Disclaimer: This article appeared In European Car Volume 35 No. 1. Please pick up this issue for the article in print as well as the nice pictures that went along with it.
Buyer's Guide: BMW E24 6 Series
For many, the big coupe is the ultimate of Munich's driving machines
By Mike Miller
If there were only one BMW model epitomizing the perfect blend of luxury, sportiveness and serious driving pleasure, for many enthusiasts it is the E24 6 Series. It had 12 years of production glory, from 1977 to 1989 (U.S.), and its design was imitated by many others but never equaled--not even by BMW. Diehard 6er owners often refuse to buy newer models, instead pouring thousands into mechanical and cosmetic work to keep the big coupes cruising.
With more engine variations than any other BMW coupe, there is a 6 Series for almost anyone inclined to own one. That there are so many so inclined is reflected by value retention unequalled by any other mass-produced BMW except the coupes preceding it (the E9 "CS").
We'll stick to U.S.-spec cars, except for a discussion of the European-spec 635CSi and M635CSi, because many have found their way here through private importation.
Birth of the E24 6 Series
In designing the E24 6 Series to suit multiple markets, then chief pen-and-clay man Paul Bracq, who created the BMW Turbo in 1972, confronted the reality that BMW doesn't always mean the same thing in Germany as it does here. It was a time to revel in traditional BMW styling, performance and personality, even though the influence of the 1972 Turbo is clearly evident on the E24 exterior. As it is even today, the German concept of sporting luxury does not always translate into American notions of, well, luxury luxury. And in many other countries, it is not a stretch to say BMW is better known for motorcycles and police cars than luxury automobiles. Still, no one here complained about the look of the new car; it was the "go quotient" that garnered criticism, and for the same reason as the E24's stablemates--more weight and less power. It seemed, at least in the U.S., that BMW was reverting back to the pre-E9 era in terms of power-to-weight ratio.
In fairness, the E24 had to weigh in heavier than the E9 due to added crashworthiness. BMW really got serious about the front and rear crumple zone, reinforced roof panel, a bar extending the width of the cockpit behind the dashboard and reinforced rear bulkhead behind the back seat. U.S. models, of course, carried on with the big aluminum "crash bumpers," which would mar our 6 Series until 1988 when BMW debuted world bumpers. In 1977, first year of the U.S. E24, that added up to 350 lb more than the last 3.0 CSi.
Now, it's a fact of life that everything gets bigger and heavier in time--cars as well as people. We are willing to put up with added girth in return for function. But what happened to U.S.-spec E24 engines was just a sin. American emissions laws mandated use of a positively horrible exhaust gas recirculation (EGR) system incorporating an air-injection system component that was akin to bolting a two-by-four board across the cylinder head exhaust ports. High-compression pistons were out of the question, and, in fact, low compression was the order of the day due not only to the EGR system but also to the demise of serious high-octane gasoline--this was way before the knock-sensing ignition emerged to save the day for compression ratios. The result was that horsepower and torque nosedived. Due to the thermal reactor exhaust manifolds, cylinder-head warpage problems in the E24's M30 engine appeared almost instantly in the heat of American summers.
You'll get varying opinions on this, but for me there were five distinct E24 generations in the U.S. market: 1977, 1978-79, 1980-84, 1985-87, and 1988-89. The prime factor here is engine configuration of the non-M models.
Rouse Mit the Old,In Mit the New!
The 1977 model year was traumatic for BMW enthusiasts. Remember how you felt when you saw your first "Bangle-ized" Bimmer, the E65 7 Series, when you realized that iDrive really would be in every BMW, that electronics would eventually supplant all mechanicals, and that, probably, the days of the manual gearbox were numbered? Well, it was an even bigger drag back then, because, you know, most people were stoned. Not me, of course, but let me try to paint the picture for you.
I was 13 years old in 1977, and I was beside myself. We were out of E9 coupes. U.S.-spec BMW 2002 production had ended in 1976, soon to be followed by the E3 "Bavaria." Stragglers were available, but it would be forever before I could buy even an old Bimmer. I had started junior high school firmly within the throes of early-onset adolescence (must have been the exhaust fumes). The school was like Stalag 13, complete with Colonel Klink and Major Hochstetter as the principal and vice principal. The President was called Jimmy. Disco was by no means dead, but Jim Morrison was.
In the midst of it all, here was BMW doing whatever it was doing to our wonderful cars. I couldn't sleep. I couldn't eat. I didn't want to listen to The Doors. I stopped stuttering when Lori Zaleski was around. I didn't care about the Soviets anymore--I thought BMW was going to end the world instead.
Car magazines and the BMW dealer were the only sources of information directly relevant to my life. The dealer had already asked me to leave with the request that I never return. Enthusiasts lamented the end of our favorite cars and said, regarding their replacements, "This had better be good." And it was good--mostly. The replacement models appearing in 1977--the 320i and 630CSi--represented visual styling upgrades and quantum leaps in interior design and comfort. Instrumentation and interior ventilation, in particular, were vastly improved. In terms of styling alone, with the E24 it was love at first sight for most enthusiasts. Performance was another matter.
The weight factor was less important than power. BMW's even-then-venerable M30 sohc six-cylinder engine was so detuned for the U.S. market that a cottage industry emerged in aftermarket modifications--or simply installing European-spec parts like pistons, exhaust systems and distributors. Yale Rachlin, former editor of the BMW Car Club of America's monthly magazine, Roundel, related seeing two engine assembly lines at the BMW factory in the late 1970s. Each had a large banner spread over it. One banner read "USA" and the other read "NORMAL." This pretty much sums up U.S. emissions legislation of the era.
The end result was that even though we had a 3.0-liter engine with Bosch L-Jetronic fuel injection, it struggled to put out just 176 bhp at 5500 rpm and 185 lb-ft of torque at 6000 rpm--figures that appear optimistic in view of virtually identical numbers for the 633Csi that would appear the following year. The new car's lack of power relegated it to last place in many car magazine reviews, even though writers generally liked the 630CSi. The 0-to-60-mph time, all important in the U.S., was 10 sec.--respectable but still a back-of-the-hand yawn compared to the 8.5-sec. time of the European-spec 628CSi.
A substantial horsepower increase lay readily at hand for those in the know, and it didn't take long for it to become commonplace among enthusiast circles. All it took was a conversion to European-spec exhaust manifolds or Stahl headers and a European-spec ignition distributor. (These modifications would also prevent the cylinder-head warping problem that would appear a few years later and become the subject of a class action lawsuit against BMW of North America, resulting in nearly all affected cylinder heads replaced with updated parts.)
Sometimes the L-Jetronic fuel injection got ditched in favor of triple Weber 40 DCOE carburetion, which, if combined with high-compression European-spec pistons and a sport camshaft, would transform the M30 from a mild-mannered, smog-strangled also-ran into a fire-breathing monster that would light up the tires at the slightest provocation. Needless to say, the prospect of spending another $4,000 to rebuild the engine on one's brand-new $24,000 coupe did not meet with the approval of many owners--at least not the original owners.
Some years later, when the California air quality bureaucracy mandated that emissions output be controlled through the use of technology originally installed on cars--however antiquated and ineffective--people scrambled to find discarded thermal reactor exhaust manifolds, EGR systems and U.S.-spec ignition distributors. Most had been scrapped long ago, and BMW's supply of replacements was used up almost immediately.
The deal was, you could make an old M30 engine pass tailpipe smog testing for that car without the thermal reactor and EGR system as long as the engine was in good condition. But then it would fail the visual inspection. Install the parts, and it would fail the tailpipe inspection due to parts deterioration. It was and is a perfect example of bureaucrats who know nothing about cars legislating them out of existence. The result was that many pre-cat Bimmers previously living in California sought refuge with owners in more car-friendly jurisdictions, and their loss was our gain as rust-free cars migrated eastward into "free" states.
Even though invasive California emissions testing has migrated to other states too lazy to write their own laws, most jurisdictions afford an exemption to registered classic and antique cars, or on age alone, and the age exemption is generally less than California's 30 years.
The rest of the drivetrain was robust and actually carried over from the E12 5 Series. A bulletproof Getrag 262 four-speed manual gearbox was backed up by a 3.45 side-loader differential. Limited slip was optional, as was a beefy ZF three-speed automatic transmission. Known as the 3HP22, this old slushbox will handily outlast its successors if given regular ATF and filter changes.
Four-wheel disc brakes with ATE calipers stopped the coupe a whole lot better than the U.S.-spec engine that motivated it, and the suspension, softened for America, was a model of BMW handling and comfort. Suspension design was also shared with the E12 and, in fact, with most BMWs since the early '60s. It was a tried and true formula--control arms with strut rods and MacPherson struts at the front, semi-trailing arms at the rear, fully independent all around. BMW carried over 195/70-14 tires on 6x14-in. wheels from the E9 coupe and E12 5 Series. In fact, the wheels were interchangeable, something BMW was infinitely cool about until only recently. Enthusiasts quickly found Bilstein sport shocks, Alpina coil springs and 7x14-in. wheels either from the aftermarket or from BMW. Tire size could be increased to 225/60-14 with no significant speedometer penalty or fitment issues. Long-lost companies such as Quickor were fast to market with larger sway bars and coil springs.
Engine issues aside, the rest of the 1977 630CSi positively rocked and had it all over the 3.0CSi it replaced. To understand how truly good the 1977 630CSi is, one must drive a domestic car from the same model year. Interior and exterior styling are ultra-modern in comparison. Outside, the lovely new body was actually fairly aerodynamic for an older model BMW--a 21% improvement over the 3.0Csi, according to BMW. However, in this era of super-fast autobahn speeds, aerodynamic downforce often took precedence over drag coefficients.
The E24 6 Series would eventually sprout several different front airdams and rear spoilers in successful factory efforts to plant the car to the road at speeds often exceeding 150 mph. The "Hoffmeister kink"--that little forward cut at the base of the C-pillar pioneered by the E9 coupe--was very much in evidence in the 6 Series and models to come. The addition of the B-pillar did nothing to detract from coupe-ness and lends the design an air of solidity and mass lacking in its predecessor. The long hood and nose panel styling cues adapted from the BMW Turbo concept car give the 6 Series an authoritative, individualistic yet luxurious presence unmatched by other Bimmers, in my opinion. The car has panache. It is never mistaken for anything else, but BMW 6 Series design cues cropped up in other marques down to and including the last-generation Ford Thunderbird.
On the downside, like all BMWs of that era, the E24 was given large, aluminum U.S.-specification "crash bumpers." These, combined with other U.S.-required bits, added a whopping 320 lb to vehicle weight. More weight, less power, not good. Still, while they are almost universally despised for their appearance and weight, U.S. bumpers provide large measures of body protection in parallel parking and other real-world tribulations. Unfortunately, the black rubber end pieces BMW used on American E24's up to 1988 are framed internally by ferrous metal. In time, the metal framing rusts and distorts the rubber outside.
The interior is equally dramatic. The 6 Series carried on the theme of driver-oriented cockpit controls and instrumentation introduced with the E12 5 Series and elevated it to the next level. With the instrument and pods robustly canted toward the driver, there is no doubt for whom or for what this car was designed--the serious driver. As with all BMWs, full instrumentation was standard save the curious deletion of an oil pressure gauge. A 140-mph speedometer greeted the driver, and the coolant temperature gauge was actually a useful functioning tool rather than the "buffered" vestige it is on today's Bimmers. Soothing orange illumination was easy on the eyes at nighttime, and the controls themselves had the reassuring personality afforded only by positive manual control.
Electronics had, however, entered the BMW cockpit in the form of the Check Control System. An electronic panel located to the left of the main instrument pod allowed the driver to check coolant level, motor oil level, brake fluid level, brake lights, taillights, windshield washer fluid level and brake pad integrity at the press of a button. With Check Control began the double-edged-sword legacy of BMW automatic system sensors. While they are wonderful driver aids, the unfortunate fact remains, to this day, that a warning light in a BMW just as often indicates a problem with the warning system itself as it does the system it is intended to protect. If anything, false warnings have grown more frequent over the years. The saving grace is that these systems will always warn of an actual problem--the question is, will the driver believe it?
Interior details in the 6 Series are perhaps the epitome of the driver-centric, form-follows-function BMW design so beloved of traditional BMW enthusiasts, and so decidedly out of favor today. Door-grip-mounted exterior mirror controls, outstanding door pocket storage space, window and seat controls ingeniously located on the center console and ergonomic perfection all greet the E24 driver. The two-place rear seating area is sometimes criticized for its size. But that criticism tends to come from larger reviewers. Ordinary-sized people tend to find the back of a 6 Series cozy but in an intimate and comfortable way. Ingress and egress is another matter, but once you're in there it's pretty nice as long as the front occupants don't use all the seat track. BMW even included a pull strap on the B-pillar to aid climbs in and out of the rear. Ingenious storage compartments are located on the rear parcel shelf, and rear-seat occupants enjoy both a center armrest and headrests.
Displacement Up: Power? Not Really
The big news for 1978, and the news that had U.S. enthusiasts chomping at the bit, was that we would get the 3.3-liter (actually 3210cc, 3.2L) M30 engine--the E24 became the 633CSi. Horsepower nudged upward just 1 pony to 177 bhp at 5500 rpm, but torque increased to 196 lb-ft at 4000 rpm. This helped the 1978 633CSi trim its 0-to-60-mph time to 8.3 sec., although 0 to 100 was days off the European version of the same car. The remainder of the drivetrain remained unchanged, as did suspension and brakes.
Air conditioning and leather became standard equipment, and the U.S.-spec E24 remained unchanged until 1980. Owners still busied themselves de-smogging the engines, while the plague of cylinder-head warpage and legal wrangling awaited those who did not.
The 1977 630CSi is both the rarest and the least desirable of any U.S.-specification E24. Of the early four-speed manual cars, the 1978-79 633CSi is far more prevalent but is still rare today.
Robert Bosch to the Rescue
The significant revisions BMW brought to the E24 for the 1980 model were all overshadowed by the wonders of Robert Bosch innovations. Using Bosch's ingenious new invention, the oxygen sensor, allowed efficient use of a three-way catalytic converter. The positively horrible and universally hated thermal reactor and EGR emissions control systems were dispensed with at once in favor of this new technology. A new factory electronic ignition system also appeared. The darkest chapter in U.S.-spec BMW engine history was finally at an end.
While actual power output remained the same, driveability was immeasurably improved. More importantly, but unbeknownst to us at the time, electronic engine management systems would eventually allow U.S-spec BMW engines to achieve nearly the same power output as rest-of-the-world variants. It would take nearly 10 years, but the course was set in 1980. In 1983-84, Bosch Motronic engine management quietly entered our lives with Motronic version 1.0 basic. Ignition timing and fuel mixture were now computer-controlled.
This early Motronic system, wonderful as it was at the time, is less than desirable today from a performance-tuning standpoint. No chips are available to upgrade the ECU--what you have is what you have. Even though the engines will still respond well to high-compression pistons and camshaft upgrades, electronic optimization is not possible. Similarly, while the catalytic converter is far preferable to the dreaded thermal reactor (writer looks down, spits), the exhaust system on these pre-1985 Motronic cars is incredibly restrictive forward of the cat. The end result was lots of header installations and de-catting prior to that becoming bad juju, and later, installation of 3.5-liter engines with advanced Motronics.
A five-speed manual gearbox backed up the newly invigorated engine, but, contrary to popular close-ratio European fashion, fifth gear was overdriven to reduce engine speeds at cruising velocities. This allowed both increased fuel economy and use of lower (numerically higher) differential ratios to aid acceleration. Traditionally, BMW gears down cars when it wants to spiff up low-end zoot either as a result of engine size, automatic transmission or, in this case, emission controls. The automatic transmission option included cruise control starting in 1982.
Outside, the lower front valence panel was revised, and the rear bumper ends were extended to the wheel openings in 1982. A silly federal law mandated an 85-mph speedometer, and BMW stuck a red LED clock in it for some reason. Independent techs sometimes played speedometer baseball out behind the shop with these units, as owners just couldn't stand to look at them. By 1984, we were back to the 140-mph speedometer. Central locking appeared; it was now possible to lock both doors and the trunk with one turn of the key at the driver's door. But the little flap covering that driver's-side door lock would wear out, and you had to replace the entire cylinder--a problem never solved on the E24.
The 1982 model year saw a mid-production suspension revision to the now familiar wishbone front control arm design, which eliminated the front strut rods. No outward indications signaled this revolutionary advancement in BMW front suspension design. The wishbone design allowed far greater high-speed stability through increased control of caster angles and afforded greater control over ride quality independent of shock damping qualities. Suspension geometry under heavy cornering loads was also improved. However, the wishbone design is not a panacea, as technicians and do-it-yourselfers are well aware. The 06/82 production date marks both the beginning of the BMW wishbone control arm design and the beginning of the now-notorious BMW front-end vibration proclivities (previous vibration problems with the E21 3 Series were isolated to that model, which did not use wishbone control arms).
The problem, near as anyone can tell, is two-fold. First, there is extreme sensitivity to wheel balancing. Second, the front control arm bushings, aka thrust arm bushings, are not stiff enough. BMW used different control arm bushings for every model 6 Series, E28 5 Series and E32 7 Series. All are too soft--except for the E32 750iL bushings. These can be made to fit the E24 and E28, but they have to be machined professionally. Aftermarket companies offer E32 750iL bushings already machined and ready to install. Among them are BMP Design (www.bmpd.com) and Bavarian Autosport (www.bavauto.com). If your post-06/82 production 6 Series has a chronic front suspension vibration and other possible causes have been eliminated, use these control arm bushings. They are also a good performance upgrade for modified cars.
During this period, the now-dreaded Michelin TRX tire and wheel combination replaced the familiar 195/70-14 tires and 6x14-in. alloy wheels. The TRX promised revolutionary handling improvements but in order to deliver them required a specially shaped wheel bead area. In order to prevent TRX tires from being mounted on wheels without the specially shaped bead area, Michelin built it in a metric size, in this case, 225/55VR-390. In truth, the TRX did offer improved steering response when the technology was new, but it was quickly eclipsed by "regular" tire technology, after which the Michelin TRX became little more than a monumental pain in the ass. Drivers couldn't mount normal tires on TRX wheels. Instead, they could only buy Michelin TRX tires, which were very expensive and decidedly yestertech in terms of performance. Michelin TRX snow tires worked better for their intended purpose but were unspeakably expensive. Still, BMW would buy into TRX for the next five, long years.
Meanwhile, BMW owners sought aftermarket wheels and factory alternatives. Today, TRX wheels are routinely junked in favor of the same options--aftermarket and factory alternatives and normal-sized tires. Typical replacement fitments include 195/70-14, 225/60-14, 215/60-15, 225/50-16 and 235/45-17. The 17-in. size often requires body modifications for increased clearance, especially on lowered cars--most drivers considering this fitment will also have a completely tuned suspension with sport shock absorbers and shorter, stiffer aftermarket coil springs. Replacement Michelin TRXs are now considered "vintage tires" and are sold by specialty vendors such as www.cokertire.com at sky-high prices.
By 1983, 633CSi pricing was nudging the $40,000 mark in the U.S. The German-spec 635CSis could be personally imported to the U.S., so-called "gray market" cars so quick and fast they could suck a U.S.-spec 633CSi into the air intake and cough it out the exhaust while costing less money in the process. This was becoming a not insignificant sales threat. Moreover, the U.S.-spec 533i had nearly identical performance numbers at a savings of over $10,000. BMW of North America was confronted with the low power situation; something had to be done. BMW AG, typical of the era, could not understand why Americans wanted more power. After all, they reasoned, we could only go 55 mph--a speed considered laughably slow in Europe, where serious drivers had access to cars that could and did triple the U.S. speed limit. The notion that there could be wholesale disregard of speed limits here was inconceivable to the Germans, when in fact that was and still is precisely the norm in the U.S.
1985-87: 635CSi, L6
Robert Bosch for President
The 1985 model year marks the end of Bosch's teeth-cutting stage and the beginning of Motronic engine management control as we know it today. Motronic version 1.0 adaptive offered variable operating parameters according to sensor inputs and provided the basis for the future of performance tuning--the eprom upgrade. But this didn't happen overnight. Not until the early 1990s did companies and luminaries such as AutoThority and Jim Conforti totally unravel BMW's code and rewrite it for more performance-oriented use. Meanwhile, though, BMW finally had the beginnings of a power increase it so desperately needed in the U.S.
Engine displacement was finally increased to rest-of-the-world spec at 3430cc (3.5L), and the U.S. E24 finally became the 635CSi. Power was now up to 182 bhp at 5400 rpm and 214 lb-ft of torque at 4000 rpm, the latter eclipsing the European-spec 633CSi. However, the U.S. engine was still hampered by a low, 8.0:1 compression ratio and exhaust restrictions, meaning it was still grossly underpowered by European standards, where the 10:1 compression, non-catalyst 635CSi cranked out 218 bhp at 5200 rpm and 228 lb-ft of torque at 4000 rpm. The low compression ratio was mandated by low-octane gasoline and the inability of early Motronics to deal with the combination of high compression and exhaust restriction in the absence of knock sensors. Later, in the 1990s, the 1985-on U.S.-spec 635CSi would respond dramatically to a simple ECU chip upgrade from either of the aforementioned suppliers. Today, a Conforti chip remains the single best engine power upgrade for the U.S.-spec 635CSi.
The Getrag five-speed overdrive manual gearbox remained unchanged for the rest of E24 production, and the 3.45 differential remained for manual gearbox cars, with limited-slip optional. The optional new ZF 4HP22EH automatic transmission marked the initial mating of electronics with the slushbox, with long-term durability results that are now matters of history. In theory, though, the 4HP22EH was interesting in that it provided an overdriven fourth gear combined with three electronic programs--normal or "E" mode, sport "S" mode which locked out fourth gear overdrive and held each gear to the redline under full acceleration, and "1, 2, 3" mode, which provided manually operated individual gear hold. In practice, most drivers likely played with "S" and "1,2,3" a time or two and then simply left the thing in "E."
The addition of anti-lock brakes (ABS) marked the proverbial foot-in-the-door for today's plethora of electronic nannies, albeit at a far more useful level. Inside, power leather seats featured three-position memory that was very useful for cars used by multiple drivers. Cruise control was now standard with both manual and automatic, and a new steering wheel greeted the driver as did a new audio system. The multiple-function onboard computer (OBC) made its way into BMW life, bringing useful information to the big coupe driver. Average mpg, average speed, outside air temperature and miles remaining until tank empty were among the more useful functions, along with a vehicle disabling code function. However, without the owner's manual you won't get far with the OBC.
Outside, the 1985-on 635CSi sports perhaps the best front airdam BMW ever designed. Constructed of durable but flexible ABS plastic, this part completely shrouds the lower front valence panel, creating downforce on the front suspension while housing effective large foglights and incorporating a cover for the front tow hook. Most unfortunately, this part is no longer available from BMW. We hope BMW Mobile Tradition will step up to the plate and reproduce this and other BMW aerodynamic parts for older models. Two different factory rear spoilers were optional accessories, and both were functional in providing downforce on the rear suspension.
A curious L6 model emerged in 1987, with more leather inside than a Berlin spank slut has outside. The dashboard and headliner were even covered in leather. The car's cockpit smelled like a tannery. It was classic U.S. market overkill. Still, like the lady, it was not uninteresting. Unfortunately, the L6's leather dashboard quickly deteriorated under North American sunshine in the absence of regular and copious high-end leather care product application, and no manual gearbox was available. A matching L7 headed up the E23 7 Series in the same model year. There was no snootier statement at the country club than his and hers L6/L7 arrivals. Enthusiasts gagged.
1988-89: 635CSi, M6
BMW enthusiasts danced in streets all across America for the 1987-88 model year. In a one, two, three punch, BMW of North America brought us the M3, M5 and M6 in rapid succession. Investments were sold. Mortgages were assumed. Work hours were increased. Marriages were dissolved. Power-starved Americans needed M cars.
While in what by then had become true to form, the U.S.-spec M6 represented a severely detuned version of the fire-breathing European M635CSi, but the fact remained that we now had the real double overhead cam engine. We lived with the fact that it was reduced to 9.8:1 CR, producing 256 bhp at 6500 rpm and 243 lb-ft of torque at 4500 rpm versus the 10.5:1 European version's 286 bhp and 251 lb-ft of torque at the same engine speeds. Later, Mr. Conforti would help our numbers out quite a bit with the simple addition of a chip--and Sunoco 94 octane gasoline in those fortunate areas of the country that have it.
The final 635CSi version marks the pinnacle of non-M U.S. E24 performance. Advances in Bosch Motronic technology allowed a compression ratio increase to 9.0:1, resulting in 208 bhp at 5700 rpm and 225 lb-ft of torque at 4000 rpm. U.S. enthusiasts were finally vindicated with something at least approaching rest-of-the-world performance as the venerable M30 engine soldiered on into the 1990s, durable and dependable as ever.
But the hard edge present in the 1985-87 635CSi was softened for 1988-89. The E24 took a decidedly luxurious turn in the U.S., a marked departure from its road-burning personality elsewhere. Almost all had automatic transmissions, even though the L6 was nixed in favor of universally increased leather content. Rear seat air conditioning and a cigarette lighter coddled passengers, while the center armrest became an air conditioning-cooled beer cooler that was perfect for those long road trips through Texas. A 3.64 differential ratio helped even things out.
Outside, the big news was BMW's switch to "world" bumpers for the 1988 model year, relegatingwThe second-generation (E-28) U.S. 635CSi and among the most common 6ers still found on the road. This example junked its TRX wheels and tires in favor of Hartge alloys. the previous big aluminum units to the history books. The TRX scourge continued unabated, but ellipsoid technology headlights allowed a slight improvement for U.S.-legal headlight efficiency. Unfortunately, U.S.-spec ellipsoid halogens still fell far short of the Hella H1/H4 headlights used in the rest of the world and commonly fitted by those in the know here as well. Double unfortunately, H1/H4s did not fit in the ellipsoid headlight buckets.
BMW's self-leveling rear suspension now found its way into the U.S.-spec 635CSi, using a complex electro-hydraulic system to maintain rear ride height regardless of squat, dive or vehicle load. The system works quite well but is very pricey to repair in its old age. Confronted with the need for new rear shocks or a hydraulic pump, many owners simply convert the car to a conventional rear suspension. This involves capping the hydraulic lines, disconnecting the electrical harness and fitting "normal" rear shocks and non-self-leveling rear coil springs. Many unknowing or simply cheap owners and techs leave the self-leveling rear springs in place. This results in very strange handling and inordinately low rear ride height.
All in all, though, the 1988-89 635CSi remains the enthusiast sixer of choice, save for the M6, for the simple reason of its higher compression engine.
A beefier Getrag 280 five-speed overdrive manual gearbox graced the M6, as did a lower 3.91 limited-slip differential. Larger brakes augmented grip from 240/45VR-415 Michelin TRX tires mounted on lovely-but-worthless-today BBS RS three-piece alloy TRX wheels. Inside, sport seats were standard. Outside, a Motorsport rear spoiler provided downforce on the rear suspension.
The M6 is the ultimate U.S.-spec E24 6 Series although still overshadowed in collector appeal by European-version 6ers.
"BMW 6 Series Enthusiast's Companion"
by Jeremy Walton; Robert Bentley, Publishers
"BMW Buyer's Guide"
by Fred Larimer; MBI Publishing Company
"BMW Coupes A Tradition of Elegance"
by Walter Zeichner; BMW Mobile Tradition
Historical Archive, BMW part number 01 09 0 004 125
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