6 axle locomotives

6 replies
1 rating 2 rating 3 rating 4 rating 5 rating
  • Member since
    August, 2006
  • 38 posts
6 axle locomotives
Posted by southernalco on Tuesday, May 01, 2018 12:26 PM

Back in the 70's, Amtrak was having derailment problems with their 6 axle locomotives.  What was finally determined to be the cause or causes of the problem ?

  • Member since
    February, 2005
  • 1,769 posts
Posted by timz on Tuesday, May 01, 2018 1:02 PM

It was never "finally determined" in the sense of finding a cause that everyone agreed was the cause. Some RRs blamed the HT-C truck -- SP and UP limited their HT-C freight units to 50 mph for a year or two until they modified the trucks slightly. Guess all the SD40-2s Conrail bought new came on pre-HT-C trucks, didn't they?

But others blamed the 1350-gallon water tank above the rear truck.

  • Member since
    April, 2003
  • 302,135 posts
Posted by Anonymous on Tuesday, May 01, 2018 1:24 PM

All derailments happened with 2 SDP40F in the lead followed by at least one light weight baggage car. FRA additionally blamed harmonic vibrations from the baggage cars for the derailments.

So there are the truck, poor track, the swashing water in the above frame water tank, and harmonic vibrations from the baggage cars.

My best bet, it was a combination of all four in differing percentages.
Regards, Volker

  • Member since
    January, 2001
  • From: Atlanta
  • 11,239 posts
Posted by oltmannd on Tuesday, May 01, 2018 4:24 PM

Lots of smoking guns and no bullet holes.  Reactions varied from ATSF "there is no problem" to Conrail "No HTC trucks, please!" 

In the end, Amtrak's end-run made finding a proven cause a moot point not worth the $$ for more testing.

-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/

  • Member since
    April, 2003
  • 302,135 posts
Posted by Anonymous on Tuesday, May 01, 2018 5:01 PM

Not all HTC trucks are equal.

The SDP40F had hollow bolster HTC truck which saved more than 5,000 lbs per truck.
Regards, Volker

  • Member since
    January, 2002
  • 3,593 posts
Posted by M636C on Tuesday, May 01, 2018 6:53 PM

Remember that there were at least two derailments of E60s using GE "Floating Bolster" trucks. These were similar to HTC trucks in having stiff secondary and softer primary suspension, while the old Flexicoils which don't seem to have been involved in such derailments had softer secondary and stiffer primary springs.

I think they were E60CPs, so they might have had sloshing water, but I think their water tanks were below the frame.



  • Member since
    April, 2016
  • 730 posts
Posted by Shadow the Cats owner on Wednesday, May 02, 2018 6:26 AM

Both derailments that involved the HTC truck happened when the water tank was half full and entering a curve.  Also Volkner this is from a retired Santa Fe Machinist friend of ours all HTC trucks have a hollow bolster in them.  You take 600-700 gallons of water and throw it in an unbaffled horizontal and the SD40F had horizontail tanks not vertical like the E units in the body.  You take that much water and throw it to one side of a carbody that is a 3 ton shift in weight that will cause your rear end to move.  Sorry my drivers in our liquid fleet deal with surge all the time and it is a pain in the rear even when they are watching out for it.  

Join our Community!

Our community is FREE to join. To participate you must either login or register for an account.

Search the Community

Newsletter Sign-Up

By signing up you may also receive occasional reader surveys and special offers from Trains magazine.Please view our privacy policy