HPI MT Assistance/Advice Needed

[Monkey Wrench]

I have a first generation HPI MT that has an OS .12CV-R mill and optional 2-speed transmission. I'm using a Futaba 3PK radio with the Spektrum module. Spur gears are 49T & 52T.

So, out running it today (because I shredded the OWB on my Savy) and I start hearing a clicking/grinding noise like my mesh got knocked out of whack. Bring it in, and adjust the mesh, sound is still there, but only when I roll it backwards. It seems to bind at the CB/spur meeting point, but when I roll it foward, either manually or under power, it's smooth as silk, but rolling backwards, "click-click-click."

I'm thinking I may have a blown diff, but I'm not 100% sure how to tell without tearing it down. If I hold it up, hold the left rear wheel and spin the right rear wheel, the left front wheel will turn and vice versa all the way around. If I hold the left rear and try to spin the right, I do feel some resistance in the left rear.

Should any of you have some advice or insights, especially on how to check a diff, I'd be most grateful!

 

[robriguez]

Well, the only time i had a problem somewhat similar I had messed up the rear diff (cracked casing, drive cup to one of the rear wheels broken). So in forward it binded a little but would still run but not go in revers at all. I would say it might be the trans or one of the diffs.

 

[olds97_lss]

I'd check your 2-speed gears for a rock. You may just have a tiny rock stuck in one of the gears causing the clicking.

 

[racin_38]

this may blow your mind ,but dbl check your brake pad
i know it sounds odd but i had a similar problem with my mt and the brake disk would go wacky backwards like not lineingup right but it was fine forwards
my savage makes a god awful sound in reverse too and it is the dual disk brakes
just a thought

and you may have a bearing starting to go i nthe diff also ,

 

[Monkey Wrench]

HA HA HA HA HA! You'll flippin' love this! Tore this sucker apart today; broke both diff's clear down, pulled the mill, took the tranny out to find out what the heck was causing this problem. After breaking the diff's down and determining they WEREN'T the cause, I start focusing on the CB to see if a bearing was going, if it was shimmed right, etc. OK, so we're well into hour 2.5 of this adventure and still, so "Aha!" yet!

So, take a look at the two-speed gears in the tranny and there it was, the "Aha" I was looking for! The set screw that sets your shift point had backed itself out and gotten wedged in the clutch assembly! Of course, the little ball bearing and spring were gone (just my stinkin' luck) BUT, I at least found out the reason!

Well, another couple hours, it's back together and running like a champ!

Thanks for the tips and advice, all! I appreciate it!

 

[rcnutcase]

Just a quick question, How well does the 2 speed work in the mt? I know its great on pavement but I only run off road and heard it is not such a good idea, just looking for input.

Bill

 

[racin_38]

in grass it will dog it down to muc hand cause it to over heat ,dirt its a blast

 

[Monkey Wrench]

RCNutcase, take a gander at this thread, man: https://www.rcnitrotalk.com/forum/showthread.php?t=38109

Lot of input on the 2-speed tranny for ya.

Good luck!