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Auto to Manual Conversion (archive)

[ Follow Ups ] [ 5-series (E34) Message Board ] [ Msg. Board FAQ ]

Posted by Simon on December 11, 2000 at 16:57:19:

In Reply to: 94 540i auto trans failing, looking at huge $$$ posted by Pierre on December 11, 2000 at 12:15:25:

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 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.

2nd and fifth gear are slipping and the pump is cavitating noticably. My local tech and Heishman are quoting $5000 to $7000 for a reman trans from BMW (out of Illinois, BTW). Does anybody know of a TRUSTWORTHY transmission shop in the DC metro area that can handle the ZF 5HP30 automatics? I'd rather rebuild my own for less $$$$ than spend $5000.

Any help really would be appreciated...

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