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Loud Frog Rear End

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Hey Guys, I have a question I hope you can help with. I built a frog kit about a month ago and decided one just isn't enough! So, I purchased another one from Japan (the XB model) on Ebay and received it in about a 1 1/2 weeks. Upon inspection I noticed that the rear is making a terrible rattling/chattering noise that my kit does not make. With the wheels off it's as smooth as silk, but when you put any rear wheels back on the sound and the vibrations start. Not sure if its the gearbox or the something to do with the dog bones and wheels. The only difference I can see is that the kit had regular dog bones and the prebuilt XB has the CVDs. Here is a link to the noise. Thanks for any help!

https://youtu.be/SSaBYr0phRQ

https://youtu.be/bCxR7ZOzgOc

 

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Something that just popped into my head could it be when you tighten the wheels it pulls the axel through towards the wheel so the CVD isn't aligning properly or is it pulling the hub close to the stub axle and hitting it. just a thought  

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If you run it with the rear arms slightly lifted ( as though the weight was on them) does the noise stop ? . It could be that the arms are dropping too low and the noise could be coming from the CV joints not turning smoothly as they are past their 'drop' limit to run smoothly . This used to happen with the old Frog etc hex dog bone shafts and needed a 2-3mm spacer inside the rear dampers to stop the arms dropping so far

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23 hours ago, KEV THE REV said:

If you run it with the rear arms slightly lifted ( as though the weight was on them) does the noise stop ? . It could be that the arms are dropping too low and the noise could be coming from the CV joints not turning smoothly as they are past their 'drop' limit to run smoothly . This used to happen with the old Frog etc hex dog bone shafts and needed a 2-3mm spacer inside the rear dampers to stop the arms dropping so far

Thanks for your replies, it's the arms that are making the noise. I was hoping it wasn't the gearbox.

 

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If you try what I said before and see if the noise stops , it could be the CV joints in the CVD shafts being allowed to drop too far , not a problem with the actual arms themselves or the gearbox necessarily  . I've had this kind of thing happen in the past .

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You may need a spacer in your rear shock to prevent them from dropping too low...

Terry

 

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Split the trans...look for worn gears and/or metal in the grease..like a aluminum paste looking stuff....I had to do this in a xb frog ....that aluminum gear in the trans was the problem...

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On 4/16/2020 at 2:49 PM, KEV THE REV said:

It could be that the arms are dropping too low

I'm with @KEV THE REV here.  

Universals have a limited angle.  If it exceeds that, it could make that noise.  It's quite common. You could shorten the shocks.

If there is any thread remaining, screw the shock ends all the way to shorten.  One other way already mentioned By @Frog Jumper is to put a bit of a spacer underneath the piston (which require rebuilding the rear shocks) to shorten the distance the shock could move.  An extra o-ring could do the trick. 

GAS5eUy.jpg

 

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An alternative to the spacer is one of my favorite vintage hop-ups from Bolink. If you can find it. “Frog Lowering Kit”...

It was a couple of zip-ties that you weaved through the springs to shorten them. 

:rolleyes:

Terry

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