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wintersdawn

Monster Beetle Build Question

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Hi, I just finished building my 2015 Monster Beetle and all went well, enjoyed every minute of it, just got the bodywork to do.

I started running it today, just to try it out, and the back wheels are free but sometimes it seems a bit noisy but I am wondering if the rubber boots that cover the rear axles sometimes touch inside the rear axle plastic arms?  I tested it by holding the back end up and sometimes full speed in forward and reverse is nice and free but sometimes there's a bit of vibration/noise.

Cheers

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14 minutes ago, wintersdawn said:

seems a bit noisy

Should be the spider gears inside the differential, but since you mention it is a new build vehicle I can not be sure. Thing is, sooner or later you'll need a new set of those. That's a design flaw, since that gearbox was first conceived for a fixed gear instead.

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Cheers.  Its all smooth in full forward/reverse with the wheels off so may just be the size of the wheels that cause some instability/vibration.  I have the alloy replacement hubs but it happens with the plastic hubs also.

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10 hours ago, wintersdawn said:

Cheers.  Its all smooth in full forward/reverse with the wheels off so may just be the size of the wheels that cause some instability/vibration.  I have the alloy replacement hubs but it happens with the plastic hubs also.

Hubs have nothing to do with the problem, mate. The Monster Beetle gearbox is a flawed design. The aluminum covers (sides) of the gearbox are too thin and the flex and the differential gears get stressed in action. You need to stiffen the gearbox with some extra bits like these:

Tamiya Gearbox Braces- Monster Beetle - Frog - Mud Blaster - Blackfoot - ORV  | eBay

The gearbox in your MB was actually designed to be fixed. It just happened the Tamiya guys thought that fitting a differential inside of the gearbox would be a good idea, back in 1983. There wasn't too many problems with the FROG buggy in 1984, but two years later when they mounted big wheels to that chassis the flaw really showed up.

This has been discussed thoroughly in this forum, I truly expected some other Monster Beetle owners here were going to share some knowledge on the subject but that didn't happened unfortunately. The good thing is that it can be fixed. You better buy a extra set of spider gears if you keep using the Monster Beetle.

 

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The transmission braces are really helpful and I haven't had any problems.  During the build, I noticed some slight issues after I assembled the rear end.  When rotating the wheels occasionally there was a "kick out" motion as if the driveshaft was too long.  I ended up taking everything apart and noticed that the instructions called for two rubber o-rings installed on diff output shaft BB17 and only one rubber o-ring on diff output shaft BB16.  Welp..  old ding-dong (me) got it backwards.  Still, when I installed the o-rings correctly things seemed a little too snug so I just left one o-ring on each and used a bit of Tamiya anti-wear grease on either end of the drive cups and things were much smoother.

IMG_20200818_084813.jpg

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Thanks for the info and advice mongoose1983, its good to know that its probably quite normal the way everything is smooth on full forward or full reverse with the wheels off but a bit unstable with vibration when the big wheels are on.  I am almost tempted to regret choosing the Monster Beetle now I'm aware of its flawed gearbox design but the look of it mixed with nostalgia makes me still love it (especially when I have sprayed it with TS-8 Italian Red).

I will keep an eye out for gearbox strengthening upgrades to make things more stable and prolong the life of the spider gears.  I'm not going to run it too hard but probably still need to address the gearbox flaw.

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Thanks Killajb for the info about what happened with your Monster Beetle regarding the o-rings.  Its got me thinking whether I got it right so will check.  It seems its only a case of removing 3 screws to release the rear axle assembly so not going to be a big job to check.

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Gave this a run today and it goes fine but if I lift the back end and select full forward or reverse speed sometimes there is a wicked shimmy going on with loads of vibration that shakes the wheels and whole shell, like its going to break/fly apart, is this part of the flawed design? If I do the same but with the wheels removed, everything is smooth, no vibration.  Cheers.

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When you pick up the rear end off the ground, the suspension goes to the full downward position, the rear axles/driveshaft/cups are trying to spin at their maximum angle, so they vibrate some.

 

When the vehicle is on the ground/running, the rear suspension is not in the full downward position, so the rear axles are not binding/vibrating due to the excessive angles.

 

If you are overly concerned about it, take the rear shocks apart, add an o-ring right below the shock piston (inside the shock body) to limit the downward suspension droop.

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52 minutes ago, spankrjs said:

When you pick up the rear end off the ground, the suspension goes to the full downward position, the rear axles/driveshaft/cups are trying to spin at their maximum angle, so they vibrate some.

 

When the vehicle is on the ground/running, the rear suspension is not in the full downward position, so the rear axles are not binding/vibrating due to the excessive angles.

 

If you are overly concerned about it, take the rear shocks apart, add an o-ring right below the shock piston (inside the shock body) to limit the downward suspension droop.

Thanks for explaining, that's a relief, I wasn't sure whether I may have built it wrong.

I just ran it again with the wheels on but this time lifted the suspension and all runs smooth.  Thanks for the o-ring idea too, I may put one in to lessen it but as long as it doesn't do it when on the ground maybe it doesn't matter.

Glad to understand it, cheers. 

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Just finished doing the modification to the back suspension to remove the vibration/rubbing/rumbling when lifting up the back and selecting forward/reverse.  It didn't seem to me that the suspension actually drooped/moved when I lifted up the back so I believe it may have been vibrating etc when on the ground running. 

I tried 3 o-rings pushed onto the rod inside the suspension housing to reduce the droop but the vibration/rubbing was still there a bit and I didn't have anymore o-rings so used something else.  I had kept the sheathes that are slid over the motor spindles when you receive a new kit.  I used one on each suspension rod and now the vibration/rubbing is completely gone because the rear axles are no longer at such an angle.  Also the rubber gaiters are pushed up more tightly to the side of the gearbox so no need to use cable ties to hold them in place. 

The other effect is that my Monster Beetle is no longer so hump-backed!  There isn't as much suspension travel when pressing down on the back but hopefully still enough to absorb bumps etc.

Also I like that the ride height is lower at the back and may help with stability.

 

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One other thing to note: Blackfoot/Monster Beetle wheels and tires are notoriously unbalanced. If you have a heavy spot in the tires, or the wheels are out of round, it will vibrate like crazy. Not a whole lot you can do, unfortunately, except try different wheels or tires.

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8 hours ago, markbt73 said:

One other thing to note: Blackfoot/Monster Beetle wheels and tires are notoriously unbalanced. If you have a heavy spot in the tires, or the wheels are out of round, it will vibrate like crazy. Not a whole lot you can do, unfortunately, except try different wheels or tires.

Cheers.  Since removing the vibration/shaking by lifting the suspension and removing the sharp drop of the dogbones, the wheels are turning smoothly so maybe the tyres are balanced ok/round and the previous uneven turning was due to the binding of the dogbones/gaiters due to the lower suspension position.

Love my Monster Beetle all over again now as the vibrating/rubbing/violent shaking was bothering me and so glad its gone.  This happened when lifting the rear end and applying forward/reverse but when running I heard some unusual sounds and believe it was vibrating/rubbing/shaking etc when running on the ground.

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Next step is to get some of the 3D printed gearbox braces.

I'm hoping when these are fitted the premature wear to the diff/spider gears will be eliminated and I won't need the MIP ball diff?

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