M535i General Information
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. They don't have the Motronic unit as later cars do, so you cannot chip them, but these engines respond very well to good old fashioned tuning. A good L-jet manual can do the trick, available from Robert Bentley is the Bosch Fuel Injection Manual which covers these engines. Otherwise a factory manual is advisable (though hard to come by). The close-ratio transmission (identified by the shift pattern with first gear being the "dog-leg") 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.
Brakes
Originally, the E12 brakes were very good in their time. Nowadays, the performance is lack-luster. The problem is that there is no easy upgrade for these brakes. No bigger calipers 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. Alpina had a vented rotor available for their cars, but these are hard to find as any Alpina pieces. 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. 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.
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 available and can be fitted with Koni's or Bilstein Sports. Alpina and Hartge both had suspension systems as well for these cars.
The Interior & Electrics
The E12's are now almost 20 years old. EXPECT problems. And count your lucky starts if you don't have problems. Make sure all the electricals work. 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, 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 interior wears well, and should not have any mildew/standing water/rips/tears/etc. Everything is very robust. 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