Buying Guide BMW E24 635CSi

BUYING GUIDE E24 635CSi

The 635CSi is a wonderful beast and still relatively affordable to buy, grab one while you can and revel in shark-nosed automotive nirvana Words: Bob Harper and Andy Everett. Photography: BMW and Craig Pusey.

Has BMW ever produced a better shape than the E24 6 Series? To us it encapsulates just about everything that was so right about the company’s design direction in the 1970s and as well as sharing a strong family DNA strand with the E21 3 Series and the E12 Five (as well as the E23 Seven that made its debut just after the Six) it was suitably aggressive for the company’s sporting range-topper. The E24 had big shoes to fill, following on from the iconic E9 CS/CSi coupés that had culminated in the wonderful CSL, and while the Six was bigger and heavier it did garner almost universal praise when it was originally launched in the UK as the 633CSi – the 630CS didn’t make it to these shores.

These days the 6 Series is starting to ride the swell of the classic car tsunami and while the non-M versions are unlikely to head for the stratosphere as far as pricing is concerned any time soon, they do make a very viable proposition as a classic car that can be enjoyed without breaking the bank. You do need to be wary though, as now prices are starting to creep up there are many at the unscrupulous end of the spectrum who are looking to make a quick buck by tarting up some well past their sell by date examples. A Six does have the ability to swallow up huge amounts of your hard-earned so the last thing you want to do is pay top dollar for something that’s actually a bit of a basket case.

We’re going to concentrate here on the 635CSi E24 – that’s not to say the lesser-engined machinery aren’t noteworthy, it’s just that running costs will be the same for all models so you might as well bag the one that offers the best performance on offer. While the E24 made its debut in 1976 the range-topping 635CSi didn’t arrive until 1978, but it was worth the wait as the additional power and torque that the biggest version of the M30 straight-six offered over the 3.2-litre version in the 633CSi endowed it with better performance, improved economy and further refinement. The 3453cc engine developed 218hp at 5200rpm and 229lb ft of torque at 4000rpm, good enough for a 7.6 second 0-62mph time for the fivespeed manual version, although the automatic version was initially considerably slower at 9.1 seconds.

The shape that had been penned by BMW was built by Karmann and for the 635 its delicate lines were added to with a deeper front spoiler and a large wedge-shaped item that sat on the bootlid to improve aerodynamic efficiency. It wasn’t a cheap machine by any means, costing £16,499 at the beginning of 1979, just after UK deliveries had started. It wasn’t fully loaded either with items such as air conditioning (£1051), electric sunroof (£562) and headlamp wash wipe (£161) being optional extras. You even had to pay an additional £60 for an electric mirror on the passenger’s door!

The motoring press of the time was impressed though with Autocar saying: “The BMW will find favour with the man who ranks style as important as performance, and who prefers a vestige of sporting sound to total refinement; it is a worthy contender here, practical and very satisfying to drive.” The first main change that occurred during the Six’s 13-year production run (the longest of any BMW incidentally) was in 1982 when the big coupé moved over to using the underpinnings from the E28 5 Series which brought about improvements to handling and road-holding, and drivability too, thanks to the introduction of Digital Motor Electronics and the 3430cc version of the M30 ‘six. At the same time the rear bumper was changed too, now featuring a more delicately shaped three-piece chrome item that wrapped around from the rear or the rear wheel arches. Inside, the dash layout changed with the adoption of the now classic BMW traditional equalsized speedo and rev counter – previously it had featured a central speedo with a smaller rev counter and combined fuel and temperature gauge either side of it. A new three-spoke steering wheel was adopted, a service indicator was fitted and the check control system was updated.

There were a couple of changes worthy of note over the coming years, mainly centred around the transmission; 1983 saw the introduction of the ZF four-speed automatic unit and in 1984 the ZF 4HP-22 switchable unit was adopted.

The most major update that occurred during the Six’s lifetime was the fitment of US-style impact bumpers in 1987 which also brought the more modern ellipsoidal headlamps to the party too. For the 1988 model year (so from mid-1987 production) the Six also benefited from the E32 735i’s engine with 220hp. All UK Sixes now came with the larger metric TRX rims fitted with 240/45 415 Michelin rubber and inside the dash, door trims and centre console were swathed with leather. Air-con was standard as were electric seats. These later machines were what are now known as the Highline cars. The last model to be considered was the UK Highline Motorsport Edition. These were equipped with all the standard features of the Highline plus the shadowline exterior trim and M logos on the seats. They were available in three colour and trim combinations; Misano red with black Nappa leather, Nogaro silver with black Nappa leather and Macao blue with Lotus white Nappa leather. The final Six rolled off the production line in 1989, but some machines were registered as late as 1990.

Buying one

There are plenty of things you need to decide when contemplating the purchase of an E24, and the first of these will be whether you want an early car (1978- 1981), an 1982-1987 machine, or one of the last of the line Highlines. The original shape cars are now becoming quite hard to find in a decent condition and we reckon the 1982-on machines with their wrap around bumpers are actually considerably better looking. Combined with their E28 underpinnings they’re probably a much better prospect.

If you want one with all the bells and whistles and the luxury of having a leather-clad cocoon of a cockpit then you’ll be after a Highline. Which model will be worth the most is anyone’s guess so the best advice is to buy the one you like best rather than trying to second guess what the investment market will eventually decide is the most desirable.

Once you’ve done that then there’s the question of manual or automatic, with the former being much rarer and significantly more sporting, the latter endowing the car with a more of a cruiser quality. Either is a fine choice, but for the really keen driver it might be worth hunting out one of the very rare cars that was spec’d from new with the dog-leg fivespeed manual. In conjunction with a limited-slip diff this really transforms the car’s behaviour. Seats might also be a cause for consideration too. Many cars have the flat ‘armchair’ style items which offer about as much lateral support as a damp paper bag – comfy for cruising though… Then there are the BMW sports seats which offer the keen driver much better support, but for the ultimate hip-huggers you’ll need to find a machine with the rare Recaro option.

While all these decisions are important by far the greatest consideration is the car’s overall condition. Sixes like to rust. And rust a lot. And they like to hide a fair bit of it too, so if you don’t know what you’re looking at we implore you to get any car inspected by a marque specialist who will know the known weak points. Look at as many as you can to get a feel of what they’re like to drive – there are plenty out there so there’s no excuse for ending up with a basket case unless you really want to embark on a ground-up restoration.

Prices start at around £2000 for a car needing a lot of work and rise to around £20,000 for an immaculate machine with no faults. We wouldn’t want to pay more than that though as at that price point the rarer and more collectible M635CSi should be on your shopping list.

Body

The main problem with the E24 is rust and there are very few that have not seen some bodywork in the past. It strikes just about anywhere and the front wings are the obvious and well-known problem. There is a reinforcing bracket spot welded to the inner wing flange and rust starts here, and when rust bubbles appear on the front of the wing above the bumper, the game is up. Wings can also rot along the top edge. New wings are in short supply, are BMW only and around £1300 a pair new. They can be repaired but need to be removed and grit blasted if the repair is to stand a chance. Front inner wings rot where they meet the front panel in the engine bay and under the arches along the top wing mounting rail.

The roof and scuttle are generally okay but beware any bubbling on cars with a sunroof – that’s virtually all of them. Sills rot of course and more at the back by the rear axle mountings – repairs here are very expensive. Rear arches rust but the doors, bonnet and bootlid are generally okay. Front chassis legs need examining and the steel front bumper shell on pre-1988 cars is both complex and rot-prone. Chrome bumpers are of course very expensive and are in fact chromed covers on a steel shell.

The face-lift cars built after April/May 1982 (full length wrap around rear bumper) have different front wings with wider arches and different doors with revised inner shells to accept E28 style door inner handles. The sunroof mechanism is all different as well but the bonnet, bootlid, screens and lights are all similar although Highlines have different E34 style headlamps. Highlines have plastic arch spats fitted. Strictly speaking, post ’88 cars (big bumper) with satin black trim are Shadowline and cars with stainless bumpers and trim are Highline models.

Wheels, tyres and brakes

From late 1980 635CSis were fitted with the Michelin TRX metric tyres on special metric wheels and their ideal use is as a plant pot. Both the earlier 390 and later (Highline) 415 tyres are around £1400 a set and they just aren’t worth it. Replace them with a set of either E34 15-inch or E38 16-inch BBS style crossspoke alloys with either 225/55 R15 or 225/50 R16 imperial tyres. Pre-1980 models have 14-inch wheels with 205/70 tyres that present no problems, and from May 1988, the 635CSi was available in mainland Europe with the E34 15-inch BBS wheels as standard with the TRX wheels becoming an option.

Brakes are now a potential problem on all cars. Pre-May 1982 E12 type cars had the dreaded twin servo E12 brakes that are becoming a liability. With a standard steel bodied master cylinder and two remote servos, the servo seals fail and leak fluid into the bellows. As new ones are NLA, the only answer is to replace them with new servos from something else such as an MGB but only as a pair. Later cars had the E28 hydraulic booster. This is a system where conventional brakes are assisted by hydraulic pressure from the PAS pump via a ram and a pressure accumulator sphere. Common problems are soft or rock hard pedal (failed sphere), sticking brakes (seized cross linkage), seized callipers and a failed pressure ram between the bulkhead and master cylinder. New spheres are cheapest from C3 BMW who supply genuine ATE parts for a lot less than BMW. Sticking callipers are often blamed but it can often be faulty brake hoses that are healing up internally – just replace them all at this age.

ABS is also a potential headache – the ECU can be damaged by jump starting while an ABS light that comes on over 50mph can be rusted trigger rings on the rear drive flanges – about £300 to supply and fit new rear hub rings. You can buy these (around £35 each) from reluctorrings.com and, if all goes to plan, about three hours work to replace. They are listed as E28 M5 rings but they are all the same.

Interior

Most cars have leather and there are three types of seat – standard seats, BMW Sports seats and the Recaros with the big side bolsters – the latter are rare and sought-after. The leather lasts well but you may find an early car with cloth or velour trim. The on board computer often needs a new bulb but beware any instrument panel problems on post ’82 cars. These have a circuit board with two small rechargeable batteries to control the service indicator system. These leak acid on to the board and ruin it – a new one from BMW is a frightening sum but a good used one from an E28 5 Series will fit. Unlike the E28 though, the cluster is a swine to remove that involves dropping the steering column. Not all Highline cars have the full leather dashboard – many early ones (mainly E registered) still had the plastic dash.

Really, the interior is the least of your worries when looking for a good E24. A worn steering wheel is fairly cheap to replace as they were the same as E28 ones. The circular push button hazard light switch on earlier cars was shared with the E21, and they have been known to short out internally and melt themselves. New ones are available again and it’s not a bad idea to fit a new one.

Steering and suspension

Another area where a lot of cash can be consumed to make an E24 drive properly. Pre-May 1982 build cars have E12 5 Series suspension and steering, and cars built after that use E28 stuff. On all cars, the dampers and springs must be good but can hide a nasty trick – the front strut spring cups rot out, seriously weakening them to the point of collapse – give them a workout with a hammer to find out how bad they are – if they are heavily rusted and flaky, budget for two new ones at around £500 each. Cars with ABS have a different strut to non-ABS cars and contemporary (E12 or E28) 5 Series struts are the same. At the back, the spring cup can also rust badly with the same results but are a lot cheaper to replace. The steering linkages and upper/lower front control arms are all liable to wear out leading to the infamous 55mpg steering wobble – also caused by sticking front callipers. The upper control arm inner bushes are the main culprit but complete Febi or Lemforder arms from ECP come complete with the bushes and are the same as the E28. Steering boxes wear out, but good used ones are cheaply and readily available. At the back, rear axle beam bushes wear out leading to a wander feel and clonking over bumps – the rear pitman arms (often called ‘dog bones’) wear out leading to strange handling. On pre-1982 E12-based cars they are bolted on but are pressed in on the later E28-based cars and require special tools to fit. Steering boxes wear out and apart from some light adjustment, a worn out one cannot be saved or rebuilt. On E28-based cars the mounting bracket on the front crossmember can also break off.

Electronics

There isn’t much in the way of electronics on these cars. Apart from central locking and electric window problems (quite rare) we’ve already touched on the service indicator board instrument cluster problems and the OBC bulbs. Pre-1982 cars have the sunroof motor in the boot area with cables to operate the roof – start praying if that doesn’t work.

Headlights are getting hard to find both new and used, and be aware that Highline headlights are different. Rumour has it that they can be rebuilt using E34 and E32 parts meaning a much cheaper repair. Some Highline headlight assemblies have E34 style plastic backing plates – much nicer than the rusty metal ones on older cars.

Central locking relays are shared with the E30 and not the E28 as you’d expect. Starter motors and alternators are of the quality you’d expect from the Bosch of old and many cars are still on the originals after 25 or 30 years. Parts such as engine ECUs and air flow meters are worth buying now and stashing away, as are heater fan motors as they’re stupidly expensive.

Engine

The M30 is a great engine, but they are now old. The 3430cc unit in the post 1982 635CSi the best allrounder – pre-face-lift (1978-1982) cars used the 3453cc short stroke unit from the original 735i with Motronic from late 1980. Highline cars used a hybrid engine, combining the E34 535i crank, rods, pistons, cylinder head and a Motronic 1.3 engine management system with the older E28 type block – E34 units have different engine mounting lugs on the block.

The two main problems with the M30 are cam wear and overheating. Overheating is caused by a neglected cooling system – change the antifreeze every two years and ensure the viscous fan coupling is working by fitting a new one at the first sign of the car running hot in traffic. Fail to change the antifreeze and the alloy head will corrode the waterways and cause a blown head gasket. The fan is very close to the rad on these cars, and many bear witness to this with a circular mark in the rad from the fan – this is due to soft engine mounts allowing the engine to move forward under braking, and most cars will need a pair of new ones if an expensive rad isn’t to be ruined.

Cam wear is caused by a blocked oil spray bar or the two banjo bolts coming loose. These must be replaced at the first opportunity by the latest prethreadlocked type from BMW that also have very slightly altered thread pitch to stop them coming loose – do not threadlock the existing banjo bolts yourself as it will congeal in the oil hole. Avoid cars with a noisy cam as removing the head to replace the cam, rockers and the four short rocker shafts is a very big and expensive job – not much change from £2500 at the least. It now seems that only BMW sell new cams for these and whilst the cam isn’t too outrageous at £406 plus VAT, the rockers are £40 each and the four rocker shafts £53 each – all plus VAT. With the head off for a cam swap, it would be worth replacing the very tame factory cam with something from Schrick or Cat Cams.

The bottom end of the engine is strong, but you’ll find that really old ones won’t like being driven too hard now. Timing chains were duplex until 1980 and single row from then onwards, but the later chain is very reliable. The pre-Highline Motronic 1.1 system is getting hard to find new and used parts for now. Carry a spare DME relay in the glovebox!

Transmission and drivetrain

Most 635CSi’s are automatics. That means 3HP22 three-speeders until late 1982 and 4HP22 fourspeeds with the 55mph torque converter lock up after that. Late 1983 saw the EH electronic control being phased in. The three-speed auto is a tough old unit that takes some breaking but the fourspeed is not as good. Revving in N or P along with long periods of idling will ruin the front drive clutch (leave it in D in traffic) while EH cars can have problems with the ECU and wiring connections – the 635CSi EH gearbox is not the same as a 5 or 7 Series unit due to differences in the wiring plug.

Manual cars are rare but worth having. Pre-1986 cars have the old Getrag 265/6 overdrive gearbox or optional 265/5 Sport unit with the ‘dog-leg’ gearshift available until the end of the chrome bumper cars in 1987. After 1982, electronic speedos were used and the Getrag 260 manual box phased in on overdrive cars from late 1985. The Sport gearbox is not always a very good unit – most have a worn out gear change mechanism, a rattly layshaft and, overall, the overdrive unit is much nicer. Diffs are massively strong and you won’t break one. Pre 1982 cars have the old E9 style ‘sideloader’ diff that was a standard LSD on the manual 635CSi until mid-1980. Propshafts and driveshafts are strong, but will wear out eventually – most cars will need a prop centre bearing and a doughnut by now. To convert an automatic to manual will be very pricey – reckon on £1500 upwards. Highlines were given a 3.64 ratio differential, replacing the very tall 3.07 on pre-Highline models and as result the later car is somewhat more lively.

Verdict

E24s are still in that phase where there are more rubbish examples than good ones. They fell so rapidly from the dealer network and became badly maintained bangers and far too many of them have at least half of the faults mentioned above.

The best way to buy one is to find a low mileage example with a stack of invoices and pay for the privilege but these are few and far between. Lesser examples only make sense if you can do the work yourself – if you have to start paying someone else to do all the work for you, then an E24 needing work will turn very expensive very quickly – you’d be surprised how quickly they can consume £2500 and then come back for more. And then some more…

If you’re not mechanically minded, then you must pay an expert to examine the car in detail because a high price and wordy advert is no guarantee that the car is actually a good one under the gleaming paint and take it from us, an E24 can be one of the biggest money pits you’ll ever own. However, a good example is a great car. It’s just that they are not really everyday ‘all weather’ cars anymore and they do require frequent and diligent preventative maintenance to keep them from becoming yet another stretcher case – it’s imperative to nip problems in the bud. As for which 635 to go for, the Highline is probably a safer bet. It had a much better and more reliable engine management system, a lower final drive gave it better performance and the stainless bumpers don’t rust.

It encapsulates just about everything that was so right about the company’s design direction in the 1970s.