Re: V8 Gearboxes & O2 Sensor

[Eliot Lim <eliot@u.washington.edu>]

On Tue, 28 May 1996, John Firkins wrote:

> Phillip Ross wrote:
>
:I find that the gearbox on our V8 is prone to sending heavy thuds through the
:car.  For example if you are in 4 (e.g. at 50mph) and put the foot down just a
:little so the car kicks into third and then lift off the box disengages with a
								^^^^^^^
:real thud.

what do you mean by "disengage"?  do you lose drive altogether?  if
you actually meant "engage" i'd guess that it's the torque convertor
locking up.  it shouldn't be too noticeable though it's not exactly
nicely slurred. it would resemble a less than perfect gearchange
in a manual transmission, like letting up on the clutch a little
too quickly.  this would usually happen on light throttle openings.

> Travelling at a constant speed above about
> 50mph, it will occaisionally have a hiccup, which produces a thud through
> the drivetrain.

i'd guess torque convertor locking up.  you get much better power and
mileage in this state than with it unlocked.

> At first I thought it to be the box disengaging, but the drop in revs would
> seem to contradict this.

this would support the above.  the car should now have a linear relationship
between speed and rpm.  50mph should correspond to about 2000 rpm.

it is a fact that the ZF slushbox in the v8 is way more backwards than
those found in much more modest american and/or japanese cars.  it is
much more lossy and does not feature gradual locking of the
convertor/coupling.  (latest 5 speed ZF finally incorporates this)
however it has tremendous load capacity (go check its towing capacity)
as well as power handling.  the 300 bhp bmw 750i uses the same unit.

the first generation software was also dumb as a thumbnail and the
current "smart" software that "learns" your style is also far from
convincing.  it is sad that audi abandoned the zig zag gate in the
latest cars because that was the perfect cure for transmission
software ineptness.  fortunately the shift quality of the manual
transmission is excellent in the a4.

eliot