Trucks on First Generation Diesel Locomotives

[garyla]

I've wondered about this before...if it's been covered in a previous thread, excuse me for missing it.

Among first-generation diesel locomotives, all (or almost all) non-EMD products with "C" trucks had the axles UNEVENLY spaced.  All the C-C EMD products I've ever seen had trucks with the axles spaced EVENLY.

This was probably just a case of two competing engineering philosophies, and we know which one won.  But is there more to the story?  If anybody knows the technical advantages of each approach, it would be enjoyable to see. 

Thanks. 

[chutton01]

I just noticed this post and the answer is yes, there is more to the story, as I read long ago in the 'Historical Diesel Spotter's Guide' (itself now a historical oddity it seems).  Prior to a given date in the 1960s (I think), 3 axle locomotive trucks had uneven spacing to accomodate mounting the traction motors. IIRC, these needed to be mounted within the footprint of the truck, they couldn't extend much forward of back of the outside axles otherwise they would foul against the underframe (or equipment mounted on the underframe) on turns. So, you could have the front axle with one traction motor, facing rear, with a smaller axle spacing; next the middle axle with its traction motor facing rearward, and finally the rear axle with its traction motor facing forward - so you needed a larger axle spacing between the middle and rear axles to accomodate this
.
Eventually technology and design caught up and the traction motors could be positioned on trucks with even axle spacings - I want to say this was true beginning with the GE U-boats and the SD35 of the mid-1960s, but I am unable to confirm at this time.

Remember, 3-axle trucks were somewhat uncommon till the 1960s (Special Duty and all that) - and those fleets of EMD E cabs road on A-1-A, so with only 2 traction motors there was no problem with having equal axle spacing.

Perhaps EMD solved the problem earlier, I am looking at on-line images of SD9s, and cannot really determine if the trucks have unequal spacing - if they do, it is not really noticible in these images (alas, the vast majority of images are the 'Glorious' 3/4 view, which is no help in determining axle designs)

[Leo_Ames]

garyla

All the C-C EMD products I've ever seen had trucks with the axles spaced EVENLY.

There were some EMD 6 axle road switchers built on trucks from trade ins that had uneven axle spacing. I know for a fact that C&O's SD18's used trucks from traded in Alco RSD-5's and can think of plenty of BB examples off hand that used traded in trucks. So I wouldn't be surprised if there were other CC instances beyond that one.

http://www.trainweb.org/chessiephotos/photos/SD18/7300cs-c&o.jpg

[jrbernier]

  EMD's 6 axle 'Flexicoil' truck had even axle spacing  The follow-on EMD HTC truck starting with the SD40-2 was different - very apparent when viewing them.  The traction motor facing the fuel tank is reversed and you can see the protective 'yoke' in pictures.  IIRC, EMD did change the axle spacing by about 6" and reversed the one traction motor to improve traction under acceleration.  This prevented wheel lift of the rear axle at initial startup.

  The Alco's and early GE's used a a truck that had uneven axle spacing.  The later Adirondack truck on GE may have had even spacing(or at least close to it).

Jim

[YoHo1975]

I'm pretty sure the HT-C truck is evenly spaced.

 

However the truck on the SDL-39 is offset. 

The flexcoil as was said is evenly spaced and was introduced on the SD7 in 1952 (I don't think it was on anything older)

[chutton01]

Duplicate Post

[chutton01]

OK, I found my copy of 'Diesel Locomotives, the first 50 years'
It has a section in back discussing trucks - remember, since this book was originally published in 1972 under a different name, at that time there were signficant numberes of non EMD/non GE locomotives still on the road.  It's funny seeing how dominant B-B locomotives were back then, a complete reversal of today where B-B locomotives are special duty and C-C are everywhere.

ALCO
    1951 thru 1967 Tri-Mount; Unequal [Axle] Spacing
    1967 - High Adhesion (HiAd); Equal Spacing

Fairbanks Morse
    Tri-Mount; Unequal Spacing

Baldwin (& Lima)
    Cast Frame Trucks (No equalization) 1951 thru 1953; Unequal Spacing

EMD
    1952: Flexicoil - Equal Spacing - since the SD7 seems to be the first production C-C locomotive GM produced for the North American market, I'd say 1952 for the 3 axle Flexicoil (except an image in the book of a BL& E SD7 from Oct 1952 has a rather odd looking front truck - the rear one looks Flexicoil, the front almost like a Bloomberg/Flexicoil hybrid, but that can't be right.
    1970: HT-C - Equal Spacin; this truck looks a lot like a Flexicoil except for the dampening struct, the 3 holes in the frame between axles as opposed to 2 holes on the flexicoil, and it's a bit longer to compensate for one of the motors being out-board of the outer axles (all traction motors on the HT-C faced the same direction in relation  to the axles, so to prevent the fouling by the traction motor I mentioned above, they simple made the truck longer and clearances bigger. 

GE
   1963-1966:Truck design is similar to ALCO Tri-Mounts; Unequal Spacing
   1966 onwared  - Both GSC & AdIrondack 3-axle versions, differing somewhat; Equal Spacing

When I started to get into prototype research more seriously in the late 1980s, the vast majority of North American locomotives in revenue freight service were EMD and GE, all with equal axle spacing. I didn't even realize before that many locomotives once  had C-C trucks with unequal axle spacing - but of course those were FM, Baldwin, Alco - more or less orphaned makes and rather rare to find in every day service (does SMS even own a C-C Baldwin).  Note also that A-1-A trucks were common enough in the 1940s & 1950s, seemed to have disappeared by the mid-1960s, and only seem to have re-emerged in the past few years with the ES44AC4 in domestic usage.

[bogie_engineer]

Axle spacing is at the discretion of the truck designer, a few inches offset of the middle axle from the center between the end axles doesn't have much effect on static axle loads, which is more dependent on where the motor and truck frame c.g.'s are and placement of the secondary springs and center bearing on bolster-type trucks.  While the EMD Flexicoil truck has even spacing at 81.5"-81.5" from axle 1 to 2 and 2 to 3, the HTC is uneven at 79.62"-83.75".  The wider spacing from 2 to 3 was done to fit the brake rigging around the transom - the brake cylinder at axle 3 operates the brakes on axles 2 and 3.  It's the same situation on the HTCR truck which has a spacing of 80"-84".

A little known fact re the HTC is that the axle spacing was designed as 79.5"-83.5" to result in the same 163" wheelbase as the Flexicoil, however, the first truck cast measured a little larger as the casting did not shrink as much as predicted by the foundry pattern makers and process engineers.  So rather than revise the pattern to correct it, the drawings were changed to match the what the pattern produced.

[JonathanS]

Actually the cast trucks used by Baldwin, Lima and some eary FM's were equalized.  The castings were hollow and had a set of levers mounted internally to perform the equilization.

[chutton01]

JonathanS

Actually the cast trucks used by Baldwin, Lima and some eary FM's were equalized.  The castings were hollow and had a set of levers mounted internally to perform the equilization.

I'm just quoting from the Book "'Diesel Locomotives: the First 50 years" - is it possible that those trucks were offered with and without equalization?

[Anonymous]

chutton01

JonathanS:

Actually the cast trucks used by Baldwin, Lima and some eary FM's were equalized.  The castings were hollow and had a set of levers mounted internally to perform the equilization.

I'm just quoting from the Book "'Diesel Locomotives: the First 50 years" - is it possible that those trucks were offered with and without equalization?

I can't imagine six-wheel trucks without equalization on locomotives or rolling stock.  In glancing over the book you mention, I don't see any reference to the FM or Baldwin six-wheel power trucks being without equalization.  Could you point out exactly where this is in the book? 

[oltmannd]

jrbernier

  EMD's 6 axle 'Flexicoil' truck had even axle spacing  The follow-on EMD HTC truck starting with the SD40-2 was different - very apparent when viewing them.  The traction motor facing the fuel tank is reversed and you can see the protective 'yoke' in pictures.  

Jim

Not protective.  It's where the traction motor's nose was suspended.