Date:         Fri, 23 Feb 2001 11:15:55 -0500
Reply-To:     "Tim Smith (by way of Derek Drew <derekdrew@rcn.com>)"
              <smithtj@NBNET.NB.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "Tim Smith (by way of Derek Drew <derekdrew@rcn.com>)"
              <smithtj@NBNET.NB.CA>
Subject:      Tim Smith On Trans FAQ
Comments: To: Syncro@onelist.com
Content-Type: text/plain; charset="us-ascii"; format=flowed

In the material below Tim Smith provides his quick take this morning on the
implication of the Transmission FAQ posted to the list late last night.

Reading his commentary is to the point, and much easier than trying to wade
through the FAQ itself. Torque brackets are a good focus.

==================================

OK,

preliminary digestion of that FAQ gives some info.

minor shit...

- bell hsgs fully interchangeable, tiny difference for Syncro ones
(presumably the vent holes)
- input shafts differ, diesel = shortest, wbx = longest
- some talk about R&P ratios used in various versions
- notes that 1st and 2nd gear are machined onto output
shaft, hence not changeable, but 3-4 (or 4-5 in 5spd/2WD)
gears are swappable.

better stuff....

- max torque of 112HP WBX engine is 176n-m, which is the max for the gearbox!
- failure occurs at double taper brgs that support the pinion end of the
output shaft!!
- failure of 4th and 5th gears also occurs, by tooth damage, in a few miles
with 280n-m modified TDI engines. (tooth failure can be by break-off or
severe surface pitting, I suspect break-off since he says after a few kms)
- high mileage failure (inc. wbx engine) of the needle bearings that these
gears spin on.

- Audi engine is 200n-m, VW-SA added two 'oil returning plates' ??????
and modified (then quit doing) the output shaft to provide more oil to
the needle and double taper brgs.  Older plastic housing needles are
better, more temp resistant (I've seen these slagged!!!)
- stronger 4/5 gears prevent tooth failure BUT gearbox still fails
  (via brgs I guess)
- he rec's 200n-m as the max, also notes driving habits affect everything.
- TDI engine 'AFN' gives 235n-m at 1900RPM need the better gears
- "two frame" flywheel....  I suspect this is like the 'dual-mass' flywheel
that Porsche uses to damp out power surges. Surges can hit 600n-m !!!!!
(note: this is considered an unreliable flywhel in Porsche and is swapped
out often)  It appears that the diesel 'roughness' is a problem for the
gearbox.
- high speed failure, oil over 120C leads to bearing cage melting, and
pitting of tooth surfaces. (Porsche went from splash lube to trans oil
pump with jets onto gear meshing region, on to coolers tied into pump,
logical development as power went from 110HP to 240HP in early 70's)

- talks about influence of gearing etc and engine choice, basically
indicating that lower gears help the transmission (presumably by spinning them
faster gives better oiling and lighter loads, lower heat?) Compensate with
larger tires (205/14 mentioned !!??)

- glass bead blasted gears can handle 300n-m, BUT barely enough for re-chipped
TDI, OK for stock TDI.  Talks about the problems of large RPM changes when
shifting (hence the Exel spreadsheet I did!)

--------------------------

synopsis:

1) stock box = 175n-m limit
2) stock SA box = 200n-m limit (needs only 2 oiling plates!!!!)
3) better 3-4 gears = 300n-m limit BUT bearing failure still likely
4) oil over 120C hurts gears and bearing cages.
5) work out what 3-4 and R&P gears you want, via a spreadsheet,
considering shift points/driveability.

bottom line, other than the torque figures and modes of failure,
there isn't a great deal new here. We knew about the SA oiling
plates already, and they should be added at any rebuilding!!!
No mention of other types of failure, like cracking of housings,
synchro rings etc. But they are 'off topic' as far as the guts
of the box go, and as far as power limit concerns go.

my opinions:

1) we're f*cked, the gear box is inherently weak!
2) get as much reduction as possible at the R&P, modify 3-4
gears to suit, once tires/engine are decided upon.
3) we need a better double taper bearing for the pinion shaft (unlikely)
4) we need needle bearings with steel housings (unlikely,
I've tried for ANY aftermarket needle brgs with zero luck)
Perhaps new 3-4 gears would allow different selection of
brgs, otherwise they are OEM/VW only. (often only 1-2mm different
in LENGTH from stock stuff, same inner/outer diameters, more
stupid-arrogant VW designers at work)
5) some form of transmision oil cooling/circulation is needed.
(Porsche run a pump off the input shaft, always spinning, and
the case is drilled and fitted with nozzles that spray onto each
gear set where they mesh. A cooler would be integrated prior
to the nozzles, would add another 1-2 qts to system, bonus!)

Engine speculations: best engine is the basic 1.9l TD (not TDI) diesel
fitted with an intercooler and tuned to 200n-m max, but across as
broad an RPM range as possible.  Not a lot of gain over 176n-m!!!!!
Looking at M. Sullivans TDI info page, (200n-m = 148 ft-lb) the stock
TDI puts out 142ft-lb (chipped is 181) wbx is 116ft-lb. Subaru
is 137ft-lb??  So we can only safely handle a 25% increase in torque!!!!
This is plenty to allow for fitting of 235/75/15 etc size tires and still
maintain good performance/accel. And I'd prefer burning diesel.
BUT.....  all diesels run out of speed at 4200RPM, forcing us to use taller
gears to maintain highway speeds. FI/gas engines will redline to 5500-7200,
meaning you can use 6.17 R&P and not mess with the rest of the box? Gives
maximum reduction offroad, and engine RPMs will give high speed cruising.
Time to play with the Exel spreadsheet, hopefully with the torque/RPM
curves for engines of interest.


HTH, post to list if you see fit,  Tim