Launched in 1985, the E30 325iX was BMW's first foray into all-wheel drive technology.
By 1985, the world hadn't just grown used to the idea of four-wheel drive cars; they were clamouring for them. And while firms like Jensen, Subaru and AMC can all make their claims to bringing 4x4 to the average consumer, it was undoubtedly Audi's Quattro system that had people's blood pressure rising. The 325iX was built to tap that market.
The first models started out as standard chrome saloons in either 2- or 4-door flavours. They used the new 2.5-litre flavour of the M20 engine; the only lump with enough grunt to power the complex and heavy new drivetrain. By mating the standard engine and gearbox to a mechanical transfer box supplied by Ferguson, BMW were able to send separate drive shafts to the front and back of the car, sending power to all four wheels by way of two viscous differentials.
This system was both primitive and complex at the same time. The transfer case was outdated before it was released, but its simple mechanicals allowed BMW to set up a permanent rear-wheel bias to ensure the car still drive like a BMW. When things got loose and wheels started to slip, the viscous differentials would kick in, locking anywhere between 10 and 100% without having to be manually locked by the driver. This meant that the car could transform from autobahn cruiser to off-road ranger in a heartbeat; perfect for the icy conditions of a European winter when every ounce of traction counts. Another boon was the weight; by crafting all the extras out of aluminium, the iX only weighs 80kg more than its two-wheel drive counterpart, and has both a wider track (13mm more) and taller ride hide (20mm) for better handling in adverse conditions.
The downside was that the setup wasn't geared for performance, and the drivetrain ultimately robbed a significant amount of power from the six-cylinder lump. But considering the target market, this wasn't a huge issue - the 325iX was never intended to enter rallies, to the point where BMW actively downplayed its performance. Official stats claimed a 0-60mph time of around 9 seconds - not exactly a slouch, but certainly a lot slower than the 325iX feels from behind the wheel. Third parties, such as the Swedish "Automobile" magazine, have claimed times as low as 6.8s in a standard 325iX, meaning the car is certainly more capable than it's given credit for.
But this performance came at a price. When launched in the UK, the list price was 17,000 pounds, which was 30% more than a standard 325i, and only in left-hand drive. Up to twelve of these cars are known to have been professionally converted to RHD by BMW dealers within the UK. However, all were recalled to BMW for a steering issue and two were ultimately dismantled. Only one 325iX in the UK is an officially registered BMW-approved RHD car.
The 325iX carried on through the 1988 facelift, with a Touring model added to the range. Despite that, the iX remains a rare beast, and with only 15,000 units leaving the factory, it is destined to become rarer still.
Alpina made an iX-based E30, which is known as the B3 ALLRAD.
Despite the beefy requirements of powering all four wheels, the iX was fitted with the exact same 2.5 litre M20 engine as the 325i, mated to the same family of manual or automatic gearboxes. But that's where the similarities end.
From the end of the gearbox, a small transfer box splits the output to two prop shafts; one forward, one rear. This transfer box is a relatively simple design made by Ferguson, and employs gears and a chain to split the power with a rear bias; 37:63%.
The rear end is similar to the E30, but the differential is a specific viscous limited slip differential with a 3.73 ratio. The front end is a completely different kettle of fish; it employs a differential inside the engine sump before sending power through the drive shafts to the hubs.
Because of the design, the iX's drive is a permanent All-Wheel Drive system rather than four-wheel drive. There is no option to lock either the front or rear differential, although the viscous nature of the rear diff means it can lock between 10-100%. However, the viscous coupling inside these differentials are known weak points, and almost all require a long-overdue rebuild by now.
The drivetrain layout means that all the mechanicals at the front of the car are custom-made for the iX, in order to squeeze everything into the relatively small space. The subframe is unique to carry both the engine and front differential, as are the wishbones and hubs. There's even a custom steering rack, which is mounted behind the front cross-member instead of in front, like other E30s. Most of these components (including the subframe) are aluminium, making repairs or modifications difficult.
To accommodate all this, the 325iX bodyshell is fundamentally different to standard E30s in almost every aspect. From the outside, you can clearly distinguish the wider arches both front and rear, which are to accommodate the wider track that the iX employs. And there are differences underneath too. The transmission tunnel is significantly wider (far wider than a simple lump hammer can achieve) to the point where the seats rub against the centre console. Open the bonnet and you'll see similar differences, with the suspension turrets moved farther forward to change the suspension geometry, which also affects the inner wings and chassis legs. Since all 325iX models are LHD, there are also bulkhead differences to UK cars.
It's fair to say that, forward of the windscreen, the 325iX is a completely different car to every other E30.
Because of the wider track of the 325iX, special wheels were fitted with the correct offset to compensate. Frustratingly, this means that the iX cannot use standard E30 wheels as they will scrub the arches. The correct offset for 325iX wheels is ET41.
A lot of people, upon hearing of the existence of the 325iX, entertain daydreams of grabbing the mechanicals and fitting them to their own car. If you're one of these dreamers, give it up now; it's not going to happen.
As explained earlier, the bodyshell of the 325iX is unique. The all-wheel-drive mechanicals will not bolt up to a standard chassis, and the changes required to do so are so involved that it is dramatically easier to restore a rusted 325iX shell rather than adapt a standard one.
There is also the issue of the steering rack. The 325iX unit is specific to that model to fit inside the subframe. Its location within the subframe makes it almost impossible to access for RHD cars, which is why hardly any RHD versions were produced, meaning no racks are available. If you manage to source a compatible rack from another non-E30 vehicle, then there's the problem of getting the linkage past the exhaust pipes.
That's not to say it's impossible given enough time, talent and cash, but it is an immense project that has not yet been done, for very good reasons.
The drive train on the iX appears to be pretty bulletproof, with only a few known problems. Of course, fluid changes are required every 36K miles to keep things running smoothly; ATF in the transfer case and hypoid SAE90 (GL-5) gear oil in the front and rear differential. The viscous coupling units do not require any service but can fail with age and require a rebuild. The transfer case only holds about 1.5 pint of ATF, so be sure to check the fluid regularly. However, the transfer case on an automatic can leak into the transmission with no visible sign of a leak.
Over time, the viscous couplings within the differential degrade. They are usually rated for 70k miles, so many are long overdue for a rebuild. They use a sealed viscous pack.
To test the state of your viscous differential, watch this video.
Front Prop Shaft
The weak link on the iX drivetrain seems to be the splines on the front driveshaft which mate with the chain-driven gear in the transfer case. These splines have stripped in several cases. Apparently, the moly grease which lubricates these splines dries out or becomes contaminated with water and allows the splines to wear down. The only way to check the condition of the grease is to remove the front driveshaft (not a complicated procedure). If the splines strip, the front driveshaft must be replaced. If the female mating gear is ruined, the transfer case will need to be removed and the gear replaced.
The transfer case is a relatively rudimentary design, comprising a cog-and-chain mechanism. Like anything else, these cogs can wear over time until, inevitably, the box destroys itself. If you hear a noise coming from the centre of the drivetrain, be prepared for an expensive rebuild.
Please also see the E30 325ix Register