5 Speed Gearbox


Download files and build them with your 3D printer, laser cutter, or CNC. Thingiverse is a universe of things. Toyota Motor Corporation's W family is a family of RWD/4WD transmissions built by Aisin.Physically, these transmissions have much in common (like the bell housing-to-body bolt pattern) with other Aisin-built transmissions, like the Jeep AX-5 and the Toyota G-series.The W55, W56, W57, W58, and W59 are externally and internally very similar aside from the gear ratios.

MGB Transmission Conversion

All MGBs desperately need an overdriven top gear for highway driving, but unfortunately, the now pricey overdrive option was only installed on about 10% of US-bound MGBs. These rare overdrive units are now hard to find and fairly expensive to install. Using a rugged, time-proven Nissan 5 speed transmission, we offer a completely bolt-in conversion for MGBs with 5 main bearing engines that requires no body modifications. You can supply your own transmission from a ’75 to ’83 Datsun 280Z or 280ZX, or we can locate one for you (be sure you get the shift lever, rear mount, clutch fork, and release bearing with your gearbox). Building the kit to your order usually requires about two weeks. When completed, you will enjoy these benefits:

5 speed racing transmission
  • A commonly available, sturdy gearbox with overdriven 5th gear (ratio .85 to .78 depending on your chosen gearbox)
  • A perfectly positioned shift lever in the original MG position and boot
  • A working and accurately reading speedometer
  • The conversion can be installed without pulling the engine in rubber bumper MGBs
  • Substantial cost savings for both parts and installation labor compared to an overdrive conversion

The Nissan 5 Speed Transmission Conversion Kit includes the following parts:

  • CNC machined aluminum adapter plate with new seal and mounting hardware
  • New drive shaft, complete and ready to install
  • Modified flywheel with new ring gear (your exchange required)
  • Pilot bushing
  • Clutch disk and alignment tool
  • Speedometer cable and ratio changing angle drive specifically for your car year
  • Adapting bracket for transmission mount into your crossmember
  • New rear seal for the Nissan transmission
  • New clutch slave cylinder with braided steel hose
  • Full illustrated instructions
  • Modified shift lever

Why Us?

You might find similar kits available online but our kit offers some unique features not found elsewhere:

  • Our drive shaft is complete and ready to bolt in
  • Our clutch slave cylinder flex hose replaces the original and maintains the steel pipe from the master cylinder
  • We modify your shift lever at no extra cost and can maintain the use of your original shift knob if you supply your MG shift lever along with your Nissan lever for us to convert
  • Although this conversion in intended for use in ’68-’80 MGBs, we have also used it in MGAs and three synchro MGBs from ’63-’67. We can offer information, documentation, and guidance for using the conversion in those cars.

Why Five Speed

The original MGB gearbox was created for the small winding roads of the British countryside, not the long, straight highways of the American West. Whether your car is a daily driver or a weekend road tripper, it could undoubtably use a boost when it comes to mountain motoring. Authenticity is all well and good, and it’s always nice to see a classic British car complete with original parts, but for people who actually like to drive their cars, we’re huge fans of the Nissan 5 speed transmission conversion. This conversion corrects the lack of an overdriven top gear on most original MGs.

Nissan 5 Speed Conversion

The Nissan 5 speed conversion allows you to drive at highway speeds with lower revs than possible with a standard transmission. The original MG engine was not built to sustain speeds of 75 miles per hour for extended periods of time. Without the conversion, the longer stroke and higher revs need to sustain such a speed will wear on the engine over years of use. Overdriven top gears, whether provided by an original unit or a new Nissan unit, allow the engine to operate at lower revs, saving it from unnecessary wear and tear. Now an autumn jaunt in the mountains, a summer road trip out west, or even an afternoon picnic in the park becomes a more enjoyable experience all around.

After driving my Model-A for a while with the stock 3-speed non-synchro transmission, it seemed like the car would be much more compatible with modern-day traffic if it had an overdrive gear. A company in Muncie Indiana, called Auto Restorations makes a kit for installing a Borg-Warner T5 transmission in a Model-A. The kit costs $895, and includes transmission adaptor, driveshaft, brake linkage changes, clutch disk, speedometer cable, etc. Presumably everything you need. After a call to get information (765 288-3291, they don’t have a web site) I ordered a kit.

The only thing you need to know before ordering is how manysplines there are on the input shaft, so that you can get the proper clutchdisk. The donor transmission comes froma Chevy S10 2WD pickup. These T5transmissions are unique in that they have the shifter placed further forwardthan a standard T5. Even though theshifter is further forward, it still is about six inches rear of the original Model-Ashifter once the conversion is done. T5transmissions are synchromesh in all gears and high gear is 0.72:1, a nice 38%reduction of RPMs while cruising. My transmission had the 14-spline input, butsome of these T5s have a different spline count. I believe all have a standard 27-splineoutput. I found a transmission at thelocal Pull-A-Part for about $70 including tax and the core-charge. They aren’t very difficult to pull out, but Idid donate a nice socket to inside the frame of the donor vehicle while I wastaking off the cross brace. Here’s whatit looks like:

The kit arrived, well packaged, in two boxes. Many of the parts were primed in redoxide. I though that it would have beena nice touch if the supplier had powder-coated them, and I considered doingthat myself, but decided instead to paint everything in black prior toinstallation. In retrospect, I’m gladthat I didn’t powder-coat them, since several parts needed to bemodified.

Instructions are included,but they are pretty sketchy and in unusual order. I suspect that no word processing was used sothat modifying and updating the instructions had long ago ceased. They do include some good pictures and drawings though, that I found to be very helpful. I didn’t have any idea if this was going to be a half-day or week-long job. As itturns out, the latter was the closest guess. If you want to see the instructions that come with the kit, here's a copy..

SpeedT5 Installation Instructions.pdf

First thing I did was to modify the transmission. This involves cutting off a tab behind theshifter and drilling a hole below the shifter to accommodate two thick steelplates that bolt to the rear of the transmission. These plates are the new support for the rearcontrol arms connecting to the axle. Aswas going to be typical in this job, the plate on one side had to be machinedto fit the transmission, and the spacers from the kit weren’t quite the rightsize, so I ended up making new ones. Also, the hole in the T5 needs to be bored to a largersize to work with the kit.

The next step was to start disassembling the car. This involves unbolting the rear spring,brake rods, and shock absorbers from the car so that differential can belowered and moved back to remove the torque tube. Here’s one step in the instructions: “Go tothe back of the transmission and remove six bolts holding the torque tube. At the differential this torque tube should release so it can be taken down. If not,you may have to persuade it.”

Those two sentences turned into hours and hours of work. As it turns out, removing the torque tube at the rear involves pulling the pinion bearings (complete with races) from thedifferential. After several hours of unsuccessful persuasion, I found a note tacked onto the end of the instructions about how to use a disk and some studs included with the kit to help.Finally, success! Here it is at work:

Once the torque tube is out, the transmission can beremoved. It’s not a bad time to also takeout the brake linkage since it will all be modified anyway later on. When the transmission is out, the new clutchdisk can be installed, using the existing pressure plate. The instructions tell you that you need to get an alignment tool, but they actually included a decent plastic tool forthis purpose. The kit also doesn’t mention, but includes a new pilot bushing that slips into the existing flywheel bushing, and extends it out and to the correct diameter for the T5. Forgetting that would be something you wouldremember for a long time since it would require pulling out everything again. You can see it in this picture.

5 Speed Gearbox5 speed gearbox for go kart

The kit includes an adaptor that mates the Model-A bell-housingwith the transmission. I was concernedthat it didn’t accurately locate itself on the transmission – it was onlylocated by the bolts, which have some slop. I pondered welding and machining to make it fit tightly around thetransmission input shaft, but then realized that it was the same situation on thebell housing side, and there was nothing to reference it to there either. I’ve read elsewhere about making sure that thetransmission is aligned to the motor within a couple of thousandths of an inch,and consequently was nervous. I calledAuto Restorations, and was connected with Mr. Lewis, who must be theowner. He said not to worry about it,just bolt it together and it will work. He was right. Maybe what’s rightfor a car that works up to 2,500 RPM is different than what’s right for a carthat works up to 6,000 RPM. It wasnecessary to redrill the mounting holes on the transmission to accept the boltsincluded with the kit, and a couple of the bolts were the wrong length, but itall went together in the end, and when painted up, looked like this:


It was necessary to drill a hole for a cotter key that holdsone end of the clutch return spring, you can see it above, just behind theinspection cover on the bell housing. Asleeve, included with the kit, slides over the input shaft tube of the transmissionto make it the correct diameter for the Model-A throw-out bearing.

You can’t see it on this picture, but the other side of thetransmission contains a bracket for holding the emergency brake. Much to my surprise, it moved several inchesto the right – not exactly friendly for the passenger. The bracket didn’t fit as sent, and theyforgot to drill the holes. Mr. Lewis gaveme the location of where to drill the holes, and then I redid the poor weld andmachined it where it interfered with the gearbox.

Prior to installing the transmission, it is necessary to, …gasp…,cut an opening in the front of the cross member of the frame. It looks like this when you are done:

I didn’t like the idea of cutting the frame, but saved thepiece that I cut out, and figured that it could be welded back in again ifdesired. The new transmission mount thatbolts under the cross member restores some of the strength lost by cutting.

The new transmission mount needed tobe reworked by heating with a torch and bent slightly to give the correct fitfor my car. It installs with two newholes that you drill in the cross member.

Once the transmission is bolted back into the car, I turnedmy attention to the differential. Thekit contains a nicely machined input shaft and housing for the front of thedifferential. This converts it from atorque-tube to an open driveshaft. Thehousing is meant to also house the speedometer sender. You take the gear from the original torquetube, and machine it so that it slips over the new shaft, then pin it in placewith a tension pin. When locating thegear, don’t believe the drawing you get with the instructions, the dimension itgives you is off by an inch. Theoriginal speedometer drive bolts onto the outside of the new housing in frontof the differential, and a long speedometer cable is included with the kit thatreaches all the way back there.

I wondered why you couldn’t just connect the speedometer to the transmission, socalled Mr. Lewis. He said that thereisn’t any reason why you can’t, it’s just that some of the later transmissionsdon’t have provisions for a speedometer. I like the idea of using the transmission output, and the speedometer was calibrated closely when I used the 0.833:1 adaptor that was on the S10 truck.

The driveshaft (included with the kit) fits well, although Ithink it could be about an inch longer so that it would engage more of thesplines in the transmission output shaft. Also, I was disappointed that at the rear, you install the U-joint tothe differential input shaft with a small key (no splines), and then install anut inside the U-joint, which is very difficult to tighten. I ended up grinding down a big wrench, but still couldn’t get it very tight in that space. It will be really tough to remove too, especially after a cotter pin isinstalled. A flanged arrangement would have been much better.

Here’s what the rear looks like now:

At this point, the drive train is pretty much complete, timeto turn to the braking system.

However, in my case, I stopped to weld up a new batterybox. When the car was converted to a 12Vsystem, the new battery was smaller, and I decided that it would be better tohave a correctly sized battery box for it. This also allowed installation of a disconnect switch under the floorboard.

Dq500. The DQ500 transmission is a 7-speed transverse mounted gearbox introduced by Volkswagen AG for larger and high torque output vehicles that is in large-scale series production.

5 Speed Gearbox

The first step for the brakes is to relocate the main pivotarm (crossbar) to the rear. It moves tobehind the cross brace in the chassis. This requires drilling four new holes in the chassis, but they are small ones. The kit comes with a new crossbarand all new operating rods. Theinstructions show that you connect the rod from the pedal to the cross-shaft ata pretty severe downward angle. Thisactually reverses the direction of the crossbar, and I didn’t like the angle ofthe lever and rods – it just didn’t seem right. So I changed it to run the operating rod in the same general orientationas was stock, Henry Ford did a lot of good things, and I think this generalsetup was good too. This required onemore hole in the frame cross member, and welding up an extension to the leverarm, but the geometry looks good now. The rods are also in generally the same location too, so they fitthrough the guides similar to original. Here’s what the setup looks like from the rear of the crossbar:

We’re getting pretty close at this point. The new brake rods all fit fine, except theone from the pedal to the cross shaft, which needed to be shortened after mygeometry change. However, there are noprevisions on the new rods for the anti-rattle springs. I can live with a little rattling, but these springs are also there to pull the brakes back away from the drums and lift the pedal. So I machined some shortextensions to where the rear anti-rattle springs mount, and then machined astop that slides over each rod with a set-screw to capture the spring and puttension on the rod. Just below the stopthat I installed, you can see the remaining factory equivalent on the loweremergency brake rod:

Go-kart With 5 Speed Gearbox

Only one brake detail left - the brake light switch. Even though my kit was ordered for a 30/31 car, it must have assumed that you would use a switch from an earlier car since mine wasn’t even close to fitting on the bracket that they provided. So I made a new little assembly consisting ofa micro-switch operating a relay. It works fine, but it doesn’t look like it came from the early 30s:

Now that we are getting dangerously close to filling up thatT5 with a couple quarts of Dextron ATF, there are only a few details left.

It’s necessary to make a new floorboard and metal cover inthe middle. Since both the shift leverand emergency brake have moved significantly, the original floorboard isn’tusable. Plus it’s nice to save it incase someone wants to reverse all this some day (and that’s not going to be me!). Here’s the new floorboard made out of plywood.

I used my torch to heat up the T5 shift lever to bendit straighter. That was a little unnerving since you can’t disassemble it because it’s clamped together, and there are plastic parts just a few inches from where you are heating and bending. Fortunately the vise tookenough of the heat headed that way to make it work.

Now, look at that little beauty sticking up in front of the seat!

5 Speed Gearbox Bikes

I’ve since changed back to a more traditional looking knobby drilling and tapping an early Ford knob to a 10mm x 1.5 thread. The T5 is metric in its entirety.

The only other comment that I have about the installation isthat changing the control arm position to accommodate the T5 puts quite anangle on the U-joints. You can see that here:

Here’s a shot of the tranny installed. You can see in this picture (behind thedisconnected speedometer cable) where the pivot for the rear control arms islocated. It’s about six inches lowerthan the stock location.

So, how does it work? Really well. I thought that thebig advantage would be having overdrive, but as a practical matter, most of theimprovement is from being able to row through the first four gears soeasily. Now it’s practical to rev it up more before shifting, easily downshift at higher speeds, and having the new 3rdgear that fills that giant hole that existed between 2nd and 3rdon the original gearbox is invaluable. It’s much easier to stay with the flow of traffic now. 5th is nice once you’re rolling along on the level at 50 or more, but don’t expect to go up steep hills in 5th. Actually, if you could have something with a slightly lower overdrive ratio it would be better.

This was a lot of work. Had I known that going into it, and without knowing the actual benefits of the conversion, I don’t know if I would have doneit. However, now that I’ve been using itand see how much nicer it is to drive, I think it was time and money well-spent. If you decide to do it though, and use the same kit, just don’t expect to easily bolt it together in a couple of afternoons as I initially thought. And plan onneeding some like a gas welder, grinder and drill press (or milling machine). The kit is invaluable to doing the job - things like the motor plate and machined parts for converting from torque tube to open rear end would be extremely hard to fabricate on your own. And while the kit takes some tweaking toinstall, it is still a good value for what you receive. After you open the boxes of parts and examine them, it’s obvious that Mr. Lewis isn’t getting rich from selling these kits.

Note: I've received several emails after writing this. One warned me about the safety of the conversion - the writer's thought was that without the torque-tube, the rear control arms are required to handle more stress, and the old original ones may not be up to the task. He suggested changing the control arms during the conversion, using stronger ones such as those offered by Auto Restorations. I've also had a couple of contacts expressing frustration with the design and/or quality of the kit. If you have done this conversion, and would like to have your email address listed on my site as a contact for other readers, let me know and I'll put it here.

Note: Since writing this, Auto Restorations has closed their doors, and the kit described in the write-up is no longer available. However, another source for T5 conversion parts is:

5 Speed Gearbox

Their offerings are shown here, but may have changed, so contact the shop directly for more current information.

Nissan 1400 5 Speed Gearbox

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