BMW Buyers Guide and Problems - Transmissions and Gearboxes

BMWs have generally reliable transmissions but they do require proper care and feeding. The following should serve as a brief guide.

Manuals are more fun!

Automatics

ZF made most of the early automatic transmissions although some mid 70's E3s had Borg Warner units. The three speed ZF 3 HP 22 was replaced by the four speed ZF 4 HP 22 in the mid-80's and in it's EH electronically controlled form had a sport / economy / manual selector knob. In sport mode top gear was blocked out and the engine was allowed to rev higher in each gear. Kick down was activated by a bowden cable mounted next to the throttle assembly on standard systems or electronically on EH versions.

The four speed box was a top gear overdrive model, third one-to-one with several first and second gear ratios depending on model and year. The four speed boxes are geared to have no first gear and a low second, this results in poorer 0-60 times but good mid range performance. The last cars to use it were made in '93. This gearbox was also used in Range Rovers and many other large cars.

These gearboxes could fail or have problems if revved hard in neutral or parked, such as during emissions testing. Pressure would build up and kill the A clutch pack. After mid '87 a pressure relief hole was added in the A clutch to help prevent this. I'd advise an oil change with Dexron III ATF every 30,000 miles using good quality oil. There is also a filter screen which should be replaced every second oil change, it's under the oil pan. You'll need a new O-ring, oil pan rubber gasket and Torx socket. Clean the two magnets in the oil pan while you're at it. Caution - the oil level needs to be checked when the engine is running!

1990s five speed automatics are normally the General Motors Strasbourg unit, they were used by a lot of brands. These have no dipstick tube so fluid changes are harder and they don't use normal ATF, you need to find out exactly which model you have and source the correct fluid. It's possible for a home mechanic to change the fluid but not as easy as with the four speed unit. These units have a learning facility to suit the driver's mood.

Around the turn of the Millennium BMW switched from GM to ZF five speed autos, usually the 5HP-19 / 24 or 30. Same comments apply as with the GM boxes. All are reliable. Worth mentioning that BMW claim these gearboxes have lifetime fluid, but they really do need a change every 60,000 miles. To avoid problems don't skimp and use cheap fluid.

Steptronic is big work for a simple idea. Basically you have the same gearbox but with very slightly different electronics to let you change up or down manually using the shifter or steering wheel buttons. There is no mechanical difference and it still takes longer to change than a manual box with a good driver.

BMW's first use of a six speed box was in 2001 on the E65 7 series, it utilised the ZF 6HP26. Since then certain models have had seven or even eight speeds. This lets them use the engine at it's most efficient speed to maximise economy. Personally I think it's a bit of competition to see which manufacturer can make a car with the most gears, possibly at the expense of reliability and certainly with increased weight.

Most cars make more power the higher they rev, but most automatics change gear before you get there even in sport mode. So an automatic will be slower on the few occasions when you're really trying to accelerate seriously hard and use all the revs. Revving helps keep an engine clean, even more important with modern direct injection engines and complex crankcase ventilation systems. Anything which makes an engine rev less isn't good for reliability in my opinion.

Since the mid-1980s BMW UK has tried to force drivers of larger cars take to buy automatics. I think this is partly due to the heavy traffic in the south of England where they're based. It's a damn shame, even the US got a six speed manual option for the E38 740i. Automatics are OK, I've had three automatic BMWs but I always wished they were manuals (in fact I converted my 635CSi).

You have a dilemma if you buy a higher mileage BMW automatic which hasn't had regular fluid changes. Doing one may cause krud to move about in the gearbox and cause problems. Not doing one could result in premature gearbox failure. If you're only going to do a very low annual mileage I'd likely leave it alone, failing that you take your chances and change the fluid.

All auto boxes should shift and kick down smoothly. At the first sign of problems or slipping change the oil and filter screen. If the car is reluctant to change up or down a gear, especially when cold, a fluid change is always the first recourse. Automatic gearboxes generally have problems if gunk gets trapped in a solenoid, sometimes the solenoid is relatively easy to access and clean or replace. But failing that it may be possible to have a hydraulics specialist flush the system. Regular fluid changes should prevent this.

Auto cars have a relay to prevent the engine starter running except in parked or neutral, this can sometimes be the cause if your BMW won't start but it's not a common fault. I've seen worn gear selector mechanisms be in a gear but not display it on the dash. If the electronics aren't showing the correct gear then the car will not work as expected.

What's the lifetime of an automatic transmission? It's a bit of a lucky dip, I've seen both well maintained and never maintained units do over 200,000 miles. It's unusual to see one fail before 150,000 miles but it can happen. Personally I'd be very wary of buying an automatic car if it has a tow bar, towing puts a lot of extra stress on the gearbox and can cause problems.

Dog-leg shift pattern.

Manuals

The manual gearbox is the weapon of choice for most BMW enthusiasts, it's just more fun that way. Almost all BMWs gearboxes have been made by Getrag and ZF. Older models, such as those used in the 2002, can have a weak synchromesh on second gear so check for easy engagement. A rumble at idle when warm can be due to too thin an oil, many folk have had luck with Redline synthetic transmission fluid to cure this. Hard shifting when cold can be due to too thick or old an oil. But generally BMW manual gearboxes are bullet proof. You should change the fluid every 50,000 miles or so but very few folk do and the gearboxes soldier on.

The shifter shouldn't be too loose. If it is you may need new shifter linkage bushings but this need not be expensive and is a good excuse to upgrade to a short shift gear lever. Gear knobs just pull off if you need to replace them.

Some '80s close ratio sports gearboxes had a dog leg shift pattern as shown above. This allows a quicker change from second to third which is useful in motor sport. They are just as reliable as other BMW gearboxes and are highly desired by collectors. My M535i had one and I loved it.

There was a problem with some E36s jumping out of gear in the mid-90s but that's pretty much unheard of with any other BMW.

Some modern BMW gearboxes have a facility to automatically match engine revs when you change gear, on a manual gearbox! I seriously hope this can be disabled as it could take a lot of the fun out of driving.

Sequential Manual Gearboxes (SMG)

The euro E36 M3 was available with a six speed sequential manual gearbox (SMG) as an option. This eliminated the clutch pedal and used a touring car push-pull style shift lever. Having done a few laps in one of these cars on a recetrack many years ago I can only say good things about the performance.

They were removed from sale in the UK early on as users experienced problems in traffic, many people tried to drive the cars in automatic mode and this still needed some work it seems. Later models were more rounded.

For the E46 M3 an improved SMG-II Drivelogic was released and sold very well. It used the same basic mechanical six speed gearbox as a normal M3 but with an electronically operated clutch and gear selection system. The driver could set the clutch speed from slow to crazy fast in several stages. The gearbox itself is as reliable as a normal M3 because it's the same box, the problems spring from the electro-hydraulic operating mechanisms. These can be expensive to repair due to parts costs but generally the system isn't that unreliable.

In 2006 BMW introduced the final seven speed SMG-III version which could change gear in 65ms using it's fastest mode. This was used in the E60 M5, E63 M6 and E85 Z4.

Some non-M cars had SMG boxes, these were not at all the same as those fitted to the M3, M5 or M6. They were cheaper units designed with lower power cars in mind.

Dual Clutch Transmission shift knob.

Dual Clutch Transmissions (DCT)

DCT replaced SMG. As it's name suggests a DCT uses two clutches, one for the odd numbered gears and one for the even. This gives much master shifting than either a manual box or SMG. BMW introduced it on the E90 M3 in 2008 as a seven speed system. It's also available on the Z4, 335i, 135i and a handful of other models.

The BMW system is built by Getrag and adds around 20kg in weight. It has 11 driver selectable settings for shifting speed. The clutches are oil cooled to cope with the friction generated heat.

As for reliability it seems to be good. But the system is fitted to high performance cars and no clutch last forever on one of these. The clutches can be replaced when they wear out, but a replacement gearbox is said to be around $13000 and (just like Porsche) they're not repairable if they break! This is not a system I'd run unless I had the car covered by a warranty which would protect me.

Clutches

BMW clutches require more force to operate than a lot of cars, most drivers like this including me. Those coming from a Japanese car background may require some gym work before driving. A clutch which is really heavy may have one of the "ears" broken off the part which pushes it and needs a labour intensive repair, but this is uncommon.

A squishy clutch or one which doesn't return to normal height after use probably has hydraulic problems. Slave cylinders are cheap, master cylinders are dearer. Neither requires removal of the transmission to install. Poor clutch operation may also be due to air in the hydraulics or very old fluid which has picked up moisture.

If you hear a nasty rattle when you use the clutch it could be the clutch release bearing. Don't worry too much unless it's loud. I've seen BMWs with as little as 5000 miles have a slightly noisy release bearing.

In some markets BMW installed clutch delay valves, this was supposed to help drivers who weren't used to manual cars. If you find your BMW isn't shifting the way you think it should it's worth investigating. I think they started doing it around the time the E46 was launched in 1999. It's easy enough to delete it, you just fit a new hose between the clutch master and slave cylinders without the restrictor.

BMW clutches are pretty reliable and parts aren't too expensive but they take a good bit of labour to fit. It's possible for a clutch to last over 200,000 miles if it's not abused. If you're good at matching revs when you shift it will reduce clutch wear considerably.

Driveshafts & Transaxles

BMW drive shafts are two part with a splined joint in the middle. This middle section is mounted to the body via a bearing. If this fails it can cause vibrations at certain speeds. If a drive shaft is removed it must be put together the same way to preserve balance, paint an alignment mark before removal.

Typical driveshaft showing centre bearing and flexible guibo joints.

A clunk when pulling away can be due to worn nylon / rubber guibos at either end of the propshaft. Around '82 BMW changed over to nylon guibos which are much longer lasting and don't perish. Driveshaft universal joints are not readily rebuildable although a few companies will do it.

Transaxles tend to be very reliable. The main problem occurs if the rubber gaiters are torn and allow grit into the universal joints. These gaiters need to be checked to avoid future problems.

For four wheel drive BMW's see my xDrive page.

Differentials

BMW differentials need a fluid change around every 50,000 miles, although few ever see one in practice. If filling a limited slip unit be sure to use the correct fluid with friction modifiers. Undo the filler plug first, this will prevent the embarrassment of having a drained diff and no way to fill it if the plug is stuck!

A limited slip differential is desirable as it provides improved traction, if one wheel slips the other will continue to turn and get the car moving on ice, mud or snow. More modern BMWs have ASC+T electronic traction control and don't need LSDs so much although some cars did have both. LSDs are more effective in snow.

Changing the final drive ratio is a good way to improve acceleration at the expense of a seldom experienced top speed. This can make the car buzzy at speed and increase fuel economy if overdone. BMW don't use that many different styles of differential so it is possible to swap between models in many cases.

Cars made after 2008 may have an eDiff. This has the ability to vector drive power to the outside wheel by means of braking force. It knows which is the outside wheel thanks to the car's yaw sensor. An eDiff mimics the functionality of a limited slip differential. It accomplishes this by applying braking to the spinning wheel and thus transferring more power to the wheel with better traction.

Even on very high mileage BMWs it's rare to hear of a differential problem. I once bought a BMW which was cheap due to a noisy diff, turned out to be both rear wheel bearings making the noise.