"Thumping" GP7

Hi,
I have a Proto 2000 GP7 (HO Scale) which has developed a thump in one of the trucks. I have checked the wheel gauge and taken the wheels off to check
them, and everything seems normal. When the engine is run at crawl speed (both in forward and reverse), you can see one corner of the truck lift up a fraction of an inch every 6-8 inches along the track. The condition is worse when hauling a load of 7-8 cars, especially going up grades and on curves. Surprisingly, when going downgrade on straight track there is no problem.
Can anyone tell me what might be causing this and, more importantly, can anyone tell me what I can do to repair it?
-- Roy
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Probably a split gear, actually common for these engines. I'm not a diesel user but understand the Athearn gears are a same replacement or Walthers (who now owns LifeLike) will also send you the gear once you find out which one it is.
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Roy & Lynn Williams spake thus:

My first guess would be a bent axle. Parts on these are very easy to replace (and I *think* fairly easy to obtain).
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in article 6c87a$46367807$cf704ad7$ snipped-for-privacy@PRIMUS.CA, Roy & Lynn Williams at snipped-for-privacy@primus.ca wrote on 4/30/07 4:13 PM:

I had the same problem in a GP9 Proto2000 loco. I contacted Lifelike (now Walthers) and without question they send me complete gear sets (front and back) for my two locomotives. No shipping, no handling, no fuss, no muss, and now both locos work fine.
--
Ed Oates
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Thanks to all for your help. I have contacted Walthers and they are sending me new gear sets.
-- Roy

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