FWD Transaxles

[Sketch]

> Somewhere I have a article with GM about the Getrag transaxle. If I
> remember it correctly, the Getrag was spec'd something like 200ft-lbs for
> warranty, 350ft-lbs in reality and 500 before destruction.

Here's something someone posted to the Fiero list which might be
interesting...

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Date: Wed, 12 Nov 1997 20:17:49 -0800
From: Gary Ohst <garyo at globalpac.com>
To: fiero-list at fiero.org
Subject: (Fiero) Performance Transaxle (Long)

Hi All,

Here is some more info on the Getrag and some on the Isuzu.  Research
continues.  Warning: There are a few opinions in this post, so please
don't believe them :).

The only other factual Getrag strength information I have found is on
the Oldsmobile mail list FAQ page.  The same Fiero and FWD GM Getrag
transaxle used three different designations.  The HydraMatic 282
(HM282), the 5TM40, and most recently the NVT550 when New Venture Gear
(GM/Chrysler joint venture) took over production in 1991.  The Olds FAQ
page states it is rated at 200 ft. lbs. torque and 7,000 rpm max. input
shaft speed.  The Getrag is built on a 75mm input-shaft to counter-shaft
centerline distance, just like the Isuzu.

I have not found any torque ratings on the Isuzu.  I have e-mail from
Isuzu on this topic and all they could tell me was it was manufactured
by Jatco, go ask them.  I'm still working on this.  It would be
interesting to compare the "rated" torque of these two units just to get
some idea of the relative strength differences.  Not opinions, but
actual numbers.  It has already been proven that the "rated" numbers can
be exceeded.

Another transaxle option might be the Getrag Gears of America
manufactured HM284, a higher strength version of the more common Muncie
manufactured HM282.  The case was beefed up, but the centerline
distance, which relates to the maximum gear diameter you can stuff in
there, is still 75mm.  With gear diameters being limited, the gears were
made wider to add strength.  As a result, the internal bellhousing area
had to be reduced.  These units use a special low-profile clutch that
*pulls* on the diaphragm fingers.  Also, sometime in 1991 GM changed
over to hydraulic throw-out bearings for both the HM284 and newer
versions of NVT550.  The rare HM284s were only offered 1991-1993 behind
the 3.4 liter, 24-valve V6 engine in W-cars: Lumina Z34, Cutlass Supreme
and Grand Prix.  I have no torque stats on the HM284, just comments by
Rick at A.C.E. that they are about 30 percent stronger.  If anybody
finds a HM284, please contact me :).  

Chrysler has continued to tinker with the basic Getrag designed NVT550. 
There was a NVT650 version and most recently a NVT750 was designed in
1996.  It is a higher strength version still using the 75 mm shaft
spacing and overall package size. SAE technical paper #962164 discusses
this new transaxle.  Torque capacity is stated at 290 N-m or about 215
ft. lbs.  They use wider gears, finer gear teeth, high grade materials
and better bearings to increase strength and reduce gear noise. 
Shifting is also improved.  These are mini-van transaxles with a
Chrysler bellhousing pattern.  The other problem is they are only being
sold in the European ECC market in mini-vans using 2.4 liter gas and 2.4
liter turbo-diesel motors.  Anybody know if they have pic-a-part yards
in Europe?  I have some New Venture Gear NVT750 spec sheets on the way,
so additional application info is forthcoming.

Another option might be the 1988-1989 Beretta FWD HM282 Getrag which
came with an aluminum intermediate shaft extension housing.  Because of
torque steer generated by unequal length axles in the front, GM added an
intermediate extension shaft on the long axle side.  This setup splits
the long axle into two sections, a fixed inner or intermediate portion
and CV jointed outer portion.  Also, the intermediate shaft adds an
extra axle bearing in the motor mount area.  The outer axles shafts are
now the same length and exhibit similar joint friction (torque loss)
characteristics as they flex during steering and suspension movement.
1988-89 used an intermediate shaft enclosed in a aluminum extension
housing. This housings adds additional rigidity between the differential
case portion of the transaxle and the engine motor mount.  1990+
Berettas used an open air shaft and separate motor mount bearing pillow
block, so no extra case to motor mount rigidity is introduced... 
beancounter engineering.

The Beretta intermediate shaft and housing will separate from the
standard Getrag case, so you might be able to add these items onto other
Getrags.  The extension housing mounts to the case using the three holes
surrounding the long-side axle seal.  The outer end fastens to a
modified motor mount bracket.

The equal length issue is not as important on the Fiero as there is no
steering induced CV joint friction.  IMO, (sorry, more opinions) the
main benefit from this setup is the rigidity added by the 1988-89
aluminum extension housing.  Correcting suspension movement CV friction
differences is one of those marginal improvements that, when combined
with others, begins to add up.

Off-list conversations with those that broke Getrags ( one road racer
with a Webster/Getrag & one drag racer with a standard Getrag) indicate
case strength problems in the differential carrier housing area. Another
road racer indicates no problems with a Webster/Getrag.  Also, one
individual e-mailed me off-list after my last post and indicated he has
no Getrag problems with his 450hp V8 in the production space frame.  It
is a very well mounted V8 installation from his description.  Draw your
own conclusions.

Just sharing some research, a few facts and ideas.  If I am missing
anything please let me know.  On the clutch stuff, I have resigned
myself to saving up for a dual disc Tilton or Quartermaster. I hear the
parts will interchange.  This is a long one, so edit your reply.

Gary

1985 SE 2M4 170,000 miles
16v SD4 Turbo U/C
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