Mazda BT-50 Gearbox & Transmission Problems

A lot of modern transmissions don’t have a dipstick at all, particularly as manufacturers move towards transmissions that have very long service intervals and are considered sealed systems. Which is fine until it’s not. And that’s when you need to check the level and condition of the transmission fluid.

The good news is that the BT-50 in question does have a dipstick. The bad news is that’s mighty difficult to get to. You need to be under the car (so safety is the key here) and then locate a 19mm fitting on the driver’s side of the transmission. By unscrewing this fitting, you can withdraw the dipstick and check the level. The other catch is that you need to do this with the engine running (to get an accurate reading) and the dipstick is located close to what will therefore be a hot exhaust system.

All of this means it’s really a job for a specialist with a hoist and is a great example of a carmaker saving a few cents per car in production at the expense of the greater running costs for the owner over the life of the vehicle.

There have, indeed, been issues with this transmission with Mazda authorising a service bulletin to attend to some vehicles. However, it‘s generally thought that affected vehicles were built between 2011 and 2014, after which point, the problems were fixed. Which is not to say your 2015-built car doesn’t have the same problems.

The best way to proceed is to ignore the dealerships and go straight to Mazda Australia’s customer service department. Unfortunately, your car is now 10-years-old and well and truly outside its warranty, but I agree that 120,000km is not an acceptable lifespan for a component such as a modern automatic transmission to fail.

You should be guided by your mechanic’s quote for either outcome. In some cases, solenoids are relatively cheap to buy and don’t require too much labour to replace. But, depending on the vehicle, they can also be very expensive and require more or less a full transmission strip-down to remove and replace.

You also need to assess the condition of the whole transmission as putting new parts into a worn gearbox will only delay the inevitable.

This is indeed a known problem on these transmissions and one for which Mazda issued a Technical Service Bulletin (TSB; like a recall but not safety related) back in 2014. Apparently, a problem with the valve-body (that controls the gearbox’s shifts) caused a scraping or buzzing noise usually when shifting form Park to Drive or Reverse. That’s not exactly what you’re reporting, but it’s almost too similar not to be related. Depending on the build date of the vehicle, Mazda either replaced part of the entire valve-body assembly.

The other problem you’ve alluded to; that of a faulty output speed sensor is a different issue to the one that sounds like it’s causing your problem. In the case of the dud sensor, the gearbox could suddenly decide to shift back to first gear unannounced. If that happened at speed, it could cause the vehicle’s wheels to lock up with some very interesting consequences.

To put your question into context, an overdrive gear is one where the output shaft of the gearbox spins faster than the input shaft. Or, put another way, a gear in which the car’s propeller-shaft is spinning faster than the engine’s crankshaft. This means the drive wheels can be spun faster (for more road speed) without making the engine rev too hard. Overdrive gearboxes have been common for many years now, typically when five-speed transmissions replaced four-speed units. Those earlier four-speeds generally had a 1:1 ratio on their fourth (top) gear which means the output shaft (and propellor shaft) spun at exactly the same speed as the input shaft (or engine).

Many manufacturers have now, of course, switched to six-speed transmissions and some do, in fact, use that opportunity to fit an overdrive fifth and sixth gear. But in the case of your Mazda, only sixth gear is overdriven (with a ratio of 0.794:1) while fifth gear takes the place of a traditional fourth gear by being 1:1. That gives Mazda the chance to make fourth gear a little lower and tighten up the gaps between all the gears to eliminate any dips in the power delivery. Ultimately, of course, how fast the engine revs at a given road-speed is also down to the differential (or final-drive) ratio fitted, and the diameter of the wheel and tyre package.

My take on it is that dealers should stop telling lies to their customers. Take your problem straight to Mazda Australia’s customer service division and side-step what is clearly a smoke-screen from your dealer. It is ridiculous to suggest that a relatively new vehicle needs ten seconds to engage a gear after it’s been sitting for a few days.

As for the problem itself, start with the basics. Check for a blocked filter in the transmission (which can slow down the flow of fluid) and make sure that the fluid itself is not just the correct grade and type, but also the proper brand. These modern transmissions are complex and intricate, and even something as simple as the incorrect fluid can create chaos. Beyond those simple fixes, the problem could also be caused by a few other faults. For starters, it could be an accumulator inside the transmission that is failing. The accumulator’s job is to store some hydraulic pressure (created by the transmission’s pump) so that the transmission always has enough pressure and fluid volume available to effect gearshifts. If this accumulator is bleeding off pressure when the car sits, it will need time to refill (again, from the pump) before the unit will be able to select Drive. The other possibility is that the pump itself is slacking off and taking too long to build up pressure within the gearbox. You could also be looking at a pressure valve that has lost the plot and supplying the part of the gearbox it’s responsible for with an incorrect line pressure. Either way, a gearbox that is slow to select gears is often headed for the scrap-bin.

Given that it’s possibly a fairly major problem, it isn’t going to get any better. Your problem is that Mazda didn’t introduce its five-year warranty until August 1, 2018, and vehicles sold before that date were covered only for three years. That said, you’re BT-50 might squeak in, particularly if you pointed this problem out to the dealer some time ago (within the first three years). At that point, it’s a pre-existing condition, and it will be covered by the factory warranty as it occurred within the warranty period, even if the dealer – as it appears in this case – elected to spin you a yarn and do nothing about it.

I’ve had a flick through the BT-50 owner’s manual (and I suggest you do the same) and all I can find relating to a transmission warning light is a single 'powertrain warning lamp' which suggests something is not right somewhere along the length of the powertrain. Sometimes this light will come on in conjunction with the 'check-engine' light and it indicates that either a sensor has failed or there’s an actual problem with the hardware. Beyond that, the light doesn’t offer any suggestions on what might be wrong, but bear in mind that the four-wheel-drive system in this vehicle is electronically operated, so there’s lot of scope for errors.

A scan at a workshop should offer up some answers, but before you do that, just check that you haven’t bumped the rotary four-wheel-drive selector dial and have triggered the system into a mode it doesn’t like being in right now.

This model Mazda BT-50 and its Ford Ranger counterpart (they’re the same vehicle under the skin) have had their share of automatic transmission problems over the years. There are known problems with the gears in the oil pump which are prone to wear, valve-body problems and a fault with the output shaft speed sensor which can also fail, forcing the gearbox back into first gear at relatively high speeds. All these problems could be contributing factors in the problems you’re seeing.

While EGR valves often need replacement (and I’m not disputing that yours did) I don’t imagine the EGR valve would have had anything to do with your gearbox problem. It’s not uncommon – nor unreasonable - for workshops to charge a diagnosis fee (it involves workshop time, after all) but servicing the transmission alone won’t fix it if it has any of the problems I’ve listed above.

Many owners have changed from a dual-mass flywheel when changing the clutch in their utes, and none have reported a major vibration problem after the change. I would doubt it is the flywheel that’s the problem, look elsewhere in the driveline.

It is a relatively common problem, and it’s made worse by towing in 5th gear.