5 Speed Tranny in a Bus
by: Mike Gensler /vwzorm58@hotmail.com

Hi, This is the canned write-up I did of the tranny conversion. Every time I mention
it on the list I get swamped with requests for details so I just send this out.
If I don't cover anything that you need to know or if you just want to chat about
it, please feel free to contact me.

BTW, if you plan to do this, Pelican parts (www.pelicanparts.com) is now selling
a conversion kit for 914's to use bus CV's and the adapters they make are perfect
for mating the tranny to the axles via BUS CV's instead of the 914 ones that I used.
I just bought a pair of the adapters and will be installing them in place of my
custom-made adapters with new bus CV's this Spring.

I used a 901 transmission from an early 911 (65-69 since 1970-72 used a slightly
different belhousing and it won't work), a 914 clutch/flywheel, 914 CV
joints for the inners, a pair of spacers between the 914 CV's and the tranny, a
914 starter, a heavily modified (can you say 'ugly'?) front shift linkage, and
a pair of custom-built brackets bolted to the rear trailing arm mounts on the
torsion tube.

On the good side (tranny-wise), this bus really moves! I can keep up with a
lot of mini-vans, sport-utes, and passenger cars around town. Under hard
acceleration, 1st gear will see me up to 30 MPH, 2nd up to 55, and 3rd up to
75. And yes, my speedo is very accurate. Under normal/light acceleration, my
shift points are something like 22, 45, 60, and 75. I can cruise at 75-80 and
keep the RPM in the mid 3000 range which greatly reduces my oil temps (as
compared to running 75 at 4300 RPM). The higher cruising speeds make
traversing the vast wastelands we call Texas much more do-able since (wind
permitting) I can crank it up to 85 or 90 without worrying about RPM and engine

On the bad side, I'm not happy with my present gearing. What I find is that
because of the substantial wind resistance of the bus that I don't have the
power to hold 75 MPH in 5th gear up any kind of incline so I'm constantly
downshifting to 4th. If I push it faster up to 85 MPH, the engine gets further
into its powerband and can hold speed fairly well, but at that speed (and
higher) the wind resistance becomes an increasingly significant factor (and
watch out for those side-gusts when your running that fast!).

Also, there is too great of a gap between 1st and 2nd which makes right-hand
residential-type turns a nuisance since 2nd is bogged when you drop down to 15
MPH. However, one really nice thing about the Porsche 901 transmission is the
extensive selection and availability of different gear combinations. I intend
to swap 2nd through 5th for shorter gears (1st is already the shortest you can
get) this next year to increase the RPM for any given speed. My target is to
run 3600 RPM at 75 MPH in 5th gear.

Doing the swap is no simple task. The 2 hardest parts are building the
mounting brackets and getting them aligned properly and modifying the shift
linkage. The brackets themselves are made from 1/4" steel and are
approximately a 4.5"x4.5"x4.5" 'U' with a reinforcement plate across one side.
They bolt up to the rear trailing arm mounts on the torsion tube via longer
bolts (I intend to tack-weld the front of the brackets where the reinforcement
plate is to the torsion tube for increased strength). I had to grind off the
captive nut that the old bolt went to so the modification is no longer easily

The shift linkage must be moved to below the heater tube since the 911 tranny
shift shaft exits at the bottom of the nose instead of the top like the VW
tranny. The rear shift rod is pretty easy - you just get a piece of 1"
electrical conduit and attach it with straps to the underside of the frame.
The front shift rod is a PITA. I removed mine and through repeated heating and
beating reshaped it to drop down to meet the rear shift rod. It is ugly, but
it works. I'll be working on a replacement utilizing a section from a 914
steering column that has a pair of u-joints on it to make the thing a little
better engineered, but for now the ugly one works.

The 901 tranny is slightly narrower than the VW one so I had a machine shop
make a pair of 9/16" spacers that fit between the inner CV joints and the
tranny flanges. I used flanges from a 914 901 tranny (direct swap-in fit) and
914 CV's for the inners since they slip right on to the bus drive axles.

You must use a 914 flywheel and clutch. This bolts right onto the type IV
motors and is the correct setup for the 901 tranny. The clutch cable (at least
on a 73) is usable by simply re-locating the bowden tube bracket to the
sideplate on the 901. You will have to force a slight bow into the bowden
tube, but it works just fine like this.
The 901 itself should be from a 1965-69 911 or 912. The 70-72 model have a
slight difference in the bell housing and won't work (ask me how I know). And
the trans mounts should be the round biscuit type found on the 911 - the square
ones used on the 912's won't work. Although you can quite easily swap the R&P
in a 914 tranny to turn the right direction, the early (70-72) 914 tranny has
the shifter input in a place that would interfer with the rear torsion tube and
the late (73-76) 914 tranny is a side-shifter and would be very difficult to
addapt to the bus's center-mounted shifter. Also, the vent tube is in the
wrong place so you would have to plug the original hole and drill and tap a
new on on the opposite corner.
Cost-wise, you should be prepared to spend anywhere from $500 - $1200 for the
necessary parts. I paid $300 for the tranny and spent an additional $300
rebuilding it. A new 914 flywheel/clutch will run you another $400. New 914
CV's are $75 each and you'll spend another $150 on the spacers and misc
hardware needed. You can't use the bus starter so figure another $25-75 for a
used 914 starter. Of course, if you have access to good used parts, these
costs can be reduced.