Differential Acting Up?

Differential Acting Up?

Post by Aaron Conawa » Sat, 28 Oct 2000 23:46:38



Here I am again.  Newbie.  Don't know the names of the parts I'm about
to talk about, but here is goes...

Background info:  My friend and I both have Traxxas Rustlers with
electric motors.  Stock everything except for the steering servo
(hasn't everyone replaced that?)

Problem:  I have serveral symptoms here, so I'll just list them then
give my theories.  I have a slipper clutch.  When I have the clutch
gear in my hand and hold it by the hex nut in the center, I can spin
the gear freely.  Is that normal in a slipper clutch?  Isn't that the
mechanism that we get the slipper part?  My big symptom is demonstrated
when I turn the axles.  I turn one wheel forward and the other one
turns forward.  I don't believe that's normal as my friend's wheels
turn opposite of one another.  When I hold down the clutch gear with my
fingers and turn the wheel, the wheels spin opposite directions.  With
that in mind, I could attribute this problem to the fact that I can
spin the clutch gear as stated before.  Another sympton in the axles is
the freedom of the axles as they turn.  They are very stiff and don't
glide very smoothly.  I cleaned up the bushings (bearing upgrade will
be soon) and all parts external to the transmission to no avial.  I
took the *** apart to see what was happening but saw nothing that
looked weird (like I know what I'm looking for or something).

My Theory:  The differential is going out.  That would cause the axles
to be tight and rough, as well as explaining the wheel-turning
problem.  The clutch gear is fine, but may require more *** "brakes"
in it to keep things from slipping.

Thoughts?  Am I way off?  Do I need to get a new diffy?  Just add some
more grease to the ***?

TIA.

--
Thanks,

AC

Sent via Deja.com http://www.FoundCollection.com/
Before you buy.

 
 
 

Differential Acting Up?

Post by Jonny Hodgso » Mon, 30 Oct 2000 00:16:24


Quote:
> Problem:  I have serveral symptoms here, so I'll just list them then
> give my theories.  I have a slipper clutch.  When I have the clutch
> gear in my hand and hold it by the hex nut in the center, I can spin
> the gear freely.  Is that normal in a slipper clutch?  Isn't that the

Right... just need to clarify a few things here.
Have you got a motor in the car when you do this?  Is the slipper actually
in the car or are you literally holding the slipper in your hand?

Take the motor out, and have the rest of the transmission built.  Hold
the wheels still (if you're sitting down with the car on the floor, put one
foot
on each wheel).  Now grab the spur gear (wrap your thumb and finger
round the outside) and try to turn it, forwards for preference though it
doesn't really matter.  It should be pretty stiff to turn, but when
something
finally slips it should be the slipper not the diff (watch carefully to see
what's
turning).  Adjust the hex nut until you can just about slip it.  If the diff
slips
really easily then tighten it up.

Quote:
> mechanism that we get the slipper part?  My big symptom is demonstrated
> when I turn the axles.  I turn one wheel forward and the other one
> turns forward.  I don't believe that's normal as my friend's wheels
> turn opposite of one another.  When I hold down the clutch gear with my
> fingers and turn the wheel, the wheels spin opposite directions.  With

Right... this all depends on how much resistance you've got where (like
whether
there's a motor fitted).  With no motor, I'd hope there's more resistance in
the
diff than there is in the drivetrain, so turning one wheel forwards ought to
spin
the whole thing forwards just as you say.

With a motor fitted, or holding the spur gear (your "clutch gear", I
suspect)
the diff will start to operate.  Now, the two main points of a diff are:

    1) it applies the *same torque* to each wheel (not strictly true for a
ball
diff, but we'll ignore that for the moment).

    2) it makes the *average speed* of the two wheels *equal* to the speed
of the drivetrain/input.

2) is the important one here.  If there's a motor in or you're holding the
spur,
then the speed of the drivetrain is zero.  If one wheel is spinning
forwards, then
for the average wheel speed to be zero the other wheel must spin *backwards*
at the same speed.

Quote:
> the freedom of the axles as they turn.  They are very stiff and don't
> glide very smoothly.  I cleaned up the bushings (bearing upgrade will
> be soon) and all parts external to the transmission to no avial.  I
> took the *** apart to see what was happening but saw nothing that
> looked weird (like I know what I'm looking for or something).

Right, first off take the motor out again and spin the whole transmission
forwards (you said it'll do this by turning one wheel, right?)  Spin it and
let it go - the whole thing should carry on spinning for a couple of
seconds,
maybe.  If it stops immediately you've got problems, but on bushings slowing
down fairly quickly is normal (the bearings will help).  Also if it feels
rough
or stiff, it's time to start taking things apart and testing each bearing /
shaft
individually until you trace the one that's causing the problem.

Then hold the spur gear still once more, and turn one wheel so the diff
operates.
Now if *this* feels notchy or rough, it might be worth rebuilding the diff
although I'm not convinced that it really makes much difference - it's
certainly
not as important as having a smooth, free-running transmission.

Bear in mind that some real racecars (Le Mans/IMSA; Indycars) run with
no diff at all (a 'spool') at many circuits - the diff ain't essential!

Quote:
> My Theory:  The differential is going out.  That would cause the axles
> to be tight and rough, as well as explaining the wheel-turning
> problem.  The clutch gear is fine, but may require more *** "brakes"
> in it to keep things from slipping.

Certainly *sounds* like you may have your slipper too loose, but it's
hard to say (you didn't describe what happens when you drive the car...)

I'm not sure about "*** brakes" - all the slippers I've seen run teflon-
-coated metal pads against a plastic (probably nylon) spur gear.  Just
tighten it up a little...

Sorry this has got a bit long - let us know how you get on.
Jonny