The engine is an L-jet, 3.5 liter (3453cc), in-line 6 cylinder. The compression ratio of the engine is 9.3:1. It is actually the same engine fitted to early 635CSi's, and it was even fitted to some early 735i's. These engines are bullet-proof practically, although due to their oversquare bore and stroke configuration (big bore, short stroke), the lateral forces exerted on the piston bores can lead to earlier wear (oval bores) at much higher mileages.
These engines don't have the Motronic engine management unit as later E28 cars did, so you cannot chip them, but these engines respond very well to good old fashioned tuning. This can consist of port and polishing, a hotter cam, headers and a freeflow exhaust, and a reasonable increase in fuel pressure. A good L-jet manual can help with tuning the fuel injection and timing the car properly and it is available from Robert Bentley (the "Bosch Fuel Injection Manual"). Otherwise a factory blue book manual is advisable (though hard to come by, because the US-spec E12 units are usually the only ones ever seen on ebay, so they do not pertain exactly to an E12 M535i).
The close-ratio transmission (identified by the shift pattern with
first gear being the "dog-leg", down and to the left) should shift well, and should not
be overly worn.
These are not as robust at the standard over-drive Getrag transmission, but
should last well into six figure mileage.
Originally, the E12 brakes were very good in their time. Nowadays, the performance is lack-luster, particularly since these cars never had ABS. The problem is that there is no easy upgrade for these brakes because there are no bigger calipers that are a bolt-on fix (like on E28/late E24). The best you can do is stick with vented rotors and try to get better pads. Fortunately, good pads are easy to come by and since these cars are relatively light and the calipers are four-piston front units with two piston rears, the braking can be quite good with the right pads. Alpina had a vented rotor available for their cars, but these are hard to find as with any Alpina pieces and they are outrageously expensive. Take care when ordering rotors for these cars as the fronts were uprated on the M535i using a 25mm (vs 22mm) spacer between the front caliper halves. This allowed BMW to engage in one of their favorite paths for an upgrade; parts bin engineering. The M535i uses wider brake rotors from the E23 7-series to improve cooling. The rear rotors are stock E12 units and are solid discs.
The only way you can seriously
upgrade the brakes is to do a complete overhaul with custom (like Brembo or any other
aftermarket firm) calipers, and custom rotors. However, for a car of this size and weight, better
pads are all you really need to keep the braking system in top notch condition as well as
maintain originality of the car.
Maintenance is key to caliper and brake component longevity as well, so make sure there
have been routine fluid bleedings. There are really no other major problems to be
aware of as far as the E12 braking system is concerned. To improve the feel (if desired),
stainless steel lines are easy to find and the kits are no different from other four-wheel disc
equipped E12 cars.
The Suspension & Steering
Unlike the later E28's, the E12's have a more robust front suspension. The design dates from the E9's and E3's. Any shimmying may more likely be due to warped rotors or misalignment than any component part. Of course, new bushings help. And bigger sway bars (from Suspension Techniques) improve roll control immensely. The steering boxes wear, as usual, but shouldn't be overly worn. If it is, it could just mean that the box is out of adjustment, but do not count on that. These cars are generally more tail-happy than their later E28 breatheren. This is due to the immense camber and toe changes in the rear suspension relative to the E28. Don't misunderstand, both suspensions gain negative camber, and toe-in as the suspenion compresses, but an E12 is an older design which allows more movement than the E28.
There aren't as many upgrade options for E12's as there are for E28's, but lowering springs from Suspension Techniques are readily available and can be fitted with Konis or Bilsteins (sports or heavy duty). The rear Sport shocks are NLA from Bilstein and the units advertised by some notable BMW parts retailers are actually slightly firmer units that are meant to fit on E3 sedans! Be careful. Any shock can be sent in to Bilstein for revalving, expanding the array of options. The Alpina E12's had different shock valving from Bilstein and the E12 M535i's stock dampers also had their own specific settings from Bilstein. This is something to consider if swapping suspension pieces (don't throw away the stock E12 M535i Bilsteins!).
Alpina, Hartge, and Hardy and Beck had suspension systems as well for these cars but are
all hard to come by and are very expensive. Alpina is the only one of the three that still
has new parts on hand to sell, the other two are very sought-after as used items. As a very
loosely defined rule, early
E24 6-series cars (up to about '82) have identical underpinnings to E12's so upgrades that
fit these cars for suspensions should fit on an E12. A notable exception is with
early E24 Alpina springs which do not lower the E12 as much as they should, perhaps due to
increased spring rates for the heavier E24 front end. With some detective work and internet
auction searches, it is possible to find E12 springs made by the following companies,
listed in order of increasing rarity (the most rare at the end). Spax, Racing Dynamics,
Eibach, and H&R.
The Interior & Electrics
The E12's are now almost 20 years old. EXPECT problems, however most are minor annoyances (instrument cluster lights burned out, eratic behavior from aftermarket alarms, inoperative door locks, etc). Make sure all the electricals work unless you don't mind tinkering with the car later. The E12 electrical system is not as complex as the E28 (for example, no check control panels). But an old E12 system cannot withstand abuse like 100W headlights, high current foglights, and highbeams. It is not recommended that you do things like that on an old, worn-out, electrical system. The good news is that it is easy to work on, wiring diagrams are available in the E12 Haynes manuals, and it's not rocket science. Also, the sanding off of the corrosion applies to ALL FUSES and the fuse box, as well as contacts at headlights and sockets in general.
The E12 M535i interior does NOT wear well due mostly to the
original, Recaro seats. Most E12 M535i's came with cloth interior, and due to the very
aggressive side bolsters in the front seats, most cars have threadbare cloth and tears
near the bolsters. The rear seats typically fare better, but again the cloth can take
a beating from sun-exposure. On cars equipped with rear headrests, the backs are usually
faded from sun bleaching. Leather interior is extremely rare in E12 M535i's and should
probably wear a bit better unless it was never conditioned. The rarest of the rare
for interior options on the E12 M535i consisted of cloth ASS seating with tri-color, Motorsport
stripes. Most E12 M535i's in the United States were retrofitted with Behr air-conditioning
when imported, and due to age and poor fit and finish of the units, the center consoles
of these cars can look very cosmetically challenged. For the rest of the interior, the seals
do wear, so door/window/windshield seals are all suspect after 10 years.
More information on E12's available in Links pages.
Written by: C. Graff & Adam Wilson