Reddit reviews BMW 3 Series (E30) Service Manual: 1984-1990

You don't need to know anything! That's what the service manual is for.

+BMW tire valve caps

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And my personal favorite, which I find to be a must-have: Bentley Manual

I have an 86 325e, I've had it for 8 years now, they're awesome cars and will definitely take care of you if you take care of it.


Firstly:
Maintenance. Timing belt every 5yrs or 40k miles. Valve adjustment every 15k miles. Spark plugs, distributor cap, and rotor every 25k miles. Oil changes every 3k. Get some "Hilton's Hyper-Lube" to go in with your oil changes, its great for high mileage M20 motors. You can do most of the work yourself if you pick up a Bentley manual from Amazon.. Get some basic craftsman tools and you'll be set.


Secondly:
Fun! Get a chip. GET A CHIP. The 325e motor comes to life with a chip, its so worth it, huge gains in horsepower and torque. Huge! Short shift kit, UUC makes a decent one for E30s, although I'm not a big fan of their other stuff. When you put on the short shift kit, upgrade ALL shifter bushings, and that includes (most importantly) the joint/knuckle that goes in between the transmission and the selector rod. I have a modest suspension on my E30. If you can get ahold of E30 M3 factory original springs, they're a great upgrade, that and some bilstein shocks, with new shock mounts, and you'll be in great shape. Its not too low and its a huge upgrade in handling. This can all come later though, maintenance first. Oh. and for a differential, just get a 2.93 limited slip, don't get anything more than about a 3.23 differential, you'll run out of gearing pretty quickly higher than that. Definitely not a 3.73 from the 325is.


Thirdly:
Brakes and tires. When it comes time for tires, get some 15s or 16s, you can't find any decent tires in 14" anymore. I like Kumho Ecsta ASX for all seasons, you can get something grippier if you want, but they're a good all around tire (and cheap to boot). For brakes, Axxis Ultimates are great pads, get some brembo blank rotors, and flush the brake fluid. Brakes will be great at that point.


Then you're done, enjoy the car, I love mine.