Gearbox & driveline

[Jeroen]

Hydraulic clutch operation & issues
The clutch system on the manual E21's is a hydraulic system running on brake fluid. The system gets its fluid from the same tank as the brake master (for LHD models, RHD have a separate tank). Pick up is about halfway the container so a leak in the clutch system can never lead to brake failure. Leaks usually appear in colder times. The already old seals will decrease in size and fail. Most times you will find your clutch is gone will be on cold winter days.

Master
From the reservoir fluid goes to the master cylinder that is located behind the clutch pedal, but it is hiding behind the under dash cover. Just a few screws removes that cover. The master might leak and spill agressive brake fluid into your floor mat and corrode the bottom of the car, make sure to clean up and dry the mat before putting it back! Newspapers can be a good protective solution as well.

The master can be replaced, but an overhaul kit from the dealer's (P/N 21521 155 030) of from any general friction parts specialist will do the same at a significantly lower price. Undo the pedal connection (bolt) and push the pedal up to make room. Place plastic over your floor and have a container ready. Remove the circlip and pull out the piston, straight towards you. Probably the brake fluid will be gushing out but that will only be a small quantity, max 100cc.

Clean up, make sure not to spill on mats or paint (with your hands too!). A simple Midlock hone tool on your battery drilling machine and some real light honing action makes sure the inside of the cylinder is clean and free of rust. The master is 19mm in diameter, the Midlock CF-64 covers 13-50mm and works well, the larger CF-63 should cover diameters from 19mm on but is too big already. Cost? Abt 10 euros I guess.

Thoroughly clean up the inside of the cylinder with a clean and dry cloth. Place the overhaul kit with a little bit of brake grease (Até or similar) and push the rod in, straight and carefully, without excessive force. The new seals are ruined easily. When fitted you can place the circlip and fit the pedal again.

Slave
There are overhaul kits for slaves as well, but as they usually are pretty cheap I recommend replacing those as a whole, easy job. Undo the line and the two bolts and it comes off. A leaking slave usually is hard to diagnose as the fluid seeps into the gearbox bell housing. But if you have no pressure and there are no outside leaks on the master (and there is enough fluid in the tank and the hoses are good), 99% sure its the slave anyway.

Bleeding
This can be no hassle at all, or a complete pain, so be prepared. After work, top off the container to the max stripe. Make sure the line descends nicely from the tank to the master. Connect a hose to the slave, open the (7mm) bleed nut 1/2 turn and see if you have any fluid at all. In many cases the bleed nipple is clogged up. Easiest is to have one person close the gap on the slave after removing the bleed nipple, while another cleans up the removed nipple. After that you may be able to just pump fluid and bleed with the pedal. A pressure bleeder like Eezibleed on the tank is even easier.

No pressure on the pedal yet? You can try to put pressure the other way around, on the bleed nipple, just beware of leaks and spray at the side of the container, brake fluid will eat your paint! Spilled brake fluid always needs to be removed with excessive water. Sometimes things will be much better already overnight. Usually I manage to get it 75% good already with the Eezibleed, and do that again after 1 or 2 nights, then all the air is pretty much out and your clutch is back to normal.

[Jeroen]

Useful diff background and build info here!
http://www.bmw2002faq.com/_/technical-a ... -build-r74


limited slip diff sper sperre lsd sperdiff

[Jeroen]

Propshaft specs gathered sofar (lengths!), additional data is most welcome!

4 cylinder models:
4sp 3-lug 163,7 cm
4sp 4 lug ?
OD 5sp 3-lug 155,0 cm
OD 5sp 4-lug ?
Auto 3-lug 150,1 cm
Auto 4-lug ?

6 cylinder models:
OD 5 sp and 5-Sport 3-lug 147.3 cm
OD 5 sp 4-lug ?
4sp 4-lug 154.7 cm
4sp 3-lug ?
5-sport 4-lug 149.9 cm
Auto 3-lug 142.3 cm
Auto 4-lug ?

[Happy_Dan]

Quick question on this old thread with great information!

I recently bought a 1983 BMW 320i with a fuel injected m10 4 cylinder. It has no transmission. It was a 5 speed in it. How would I know which one to try and find? Is is a Getrag 245? Any other hints about replacing the transmissions or any other options based on availability?

I am a long time GM guy and this is my first BMW so be kind.

[uwbuurman]

Best you'll start a topic for your car in the 4 cilinder section. We like to read more from you about this e21 and its owner.

When you source a box, be sure to get one with a mechanical speedo cable output. That is at the rear end of the box, in the lower corner. Gearboxes for m10 without that cableslot are for e30 or e28. The'll fit, but you won't have a speedo signal.

[Happy_Dan]

Thank you, I will post about the car in the 4 cylinder section.

[Jeroen]

Welcome Dan! More gearbox info on our regular website https://www.bmwe21.net/?page_id=124