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maraach

Hotshot gearbox problems

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Hi all

 

Building up my new super hotshot which just arrived but having some challenges.

 

When I'm screwing the gearbox together (2 sides the diffs become really tight and notchy). I'm not familiar with the hotshot but every other car I've had you want this to be smooth and free moving.

 

Any ideas on what I may be doing wrong? I've had it apart 3 times and can't see the mistake I've made.

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Sometimes the ball bearings don't get seated inside the plastic.  Those bearings should be pushed in firmly.  They fit quite tightly.  If I remember correctly, the bearings were flush with the inner surface of the gearbox.  If not, it could reduce the clearance for the diff, making it tight.  Hotshot family diffs are smooth.  So, off the top of my head, that's all I can think of...  

BFpsfod.jpg

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If its the rear gearbox, then the diff is tight, I had the same on my boomerang that have the same gearbox.

I checked it a few times, if you drive it it wil loosening and get smoother.

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It's the rear. I Did take it completely apart. Tried different bearings and still the same. I think like you said it's just a lot tighter than I'm used to. I'll run it acouple times and see If it loosens up. Not sure how it would but I Guess we'll see.

 

Front on the other hand is light and free.

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7 hours ago, Juggular said:

Sometimes the ball bearings don't get seated inside the plastic.  Those bearings should be pushed in firmly.  They fit quite tightly.  If I remember correctly, the bearings were flush with the inner surface of the gearbox.  If not, it could reduce the clearance for the diff, making it tight.  Hotshot family diffs are smooth.  So, off the top of my head, that's all I can think of...  

BFpsfod.jpg

Did check the bearings and unfortunately they are flush so not that :/

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I have read it on this forum and you are not the only one that noticed it, so you did nothing wrong its how the car is.

On  the front gearbox the diff is smooth on mine to.

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Indeed. Now I know what I'm looking for you are right there is plenty of discussion on the topic. I mistook my problem as different as most of them state the diff is a "little tight" where for mine it is barely moveable without some serious pressure. 

Ive since learned the problem seems to be with the steel diff gears and poor manufacturing in some kits. That makes sense to why they would also free up as they bed in with the plastic gears. 

Just feel like it would have been clever to use a little more grease in the boxes had I known.

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I know this is a bit old but I experienced the same thing with my super hotshot rear gear box. If I crank down the two acres that hold it together the diff won’t move.  I have to back off, especially the machine screw with bolt on the bottom like a full turn and a half and the diff frees right up and is smooth.  Since that screw using gel thread lock I’m not too worried about back it off a little.

Any adverse effects of this? The gearbox is still solidly together and not loose, I guess it just needed that little bit of relief.

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hi all, first time poster here!

as i have just finished a super hotshot too, i wanted to confirm that the gearboxes really are pretty tight, especially the rear. i have not experienced this with my other cars.. but it drives without issues, and i feel it did loosen up a bit.

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I know nothing about the Hotshot, but I have a Fox with a transmission that would get really tight if the pinion gear was too high on the motor shaft, as the pinion would then rub against the far side of the transmission.

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I would give all the diff bevel gears a very thorough visual inspection. These are what I would call 'pot metal' (they're not steel) and the gears are cast and not machined, so there can be 'flash' on them, round the edges or on the gear teeth. This can potentially make the diff tight (same goes the 3 tiny gears that fit inside the main diff housing gear). As others have pointed out that the diff gets smoother over time, it's probably this soft pot metal wearing away where it's binding. My hotshot (A re-re I bought in 2007) has a rear diff that is tighter than the front diff, but the rear diff can still be turned easily (Although it does not freewheel when one wheel is spun). I suspect that the front gearbox housing is slightly wider than the rear on all the cars. 

You can always swap the front and rear diff gears over and see if the rear diff spins freely in the front. If it does and the front diff is tight in the rear gearbox then it might be a malformed gearbox casing. You could also look at the circlips and the splined ends of the drive cups. If you have a file you could try filing a bit off the end of the splined end of MR15, and a bit of material off the back of MR10, this would provide slightly more width clearance for the diff and would loosen it off, but this would be a last resort as obviously filing material off is a one way trip

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1 hour ago, MadInventor said:

These are what I would call 'pot metal' (they're not steel) and the gears are cast and not machined, so there can be 'flash' on them, round the edges or on the gear teeth.

sounds like when you brake in slot car gears is to use tooth paste for a time and then clean and lube.

since i have not built the Hot shot i purchased some time ago this was helpful for me, this thread that is, and that i give thanks.

out of every car, truck i've built my MST FMX 2.0 trani is the only one that binds and till this day i was so turbed i shelved it until i get over my anger about it, Amain gave me advice but it did nothing, MST never returned my emails. so if this happens on the Hot shot (assuming the same as the Super's trani-) i'll be ready.

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