//M Car



BMW E24 635CSi


BMW E24 Mechanicals


BMW m30 engine

M30 M102

Six cylinder 12 valve

2.5, 2.8, 3.0, 3.3, 3.4 and 3.5

1968 - 1993

BMW S38 engine

S38 M88

Six cylinder 24 valve

1978 - 1994

All sixes expect the M635CSi and M6 use the M30 engine. Only the 630CS wasn't fuel injected all others used Bosch Jetronic-D/L or Motronic injection. The only cars with Jetronic-D were very early US 630CSi's which used the E3 3.0Si engine along with it's dreadful thermal reactor emission control system. Most others used Jetronic-L which is an excellent setup and generally very reliable.

From late 1980 (UK/euro) onwards the 635CSi used the Motronic micro-processor controlled system. This is the only car which can be "chipped" to give more power by adjusting the fueling and spark advance. Motronic interfaces with the ZF 4 HP22 E/H electro-hydraulic gearbox which was standard on 635CSi's from around mid-83.

Later cars deleted the cold start injector and thermo-time switch system, they also changed the source of the engine timing signals. On Motronic pre-88 cars there are two Hall Effect speed and Top Dead Centre (TDC) sensors on the bottom of the transmission bell housing, later cars used a pulse sensor on the front of the engine. The early cars also have a sensor here but it's purely for diagnostics.

For more details see the M30 and S38 engine pages. If you're having running issues see the E24 problems page.


BMW E24 rear subframe

E24 rear subframe.


Early cars have similar suspension to the E12 five series with some parts from the E23 seven. The E23 didn't come out until after the E24 and some parts took a while to migrate over. Early car's lacked the anti-dive front suspension system developed for the E23 and it wasn't until around 1978 this was adopted.

The system follows the BMW tradition of Macpherson struts at the front and semi-trailing arms at the rear. At both ends the shocks are mounted inside the springs. Front and rear anti-roll bars were always standard.

The E12 system could be quite tail happy in the wet and was prone to breaking away under power or when weight transferred to the front whilst braking in a corner. In 1982 the adoption of the E28 five series rear subframe helped reduce this tendency but not eliminate it by any means, the main change was to adjust the trailing arm angle by 12 degrees.

Some later cars had self leveling suspension, this is overkill and in my view not required. If it gives any trouble replace it with normal springs and shocks.

Pitman arms, often called dog bones, are used to prevent side to side motion of the rear trailing arms. If your suspension wanders this may be a cheap and easy fix. The rear subframe is held to the body by a pair of large rubber bushings, these don't last forever and can be another cause of wandering.

Semi-trailing arm systems will have their geometry compromised by overly lowering the car, 25mm would be my limit.


BMW E24 pitman arm

Pitman arms prevent sideways trailing arm motion.


All E24s used power assisted worm and sector steering rather than rack and pinion. The steering box is mounted on the same side of the car as the steering wheel, the other side has an idler arm. A centre drag link joins the steering box arm and idler arm whilst tie rods connect the ends of the drag link to the wheel hubs. If the system has play in the centre it can sometimes be adjusted out, but normally a new steering is the only solution.

There are numerous bushings and bearings in this system and wear in any of them can cause problems, especially with wheels larger than 16" or wide tyres. The easiest way to check for play is to brake hard from speed and watch for vibrations in the steering wheel.

All cars had a power steering fluid reservoir in the form of a metal can. At the bottom of the can is a filter which can be changed or even removed by the unscrupulous, if only BMW had retained this system on the newer cars.


BMW E24 front subframe

E24 front subframe.


At the heart of the sixes brake system is a bomb. But this bomb contains nitrogen on one side of a diaphragm, hydraulic fluid on the other and is called a bomb because it looks like the type of thing the Pink Panther uses to throw in the cartoons, a big black sphere. This hydraulic accumulator design came from Citroen and it was also used on the suspension of some Rolls Royces.

The purpose of the bomb is to amplify the force from the brake pedal, on most cars a vacuum servo is used but not on this car. The bomb gets pressure from the same hydraulic pump that drives the power steering. I once had my drive belt snap at a speed I'd rather not mention, the bomb had enough pressure to let me stop half a dozen times after that.

On right hand drive cars a linkage rod is used to transfer braking force from the brake pedal to the other side of the car where the bomb and master cylinder live. The linkage is on the dirty side of the firewall so the pivots can deteriorate with age and become stiff, in extreme cases it stops the brake pedal returning upwards and the brake lights stay on.

Pre-82 sixes used four pot front calipers with 280mm vented discs at the front and 272mm rear. 82-87 cars had single pot calipers from the E28 five series with 282mm front, 272mm rear. The final cars had E34 535i brakes, 302mm front, 300 rear.

ABS was fitted as standard from 1982 on UK cars but not until around 1985 in America, which is surprising. It works very well and is a real boon in poor conditions. Sixes use a finer stator ridge pattern than later BMWs and this makes them more prone to rust sadly. Front stators are built into the hubs, rears are a replaceable ring which goes around the outer part of the transaxles.

E34 brakes are a must have upgrade on 82-87 cars, easy and cheap too.


Early sixes used four speed Getrag gearboxes, later versions used either a five speed overdrive or dog-leg sports box. The normal boxes have a 1:1 fourth gear and 0.81:1 overdrive whist the dog-leg uses a 1:1 fifth gear and closer spaced gears below that. There were two styles of gear level mounting console which attached to the gearbox. Until around 1985 a "sheet metal console" held the gear lever pivot but this was replaced by a cast metal part in later cars. The difference is important when it comes to renew the nylon bushings or fit a short shift kit.

Automatics were always provided by ZF and were initially three speed with a 1:1 direct drive top. These were soon replaced by the more common four speed with 1:1 in third and overdrive 0.81:1 in top. Both of these boxes used a mechanical kickdown linkage attached to the throttle body. In 1983 the EH electro-hydraulic version became available as an option but by 1985 was standard. The EH box had a sport mode which locked out the top overdrive gear and held the engine revs higher in the other three gears, this made overtaking much easier and is a huge improvement. It was only available on Motronic cars.

Pre-82 and later cars use different differential mounting styles, early versions are often referred to as side loader. On post-82 cars 3.07:1 was the most common drive ratio for both automatics and manual cars. It's possible to find 3.25:1 and 3.46:1 especially in markets such as the US where the cars had less power and BMW adjusted the ratio to improve acceleration at the expense of economy and top speed.

A 25% limited slip differential was a very common optional extra and became standard as the years progressed. 40% was sometimes fitted but is rare. LSDs have an S or Z on the diff's identity tag.