BMW Modifications & Tech Tips

BMW's lawyers have asked me to remind you (seriously, they wrote me a nasty letter) that any modifications to your car may put your warranty at risk. If in doubt ask your dealer and be sure to tell your insurance company. Some modifications may also contravene local laws and / or affect the safety of your vehicle. If you are not a BMW approved mechanic you should consult one before trying to "improve" things.

One other tip for recent owners of used BMWs. The best modification you can make is to ensure everything works 100% as intended by BMW before deciding where to spend the upgrade money. BMW built your car the way they did for good engineering reasons, those German engineers don't make many mistakes. All engineering is a compromise and most changes will have both positive and negative consequences.

E36 318iS Upgrades

100 watt main beam headlamps

K&N conv filter. Made the car sound nice and rev a bit better but the fit and finish were very poor and it killed the mounting bracket.

Heated windscreen washer jets

Mudflaps (bad idea, they scrape under hard cornering).

Vredestein Snowtrac snow tyres on steel rims, well worth the price.

BMW E24 635CSi dashboard

Inside the 635CSi's dash.

E24 635CSI Fixes / Upgrades

I love my 635CSi and I've fixed quite a few things on it, I'm a bit of a perfectionist. I'll post more details on each item when time permits, for now just email me if you need help.


Replaced thermostat (and broke the housing by over tightening it!)

Cleaned idle control valve

New ignition leads

New battery

New hydraulic drive belt

New fan clutch

Installed new rear box for exhaust

Removed and polished valve cover, replaced gasket

New oil pressure sensor

New fuel pump and main relays

Fixed intermittent stalling problem

Fitted new viscous fan coupling to solve traffic overheating problem

Final drive oil change

Auto transmission filter and fluid change

Auto to Manual Conversion

My ZF 4 HP 22 EH auto transmission started slipping at 148,000 miles. The oil was very dirty and the magnets in the bottom of the oil pan were covered in iron filings. One day it died completely and would only move in reverse, classic A clutch pack failure. This can be delayed with frequent ATF changes with a good quality Dexron II oil and a new filter screen every 24,000 miles.

One week later I had bought a kit of parts from a dead car to do the conversion. Some of the things you will need are:

Gearbox. You have a choice of close ratio dogleg or normal gate overdrive box.

Longer propshaft

New propshaft flex discs (guibos)

Propshaft centre bearing

Rear gearbox mounting cross member

New clutch kit and release bearing

Clutch master and slave cylinder, preferably new

Clutch fluid reservoir and tubing

Different exhaust mounting bracket for bottom of downpipes

New flywheel (auto is lighter due to mass of torque converter)

New pedal box and clutch pedal. Brake pedal is narrower

Nice new gear knob and leather gaiter. Some gaiter colours are no longer available

The centre console is the same for auto and manual cars

Gear lever and selector, use new bushings

New oil seals for the crankshaft and gearbox

The bit's I've forgotten!

You must remove the steering column to change the pedal box as it goes through the hole in the middle.

The propshaft is in two parts and is balanced that way. You must ensure paint marks are used to re-align the halves before removal.

Ensure your bell housing has mountings for the Motronic speed and TDC sensors if applicable. The flywheel must also be from a Motronic car if your car has Motronic. You need the TDC sensor pin if you'd like the engine to ever start again!

If you opt to replace your dead auto box with a used one make sure it has the same wiring connections, there are several types. Jetronic-L and Motronic cars have different trannies, the L-Jet has a mechanical kickdown cable vs an electronic interface on the later cars. It's worth noting that the auto box is about 30kg heavier than the manual.

I could only find an overdrive gearbox, a close ratio unit would have suited my driving conditions and 3.07:1 rear end a lot better as my car is a little highly geared now. It would be a very good and economical motorway car though. If I had the time without a dead car I'd look much harder for a close ratio box. Failing that a 3.25:1 or 3.46:1 rear end would be good. Interestingly my car with the overdrive and 3.07:1 is the correct original BMW european configuration, US cars were 3.25:1.

The car feels a lot faster now and the conversion was worth it. My clutch is a bit stiff and has a fairly short travel which I like, it wouldn't suit serious town driving though. I find the normal pedal configuration doesn't suit heel and toe gear changing as the brake and accelerator are too far apart for my smallish feet. It would be worth bending the brake pedal an inch to the right before fitting, it's very thick metal though. I'm probably going to have to extend the accelerator an inch to the left with a custom steel plate.

I thought about having the flywheel lightened but decided against it. This was the wrong choice. My idle is very stable but the engine could spin up more quickly. This might be a better idea if combined with a custom chip.

I also find the throttle is a little heavy for heel and toeing. This is due to the springs on the throttle body, I didn't mind this with the auto. I am going to see if I can modify or remove one of the two springs on the throttle body, the pedal return spring has almost no load as you can see if you remove the throttle cable from the throttle pivot arm.

Now that I have a manual car I will investigate aK&N cone with heat shield and a chip. Fitting the valve cover from a post-87 M30 engine gives a much better mounting for the air flow meter if you're installing a cone on an pre-87 M30 and I may try this in the Spring. The standard metal AFM mounting and metal airbox are surprisingly heavy, the later setup is much cleaner looking and better designed. I'll also need the rubber tube from the AFM to throttle as it looks shorter.


Fixed squeaky heater fan blower motor

Replaced heater control valve

Fixed heater control electronics

BMW M30 635CSi engine

The best place to spend a weekend!

Body and Interior

Got rid of lots of "wee bits" of rust

New rear tail light gaskets to stop water leak in boot

Welded rust hole in inner wing

Fixed seized headlight bulb holder and removed headlight assembly

Fixed loose rear spoiler

Fixed sticking boot lock barrel, there's a lot of dirt back there.

New front wings to replace the old rusty ones (no inner liner!)

Replaced bubbling chrome wing mirrors

Adjusted front window alignment

Removed rear seats and trim

Retrimmed rear trunk wall, condensation had rotted away the hardboard backing.

Removed centre console

Removed centre dashboard facia

Remote mounted Snooper 915iR radar/laser detector

Removing The Inner Door Linings

The door lining is in three parts. The top one has a bolt at each end. You must also remove the door handle. Pop out the panel in the top of the handle and remove the two screws, the bottom pivots out.

The lower section has bolts inside the pocket, underneath the flap. The moulding pops out at the back and pivots into the front of the door. Be careful not to break the plastic clips.

Remove the cover around the door handle by pushing it back and out. The last trim panel has a plastic popper at either end. While you're there check the door drain holes are clear and don't change the window alignment, it's hell to get right again!


Fixed interior lights

Fixed electric aerial

Replaced on board computer (OBC) back light

Fixed windscreen wiper electrics problem (fitted new control relay, 50 GBP!)

Suspension, Brakes & Wheels

Replaced front and rear brake pads and discs

Ditched the TRX wheels/tyres in favour of 15" cross spokes I reconditioned myself

Fitted new ABS hubs

Replaced worn old springs and shocks with a nice new set (System 2, firm but not too harsh)

Replaced anti roll bar links and bushings

This may seem a long list but I deliberately bought a six in less than perfect condition so that I could play with it. I'm very proud of how much I've improved the car and I get a real kick out of driving it. A national Scottish newspaper even did a feature about it!