Fitting A Toyota
Overdrive Box In A Mk1
By John Martin
I bought my ’55
Mk1 Zephyr in 2003 on ebay, it had an almost seized engine that I was able to
free up with a bit of patience, and enjoyed over 1 year of motoring before the
motor said “no more”.
In the mean
time I had bought a very rusty spares car that had been sitting for over 30
years fitted with a tired Mk2 motor with a Mk2 diff centre (3.9:1) and modified
Mk2 axles all fitted into the Mk1 housing.
The motor was
bored .020” over, new bearings fitted after the crank was checked. The original
head was needing major work so another unit was found that only needed a valve
grind , the cam was then reground to mild sport specs and double valve springs
fitted, a set of extractors have also been added.
Well with all
this I have been swapping and changing wheels, first I had a set of classic
Tasman Mags but found a couple were out of round causing the back axle to hop
at certain speeds, so I found a set of Globe Sprint master mags at the local
wreckers that I reckon are rare considering 14” and Ford stud pattern. I had
these fitted with 60 series tyres, so sadly I went forward with diff ratios
then went backwards with the tyre selection so the only alternative is to fit a
5 speed or an overdrive gearbox. I was definite that no extra holes ( floor
shift) were going to happen and a genuine Zephyr overdrive was going to be
almost impossible to find. I then just waited until my regular visits to the
wreckers paid off with finding a 1966 Toyota Crown station wagon fitted with a
3 speed all synchro box with electric overdrive.
I removed the
gearbox myself, so I was able to get the rear cross member, tail shaft, part of
the wiring, kick down switch, and the lockout hand control. The only part I
missed was the electronic control relay that is adjustable to set cut-in speed
and max speed for kick-down. Removing the box myself also saves valuable
folding stuff.
The new and old
boxes were sat side by side to see at a glance if it will fit, looks good!!!
Adaptor fitted
I used a lathe
at work to make an adaptor that allows the new box to mount to the Zephyr bell
housing so the original clutch mechanism, hydraulics, clutch fork, and throw-out
bearing could be used etc.
Speedy sleeves fitted
The front
sleeve /front bearing retainer part of the new box was slightly smaller in
diameter than the Zephyr unit and I was a bit concerned the throw out bearing
may have problems, I checked the local bearing suppliers and bought two “Speedy
Sleeves” #99121 that were fitted onto the bearing support sleeve, the other
option would to have a spacer bush fitted inside the throw out bearing carrier,
but the speedy sleeves worked well.
The forward selector
linkage was a problem with wrong angles, too close to the box and pointing down
when in neutral, so the same linkage was cut from the zephyr box and welded to
the Toyota linkage. To bring the linkage up (they are fitted by means of cotter
pin) it was removed and a new flat was ground to allow the selector to be set
to the correct angle.
Gear linkage mod
Before fitting
the new box, the "Damper unit" is removed and the mounts for the
damper ground flat as these will bump the floor reinforcing member!
Below: The
brass spigot bush was removed and a ball cage bearing fitted after a reducer
bush to match the input shaft was fitted.
Since I am
still using a Mk1 flywheel it limits the clutch plate to 200mm , a drive plate
to suit a RT40 Corona is fitted.
Now the fitting
of the box to the engine was straight forward, the rear cross member took a bit
of trial and error, the original mount brackets were cut off, including
grinding off the parts that were welded. Now a part of the Toyota gearbox mount
that came with the Toyota cross member( a plate shaped the same as the bottom
of the mount) is fitted to the bottom of the Zephyr cross member by cutting a
opening in the bottom of the cross member and tack welding it in position to
test for proper fit before fully welding.
The gearbox
also needs to sit lower into the cross member so an arc was cut into the top
(front and back) and the edge is rolled and reshaped to retain strength and
looks.
Fitting of
linkages is straight forward with adjustments made to allow easy gear
selection. The unmodified linkage will need a spacer bush due to the size
difference, Toyota 14mm, Ford 8mm.
Speedo cable is
KE10 Corolla with a copper sleeve crimped onto the gearbox end to suit the
Toyota drive, the other end fits straight onto the Ford speedo , if the Ford
cable had been longer it would fit the Toyota drive connection!!
The Toyota tail
shaft was sent to the local repairer with a mk2 donor shaft with required
measurements, 4 days later a modified shaft was fitted to the Zephyr.
I still don’t
have the control relay so I am operating the overdrive with a toggle switch.
At 105 km/h the
Zephyr goes from 3900 rpm to 2800 approx and it now seems to just idle along.
The
similarities between the Toyota and the Zephyr overdrives are hard to ignore.
With the way
they both kick down by momentarily killing the ignition to allow the boxes to
kick down.
The
freewheeling system operates the same. Takes a bit to get used to when there is
no compression braking…
Lockout cable
operation, same.
The Toyota uses
a generator to sense the speed via the control relay to control the cut in/out
and kick down speeds.
The Zephyr unit
uses a centrifugal type switch to do the same but I am not sure if it limits
the kick down speed.
In the end I
have a 3 speed all syncro gearbox with electric overdrive, best of all the car
can be completely returned to original as no part of the body was altered to do
it.
Cost of
modification
$100.00 Toyota
gearbox and bits
$70.00 Speedy
Sleeves
$160.00 Tail
shaft alteration and rebalance, inc 1 new uni joint.
$130.00 Corona
Clutch plate
$4.00 Spigot
bearing
$10.00 Second
hand Corolla speedo cable
I suppose now I
will have to do something with the body, I keep thinking others want to park
next to mine ‘cause it makes theirs look better ;)
Disclaimer:
The advice and guidelines given in these articles are given in good faith.
The owners and managers of the Galeforce Zephyr site will take no
responsibility for any injuries or loss sustained while carrying out the
described tasks and procedures or any consequences arising. Please read
the Safety
First Article