Re: Dyno Testing Problem

[Iain Mannix <mannix@privatei.com>]

I doubt it has anything to do with the car/alignment - we've had
dyno-emissions for the past few years anyway(Boulder, CO), I've tested
several of my own cars as well as watched several on the chassis-dyno
emissions deals; most seem to wander a bit.  I've also run my VW
Rabbit on a chassis dyno a few times(two different dynos), and both
dynos made the car wander around a bit.  Who knows why, but they all
seem to do it.  

My Rabbit(an autocross car) tends to wander severely on dynos - the
emissions dynos around here have little bumpers that extend from the
sides to keep the car on the rollers - they don't strap the car down
like the private dyno people, due to time constraints, I'd guess(it
takes 15ish minutes to strap a car down well, and even so, it takes an
operator to manipulate the steering wheel). 

I tried to drive my car on the dyno once; practically drove it off the
rollers.  Crotchety old dynoguy made me get out, he got in, feathered
the gas a little - car wandered right, left, then he figured it out &
no more wandering.  Seems as though the dyno operators have to sorta
"feel" the car out a little before they can keep it straight.  

Worried me the first time, but it seems that _all_ cars wander some;
my Rabbit(-3.5d camber, 1/8" toe out) wanders more than most, but I've
not noticed a car that did not wander a little initially.  

Would not worry about it.


I.Mannix


On Wed, 3 Nov 1999, Alexander van Gerbig wrote:

>     I went to the garage prepared to do the new dyno emissions test.
> Everything was fine, the mechanic got the car on the dyno, did all the
> computer work, then they needed to center the front end on the dyno.  They
> put the car in Drive and let the wheels spin under their own power.  The car
> slowly started to slide to the left so the mechanic applied the brakes.  He
> let up on the brakes and the car wnadered back to the right side of the
> dyno.  The car wandered from side to side twice.  What is the cause of this?
> Alignment seems fine.
> 
> Thanks!
> 
> Alexander van Gerbig
> '88 Audi 80 -- Koni Yellows, G&M Springs
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