It seems that from time to time, questions pop up about the TQX 5-Speed gearbox Mazda fitted to some of their Rotary engine equipped cars in the mid to late 1970's. I think there is merit in having a dedicated thread, and I welcome anyone to add any information on the TQX gearbox to the thread. As this box was not fitted to anything released in Australia, information here is hard to come by, so if anyone has any material relating to the gearbox, advertising, parts manual information, what they were fitted to etc please add it to this thread.
For those who have never seen one before, the TQX 5-Speed setup is very unique, in that it is paired with a fluid coupling (similar but not the same as a torque converter) between the engine and flywheel housed withing its own housing. The flywheel and clutch then bolt to the rear of that and are housed within a unique bell housing.
The aim of the fluid coupling was to introduce some slip at lower speeds, primarily to reduce the bucking on deceleration that the Japanese executive types were not so fond of. A quirky result is that you can sit with the car in first gear with the clutch out, foot on the brake, and the car will typically not stall. You can then release the brake and accelerate normally. Not a particularly handy feature in all honesty, and having driven a car fitted with one of these gearbox's I always took it out of gear when sitting stationary anyway.
As fitted, the fluid coupling is driven by the engine oil which is delivered through the rear of the eccentric shaft. There is also a return hole in the bottom right hand corner of the rear end plate which returns the oil to the sump. If you have a TQX motor and do not want to use the fluid coupling, you need to reinstall the blind plug into the rear of the eccentric shaft and block the hole in the rear end plate other wise you will fill the bell housing with engine oil, as well as having the sump oil spill out through the hole in the end plate!
The TQX gearbox also features a Park position located across and up, directly to the left of 1st gear which locks the gearbox from turning, as with the fluid coupling fitted the engine has no "park brake" effect like when you leave a normal manual transmission in gear. I can't remember ever having to do it, but I have read it is very difficulty if not impossible to "clutch start" a car fitted with these gearbox's as well.
As far as I am aware the gearbox features the good RX-4 4-speed / 121 gear ratio's.
1st 3.380, 2nd 2.077, 3rd 1.390, 4th 1.000, 5th 0.862, Rev 3.389
I have read however that there are an alternate set of ratio's quoted that are possibly for the TQX 5-speed, but cannot confirm this, those being:
1st 3.403, 2nd 2.005, 3rd 1.373, 4th 1.000, 5th 0.854
If anyone has an un-assembled TQX gearbox, could you please count the teeth on each gear to confirm!
The clutch slave cylinder is mounted on the bottom of the bell housing as opposed to being on the top on most single dizzy motors. From the factory there is a metal tube which connects to the hose from the clutch master cylinder and runs down to the bottom of the bell housing so it is not flexible hose all the way.
A quirk of the gearbox, is that is is designed to fit in the same place as an RX-4 4-speed or RX-5 5-Speed gearbox in relation to the gearbox mount and gear stick position being in same position relative to the cars gearbox cross member and gear stick hole. However, because of the fluid coupling housing, which is approx 120mm thick, the gear stick sits much further forward on the extension housing than the RX-4 4-speed or RX-5 5-speed. The measurement from the front face of the gearbox (where the bell housing bolts) to the gear stick position in neutral is approx 433mm. The gearbox mount bolt holes are approx 440mm from the front face of the gearbox. (I don't have an RX-4 or RX-5 box to compare with but it would be handy to know the measurements).
Another quirk of the gearbox is that the main case is tilted over more than the RX-4 or RX-5 gearbox, and the extension housing is the counter tilted so the gear stick comes up basically vertically and the gearbox mount is also horizontal. This is not a problem with the fluid coupling fitted, but if an RX-4 or RX-5 bell housing is used the gear stick then tilts clockwise and wants to come out pointing towards the driver, and the gearbox mount leans a similar amount.
Not only is the angle an issue, but if a normal RX-4 or RX-5 bell housing is used (no fluid coupling), then the gear stick and gearbox mount will be somewhere around 120mm further forward than the normal RX-4 or RX-5 position,
When using an RX-4 style bell housing, the gearbox input shaft projects past the bell housing to motor mounting face, and needs to be machined back, otherwise it will bottom out in the back of the eccentric shaft before the bell housing meets the motor.
The shifter and gearbox mount position can however be a handy feature, if you wanted to shift the motor back from its standard position in the engine bay. If you shift the engine rearward by approx 120mm, you will then have the gear stick and mount in the same position as an RX-4 or RX-5 gearbox would be with the engine mounted in the normal position.
Doing this will still leave you with the gear stick and gearbox mount on an angle. This leaves three distinct possibilities though which may suit a particular situation.
Leave the motor mounted horizontally and gearbox twisted, fabricate a gearbox cross member to suit and put as much of a bend in the gear stick as possible to get it as vertical as possible.
Twist the motor and gearbox counter clockwise (ports up, plugs down) half the amount of the twist in the gearbox, and end up with the engine slightly twisted from horizontal and less of a lean on the gear stick and gearbox mount.
Twist the engine and gearbox so that the gearbox mount and gear stick are in the perfect vertical and horizontal plane, and have the engine sitting twisted so the ports are higher and plugs are lower relative to horizontal. The advantage of this, depending on your inlet manifold style and type, is less of an angle needed to meet the inlet port runners. Leaving the gearbox horizontal and twisting the motor to suit would mean fabricating a new sump and pickup, and inlet manifold at a minimum to keep the carby level. If using injection inlet manifold angle is not an issue.
Below are some pictures I have taken that show the features of these gearbox's and the degree of twist compared to the normal RX-4 or RX-5 gearbox.
You can see here the fluid coupling section directly behind the motor, with the motor fitted in the std position for an RX-4.
Not great pics but you can see the gearbox in an RX-4 mounted on the original cross member as it was designed to do when using the whole fluid coupling section.
You can see the bottom mounted clutch slave cylinder in this image.
The TQX gearbox with the unique TQX bell housing attached. This will only bolt to the fluid coupling housing and will not match any engine bolt pattern. You can also see the shifter position much further forward than the normal RX-4 4-speed or RX-5 5-speed.
TQX Gear Knob showing the park position to the left of first gear.
Removed from the car, you can see the flywheel and clutch assembly on the rear of the fluid coupling section. That housing is approx 120mm long between motor and bell housing mounting faces.
TQX Gearbox set up as it normally sits with the fluid coupling, except it has an RX-4 bell housing fitted here. You can see the extreme tilt in the main casing with the shifter and gearbox mount left horizontal.
Some more exploded images for reference thanks to circle_w3rk.
TQX Gearbox featuring heavily angles gear stick.
TQX Bell Housing sitting upside down, the clutch slave cylinder and fork are situated on the bottom when in the car.
TQX Fluid Coupling Housing with Flywheel and Clutch assembly.
Fluid Coupling section with flex plate that bolts to the Auto Counterweight on the rear of the motor
Here is a rear end plate attached to the RX-4 bell housing bolted to the TQX gearbox. You can see the yellow spirit level to the left which is perfectly vertical and the resulting twist of the engine that results from using the RX-4 bell housing.
I made a template of the housing surface, as attached it in what would be the normal engine position to illustrate the degree of the twist.
You can see the inlet ports have risen up on an angle, about half the height of the port runner. Lines on the template represent the top and bottom of the port runner in the normal location.
You can see the bottom of the port runner is now approx 23mm higher with the engine twisted.
End of the tape measure represents where the bottom of the exhaust port floor would be, against the drawn lines, the bottom of which is where the port floor would normally be.
Here you can see the bottom of the spark plug side of the motor. The twist drops that side of the motor approx 25mm and kicks it across by a similar amount.
Here the inlet and exhaust port side of the motor kicks across towards the chassis rail by 26mm and up by a similar amount.
Here is the hole in the bottom right hand corner of the rear end plate that needs to be plugged when you don't use the fluid coupling section. With the fluid coupling in place the oil returns to the sump through this hole.