The Unix Nerd's Domain

BMW Modifications & Tech Tips

Warning!

BMW have asked me to remind you 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

E36 Tech Tips

Where these are not originally by myself I have creditted the original authors and have their permission to reproduce these articles here.

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.

Mechanical

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:

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 accelarator an inch to the left with a cutom 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 combinded 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 heatshield 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.

Heating

Inside the 635CSi's dash.

The best place to spend a weekend!

Body and Interior

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!

Electrical

Suspension, Brakes & Wheels

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!