Western Railroad Discussion > Can a locomotive spin its wheels backwards?

Now before everyone jumps to conclusions about what sounds like a rather silly question. . . let me explain what I am asking about.

It refers to a couple of threads about the recent railroad wreck in Bayard, New Mexico where it appears that for whatever reason a train coming down a grade of maybe 2% "ran away", with the locomotive jumping the tracks and winding up on its side in a gully maybe fifteen or twenty feet below the level of the tracks, killing the three people in the cab. The eight cars the locomotive was escorting down the grade stayed on the tracks, went past the derailed locomotive, and then came off the tracks themselves, but not in such a spectacular fashion as the locomotive did.

There is some speculation that the dynamic brakes on the locomotive weren't functional, and that the air system was leaking, essentially leaving the train brakeless or at least with minimal breaking ability.

So my question is. . . .is it possible for a locomotive -- with a non-functional dynamic brake system -- to be put in reverse when it is going forward, resulting in the traction motors spinning the wheels in the opposite direction of travel?

Thanks in advance. . .

Yes, they could have "plugged" the locomotive. Not a best practice, but effective in some cases.

While I have no first hand knowledge, it was claimed that a early 1990's runaway on Cajon (that ultimately didn't derailment and came to a stop in the San Bernardino Yards) got its three SD40-2 locomotives into reverse. The traction motors were of course toast afterwords.

I've never tried it, but I've been told it could be "put in reverse", although rather than the wheels spinning backward, the traction motors would more likely lock up solid. Even if they didn't, I wouldn't think that the wheels spinning backward would slow it down any quicker than locked axles would.

The UP Cajon runaway in the early nineties did involve putting the locomotives in reverse and actually into throttle position one. Suprisingly it did little damage to the traction motors. The lead motor was actually a CNW SD 50 or 60, can't remember which. As an example of what NOT to do Santa Fe passed out copies of the event recorder tapes from that incident which I still have somewhere? Speed in that runaway reached over seventy mph, a miracle no one was hurt and very little damage to anything. A very interesting document. UP dodged a major bullit in that one.
JB

Put the reverser in a different direction while moving (say, reverse while going forward) on newer EMD's, and the unit will go into dynamics...

JB, hope your memory is better than mine. I recall news of an SP runaway train that derailed not far north of San Bernardino city limits? Was that also sometime in the 1990's? Seems like at least one of the SP crew survived that accident?

I "think" the SP runaway was in '89, it was dubbed the "Duffy Street Disaster", every thing but the rear helper unit derailed.
JB

3rdswitch Wrote:
-------------------------------------------------------
> I "think" the SP runaway was in '89, it was dubbed
> the "Duffy Street Disaster", every thing but the
> rear helper unit derailed.
> JB

I remember reading an article about that. Trona-train that was heavier than what they were told, shotty power etc. A reporter interviewed a SP engineer who said the head-end engineer should of at aleast tried reversing the traction motors.

Posted from Android

Best way is to Turn all the sanders on , Apply the independent brake, and apply full power in the other direction. This keeps the wheels from sliding from the full service brake application but the wheels are trying to turn backwards so they arn't adding to the speed of the train. There used to be a rule on the SP called Rule 13 Sand and this was that rule. But I have only read of such in Trains Mag. I have no first hand knowledge of this rule existing.

>Put the reverser in a different direction while moving (say, reverse while going forward) on newer EMD's, and the unit will go into dynamics...

Nope, all that will happen when you throw the reverser to "reverse" while moving forward is that one motor in each pair of motors will start generating and turn the other one backwards; this is what is called 'plugging". It makes no difference whether the locomotive is an EMD or GE (or even a Pennsy E-44). The situation with AC traction motors is a bit different.

This belief that spinning the wheels in reverse would help out is nothing but a myth. The coefficient of friction for a sliding railroad wheel is virtually nil. Think about it, spinning the wheels forward doesn't help a bit for trying to start a train or accelerate.

Lacking air brakes, dynamics are your best option. Without either of those, look for a (somewhat) cushy landing spot to jump.

In an emergency situation, you can reverse the locomotive, and open the throttle to R-1, but you will do damage to the wheels & traction motors unless you're going very fast. Probably every engineer on TO's has done that at some point to avoid a rough joint when backing down onto his train and things just aren't working out otherwise. They will most likely slide some, if not all the axles. After more than a few seconds, I would imagine the ground relay would trip and cut off any power you are trying to use backwards. Newer computerized engines might behave totally different, but the engine in this wreck looks like an older Geep of some sort. And of course the reverse worked quicker on older units with mechanical reverse gear, some used a motorized relay that took several seconds to make after the reverser was thrown, and even then wouldn't completely make contact until the throttle came out of idle. Most EMD DASH 2 models were like that. Hard to switch with because it took several seconds for them to load after reversing. You could hear the reversing motors whirring away in the electrical cabinet followed by a couple of clicks, then another click when you opened the throttle.

I can confirm that SD70MACS will go in dynamic braking if the engine is rolling in the opposite direction of the reverser. I remember SP engineers putting the SD9's in reverse and applying power to slow down, stop, and go the other direction while switching without using the brakes. I've done the same with a GP7 light engine at low speed, and it will bring you to a stop in short order.

Ted Curphey
Ontario, OR

I second that the dynamic brakes will come on when the reverser is reversed. This can make for a tricky situation when starting heavy tonnage on a grade. If insufficient throttle is applied to start a train up the grade as the air brakes pump off and release, the train may roll back a bit. If this is not corrected quickly enough and you roll backwards the sd70mac will transition over to dynamic and you will have to re-apply the train brakes and start all over again without allowing the engines to roll back and possibly cause a knuckle when the next attempt to start is made. GE AC's dont do this.

Posted from Android

At this point in the discussion this needs clarifying: DC drive locomotives (DC traction motors) plug if you reverse them while moving, AC ones may or may not go into dynamic braking. So the statement "the dynamic brakes will come on when the reverser is reversed", which has been stated several different times and ways in this thread, is misleading because it fails to take into account this difference. To avoid all confusion and controversy, it should read something like this "with some models of AC-drive locomotives, the dynamic brakes will come on when the reverser is reversed while you.re moving forward".

To amplify on some other posts:

>I remember SP engineers putting the SD9's in reverse and applying power to slow down, stop, and go the other direction while switching without using the brakes.

Very bad practice because these guys were plugging the motors and sliding 1/2 the axles.

>I've done the same with a GP7 light engine at low speed, and it will bring you to a stop in short order.

Yes you do.

>In an emergency situation, you can reverse the locomotive, and open the throttle to R-1, but you will do damage to the wheels & traction motors

Yes (assuming DC drive). 25-30 years ago it cost something on the order of $20-30,000 to rewind a traction motor.

>unless you're going very fast.

In which case you'll do even more damage (also assuming DC drive).

>Probably every engineer on TO's has done that at some point to avoid a rough joint when backing down onto his train and things just aren't working out otherwise.

Although I experimented with plugging every now and then and demonstrated it to students, I never did this.

>They will most likely slide some, if not all the axles.

With DC drive, you'll slide 1/2 the axles, minimum.

>After more than a few seconds, I would imagine the ground relay would trip and cut off any power you are trying to use backwards.

When the motors flash over, it trips the ground relay. They will continue to provide braking, such as it is, until there is an insulation failure in one or all of them.



Edited 1 time(s). Last edit at 12/05/13 00:11 by EtoinShrdlu.

The subject line reminded me of an otherwise unrelated story from the San Bernardino Shops 40+ years ago. A six-motor Alco unit was being fired up after being pushed out of the shop building. One of the traction motors had been connected up backwards, so they had five motors trying to go forward, while one was trying to go the other way.

In the world of streetcars, the "if all else fails" way to attempt to stop a car is to put the reverser in reverse and take one point on the controller (it's presumed that the controller is already in the "off" position). This is called "slugging" and can damage the motors, but if the alternative is a disastrous collision that's the technique.

>The subject line reminded me of an otherwise unrelated story from the San Bernardino Shops 40+ years ago. A six-motor Alco unit was being fired up after being pushed out of the shop building. One of the traction motors had been connected up backwards, so they had five motors trying to go forward, while one was trying to go the other way.

About 40 years ago the late Addison H. Laflin Jr. once related a similar story in the BAERA Review. It went something like this: "In the halcyon BRE days (Before Russell Eficiency), one day the City of SF went to Ogden with one of the traction motors trying to go to San Francisco."

When I was a switchman at Bayshore, one of the older guys told me a tale of a B unit which had the motors in one of the trucks connected backwards. The roundhouse guys spent a few afternoons parking it dead center on the turn table, waiting for everyone to fill up a hard hat (with money), and then gunning it to see which way it would go. The winners were the ones who picked the right direction. It took several days for the Sac Shops to tell them how to correct the connections (had to be done to Company standards, ya know).

>In the world of streetcars, the "if all else fails" way to attempt to stop a car is to put the reverser in reverse and take one point on the controller (it's presumed that the controller is already in the "off" position). This is called "slugging" and can damage the motors, but if the alternative is a disastrous collision that's the technique.

This is precisely the same as with DC-drive diesels.

A couple of days ago, I heard on the scanner about a train stalling out on the San Gorgonio grade (near Palm Springs). Turns out thar the DPU was " linked" in the wrong direction. Meaning, I guess, that instead of pushing, it was pulling. Origin unknown, but probably Colton. Toasted motors on DPU?

Nice safety feature! But what if you have a GE in the consist: will it self destruct?