A solution found to the Hot Racing motor mount/center diff fitment problem...

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Bigfella

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Arrma RC's
Kraton, Typhon
Like many I bought the Hot Racing motor mount and center differential holder. They are well made parts and the motor mount offers unheard of convenience when servicing your truck.

The major problem is that when used together, they create front and rearward play in the center differential that equals .4mm. This is unacceptable. Having the spur gear move backwards and forwards on the pinion .4mm while under power is a recipe for bad things to happen.

What to do?

I contacted Hot Racing about this issue. They said they were unaware of this issue but would look into it. That's great but how does that help those of us who bought the parts but can't use them?

I experimented with many fixes and finally found one that works. It allows you to use both the HR motor mount and the HR center differential holder without any play. The fix is rock solid.

You have to buy these shims:

https://www.amainhobbies.com/protek-rc-8x12x0.1mm-pinion-gear-washer-10-ptk-h-5909/p188797

Take 4 shims (which equal .4mm) and place them between the center differential spur gear and the ball bearing. This is on the external, rearward side of the center differential. It is essentially externally shimming the center diff. It takes all the play out.

Their you go. Go ahead and enjoy the convenience of the motor mount and the strength of the center diff holder......without the dealbreaking front rear play. :)
 

Exceeded

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Singapore
Arrma RC's
Typhon
Thank you Bigfella! It seems that the veterans here are really looking out for the new guys! What you mentioned about the shims being placed on the rear ward side of the centre differential,do you mean the front diff's dog bone's rear where the dog bones end ball bearing where the part of the plastic mount for the centre differential is?
Sorry. Had to clarify as different vehicle has different setups. (Like the vorza has a different setup from the serpent cobra 811 be) thanks in advance!
Cheers
Like many I bought the Hot Racing motor mount and center differential holder. They are well made parts and the motor mount offers unheard of convenience when servicing your truck.

The major problem is that when used together, they create front and rearward play in the center differential that equals .4mm. This is unacceptable. Having the spur gear move backwards and forwards on the pinion .4mm while under power is a recipe for bad things to happen.

What to do?

I contacted Hot Racing about this issue. They said they were unaware of this issue but would look into it. That's great but how does that help those of us who bought the parts but can't use them?

I experimented with many fixes and finally found one that works. It allows you to use both the HR motor mount and the HR center differential holder without any play. The fix is rock solid.

You have to buy these shims:

https://www.amainhobbies.com/protek-rc-8x12x0.1mm-pinion-gear-washer-10-ptk-h-5909/p188797

Take 4 shims (which equal .4mm) and place them between the center differential spur gear and the ball bearing. This is on the external, rearward side of the center differential. It is essentially externally shimming the center diff. It takes all the play out.

Their you go. Go ahead and enjoy the convenience of the motor mount and the strength of the center diff holder......without the dealbreaking front rear play. :)
 

smithgpz

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ohio
Arrma RC's
Fazon, Fury, Typhon
thanks for the info.i have the diff support and was looking at the motor mount. does the motor mount stay secure when tight?
 
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Bigfella

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Yes. My HR motor mounts in both my Kraton and typhon have been rock solid and stay secure.. No problems so far. I use blue loctite on the motor mount plate screw. If I ever start having problems I'll use red loctite as it is easy to remove with a heat gun.
 

rcdabbler

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Senton
That HR motor/center diff mount is one of the hop-ups I ordered to build up the pre-roller chassis I purchased. Thanks for the tip! I'm ordering a pack of those washers.
 
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Bigfella

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Excuse the mud lol. The shims go here. You will have to take the diff apart to properly place the shims as they go in between the rear bearing and the spur gear. You can slide them right onto the protrusion on the spur gear. Then reassemble diff as normal.
 

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Exceeded

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Excuse the mud lol. The shims go here. You will have to take the diff apart to properly place the shims as they go in between the rear bearing and the spur gear.
oh my Bigfella! thank you so much! it is so clear right now! btw, no car is too clean after unboxing.
thanks for the pic! it certainly helps a lot
;)
 

Sully_

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How is this fix holding up for you? Has anyone else tried ? i have both , and the shims are on the way. Hoping this fixes it :D
 

Sully_

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OK . This 100 percent fixed the issue. For some reason though i needed 6 shims to completely eliminate the slop. with 4 i still had some play.
 

msmy300z

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Arrma RC's
Kraton
Anyone have trouble with fitment of the diff bearing with this mount? I have tried to place my diff 2-3 times and it always gets stuck before bottoming out. I have tried both sides of the diff to see if one bearing was off but it is the same either way. I also tried greasing the hole lightly and it still got stuck with ~1\3 to go. I mean stuck! I had to put the out drive on the floor and push down on the mount until it popped out.
The same bearing goes into the stock mount easily. I don’t see any defects on the anodizing or anything... any help would be appreciated. I don’t know if it is a defect or if I will have this problem with any of them?
 

olds97_lss

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Couldn't you just use 13x16mm shims on the outside of the bearing like we do when shimming the front/rear diffs for better ring/pinion mesh? Less hassle than dry fitting it with the shims on the inside pushing the bearing out.
 

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