Toyota Overdrive for Mkl's.
Here is a system designed by John Martin who has very kindly shared all his hard work with us. We are very lucky to have members willing to share like this.
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!!!
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 throwout bearing could be used etc.
Above Pic shows adaptor fitted.
Pic shows 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 throwout 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 throwout 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.
Top shot shows 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 crossmember 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 crossmember( a plate shaped the same as the bottom of the mount) is fitted to the bottom of the Zephyr crossmember by cutting a opening in the bottom of the crossmember and tack welding it in position to test for proper fit before fully welding.
The gearbox also needs to sit lower into the crossmember 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 tailshaft 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 aprox 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 centrifical 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 Tailshaft 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 ;)
John Martin.
DO YOU HAVE A STORY ON THE CONTINUING BUILD UP OF YOUR CAR? CAN YOU SEND US A FEW WORDS AND PIC'S ON THE CAR YOU'RE DRIVING AND THE PLANS OR STORIES OF IT? AVOCALEA@XTRA.CO.NZ
Disclaimer: The advice and guidelines given are given in good faith and the owners and managers of this site can take no responsibility for injuries sustained while carrying out the described tasks and procedures or any consequences arising.
