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Type 1 Conversion to Porsche 5 Speed Transmission

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Type 1 Conversion to Porsche 5 Speed Transmission

Post by LhYnxz on Thu Nov 27, 2008 3:36 pm

A Porsche 5 speed
conversion is one nifty modification! The close ratio gears of the Porsche
tranny handily keeps a high performance engine in its power band, but
the 5th gear ratio allows for easy highway cruising as well.
The Porsche transaxle is strong from the start because it is engineered
for the power of a flat six engine.

BE WARNED!
The Conversion to a Porsche 5 speed tranny is NOT a "weekend mod"
- and should only be undertaken if you are an experienced fabricator.
You will
also need to be prepared for some fine tuning in order to achieve perfectly
smooth shifting.


An IRS
rear suspension setup is required rather than a swing axle setup, because
the Porsche box is only available in an IRS configuration, and can not
be converted to swing axle. And of course, you will need to locate a
good used Porsche 901 5 speed gear box.




Step
1 is to adapt the rear tranny mounts to the 901. This is done by drilling
holes in the 901 to match the holes in the original beetle transaxle.
We recommend a spare set of Urethane
rear pad mounts because they do not have studs (they use nuts and
bolts) so you can place the mount right over the area and mark it perfectly.
Once the holes are marked, drill them. Use a bit that is just larger
than 8mm so that the mounts fit nice and tight.





The nice
thing about performing the rear mount adaptation first is so it gives
you a static point to work off of for fitment to the VW pan. Now that
the the transaxle can be coupled to the floorpan, we can start Step
2: clearancing and further fitment.

When you
first lift up the 901 and try to fit it using the rear mounts as reference
to where it needs to be, you will begin to realize how much larger and
longer the 901 really is! Place a straight edge parallel to the ground
and on top of the input shaft as a reference, then measure to the torsion
tube one foot from the center on each side. With the beetle trans this
measurement was 22.75 inches. It is important to have the 5 speed as
far forward as possible because it is about 1 inch longer than the beetle
trans. It's far easier to modify the car to accept the new 901 location
then modifying the body for an engine that sits 1" further back!
Clearance the frame horns for the sides of the gearbox and for the clutch
tube bracket off the side of the box. Mark the areas to be clearanced
using a paint pen or marker. It is good to clearance as little as possible
to keep some strength in the frame horns. The input for the shifter
on the 901 exits the bottom of the trans rather than the middle like
a beetle. A hole must be cut into the bottom of the pan. In order to
get the rear of the 901 as close to 22.75" back from the torsion
tube. Also lightly clearance the front of the trans and also the torsion
tube. Do not remove any more material than necessary!



Clearancing for clutch bowden tube bracket



Clearancing for right-front of trans case


Step
3: With the rear mounts bolted down and a floor jack supporting the
front of the trans, you can begin to figure out the front mounting system;
you can't buy this stuff, you have to make it! Keep using the straight
edge on the bell housing and measure to the torsion tube to keep the
bell housing parallel and square. It is helpful to have the floor pan
upside down at this point for obvious reasons. It is possible to adapt
the original 911 front mount. In this conversion, I elected to build
my own mount system because the 911 mount needed over four inches added
to its width to fit the way I wanted. I determined that a mount built
from scratch would look and fit best. I used Volvo trans mounts. These
are quite generic and I found at least four different brands. I selected
the hardest rubber versions for maximum rigidity. These mounts will
also make it simple to swap in solid aluminum mounts for the strip just
like the Gene Berg intermediate mount. I welded ears to the outside
of each frame horn for the Volvo trans mount studs to bolt to. With
the mount position determined, and the trans in a static position, build
a front mount.








Note the clearancing to the trans case.



Bottom view of fabricated front trans mount

Step 4:
Now that the trans is located where it's new home is going to be, it
is time for shift linkage! There are three options for shift linkage.
Adapt the Porsche parts, adapt the VW parts, or full custom. I chose
to use the 911 components to have a proper reverse lockout and to retain
the "Porsche Look". It is hard to mistake the 911 shift lever!

The parts
needed are the shifter, the shifter to shift rod connection link, the
actual shift rod, and the special rear coupler. www.pelicanparts.com sells the Porsche
bushings to tighten everything up, and they are essentially the ACN
equivalent of the Porsche Parts business (good guys)..

The first
step is to modify the frame tunnel so that the 911 shifter can bolt
down. It is best to have the actual clip of the tunnel from a 911 but
I didn't have this option. The 911 shifter uses two front bolts and
one rear. The tunnel is flat and wide enough for the rear mounting bolt
to fit; simply drill and tap. The front, however, is more of a challenge!
The tunnel curves down too abruptly for the shifter to bolt down. The
solution is to weld in some material to box this area in. Cut pie like
slits into the metal needing to be boxed in. Next, pull the metal out
and using body tools form it into a box shape. Next, a scrap piece of
14 gauge steel was welded in. Weld up the pie cuts and the piece of
strip steel then dress it all up so it doesn't look like you are some
hack. :-)



The problem; flat shifter base-flange vs. round tunnel.



Tunnel boxed in, rough.



Here the welds are ground smooth.



The shifter now fits the tunnel!

_________________

LhYnxz
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Type 1 Conversion to Porsche 5 Speed Transmission pt2

Post by LhYnxz on Thu Nov 27, 2008 3:38 pm

Repeat
the above outlined shifter flange steps again for the right side of
the tunnel. The curve of the tunnel and shifter flange area is less
abrupt on the right side so less work is required. With this step finished
the shifter now bolts down to the frame tunnelj, and would make Dr.
Porsche proud!




Step
5 is to connect the shifter to the transaxle. The Porsche shift rod
is a much nicer piece than the Beetle shift rod. The Porsche rod has
a pivoting rear coupler with splines that telescope in the actual shift
rod for for/aft adjustment. The front of the shift rod uses a right-angle
link piece that connects it to the bottom of the shifter. The shift
rod is almost six inches too short to work right from the start with
a 68+ pan (remember early pans have the shifter further foward). It
also does not have enough S-bend down to interface with the transaxle.
The rod must both be S-bent down and also lengthened.





5.5" length of 1" OD pipe to extend the shift rod.





The shift rod after S-bending and lengthening.





Close-up picture of the extra length welded in.





Polished 911 rear shift coupler with new rubbers




Once
you have the tweaked shift rod installed inside the tunnel it is time
to build a shift rod bushing support. I bought a new shift rod bushing
from Pelican Parts and built a sheet metal bracket to hold it in place.
The bracket has to be welded inside the tunnel exactly like the stock
beetle support. You can't use the beetle part because the 911 shift
rod is 1" OD vs. the Beetles .75" OD (approximate, actual
numbers are metric). I cut a window in the side of the tunnel to position
the shift rod support, and welded it in place, then welded up my access
window. It helps to drill holes through the top of the tunnel and spot
weld through them (welding upside down through the window cut in the
side of the tunnel isn't easy).





911 shift rod bushing left, Beetle right.





Layout the pieces for the new bushing support





Fabricated shift rod buhing support to be welded into the tunnel.





Bushing support tach welded in place.





View of the bushing support from side.




Now
the shifter is installed, the shift rod is in place and positioned in
the bushing and all is hooked up. At this point your shift rod will
probably be a bit too long or two short to work. It needs to be fine
tuned. We carry an adjustable
shift coupler which solves this problem. It works just like an adjustable
pushrod so that you can have a small amount of adjustment. You can purchase
one or built your own.




Hopefully
you can get all five gears plus reverse now!



Step 6:
Axles and CV Joints



You can
use stock length axles with the 901 because it is close to the same
width as a stock transaxle (unlike a Bus tranny conversion). At least
this makes the conversion easy in this one respect! The flanges on the
early 901 transaxles are sized the same as a Beetle T1. The difference
is they have four bolts and two dowels. The easiest solution here is
to Timesert
the flange so that it uses six bolts. This must happen if using the
early small flanges or the late 911/01 (930 size) flanges. It is also
possible to weld, drill, and tap the holes which formerly hosted dowel
pins. The last choice is to drill out the CV joints and use dowel pins,
but the simplest way is to just Timesert
the flange.





T-II on the left and Lobro 930 on the right.





T-II left, 930 right. 930 CVs are thick!



Option
1:
901 flanges, stock
beetle CV Joints inside and outside, stock beetle stub axles, and
stock beetle axles. It doesn't get much simpler than that!



Option
2:
901 flanges, Racing
beetle axles, Porsche
CVs on the inner, and Bus
CVs on the outer. To use Type 2 (Bus)
outer CVs you need early Porsche 944, Type 181, or aftermarket
stub axles. The outer T2 joint is slightly thicker. The solution
is to machine the joint to a thinner dimension, modify the axle, or
just buy full floating beetle length Racing
axles which don't have the problem (because of full floating splines).



Option
3:
911/01 flanges, conversion
beetle length axles with Porsche splines (unlike the above two choices
which are VW splines), 930
joints, and Chromoly
conversion stub axles. This is the strongest solution, but also
the most expensive and heaviest.

_________________

LhYnxz
Site Administrator
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Number of posts : 485
Age : 37
Location : Bayamon, PR
Reputation : 0
Points : 30
Registration date : 2007-12-01

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