Suspension

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Suspension

Everything that connects the Wheels to the Bodywork of your E30 is the Suspension. This arrangement of springs, shocks and arms is responsible for keeping the rubber of your tyres on the road at all times; without it, you'd be bounced around like a pinball.

Suspension comes in two flavours; soft or hard. Soft suspension will give you a delightful wallowy feeling, like driving a mattress, and is the sort of ride big American cars are famous for. By absorbing all the knocks and shocks , the comfort of your ride is greatly increased. This is wonderful for the big flat German autobahns, but useless for aggressive driving, where body roll will have you lurching drunkenly round every corner.

Hard suspension tightens everything up, giving the car a much more rigid feel. Stiffened joints and tighter coils force the tyres back onto the road after every bump, allowing you to force the car into harder and faster corners. The downside is that every jarring bump will be felt throughout the car, and transmitted directly into your spine and teeth.

The E30 setup aims for a compromise between the two. The stock setup provides a good balance of comfort and performance, with many possibilities to upgrade the system if you need it. But as the cars age, it is important to keep on top of all the maintenance to make sure that at the car drives as well as it did when it left the factory.

For a better understanding, learn more about how suspension works.

Rear suspension layout, including braking parts
Rear suspension layout, including braking parts

Contents

Overview

The E30 employs a lightweight but efficient suspension setup, comprised of independent front struts and independent rear semi-trailing arms. This allows each wheel to react to the road surface without affecting the geometry of any of the other wheels. All E30s are equipped with this suspension layout, with small differences between each model depending on body style and and engine.

Sturdier components were fitted to the six-cylinder models (M20 and M21 engines), incorporating sturdier springs to carry the heavier weights. Bigger struts were fitted to all Touring and Cabriolet models, as well as different rear springs to carry the heavier bodies of those cars. Upgraded suspension was also part of the sports package.

Front and rear anti-roll bars were offered to various models to increase responsiveness.

Components

Front

Front suspension layout
Front suspension layout

The front suspension is comprised of two struts which each incorporate a shock absorber and a spring. At the lower end of the strut, the stub axles carry the wheel hub via a wheel bearing. The top of the shock absorber screws to the upper strut mount, which bolts directly to the vehicle bodywork. Between the two ends of the shock absorber, two metal plates squeeze together the spring, which is the main reaction element of the setup.

While the strut is purely the metal leg, the entire suspension assembly is also referred to as the strut on occasion.

If you want to remove the entire front assembly, learn more about replacing the struts.

Struts

The struts are solid metal "legs" which allow all other suspension components to be fitted. At their lower end they contain the mounting point for the stub axle, as well as mounts for the brake calipers. At the top end, a cupped plate will hold the springs, and a threaded collar will hold the shock absorbers in place.

Struts come in two sizes: 45mm and 51mm. The bigger size was standard on all 323i and 325i models, all Tourings and all Cabriolets. If you are unsure of what size strut your car has, and you can't remember your maths lessons, then use a bit of string. Wrap the string around the strut, and then measure its length; 141mm means a 45mm strut, and 160mm means a 51mm strut.

Shocks

Each front shock fits to the top of the strut, and is held in place with a threaded collar. From there, the shock rod goes up to the top mount, which it grips with a 17mm nut. Sandwiched between the two ends of the shock is the bump stop, the spring plate and the dust cover for the shock, which helps prevent grit and dust from damaging the rubber seal of the shock rod.

Shocks can and do fail, especially with age, resulting in a wheel that slaps the road like a beaver's tail as the oscillation is not suppressed. When that happens, the shock needs to be replaced. The Zone recommends fitting Bilstein B4 or Boge turbo shocks.

Top Mount

The top mount screws directly to the top of the shock absorber rod. From there, it mounts inside the suspension turret on each side of the car using three nuts. It can be seen as soon as the bonnet is opened inside the vehicle. Over time, or in extreme circumstances, the rubber cushion that forms the centre of the top mount can fail, and therefore requires routine replacement. Since the top mount is a type of bush, learn more about suspension bushes and how to replace them.

Bump Stop

Beneath the Top mount is a large rubber lump, known as the bump stop. Its simple purpose is to cushion the blow of the shock absorber if it retracts completely, therefore preventing the steel case of the shock from damaging the top mount.

If you find that your car is hitting the bump stop regularly, then your suspension is probably too soft. This is caused by ageing components, and will need to replace either your shocks or springs, or both.

Springs

The springs are fat coils of steel that compress under force, allowing the entire front suspension to react to the road conditions. There are a wide variety of springs available for the E30, and they are the single biggest factor when contemplating changes to your suspension setup. In terms of compatibility, the spring must be matched to the size of the strut. Note that there are also significant differences in the rear springs if buying a complete set for your vehicle.

The springs themselves are sandwiched between two plates. The lower plate is an integral part of the strut, cupping the bottom of the spring. At the top end, a moving spring plate is sandwiched between the bump stop and top mount. There are also two rubber pads, known as spring pads, which prevent the springs rusting onto the plates.

Because of the suspension design, the spring is kept under a constant pressure, and therefore must be treated with respect during any maintenance or upgrade work.

While performance upgrades are available, the E30 zone recommends Eibach or H&R springs of OEM height.

If you are planning on lowering your vehicle, learn more about lowering your car.

Spring Pads

These were briefly mentioned above, there is a pad at either end of the spring which both acts to prevent the spring rusting to the spring plates but also provide a touch of cushioning. BMW offer two different thicknesses of upper spring pads, 9mm and 3mm. The 3mm pad will obviously lower the car 6mm over the 9mm pad, however no one has found anything to confirm what cars come with what pads. The lower spring pad only comes in a 3mm thickness.

Upper Spring Plate

While the lower spring plate is a fixed part of the strut the upper is a seperate part which holds the spring inplace and also acts as a housing for the top mount to sit in. Now this is a relatively uninteresting part, however it has recently come to light that this can be replaced by a spring plate from an E92 3-Series (part number 31336764093) which actually lowers the car by approximately 10mm by allowing the spring to sit higher in the wheel arch.

Stub Axle

The lower element of the strut is the stub axle. On standard E30s this is a non-removable component, welded to the strut, although it is removable on M3 struts.

The stub axle is responsible for carrying the entire wheel. It does this through a bearing which slides over the stub axle. The wheel hub then fits over the top of the bearing and stub axle, and is held in place with a 36mm nut, covered by a dust cap.

Wheel Hub

The wheel hub is little more than a sturdy metal disc. It is shaped to fit over the wheel bearing and stub axle, and is locked in place with a 36mm nut. Its bolt pattern and hub rim determine the wheels that can be fitted to the E30; 4x100 with a 57.1mm centre bore.

However, changing the wheel hub is a lot more involved than simply pulling it off and fitting one with a different bolt pattern. If you're looking to change your wheel hubs, learn more about a converting to 5-stud.

Wheel Bearing

The front wheel bearing allows the wheel hub to rotate around the stub axle smoothly and freely. It is a standard bearing with an inner and outer race, and simply slides onto the stub axle; there is no need for a press when fitting a new wheel bearing. However, removing an old and worn bearing may require the use of a three-legged pulling tool, since the inner race can stick to the stub axle over time.

To remove a wheel bearing:

  1. Remove the wheels, calipers and discs.
  2. Prise out the dustcap from the stub axle
  3. Remove the 36mm nut
  4. Gently tap the side of the hub as you apply pressure from the outside and the bearings will come free of the stub axles in one piece. If you try to force it the inner races will stay behind. If that happens, warm the race with a blow lamp and it should free itself up. If you don't have access to heat, carefully split the race with a chisel

Subframe

Not essentially a suspension component, the subframe is little more than a shaped metal tray to which everything in the engine bay is bolted. The subframe mounts to the chassis rails with four solid bolts. From there, the inner ball joints of the wishbones bolt through at the sides, to locate the suspension horizontally.

The subframe also carries the engine and steering rack.

All subframes are identical, regardless of engine or body style.

Wishbones

Also known as control arms, these L-shaped curves of metal hold the bottom of the strut in place, relative to the chassis of the car and the subframe. Each wishbone has three flexible joints: the lollipop bush at one end, holding the wishbone to the chassis; a ball joint at the corner bolted to the subframe; and a final ball joint to the wheel hub.

Ball Joint removal tool
Ball Joint removal tool

The standard wishbones are made of steel. Lighter aluminium wishbones were fitted to the M3 and to the 325i Touring. While these may seem desirable for their lighter weight, it is impossible to replace the ball joints on them, and therefore very few cars still have them fitted. The cost of new parts definitely outweighs any advantage the aluminium wishbones may offer.

Since the ball joints in steel wishbones can be pressed out and replaced, it leads to significantly cheaper repairs. If you're hanging on to your E30, it may be worth investing in a ball joint removal tool (pictured) so that you can press them out yourself, rather than having to lug two heavy wishbones to a mechanic.

Lollipops

The lollipop bush is a strong circle of rubber, held in place with a circle of steel that directly bolts to the front chassis rail. The idea of the bush is to locate the wishbone to the car while allowing it to turn, based on the flexing of the rubber inside it.

The standard bush is a concentric design, meaning the hole for the wishbone is in the centre of the bush. M3 models were fitted with eccentric bushes, which pushed the end of the wishbone closer to the centre of the wheel arch, increasing the caster. This is considered a worthwhile upgrade for all E30s.

Ball Joints

The ball joints are special pivots that allow two joined parts to move around each other. E30 wishbones have two ball joints each, allowing the wishbone to rotate up and down around the subframe, therefore lifting the wheel hub without affecting the camber of the wheel.

Ball joints are service components, and will fail with age. They can be pressed in and out of steel wishbones (but not aluminium), but at current prices it makes sense to replace the whole wishbone.

The actual knuckle of the ball joint is covered with a rubber boot. These boots can tear over time, compromising the life of the joint as well as being an MOT failure. It is possible to replace this rubber boot without removing the ball joint; spare boots are available on popular online auction sites.

Anti-Roll Bar

Main article: Anti-Roll Bar

On all cars a front anti-roll bar or ARB was used to tie the two front wishbones together, relative to the bodywork. This firms up the suspension and dramatically reduces body roll, especially for spirited driving.

The ARB itself mounts to the car body using two rubber bushes, held in place with steel shells. The two ends of the ARB then mount to the wishbones via drop links. These drop links operate similarly to ball joints, allowing for lateral movement in the suspension without compromising stiffness, but are actually another type of bush and need to be replaced with the same regularity. There is an upgraded drop link available, which involves using Ford Mondeo parts.

A number of sizes of ARB were fitted to the E30, and upgrades were available from a number of manufacturers including AC Schnitzer and Racing Dynamics. The thicker the ARB, the stiffer the suspension. If you want to know which ARB was fitted as standard to your E30, learn more about ARBs.

Rear

Rear suspension layout
Rear suspension layout

The rear suspension can be considered a one-piece unit. The rear beam acts as a subframe to which all the other suspension components are mounted, while the beam itself is attached to the car via two large bolts. This arrangement allows the drivetrain to react to the road as a single system, offering good grip as well as a smooth ride, since the rear beam also carries the differential which subsequently bolts to the car body via a large rubber bush.

From the rear beam, two trailing arms extend backwards, pivoting around the beam. At the end of each arm a shock absorber connects the arm to the car body, with springs mounted half-way along the arm. An anti-roll bar used to add a degree of stiffness to the system, if required.

Rear Beam

The rear beam is a metal frame made of thick steel. It is essentially two hollow lengths welded to either side of a cup. This cup carries the differential, while also allowing the prop-shaft to pass through the rear beam. The rear beam is essentially the same across all models; the only differences is whether or not an exhaust hanger is fitted.

At each end of the beam are the rear beam bushes. These allow the beam to be mounted to the car with a small degree of flex, so that sharp impacts don't damage or break the mounting points. Since these two bushes are subject to all the forces of the rear suspension, they do fail over time and need replacing. Since this is one of the worst jobs on the whole car, learn more about replacing the rear beam bushes.

Trailing Arms

The trailing arms are V-shapes of tubular metal, with each "leg" bolting to the rear beam. These joints are also bushed, since they swing up and down constantly as the wheel travels over the road.

The "head" of each trailing arm carries the wheel hub, wheel bearing and rear braking system. Because E30s could be fitted with either drums, discs or ABS at the rear, there are three flavours of trailing arm available. You cannot fit brake discs to a trailing arm designed for drums, and vice versa However, you can fit ABS arms to a non-ABS vehicle if required. The arms simply unbolt from the rear beam and swap over with no problems.

Rear Wheel Hubs

Much like the fronts, the rear wheel hubs are simple metal discs that allow the wheels to bolt up to the trailing arm. However, since the rear wheels are driven on an E30, the rear wheel hub has to accept incoming power from the drive shafts in order to make the wheels spin. Therefore, the inside of the wheel hub is splined, to mate up with the splines on the drive shafts.

The drive shaft therefore acts as the stub axle at the rear. It pokes through the trailing arm, rests on the wheel bearing, and slots into the wheel hub. The wheel hub is then squeezed onto the drive shaft with a 30mm retaining nut, locking the whole assembly in place.

Rear Wheel Bearings

Rear wheel bearing and wheel hub
Rear wheel bearing and wheel hub

The rear wheel bearings are pressed into each trailing arm to carry the wheel hub. Unlike the front bearings, the rears are pressed in, and changing them is considered to be a properly horrible job. Removal is normally with a hammer and chisel, while replacement will require either creative use of threaded bar to wind them in, or access to a proper press.

If you can pull your rear wheels back and forth and side to side when the car is raised, or if you're getting a whining or rumbling noise from the rear, then you may need to change your bearings. The OEM manufacturer of these bearings is FAG. For the correct procedure, learn more about changing your rear bearings.

Rear Shocks

The rear shock absorbers are one of the few suspension components that are standard on all E30s. They are all the same length and damping force.

At the bottom end, the rear shock bolts directly to the trailing arm, while top end bolts to the bodywork via the rear top mount. Since the rear suspension is not a strut design, the shock absorber is not located inside the spring, so installation and removal requires little more than unbolting each end.

Note that the OEM shocks are fitted with washers on the shock rod; a piece that is not always included on aftermarket shocks. It is essential that this washer is fitted to the new shock if replacing, otherwise you will destroy your top mounts in a matter of days.

Rear Top Mounts

The rear top mounts are a type of bush that locates the top of the shock inside the body. The shock screws to the top mount with one 17mm nut, and the top mount then fixes to the car body with two 13mm nuts.

Rear top mounts are interchangeable on all E30 models. However, we have found that E46 Convertible mounts are also compatible, and are a stronger component too. They are considered a useful upgrade when refreshing your rear bushes.

Since the top mount is perishable, it requires replacement after certain intervals. If your top mounts are dead, learn more about replacing rear top mounts.

Rear Springs

The rear springs are a much smaller type than their front counterparts, comprising a squatter, fatter profile. They sit on special plates welded to the trailing arms and bodywork, cushioned with rubber pads known as spring pads.

The strength of the rear springs is relative to the vehicle they are fitted to; Touring and Cabriolet models will have uprated springs to cope with the increased weight at the rear of the car.

Rear Spring Pads

These perform the exact same role as the front ones, although the top one is in direct contact with the car's body. As with the fronts there are different thicknesses available, albeit for the lower one on this occasion. Thicknesses available are 10mm, 7.5mm and 5mm.

Rear Anti-Roll Bar

Main article: Anti-Roll Bar

Just like the front, an anti-roll bar was used to stiffen the suspension under load without making the springs themselves too hard. However, this component was not fitted to all vehicles, and the thickness of the bar fitted seems to be almost completely arbitrary at times. For a complete list of ARBs, check the main article.

The ARB itself is mounted to the body using steel shells and rubber bushes. The two ends then curve down where they slot into drop links. These rubber-bushed arms then bolt directly to the trailing arm. To remove or fit a rear ARB is relatively easy, and does not require the dismantling of any other suspension components; it just requires a certain patience to thread the bar sideways and into place. Learn more about fitting a rear ARB.

Common Problems

Inner Tyre Wear

As you lower an E30, due to the semi trailing rear suspension, camber and toe out are increased. This puts wear on the inside edge of the tyre.

Another significant factor is worn bushes as well as tyre under-inflation, and you will find yourself rapidly wearing through the inner shoulder of your rear tyres.

If this is the case, it is time to overhaul the rear suspension components, including renovating the bushes.

Maintenance

Bush Renovation

Over time, the rubber suspension components will dry out, harden and perish. This inevitable deterioration means that all the bushes will need replacing at some point. Renovating the bushes with original rubber components will dramatically improve the ride quality.

Our list of bushes links to all the articles you need to replace every rubber part on your car.

Upgrades

Bigger Struts

The front end of each E30 is designed to carry the weight of its engine. If you've gone through the labour of an engine swap, you'll want to increase the front struts to cope with the heavier weight of the new engine, especially if you've upgraded from four to six cylinders.

Better Shocks and Springs

The rear end can also get tired over time, after 20 years of tail-sliding abuse. Upgrading the rear suspension can yield a much tighter driving experience for these cars.

Coilovers

Coilovers are an increasingly popular modification to cars fitted with McPherson-style front struts, and the E30 is no different. While their basic operation is the same as the strut design, their method of construction makes the spring and shock a one-piece unit by fixing the spring plates directly to the shock.

The modern application of coilovers refers to their adjustability. Instead of having the lower spring plate welded to the strut, it is fixed to the strut by a threaded collar, which can be raised or lowered as desired. This can tighten or loosen the spring, affecting suspension stiffness, as well as affecting ride height and therefore offering an element of lowering. It is this versatility that makes coilovers so popular.

While cheap sets are available, the recommended brand is GAZ. Proper coilover installation requires the kit to be welded to the strut, and they are normally only available for the bigger 51mm struts.

Lowering

Lowering is a cosmetic modification to the vehicle that affects the overall ride height. By reducing the height of the springs, the wheel is brought closer to the top of the wheel arch, and all underbody elements of the car closer to the road.

Since lowering is purely for aesthetics, the amount of "drop" required is purely relative; however, there are practical limitations to be considered when deciding how much to lower the car. For example, the lowest point of the car is undoubtedly the engine sump. Therefore, lowering the car by an extreme amount will put your sump at increased risk of being smashed by road objects.

As a simple guideline, 30mm is considered the lowest practical level, while 60mm is the absolute maximum level. That's not to stop others lowering their cars by 80mm or more, but for the design of the E30 it is not recommended. Even at 60mm you will be chewing through a set rear tyres every few months.

Please remember that making cosmetic adjustments to your vehicle's suspension will have a detrimental effect on the performance of the car. In the short term you will suffer inner tyre wear, but in extreme cases it can put both you and your car at risk.

Strut Brace

Strut braces are tubular beams that bolt to the top of your suspension turrets. By locking together the two points of your suspension, you will reduce chassis flex which will give the suspension a much tighter feel, especially when driving hard.

The fact that cheap strut braces bend and snap under duress should prove that the turrets can and do move under strain. Providing suitable reinforcement will therefore yield noticeable gains if the correct equipment is fitted.

However, a strut brace is only worth fitting if the rest of your suspension is already in good condition. Make sure you have maintained or upgraded your primary suspension components before fitting a brace.

ARB Drop Links

Mondeo ARB fitted
Mondeo ARB fitted

A surprising discovery was made regarding the front drop links that hold your Anti-Roll Bar; you can replace them with the rear drop links from a 2000-2007 Ford Mondeo Estate. These units are rose-jointed, giving a firmer, stronger hold over your anti-roll bar, so they should last a while. They're also available from Lemforder who, being an OEM manufacturer for BMW, guarantee that you're not polluting your E30 with Ford scrap. Lemforder part number is LMI 2581102

This upgrade is pretty much mandatory as part of a front suspension rebuild.