Help! Sportmaxx Running in Reverse

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cobra198

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Hey guys,

A buddy of mine and I went to go run our RCs the other day. I previously got mine all tuned and ready to go, but his had not been started probably for a few years. We started up his sportmaxx (2wd, forward only, and 1 speed) and discovered a problem: It only runs in reverse. He did a bunch of mods before he packed the truck away, but never really touched the tranny. Before we arbitrarily pull the entire truck apart I thought I would see if anyone has suggestions where to start. I am just trying to think what could have been installed backwards to cause this; maybe the differential? Anyways like I said we haven't had time to pull it all apart yet, so any suggestions are appreciated!

Thanks!
 

Tmaxx96

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the engine OWB could be backwords and wen the engine starts it could be starting the engine backward happened with my stampede
 

ajames942

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I disagree. OWB only goes one way. If you put it in backwards, your motor wont even crank.
 

Rolex

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These engines are capable of running in reverse. It's common when flip starting an airplane engine.
it won't be in the trans since it's forward only. If he or the previous owner did a tear down on the diff, that might be in backwards.

I just re-read your post, and if it's a sportmax, it's the same diff as they use in the Tmaxx. It's in there upside down. Common mistake.
 
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jerry7007

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I disagree. OWB only goes one way. If you put it in backwards, your motor wont even crank.

it would only run backwards if you put the OWB in backwards and you reversed the connections of the starter motor. also, if you use a pull starter or a bump box they can start in reverse, they kinda stop and then fire, it happens to airplanes every once in a while.
 

kswiencki

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I agree. The diff is definintly backwards.. You would notice the engine running backwards.. It would run like crap... had that happen on old nitro sport.
 

cobra198

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Hello again,

Thanks for the help. I agree with you that it is the differential that is flipped (I know its not the OWB because it is has a pull start and the cord would not retract if it was in backwords). I had the sneaking suspicion, but wanted to make sure before he tears the truck down to the dif!

Thanks again!
 

cobra198

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Sure enough it was a backwards diff. The Sportmaxx is good to go now. Thanks again for the help!
 

olds97_lss

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I know it's strange, but I've had pullstart engines run backwards on me. Usually when it's cold outside and when the OWB is older and a bit worn.

I know you have your problem sorted out, but just in case anyone doesn't have the diff backwards, knowing they aren't crazy may get them through the day! ;)

As a side note, the 3-4 times I had it happen, the engine sounded really strange, but ran and idled. Just didn't have any real power... then again, could have been because it was fighting the OWB. The exhaust note did sound really weird though. Like it was sucking air somewhere.
 

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