'Square wheels' on Pacers?

[gareth950]

Is there such a thing as DMUs, I'm thinking specifically Pacers and 150s, developing what sounds and feels like 'square wheels'? Most of the ATW fleet of Pacers and some of it's 150s have developed this with wheel sets recently, and the only way to describe it is as 'clunking' when moving that gets more frequent the faster the speed, and you really notice it in the ride quality at low - medium speed. It really does feel and sound like the train has square wheels or that the wheels are about to come off.

What causes this? Poor maintenance? Is it a sign that wheels sets need replacing? I'm presuming it's safe as most of the ATW Pacer fleet have been operating like this for weeks now, but it's not pleasant.

 

[Bletchleyite]

Yes, it's wheelflats, which are much more common at this time of year as slippery rails result in sliding on braking. It's not dangerous in that sense but does accentuate track damage. The units will require a visit to the wheel lathe to fix it.

 

[gareth950]

Thanks for that, I didn't know what the technical term was. I guess ATW have taken the decision to keep trains in service rather than withdraw them for wheel maintenance as they haven't got enough stock when the fleet is maxed out as it is.

 

[61653 HTAFC]

One 142 was fitted with square wheels while on demonstration runs in Canada...

(#southpark)

 

[Mugby]

Became very much more prevalent with the introduction of disc brakes. With shoe brakes, as on the old DMUs etc, the brake shoe acted directly on the tyre with less likelihood of a flat developing and more chance of correcting it if one did.

 

[Cowley]

I was painting a customers house the other day who lives right next to the Barnstaple branch and he drives for FGW. A pacer went past a couple of times during the day with very noisy wheelflats and I commented on it. He said that it was a real problem this time of year with lightweight 143s sliding on slippery rails.

 

[GrimsbyPacer]

One 142 was fitted with square wheels while on demonstration runs in Canada...

(#southpark)

Ha ha ha!
That's probably true aswell seeing the Canadian cars on the series.

 

[gimmea50anyday]

Became very much more prevalent with the introduction of disc brakes. With shoe brakes, as on the old DMUs etc, the brake shoe acted directly on the tyre with less likelihood of a flat developing and more chance of correcting it if one did.

Think you got that the wrong way round. Wheelflats are more likely as shoes clasp the wheel. A flat spot on a wheeltread the shoes will grip into that flat thereby causing another and potentially worse flatspot. Disc brakes on the other hand have anti-lock braking systems fitted which minimize (but doesnt entirely eliminate) wheelslide. Mk1 and mk2 LHCS, Pacer and some sprinter stock still use tread brakes.

The irony is tread brakes acting on the wheel actually help clean the wheel of all the leaf mulch etc and aid track circuits to operate. Disc brakes dont do this causing trains to insulate themselves from the track circuits and therefore "disappear" off signalling panels. The track circuit actuator which is essentially an electro-magnet was developed to prevent this. If you look on the bogies of sprinter stock particularly under the cabs you will see what looks like a pipe joined to itself in a square behind and inbetween the wheelsets of the bogie.