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Nova1

Tamiya Avante/VQS ball diffs

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Just wanted some advice following assembly of both an Avante and VQS. Most of my Tamiya fleet has geared diffs so I’m a little inexperienced with ball diffs.

During assembly I’ve tightened the central ball diff to what I think is the correct amount. Initially the differential seems correct when I turn the wheels by hand with one wheel turning the same amount as the other and in opposite direction. However even after a short test run the wheels seem to slip a little when I manually turn them.

Is this normal and to be expected or should I be taking out the diff and tightening? Seems a bit of a hassle to get to the diffs in these models.

Any advice much appreciated 

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It shouldn't slip.  

You need to tighten more. But I've broken the screw a couple times in the past.  Tamiya's ball diff grease is the same whether you are using it in a small 900 gram M-chassis running on tiny tires or 1300 gram buggy with much larger tires.  That part made no sense to me.  I think the grease should be stickier for off-roaders.  On geared-diffs, people use all kinds of stickier grease too.  

So I'm using this Danco plumber's faucet grease as ball diff grease.  It is slightly thicker.  Yet, it gives you more adjustability.  Try tightening it only as much as you did before.  Instead of slipping, this would make the diff a lot tighter.  For making an effective Limited-Slip-Differential worthy buggies, $4 on this was one of the best investments I made.  (If you don't like it, use it to make gear boxes water-resistant by applying it on the seams. It's plastic safe. Just like Tamiya ball diff grease, this thing wipes off relatively easily too.)  

YiFE5DS.jpg

 

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Thank you for the advice - much appreciated. Also wondering now whether I used too much of the supplied ball diff grease. Perhaps this is not allowing balls to make enough contact with pressure plates??

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I don't think you need to worry about the grease at this stage, whilst not necessarily optimal, the Tamiya grease is fine to start with and it's unlikely that you've used too much (Tamiya don't actually supply enough to use too much). 

Most ball diffs will loosen during the first few runs, it's not unexpected to need to tighten them up and you should be able to do this whilst they're installed (removing the drive shafts of course). Set -> install -> run -> adjust -> profit.

You eventually get the hang of how a correctly set ball diff will "feel" in the hands... you shouldn't be able to turn them by hand with the drive cups installed until you put something in the outdrive slots and then you should be able to turn by hand and feel the resistance.  

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Thanks for taking the time to explain this. Guess I’ve been over cautious about not over-tightening the diff as stated in the Tamiya VQS manual 

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Do they supply the parts for a locked centre diff with these kits? There is no reason to run the centre ball diff, it just adds unreliability and decreases performance. Just an example of Tamiya's fantasy idea of what a 4wd racing buggy should be, which was proven completely wrong on the track.

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How easy is it to remove the centre ball diff in the Avante/VQS once assembled? If the central drive shaft has to be removed to allow diff to be removed then does the front or rear part of buggy have to be removed from chassis?

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On 8/10/2021 at 9:39 PM, Nova1 said:

How easy is it to remove the centre ball diff in the Avante/VQS once assembled? If the central drive shaft has to be removed to allow diff to be removed then does the front or rear part of buggy have to be removed from chassis?

It's possible to get it out without complete discombobulation of the entire buggy, but it's super fiddly getting it all back together. 

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Is it? The Egress buggy line is one of the easiest for maintenance in my eyes? You get extra openings for every diff, also the centre diff on VQS is built out in a minute? 4 screws on top case, lift the cover, take the complete centre diff out!

Also I´m not agreeing with @sosidge this time.;) Many users here prefer the centre diff for the fixed (Egress) main spur gear. But it´s kinda cool on this chassis line, that you can choose centre diff / spool / torque splitter option. For sure, its also a matter of driving styles and personal preferences. But with some lock in the axle diffs, it´s quite interesting to combine it with the centre diff. Gives good turn in in my eyes. 

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For a little demo, I have a small video taken with my nephew from my restored Vanquish runner project, running with Black special ball diffs locked with Tamiya AW grease and the original centre diff. My offroad driving is a bit rusted, but on the 180° hairpin corner I got confident more and more with every lap. You really just had to steer and trust the car, and it just turned in. Was a big fun for us.;)

Of course, original pin spike tires have their limit under these loose sand conditions.:lol: But the limited grip made it even more fun sliding the old buddy around. With 4WD, just stay on the gas...

https://www.youtube.com/watch?v=IlMJPVZiEiE

 

Kind regards,

Matthias

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I’m not sure it is that easy to remove the centre ball diff on a VQS as you would surely have to remove the drive shaft to access it? This would involve quite a bit of disassembly. Cloud be wrong but it doesn’t look to be as straightforward as just removing the screws to the top cover. 

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12 minutes ago, Nova1 said:

I’m not sure it is that easy to remove the centre ball diff on a VQS as you would surely have to remove the drive shaft to access it? This would involve quite a bit of disassembly. Cloud be wrong but it doesn’t look to be as straightforward as just removing the screws to the top cover. 

You´re right, you have to take out the centre drive shaft! But usually, it comes up with the diff and the bearing housing. On the Vanquish, I may have forgotten, taht you have to lift or partly lift the upper radio deck, to get the drive shaft high enough. No problem on the other chassis of the line, but a specialty of the VQS / Vanquish.

With a little practice, it´s still no big deal in the end...

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Many thanks for tips - yes I was thinking that the top plate would have to come off which also involves servo disconnection - not a huge task but a tad fiddly! 

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14 hours ago, ruebiracer said:

No problem on the other chassis of the line

If you think it's straight forward on the Avante too, I'm guessing you haven't done it recently :p. On the Egress it's probably easy, as the top deck doesn't get in the way of the shaft as you pull the spur out. Not so much with our friend the Avante.

 

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16 hours ago, Howards said:

If you think it's straight forward on the Avante too, I'm guessing you haven't done it recently :p. On the Egress it's probably easy, as the top deck doesn't get in the way of the shaft as you pull the spur out. Not so much with our friend the Avante.

 

O.k., Original Avante I´ve never built, but from the Vajra chassis I see your point @Howards! Thanks for the clarification on this one! But totally agree, Egress/Avante 2001 is the best one regarding serviceability! :)

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