SCX10 Drive train chatter and clocking axles

[Westside Charlie]

I've been reading a lot of posts about the reasons that the front wheels/axle may chatter or shudder especially when starting to accelerate and the two causes seem to be:

-- drive shafts not aligned properly so that pins are parallel (matching notches)
-- angle from axles to motor too steep

My drive shaft alignments are fine (checked them five times.) I am guessing that my problem began when I replaced the Axial stock shocks (90mm) with Integy Piggyback shocks (107mm). That difference may have increased the angle enough to cause the problem. Prior to swapping the shocks, there was no drive shaft issue.

So, to flatten the angle, I need to clock the axles a bit, right? If so, does that mean replacing my current links (aluminum, so they're good and rigid) with shorter links? I think I just need to point the axle down a scooch towards the motor to straighten out the drive shafts a bit.

Is this a good approach and method? Other ideas?

Thanks!

 

[Ohioskills]

make the top links a tad longer and make sure the notch on the drive shafts are lined up

 

[micro racer]

Are you running the three link suspension? If you are, the little ball end on the end of the y-link tends to wear and become really sloppy.

 

[JatoTheRipper]

You can clock the axle by lengthening the top links and/or shortening the bottom links. Make it so that the wheelbase matches your body and the shocks are nearly vertical again.

 

[TacoCrawler]

lower your suspension by using alloy riser/drop plates (sold on ebay - etc)
they will mount the upper eye of the shock slightly higher then the stock position.

A shock longer then 100mm is going to be too long for the original upper mounting positions (JMO)

Your suspension travel should be near 60/40
that means 60% up travel (compression) and 40% down travel (extension)
The pre-load/rate of the coil springs will determine the static ride height.

I run my suspension travel set at 50/50
in other words... my suspension's static ride height
is 50% up travel and 50% down travel.

If you clock the axle...
realize this will require more things to be done to make it correct.

ie:

the servo will get pushed forward...
the servo horn may interfere with the front cross member
and that may need be removed or trimmed to clear.

the caster of the steering knuckles will be reduced...
and so adj. caster knuckles and chubs may need be purchased
so as to compensate.

Like said previously...
if 3 linked... the factory mount is fubar from the get go.
slop there could cause the chatter.
the slop there is caused by the little ball fitting loosely in it's mount/cup.
It will pop in and out... during throttle and braking.
a small washer placed on both forward and rearward sides of the ball
may help minimize the excessive movement.

Generally...
The upper link rod lengths control the axle rotation...
the lower link rod lengths designate the wheel base.

 

[Meatwad]

And then the chain starts, upgrading one thing leads to the need of upgrading another. Its all part of the fun :mrgreen: Pretty much all of what TacoCrawler said is right. But there's personal preference involved as well, along with how one chooses to drive and set up their rig.

For myself and the front axle, a cms/3link setup with a level axle pinion for panhard alignment and almost straight links to protect the axle pinion from rock contact (the bearings thank me). Allows for a ton of caster and decent driveshaft working angle. The rear, doesn't matter as much.. point up the axle pinion at the transmission and out of the rock with an upward driveshaft angle.

Also keep in mind, the scx platform when near stock doesn't lend itself well to a monster truck style. Its meant to sit a little low and have limited suspension articulation. Anything more than a tire height of travel is a waste and can be problematic.

 

[Westside Charlie]

Thanks for all the helpful information!

I realize now that my new shocks are a little too long, but I may still be able to get everything to work with a bit of fiddling. This morning, I added a spacer (about 0.5 cm) to extend the 3-link on both the front and rear. That change clearly smooths out the drive shaft shudder. Next, I'll readjust my shocks, much as TacoCrawler suggests. I already experienced the effects of the shoddy stock 3-link and added a couple washers. I'll add a couple more since that's clearly a weak "link".

I had already upgraded adjustable aluminum knuckles after I broke the stock plastic ones, so those newer knuckles ought to help with my adjustments.

Meat wad pointed out that my scx is not intended to be a monster truck, and that's not what I want. In fact, I'm not sure that the longer shocks were a good idea to begin with. Even though I seem to have no problem with the servo and horn, after the minor clocking I've applied, I would prefer to keep my axle pinions straight. Maybe by adjusting the shocks themselves I'll be able to avoid excessive clocking.

After I make some modifications, I'll report the results.

Thanks again for great advice and encouragement.

 

[TacoCrawler]

the drive shaft pinion angle does not need be angled perfectly straight...

but at full droop it should not have such an extreme angle to it...
that causes it to bind/cog.

My drive shaft angle is near it's angle limits at full droop...
but during the chassis's more regular static ride height...
the pinion angle is less severe and helps improve the universal's consumable life expectancy.
High speed runners may need to have the pinion angle more in line
when bashing or hauling butt, to reduce the DS's consumable wear.

I added 2-3mm to the upper link rods for axle clocking (forward rotation)
this pushed the servo's horn into the forward cross member.
So... I shaved the servo mount(s) forward surfaces slightly to mount the servo slightly rearward. (not the plate, just the servo)
I used Axial 8* Chubs and knuckles to bring caster back in line.

I also replaced that forward cross member with a single tube.
* some folk just notch or grind clearance on the stock cross member.
But I also discarded the forward battery mounting plate in favor of running saddle pak designed battery mounts.
so no longer needed the stock cross member's battery plate support.

After I make some modifications, I'll report the results.

trial and correction is a good process...

I think you have a fairly good understanding...
so don't be afraid to try things... and figure it out for yourself ;-)

 

[Westside Charlie]

I think I'm making progress. adding the spacers to both the front and rear links pushed the axles forward enough to stop the drive shaft chatter. The servo and horn seem fine and there is enough clearance for the steering links without having to do any mods.

The camber is off now, and I'm going to have to fiddle with chubs and knuckles to adjust that. I already have the Axial alloy chubs and knuckles installed from an before the shock upgrade, and I don't see yet how to further adjust them to offset my negative camber. I may need different parts.

What I haven't yet modified my upper shock positions, so I'm going to find some riser/drop plates to fix that before I mess with the camber.

I'll post a few photos soon.

Thanks!

 

[TacoCrawler]

camber is a fixed position on a solid axle.

do you mean caster ?

Or is there the possibility you installed the
Chubs and Knuckles incorrectly on the wrong sides ?

 

[Westside Charlie]

OK, here are some pix of my new shocks that probably need riser plates to set a little higher, and the current caster that needs to be adjusted.

The shocks that need to be positioned higher, I think:

And the caster I need to adjust:

With any luck, I just have to properly adjust the existing chubs and knuckles.

(Apologies if the images posted twice.)

 

[Westside Charlie]

And yes, I've confused camber and caster. (Lot's to learn.)

I hope I can correct what's wrong with what I have. Otherwise, i'll have to buy more cool stuff...

 

[Westside Charlie]

After a bit more fiddling, I believe both the original drive shaft problem, as well as the resulting caster problem, are now fixed on my SCX10.

To fix the drive shaft problem, I had added spaces to both the front and rear top links. Those 7mm spacers worked fine to chill the drive shaft chatter but even with my adjustable knuckles on the front axle, the caster was off. I backed off the 7mm spacer to 3mm, using a few washers, and that lined up the knuckles correctly so I have very close to zero degree caster, and still have reduced the drive shaft angle enough to eliminate the chatter and binding.

Thanks to all for great insights and suggestions.

I think I'm ready to crawl again...

 

[Westgraphix]

this thread solved my problems!!
"thumbsup"