One of the final projects of last week.

(4/20-4/24) Electrical Reflection

Jeff wanted us to answer the following questions in regards to our introduction to electrical:

1. How do you know what you know you know?

2. How do you know what you know that you don't know?

These questions were referencing to shorts, voltage drops, and opens in a circuit. I know these things because we have seen them demonstrated in class.

A short, for starters, is a pathway that provides less resistance than the intended route for current to flow through. This results in the circuit not providing the intended load with power. In many cases a short will cause a larger amount of current to flow through the circuit causing the fuse within the circuit to overload and blow. An extremely useful technique we learned to help isolate where the short in the circuit is located was "replace the fuse that blows with a fuse that glows". In other words, replace the fuse with a light bulb. This will allow you to isolate where in the circuit the short is located. If the circuit is still shorting out the bulb will illuminate.

Voltage drops are areas of the circuit that are placing excessive resistance to the circuit and thus causing the voltage in the circuit to drop. They may be caused by loose connections, corrosion of the cables or wires, improperly sized wires or cables, and improperly crimped connections. Voltage drops may be found on the power side of the circuit as well as the ground side of the circuit. Once completing the test on both sides, both measurements will be added together to find the total voltage drop in the circuit. A general rule of thumb to use is if more than half a volt (.5) is found in the circuit, then the circuit has a problem that will need to be found and fixed.

Finally, we have opens withing a circuit. Opens are fairly easy to explain. A circuit needs to have a pathway to the ground of the circuit for the current to flow freely. If an area of the circuit is damaged, say a wire has been cut, now the circuit has been "opened". The current cannot complete it's intended course and the system does not operate.

This is just the tip of the iceberg for electrical. But at least we now have a firm foundation in the basic knowledge of a circuit and I know it will greatly assist me in my career in the future.

In regards to the second question, I suppose I have a hard time seeing how to use this knowledge in the real world. I know that once I get more experience in real world scenarios, it will make more sense. It's hard for me to visualize these circuit boards as actual trucks versus a board laying on the table. Most of my uncertainty comes from there I suppose. 

BTC Hours: 12
Total Hours: 192.5

4/13-4/17: Light Bulb!

The most profound thing I learned last week had to be in regards to a circuit board we used that simulated the running lights on a truck. Everything worked as it was supposed to on the board, however, we were asked an interesting question. Why did the turn signal light alternate on/off opposite as the brake/turn signal light when the turn signal was activated?

As you can see, power goes to both bulbs when the lights are activated. However, when the turn signal is activated through the board, a relay is activated and sends power down through the right hand side of the circuit which leads to the RH Front park/turn light and sends positive flow to the other side of RH right marker light and thus taking away its closed circuit. When the relay disconnects the current flows back through RH right marker light and has a complete circuit by making RH front park/turn light essentially a ground. 

O2 vs "Air"

Terminology is critical. Especially when using an acetylene torch. Oxygen should be referred to as an oxidizer or just O2. When you call it "air", it can be misinterpreted and used for tools that should never have pure oxygen plumbed into them. Such as a die grinder. The following image was from the VMMC that the Lincoln rep was passing around. The gentlemen who used this tool miraculously lived. Just because there is an attachment that looks slightly like an air compressor hook up does not mean it is just compressed air. In this case a custom attachment was made to plumb his die grinder into pure O2. The result was a bright flash of blue and temperatures that melted the tool. Always know what you are using and make sure you know the terminology.

 

4/7-4/10 Introduction To Electronics

We are getting an introduction to electronics this last week. A lot of information to process and hold onto. For starters, we learned about Ohm's Law, which states, "that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship." 

A very useful visual picture to help in the application of this law has been the following pie chart 

There are three basic circuits: Series, Parallel, and Series-Parallel 

Series is, as the name suggests, all the loads in the circuit are in series. 

Parallel circuits have there loads branching off of the main line and are placed along side of each other. 

And as you can imagine, series-parallel is a combination of both. 

We had an introduction course to the basics of electronics which had a practice test at the course. It did not give me a final grade so I took video. 

Hours: 10
Hours Total: 168.5