NYC U25B gear ratio

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NYC U25B gear ratio

Postby Allen Hazen » Sat Sep 28, 2013 6:09 pm

The "Trains" Locomotive Annual for 2013 has arrived at my local magazine shops.

On page 85, with a small photo of preserved NYC 2500, Kevin P. Keefe reminisces about seeing mail & express train 13 on the Michigan Central in March 1966, with "four U25Bs, shiny in their black-and-white cigar-band NYC paint, rumbling urgently westward with a long line of baggage cars, mail cars, and the requisite rider coach on the end -- doing all of 79mph."

79 mph? By the time the U25B was in production, GE felt that locomotives with 752 motors and the standard 74:18 gear ratio were good for 70 mph (earlier 65 mph seems to have been the standard top speed for units with this ratio), but 79?

Does anyone here know what gear ratio the NYC's U25B had? (If you ALSO know the ratios for NYC and P&LE U28B, NYC U30B and PC U33B, I'd love to know them, too!)

(Also posted to New York Central forum.)
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Re: NYC U25B gear ratio

Postby Allen Hazen » Sun Sep 29, 2013 10:55 pm

As I said, I posted this question on the New York Central forum as well. Noel Weaver and Pat Fahey replied: go there for the details. Short answer: all these NYC/PC U25/28/30/33B were geared for 70 mph (74:18), and it's not always easy to judge the actual speed of a passing train from line side.
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Re: NYC U25B gear ratio

Postby MEC407 » Mon Sep 30, 2013 9:20 am

Agreed: while standing near the tracks, 70 and 79 look pretty much identical. And freights often seem like they're going faster than they are, due to their increased size and noise. An audio-visual illusion, if you will. Not that 70 is anything to sneeze at! My local railroad thinks they're doing a good job when they get the 10 MPH slow orders resolved and they can run their mainline hotshot freights at 25 once again. :wink:
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Re: NYC U25B gear ratio

Postby Allen Hazen » Mon Sep 30, 2013 8:09 pm

"RSD 15" has posted further information about gear ratios on New York Central locomotives from the 1960s to the corresponding string on the New York Central forum. Rather than copying or summarizing, I'll just recommend going there for details. It's more complicated than I realized (but 79 mph would still have been serious over-speed for the Central's U25B).
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Re: NYC U25B gear ratio

Postby JayBee » Tue Oct 01, 2013 2:05 am

The Rock Island's U25Bs were delivered with 74:18 geared, regeared with 79:24 gearing, and then went back to 74:18 as the track deteriorated. A few RI U28Bs were delivered with 79:24 gearing, and those delivered with 74:18 with regeared up and then down. All RI U33Bs were delivered with 79:24 gearing, and only the "Slug Mothers" were regeared to 74:18 gearing.
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Re: NYC U25B gear ratio

Postby Allen Hazen » Tue Oct 01, 2013 10:06 pm

JayBee--
Thank you! ... At some point I should try to merge the data on this string with what's on the "Traction motor gear ratio miscellanea" string.

It seems to me that a number of railroads in the 1960s and 1970s had wildly optimistic ideas about freight train speeds, in a way that is analogous to the ordering of many early (late 1930s-early 1940s) passenger units with gearing for a 117 or 120 mph top speed. Is there some good reason for wanting one's diesel locomotives geared for a top speed significantly higher than anything they will use in service?
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Re: NYC U25B gear ratio

Postby Typewriters » Sat Oct 05, 2013 11:55 am

The listed "70 MPH" top speed is not the geared speed, but the timetable limited speed that governs railroad employees.

The book quoted in the NYC forum (Edson, Vail, et al) lists the U28B and U30B units, in a table on page 168, as having a "geared speed" of 75 MPH. Continuous efforts are listed as 55100 lbs; this is at 15.5 MPH for the U28B and 17.0 MPH for the U30B.

This of course means exactly what any researcher should suspect, which is that the units have the factory standard gear ratio introduced with the U28B for all four axle high horsepower domestic U-series units which means 81/22. The sales brochure I have introducing the U28 series lists the standard top speed for the U28B as being 75 MPH, which is the 81/22 ratio, as do brochures for the U30 series (relative to U30B) and U33 series (relative to U33B.) Six axle units retained the 74/18 gearing, top speed 70 MPH, as standard, with the exception of course of units U28CG, U30CG.

In the U30 brochure, the following description of the 81/22 ratio is given:

"The new gearing, with an 81/22 ratio for 75 MPH operation has a tooth design to provide low wear and long gear life. This new gearing lowers traction motor speed for a given locomotive speed aiding commutator performance and giving long bearing and grease life."

The implications inherent in that passage relative to, say, continuously running a 70 MPH geared unit at 65-70 MPH are obvious; poor commutation and high bearing and lubricant wear. The use of a new ratio for high horsepower per axle units intended for priority service makes sense if railroads are wishing continued high 60 to 70 MPH speeds.

So, yes, the NYC timetable information that employees could see and which governed operation of the equipment and railroad limited the locomotives to 70 MPH, but the equipment in question was constructed with the 81/22 ratio that the manufacturer certified for 75 MPH maximum speed operation.

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Re: NYC U25B gear ratio

Postby Allen Hazen » Mon Oct 07, 2013 6:46 pm

Will Davis--
THANK YOU!!!! (I have had to thank you for your very informative comments so many times that I felt I should capitalize it this time!)
This makes things a LOT clearer. On two fronts, at least.
(i) Why, when very few freight trains ran at speeds over 70 mph, did GE build and the railroads buy freight units (the U28/30/33B line) geared for a higher speed? And I think you've answered the question: sustained operation at (close to) the maximum permissible speed for a traction motor leads to "poor commutation and high bearing and lubricant wear." Solution: use a lower (so: higher speed) gear ratio so there is a safety margin between the actual motor speed in operation and the nominal maximum. (Is this perhaps also why so many passenger locomotives in the pre-WW II era were geared for absurdly high speeds?)
(ii) Why the odd sequence of introduction of the smaller-tooth gear ratios for different speeds? It sounds as if GE was introducing a NEW bunch of gear ratios in the mid-1960s for 752 traction motors on locomotives with 700 or more horsepower per motored axle. Makes sense that, if this was an all-new line of gear ratios, they would go to the more robust, small-tooth, design for it. The 74:18 was to be used for lower power/axle applications (six-axle diesels, maybe ??? U23B and U18B), and was widely accepted, so they didn't immediately change it for those applications. (Note that the E-44 electric locomotives of the early 1960s had-- on the simplest assumption about what's wrong with the PRR diagrams!-- had the 103-tooth-ratio tooth size. So what GE was doing in introducing the 81:22 ratio on the U28B was making use, in a diesel application, of something they had already developed for a high horsepower electric locomotive.)
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