We run four brushed Losi SCBs on asphalt. They get hammered from the close combat but aren't otherwise stressed. All the cars use standard NiMh battery packs, either 3000mAh or 5000mAh. One of the cars will now only run at about 75% speed and accelerates slowly with a 5000 pack, but runs normally with 3000. The same 5000's run the other cars without problems. The car's ESC modes have checked out okay. What would cause this? Is it fixable?

Ck your brushes and use motor spray to clean your brushes and armature.

I'm not meaning to be argumentative, I'm just trying to understand. If the motor runs fine with a 3000mAh battery and slower with a 5000mAh battery, why would the brushes be suspect? With bad brushes wouldn't the motor run poorly with any mAh capacity battery of the same voltage?

Argumentative? It was suggestion! If I was adding 2amps I would always make sure connection b/n brushes and commutator is clean. I always use motor spray every other battery pack run.

Depends what motors you are running. most stock motor are throw away.inermediate 7 Mod motors rebuild able. In the hobby so long NiCads was the thing in '84. Heavy into AE models and Team Checkpoint!!! lol!!!! RC10 Gold Buckets and Losi!! In this hobby too long!!!

When are you going to Brushless like everybodies doing?? I got rid of my commutator truer in '12 when you turned a member of RCTech. Brushless the fad now, Motor & lipo's the seen now. More power, longer running,quicker, hardly no maintenance. Or maybe just collecting for your museum.

Mah increase only improves on time. More power you have to increase the voltage. Lipos does that. 1s, 2s, 3s & 4s, 3.7v- 14.8v.NiMa add cells like to 8 cells pack.

Checkout my avatar. It’s a gearbox from the first RC car I built in 1969 called the Ra/Car ‘Sonic'. I’ve seen a lot of scenes come and go, as have the guys I race with. We all have brushless/LiPo cars, too, but we prefer the brushed Losi SCB’s on our tight asphalt course because they run a little slower [i.e. scale]. NiMh and brushed motors are still readily available. They are simple and inexpensive, and get the job done. Often, less can be more.

Thanks for the feedback.

Are you referring to the 5000 pack you're using verses the 5000 others are using? Could be your 5000 pack is bad. Try someone elses pack and see if that makes a difference.

Andy, we've passed the batteries around and done the cross checking. Only one of the SCB's doesn't like 5000 mAh packs.

From what Google has been showing me, the ESC might have a blown transistor. That isn't something I can adjust, so I've ordered a replacement MSC12L.