Locomotive Fault Question

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New Member
A couple weeks ago, I watched a westbound train make a lift from a certain spot that is on a fairly heavy grade for westbounds. When this train stopped, the entirety of it was on the hill. It was powered by two SD90s. Once the train was back together, the engineer throttled it up and got everything moving. When they went by me I could hear a "blowing" noise (quite loud) coming from the second unit. I then heard the units back off to about half throttle, the blowing noise continued. After a few seconds they both went to number 8 again. I then heard the engineer ring up the RTC, and when she answered he said that he was getting alarms from his second unit, and that he would go back and see what was wrong as soon as they topped the hill. The hill only being another mile or so long, I followed.

Like I said, the noise sounded like blowing air, but very loud (I could hear it as I drove past on the highway which is 200+ feet away). Once they stopped, the engineer went back, cut out a truck and then continued.

What exactly was this "blowing" noise?? I can't figure it out for the life of me.


New Member
I second Jeff. There is a flex hose that feeds the brake cyl's. My guess is it burst. We don't change them unless it's bad so it could be the original one. I have seen one's on old switchers that look older than dirt and one's that look new but have a cut/hole. The piping feeding the cyl's is all hard lined and ridged so I wouldn't think there was a leak there. I also wouldn't think it was a brake cyl cup, they go bad and leak somewhat quietly.

Now that I typed this I got to thinking. Where on the unit did the crew member cut it out? If the train was rolling past you while blowing there shouldn't be any air going to the cyl's when released. Was it at the back or front of a unit? If it was that is where the MU hoses cutout cocks are located. The cutout cocks are either underneith/behind the stepwell or just in front of the steps. In that case there was a problem with a MU hose.


New Member
The blowing sounded like it was coming from the rear of the unit, but it's tough to say for sure. I didn't get a chance to see where he cut it out as it was dark out and I was on the other side of the unit. After the truck was cut out he said that there was no dynamic braking on the second unit now account of cutting the truck out.

I believe the unit was the UP 8282.


New Member
In that case he must have cut the truck. However the dynamics are not affected by the brakes. As a matter of fact when an engineer goes into dynamics the DBI (Dynamic Brake Interlock) will dump the air if the engineer did have them applied.


Sounds more like a ground issue to me. The blowing air could come from a number of things, but I don't think it is related to the issue. If he stated that the dynamics would be lost on the second unit, it means he cut the truck out electrically, not pneumatically. Not sure with EMD AC units, but GE AC units will still have dynamics, albeit reduced, with one or more motors cut out on the same truck.

CN Sparky

Electrician at CN
Without hearing the noise, it could have been anything. There are many different places for air to leak on these units.. It could have been the air dryer or main res with a sticky blowdown valve. Happens all the time on our units.

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