Fitting a five-speed transmission to your classic European sports car

[Editor's note: This article originally ran in the July 2007 issue of Classic Motorsports]

Back in the day, most European cars were ahead of their American counterparts in the gearbox department. While American cars usually had three-speed transmissions featuring widely spaced ratios, sloppy linkages and vague shifting action, our European classics often came with four-speed boxes that featured close ratios and tight, positive shift linkages.

As highway speeds increased, car manufacturers started to add overdrive ratios to their gearboxes—first with planetary add-on units fitted to the back of the conventional gearboxes, then with five or more actual speeds built into the transmissions themselves.

Today, five or more speeds with at least one overdrive ratio is the norm for all new cars. We’ve all gotten accustomed to these ratios, as well as the overall ease of use, low noise, and tight feel that modern gearboxes offer. And now our classic European gearboxes, once ahead of their time, seem dated, even obsolete.

What to Do?

Gearbox technology hasn’t changed very much in the past 80 years or so. Most cars after the Ford Model T have used some form of a sliding gear transmission to transmit power from the engine to the wheels. 

But while the technology itself remains the same, its design has resulted in some huge changes. The synchronizer made shifting easier, especially downshifting. Helical-cut gears reduced noise. Improved metallurgy made components last longer. And better designs and manufacturing techniques made components work better in the first place. The practical applications of the gearbox’s operating principles have improved considerably.

Take the average British gearbox from postwar to the mid-1960s, for example. To save money, manufacturers built the gearboxes to share the smallest gear on the laygear (aka cluster gear) for first and reverse. As a result, first gear had to be straight-cut instead of helical-cut. Worse yet, there was no synchronizer on first. 

If you’ve ever driven one of these, you know that first gear is a noisy beast. Worse yet, downshifting into first while the car is moving makes a different noise--one that can cost a lot of money in terms of chipped or broken gear teeth.

After first gear, these early gearboxes did get helical-cut gears and synchronizers, but there were still weaknesses. Their brass and bronze synchronizers quickly wore out, with the ones on second gear usually croaking first. Layshafts wore quickly, too, and sometimes destroyed entire gear sets as the situation progressed. 

For kits that use a Japanese gearbox, a new engine backplate is usually supplied to mate to the gearbox. Here’s the Rivergate Datsun 210 kit mounted on a Spridget engine.

The Datsun 210’s gearbox is a solid five-speed choice for small British engines. They are getting hard to find, however

Many kits require some changes to the clutch hydraulics. These are the parts required for the Rivergate kit, but some other kits use similar parts.

By the later 1960s, most European gearboxes had improved considerably. For many cars, synchronized first gears became the norm, and beefier steel synchronizers replaced brass or bronze. Bearings, layshafts and other internal parts benefited from improvements in metallurgy. So where the earlier gearboxes would typically be very worn by the time 50,000 or 70,000 miles had passed, the later ones could soldier on for two to three times longer. 

Another improvement was the overdrive. Rather than completely redesign their improved gearboxes, manufacturers fitted an overdrive to the back of the traditional gearbox as a secondary transmission. These units (which borrowed planetary gears from our friend the Model T) typically could be engaged when the transmission was in third or fourth gear, effectively making six speeds from four. These units usually offered about a 20% overdrive, dropping the engine speeds when on the highway and offering much nicer cruising. 

However, these units were complex, having both hydraulic and electrical circuits. They were relatively expensive, too. As a result, overdrive was an option that very few people chose. For those cars that did get overdrive, a concern quickly arose: Does the overdrive actually work?

Is History Bunk?

Enough history, let’s talk about today. Most of us want an overdrive ratio in our gearboxes so we can cruise at highway speeds without running our engines north of 4000 rpm. We also like reliability, longevity, and synchronizers on all the gears. When we start thinking about a gearbox swap on our classics, there are usually two choices. 

The first is to replace an OEM four-speed gearbox with one paired with an overdrive. In some cases, like with MGBs, Spitfires, Triumphs, Volvos and more, it’s pretty much a bolt-in. In other cases, like fitting an MGB overdrive to an MGA, or putting a Spitfire overdrive in a rubber-bumper MG Midget, there is some engineering and fabrication to be done, but it’s still pretty straightforward work. 

This path will preserve the history, originality and spirit of the car, but it is often a difficult route. First, you have to find the overdrive gearbox--and they rarely come cheap. Then you usually get to incur the frustration and expense of repairing all the worn components. When everything is said and done, you’ll be happy with your choice, but you’ll also have paid your dues.

The choice that is getting more common every day is to swap in a modern five-speed gearbox. Kits are available for many common classics, including most postwar British cars. This type of swap can be cheap: Most for the British cars seem to cost around $1500 to $3000 for complete kits, less if you’re willing to scrounge for some parts yourself. These setups often cost less than a proper rebuild for an OEM gearbox and overdrive unit. 

Most of today’s five-speed conversion kits fit either a modern Japanese gearbox or an American BorgWarner T9. The Japanese boxes usually only require an adaptor plate, while the BorgWarner conversions typically include a custom bellhousing for that particular application. For a few kits--Jaguars and Mustangs, most commonly--the BorgWarner T5 is the gearbox du jour. 

Most of these kits also require some sort of gearbox crossmember modification or replacement, and they include a replacement clutch disc or assembly. A modified driveshaft is also usually required. Small bits of hardware and a different shifter will round out the kits. 

Despite all of this new hardware, most of these kits require few, if any, modifications to the body of the car. If one desired it, the car could almost always be brought back to stock with little or no drama. 

Some cars, including the MGB and Triumph TR, actually have more than one option. Some kits use a Japanese-built gearbox, while others use the T9. As a result, comparison shopping actually becomes part of the decision-making process. Here’s our opinion on the matter: Generally speaking, the Japanese transmissions are lighter, easier to install, and seem to shift better. However, the BorgWarner boxes usually have more ratio options available for a reasonable cost.

What’s Involved?

With most of the kits on the market, a five-speed swap is usually a little more work than a conventional gearbox removal and replacement operation. All of the fabrication and engineering has already been handled by the company building the kit.

First, the original gearbox obviously must be removed from the car. Then there's usually some work at the back of the engine to accept the gearbox. For Japanese gearboxes, it’s often a matter of removing the clutch and flywheel and replacing the backing plate with one that is drilled to match the new gearbox. Then a new or modified flywheel can be assembled, along with the correct pilot bearing and clutch. Finally, the new transmission can be installed.

Nissan gearboxes work well with other British classics. Here’s the Datsun 280ZX box that’s popular among MGB owners.

The Japanese-based kits usually have a modified flywheel/ring gear so that the starter will properly line up. All kits will include a new clutch disk that has the same spline pattern as the gearbox.

For some cars, like MGBs, converting to an OEM overdrive gearbox is still a good option. Here is a stock MGB gearbox compared to an overdrive unit. The picture skews things a little, but the gearboxes are almost exactly the same length, making for an easy swap.

Also popular is the BorgWarner T9 kit, in this case for an MGA. Unlike the Japanese gearboxes, the T9 does not have an integral bellhousing, so the kit supplies a custom cast bellhousing. This makes changes to the flywheel and rear engine plate unnecessary.

BorgWarner swaps typically involve a bit more work, as some of these kits also require work on the clutch linkage. Parts might also need to be transferred from the old box to the new one.

The biggest issue with these conversions centers around the speedometer. While the kits provide a cable, they leave it up to the installer to get the speedometer to read correctly. Many classic cars have multiple gearbox, speedometer and rear-axle ratio combinations, and knowing all of the permutations is difficult at best. Fortunately, making the speedo read properly is not too difficult, as a specialist like Nisonger or Palo Alto Speedometer can sort things out. 

What’s the Best Choice?

Faced with all of these options, here’s our advice: The right answer depends on the particular situation.

Overdrives are cool, maintain the originality of the car, and are a good option if you can find one and afford it. While they can have reliability problems, they can also go for a long time with no issues whatsoever if properly maintained. 

On the other hand, a modern five-speed will sometimes offer an overdrive gear when there is no OEM option. Remember, finding an overdrive unit for some cars, like the A-series MG Midget, is nearly impossible. These late-model transmissions are also generally very bulletproof, meaning it could be less expensive than rebuilding a period-correct box.

Downsides exist, too. Some people don’t like the feel of the modern units, especially the T9. Sometimes the five-speeds will cost more. Some of the kits on the market have weak designs in spots. And of course, not only will originality be affected, but someday you’ll need to remember where the conversion parts came from. For example, if the 280ZX conversion in your MGB needs a new throw-out bearing, you’ll need the right Nissan part. 

With those considerations in mind, we tell everyone who asks about these swaps to do some homework. First, find out what options exist for your car. Then ask the suppliers about their kits. Better yet, ask for a copy of the installation instructions before buying anything--that will tell you what you’re in for. 

Then, get some references. You can easily go on a message board and ask for feedback from people who have done a conversion. This can be tricky, though. For example, ask what route to take with an MGB, and you’ll quickly get three answers: MGB overdrive, BorgWarner T9, and Datsun 280Z or 280ZX. You won’t be able to tell the objective responses from the subjective ones, but you’ll get some clues anyway. If you’re lucky, you’ll maybe have a friend or fellow club member who will let you drive a converted car. This, of course, is the best choice, as you’ll be able to sample it all first-hand and form your own opinion.

The bottom line typically follows our MGB example: Most of these choices are pretty good. You need to sort through your budget, preferences and tastes to get the right answer, but you’ll find yourself happy any way you go.

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