Date: Thu, 9 Aug 2001 22:08:35 -0700
Reply-To: pensioner <al_knoll@PACBELL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: pensioner <al_knoll@PACBELL.NET>
Subject: Re: transaxle life
Content-type: text/plain; charset=iso-8859-1
Hi Volks,
I have done a bit of consumer research into the 094 transaxle and it's
failure modes and lifetime in higher torque applications.
Here's what I've learned so far.
Shaft torque is the issue. Rated whorespower doesn't matter. Moving a
westie on flat ground at 70 MPH sustained requires a certain amount of
"horsepower". What that really means is thrust or torque delivered to the
tire/road interface. It's independent of the motor unless the motor cannot
produce the necessary torque multiplied through the drivetrain. For a
4.86/0.86 system that's a 4.18 drive ratio in top gear. Simple arithmetic
will give a result that dictates how much torque is required for a given
tire circumference. BUT as I asked before it is quite handy to know the
drag coefficient as this and the tire losses and drivetrain losses make up
the significant components of the required power.
For our beloved bricks, aerodynamic drag is the problem. We do know that a
95 HP WBX will propel a sing crow westie at 70MPH on flat ground in still
air a little shy of WFO. Anything more is gravy, useful for passing, hill
climbing and other accelerations.
The point is the transmission knows nothing other than shaft torque demands.
To accelerate or climb hills requires more torque/thrust than flat travel at
constant speed. The more torque the transmission is required to deliver,
the more wear it suffers. Swepco or Redline or similar lubricants can help
assuage the wear but not eliminate it completely.
With the 2.ll WBX WFO in top gear the transmission is passing the motor
rated torque at that rpm to the axles. If the torque required is balanced
by air friction or incline the van stays at a constant speed with a constant
torque passed by the transaxle. For the 2.1 WBX this is full utilization of
the motor capabilities
With the 3.3l SVX going up the same hill at the same speed, the same amount
of torque is passed by the transaxle. However if you have an additional
2000lb load or a steeper hill the torque required is higher and although the
2.1l can't deliver that amount of torque, the SVX can and will stress the
transaxle to a greater degree. If you would like to pass that Ford Exploder
in a brisk fashion on the same hill, more torque/thrust will be required
with corresponding increased stress on the drivetrain. Even more with the
2000lb load. Now if you reach a hill or situation where you are WFO on the
SVX at 4500RPM the rumor is that the transaxle will pass 225lbs-ft of torque
to the axles. This is a bit more than twice what the WBX can do and the
issue is how well the transaxle will handle the demand.
Failure occurs primarily through two mechanisms, increased wear and
fracture. The increased wear can be mollified by using very good
lubricants. The fracture of parts due to metallurgical stresses can be
minimized by careful selection of these parts and careful assembly. Stress
reducing treatments such as shot-peening to reduce stress risers on the
parts can help reduce the catastrophic failures.
"It's just fizzix, it's always just fizzix" apologies to Dr. Feynmann.
Drive gently but briskly and you will have a normal life expectancy, so will
your transaxle. Push the limit and...Transaxle Engineering in Chatsworth CA
can help with the repairs. www.transaxleengr.com. If you want to push the
limit, Brian at www.smallcar.com can do the upgrade.
cheers,
pensioner
