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NZJohn

Frog - noise coming from rear post hop up of shafts

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I’ve just done my first hop up of a Frog. But I’m getting a horrible grinding noise at low speed. 
The upgrade was 53908 FROG Assembly Universal Shafts. And whilst I’m pretty sure I follow the instructions I’ve clearly missed something. 
The only part I did add was to put a plastic o ring into each of the two parts that go into the gear box. 
There’s nothing obviously wrong I can see  

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Make sure the cross pins haven't worked loose. Was it making the sound before you installed the new universal shafts?

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Cheers. It was running smoothly before with the kit standard shafts. I’m going to strip it back to the gearbox. And start the hop up assembly again. 
 

I kind of got caught up today with painting a decals 😜

FDFDF8AF-432C-427B-B06E-E7DE35FE89E0.jpeg

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Ok, I’ve taken the universals and wheels off. 
With just the two shafts left sticking out of the gearbox the motor and gearbox is running smoothly and no issues. 
But as soon as I put the universal shafts and wheels back on I’m getting the same awful grinding sound at low revs… see attached video. I need help!

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Maybe I’m old and deaf but that sounds like it’s supposed to.  It is a little clicky but I think as the parts break in, the sound will diminish…

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If you remove the rear shocks and prop up the rear suspension arms so that the drive shafts are horizontal does it still make the noise?

If not, how far can you lower the arms before the noise starts again?

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19 hours ago, Fuijo said:

If you remove the rear shocks and prop up the rear suspension arms so that the drive shafts are horizontal does it still make the noise?

If not, how far can you lower the arms before the noise starts again?

Yes. This does make a huge difference. If I push the wheel up so they are closer to horizontal you don’t get the grinding noise at all. 
 

So is this normal. And when slack the rear wheels are just at too much of an angle? So the weight of the car pushes the universal joints more horizontal and reduces / eliminates the noise?

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32 minutes ago, NZJohn said:

So is this normal.

I don't know tbh. I'm sure I've read somewhere that the universals don't work as well as the dogbones at extreme angles. Which is odd; you would think the hop-up designed for it would work with it, wouldn't you?

If it were me, I'd either go back to the dogbones, or keep the universals and put an internal spacer, like an o-ring or two, under the damper piston to stop the shocks extending so far.

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1 hour ago, Fuijo said:

I don't know tbh. I'm sure I've read somewhere that the universals don't work as well as the dogbones at extreme angles. Which is odd; you would think the hop-up designed for it would work with it, wouldn't you?

If it were me, I'd either go back to the dogbones, or keep the universals and put an internal spacer, like an o-ring or two, under the damper piston to stop the shocks extending so far.

Ok cheers. That’s a bit of a let down. The hop up isn’t cheap either. I’ll revert to the kit dog bone joints and test again

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UPDATE; I’ve found a solution. And thanks to those that commented here. 

TLDR: the hop up universal joints cause a grinding sound at high angles. When moving the wheels closer to horizontal they operate smoothly and without the rough noise. So I opened the shocks and put a 5mm piece of tubing over end of the piston. This reduces the distance the shocks travel and makes the car lower to the ground. And problem solved!

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This makes sense as the frog has really short half shafts for a rather large amount of suspension movement. Newer cars have longer suspension arms and longer shafts so the angels aren't as extreme. I believe this is why the original frog hex shafts would round off.

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On 7/24/2021 at 7:11 AM, NZJohn said:

 

FDFDF8AF-432C-427B-B06E-E7DE35FE89E0.jpeg

That's a good looking Frog!  

When I restore my Frog, I want to go with the original color scheme.  Maybe I'll leave the roof clear too! 

 

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