Mother and Slug (Railroad)

While I was on the Cicero Avenue bridge taking pictures of a Chicago Belt Railroad east hump yard, I noticed some units moving eastbound just beyond the train that was being shoved over the hump to the west hump yard.

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Note the grey engine past the orange coil car and another one past the first tank car. But that you can't see anything past the white covered hopper car in between. This means that there is a slug in the consist. So I took off trotting north on the bridge to get to the other side of the train.

Indeed, it was mother and slug 302 and 303. A slug is the same as a regular locomotive from the frame down. But its superstructure is just a bunch of concrete blocks for weight. It gets the electricity to drive its traction motors from the mother unit. This helps use the horsepower that would otherwise go to waste during low speed operations such as transfers and humping. In fact, shoving trains over a hump is very low speed, 2-3 mph.

According to The Diesel Shop, the mother unit is an SD40-2.When I first looked at my closeup of the mother unit to check the number of axles, I missed that they were C-C units because the trucks were underexposed. I enhanced the brightness of the following photo.

I was not only fighting the dark side of the engine, I was fighting a glare off that switch control in the foreground and the time pressure of the units disappearing under the bridge. The picture to the right shows that my first attempt caught the glare squarely. Fortunately, I did not have to move very far further down the bridge to avoid most of the glare. So I cranked up the brightness on the best picture I got of the slug to reveal that it also has 3-axle trucks.

So the slug doubles the number of axles to 12 total to maximize the tractive effort produced by the 3000 horsepower of the mother unit. Doubling the number of traction motors handling the 3000 horsepower also allows the motors to run cooler. I noticed even when they are running light back to the east to get another train to shove over the hump, they run quite slowly. I wonder if they are geared differently than a normal road unit. I have never heard of gearing options for locomotives.

Earlier, when I was driving along the south side of the yard, I caught the end of a train that was working the hump.

At the time I was disappointed that by the time I got parked, etc., there was only the last unit showing. But now I'm glad. It was enough to catch the mother unit, 302, in action, and it revealed the neat railroad yard buildings that are still standing.

Steven J. Brown posted one of his photos
Santa Fe GP7u 1311 paired with an unknown slug at Corwith Yard in Chicago - July 19, 1977.

Mike Breski posted
RailPictures.Net Photo: IHB 477 Indiana Harbor Belt Railroad Slug at Riverdale, Illinois by Robby Gragg
Rick La Fever The two covers that on either end covered the traction motor blowers and related equipment.
The one in the middle may have been just a slab of concrete.
When used this way, the speed is cut in half but the traction effort doubles.

Edward Kwiatkowski posted

Switching the South hump, at the Atchison, Topeka & Santa Fe Railroad Corwith Yard.

Chicago Illinois. April 1984.

Jerry Jackson posted three photos with the comment:

IHB SW1500 9204 and PB1 were pretty much a pair. I first caught her with this small, maybe, work train. I don't get the three CNW hoppers, but the flat with spraying equipment and the older tank car, say weed spraying. LaGrange, 1987. The second shot was between CA tower in Summit and the ATSF Diamond in McCook, 1990. Third shot was in 1990 at Agro Yard in Summit, IL.

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Bill Molony posted
Indiana Harbor Belt EMD SW1500 #9215, slug #PB3 and transfer caboose #31 at Hammond, Indiana on March 26, 1983.
[IHB built them with just the weights so it was pretty obvious the "Power Boosters" were slugs.]

Mark Llanuza posted
Its 1977 rebuilt GE Slug set leaves Bureau IL
Jack Fuller Train 01A, I'd say, based on the reefers and time of day. Power swap st Silvis.

Kevin Piper posted
EJ&E was an early user of slugs. They were used on steel mill high-line and hot metal jobs where extra braking and power was needed. The original five were mated to NW-2's. T-5 was built from VO 660 270 in 1964. Gary, IN, 2-1-79.
Kevin posted again
Wayne Evans Used them in the South Works also.

David Jordan posted
Look what Santa brought Peoria railfans late last night? A slug! IAIS 721/651 and 150 are parked on the Creve Coeur Team Track awaiting the next train this afternoon. What I think is the outbound train, btw, is heavy with alcohol tank cars. Did NS again detour an empty ethanol train to Peoria instead of Chicago?

Bill Molony posted

Indiana Harbor Belt Railroad EMD GP38-2 #3801 and Powered Booster #5, which had been converted from Illinois Central SW9 #1243.

Dennis DeBruler You can tell by the bridges that this was taken at Blue Island Junction: http://industrialscenery.blogspot.com/.../blue-island...

Dennis DeBruler Note the B&OCT train in the background.

[The hood is rather high for a slug. And I thought the name "Powered Booster" meant it was powered. But some research indicates it means it is powered by something else. A calf is called "Powered B units". [IHBarchive]]

Kevin Piper posted
There were five slugs in use with NW2 mothers on the J by the 1960's. From an engineer's perspective, the slugs provided some extra tractive effort, and especially much better braking power, but they did not equal another locomotive as may have been intended. Gary, IN, 5-80 STEVEN SUHS PHOTO/KEVIN PIPER COLLECTION
Mitch Johnson Kevin, can you tell me what the tower is behind the switcher?
Steven Suhs Mitch I think it’s the old sanding tower
Sam Carlson I don't think that was the intention, if for no other reason than the slug is too light.
Rick La Fever As I understand it, slugs basically doubled the tractive effort of the mother unit but would cut the speed in half due to the amperage required.
Maybe if Neal Stringer reads this, he can explain it better.

John DeWit Woodlock II posted
BRC 526 @ 100th Street Yard-Chicago,IL 17 FEB 02. Converted to a cabbed slug, the 526 looks good in new paint.
[If they don't remove the cab and reduce the height of the hood to fit the weights, you can't spot it as a slug. You have to know that 526 has been converted.]

Steven J. Brown posted three photos with the comment: "Rock Island U33B/Slug set, The Great American Energy Saver, at Burr Oak Yard in Blue Island, Illinois - June 29, 1977. 284 was slugified from U25B 222."

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Rob Olewinski Cmraseye posted
It only took 58+ years for me to get a photo of this particular 'job'....would have loved to chase it, but had a long day of work ahead of me....7/15/18....5300 S. Kildare
Chuck Guzik Central Steel Job
Mark Losiniecki I can't speak to present times, but 20+ years ago when it was new it was an actual fuel tank and served as a fuel tender for the mother unit.

Bill Molon posted
Indiana Harbor Belt SW1500 #9221, along with DHT-2 (Diesel Hump Trailer) #477.
The 477 had been converted to a slug from IHB NW2 #8777, which had been wrecked in 1960.

Bill Molony posted
Indiana Harbor Belt SW1500 #9222 and slug #PB2 with Milwaukee Road bay window caboose #992186 at Dolton Tower at 10:30 AM on September 17, 1983.Dennis DeBrulerYou and 1 other manage the membership, moderators, settings, and posts for Chicago Railroad Historians. They must have used something really heavy on the slug. Given the white shade, I assume it is a slab of concrete. That is the lowest profile I have seen for a slug. I'm sure the engineers appreciate the better visibility.

Joe Usselman posted
'll throw my hat in on the throw backs for today. This one out of my slide collection from April of 1980 at East Chicago. Unknown photographer.
Dave Panek Memories from my Ingot Mold Foundry days at Inland right there.Keith SchmidtKeith and 26 others joined Chicagoland Railfan within the last two weeks. Give them a warm welcome into your community! Wow I was just on the pedestrian walk in the background on Monday. The building is no longer there.

Three slugs in less than a week.

Bill Molony posted
Indiana Harbor Belt #PB2 was constructed in November of 1976 from IHB NW2 #8728.
Power Booster was the IHB's name for their slugs - units that had traction motors, but no prime mover or generator, and received electricity from the diesel locomotive that they were mated with.

Sylvain Villeneuve posted
is it a pusher ?
Ugo Castellarin It's a slug
Wesley Smith Daughter unit
Paul Deevy It has traction motors, but no engine. All the power is generated by the mother unit (a full locomotive) and then some is distributed to the slug. This makes for more powered axles and more traction, but no actual power increase, since there is only one engine powering both units. They're generally used when they need to move a heavy train but speed is not an issue. The most common use I've seen is for hump yard pushers.
Rob Pownall Justin J Doyle not really an engine, just traction motors and brakes. The yard engine they are attached to have only half the brake pressure of road units so they won’t lock up the wheels and cause flat spots when switching in the yard.
Kevin Marshall SLUG or MATE how it works is The engine "prime mover" is removed and replaced by concrete for weight and traction motors are active through the MU cables....it's used for traction and braking effort.
Richard Stern Gee, lots of people using "slug" without describing what it is. It is indeed a "slug", which is US jargon for a unit that lacks its own prime mover and generator. Instead it takes its electric power from the attached locomotive(s). The purpose is to add tractive effort for low speed work without the cost of the Diesel and control cab. Which it does quite effectively so long as speed is not too high. So it's often used in hump service or similar applications. 

Some have described it as a "calf", which is not correct. A cow-calf combination is just two MU'd switch engines, like an A and B unit so one has no cab. A calf (B unit) would normally have the Diesel and generator, controlled by the cab in the "cow" or A unit.
Ken Bynum Also called a PB unit ( power booster )
Patrick Fogarty Sometimes you will get the odd Yardmaster who jokes with you about letting the slug run out of fuel. Jim Marshall Very little maintenance on that huge concrete block they put under the hood.
Dano Koch Slug lt was traction motors hooked to an A Unit ran thru the 27 pin power cable & they had a cut down car body with cement to give added weight.
Shawn Hébert also called TEBU traction effort booster unit
James Leivo At CN I've only heard as being called a calf. The locomotive that is providing power to it is called a cow. So it's a cow and calf together. The calf has no engine, but has traction motors that get their power through cables from the cow. It has it's own air brake system and a air tank to keep pressure up, but, it has no air compressor. It is also not effective at pulling above 15 MPh. It is therefore only used for yard work and also adds very effective braking power. It also uses compound brakes shoes just like the cow to reduce flat spots. Just some thoughts from a railroad employee of CN rail.
Kyle McGrogan Interesting, as in the US we had GM TR5 or 6's, 1200 HP SW1200s (Cows) that were mated to engined, but cabless SW-1200 calfs.
Kyle McGrogan In the US shome shortlines use them, see Winchester & Western of Virginia's ex Alco RS-11 Slug (from Conrail) fitted with an SW-1200 Cab and control and brake stand so it can control its "Mother"unit, a GP-9 or GP-10M.
Darren Fuoco I bet it's been at least 20 years since I have seen one.
Azhar Abbas Darren Fuoco come to Edmonton. We have the everywhere.

Iyan Andriyana posted
Can explain what it's for
[Because of the low hood that can only house weight such as concrete, we know it is a slug. I've read that when there are two mothers hooked to the slug, sometimes each mother powers just one of the trucks.]

Marty's post includes an IHB slug.

1966 Marty Flickr photo (source) of two mother-slug units shoving cars over the hump.

Arturo Gross Flick 1998 Photo

BN 65 slug (source)