The Hack Mechanic

If you are not a car person, bare with me. There is a hell of a story buried in the jargon, just read on it's worth your time.

Last summer I replaced the clutch delay valve (CDV) in my M Coupe. The CDV is a restriction in the clutch line of modern manual transmission BMW's that delays the actuation of the clutch. Common wisdom is that BMW engineers did this to prevent novice drivers from burning up their clutch. The real world result is inconsistent clutch actuation that is annoying, frustrating, and down right infuriating! I removed mine. It was a bitch. The Z3 platform wasn't designed for the M division's S54 engine. BMW Motorsport GmbH literally shoe-horned it in. With Jonny V's help, after trying many different angles and body contortions I would the right angle to pinch two flare nut wrenches together to break the seal of the old line. After that the job was a breeze. I did the rest of the brakes while I was at it.

Flare Wrench Set Up to Break the Old Line

New and Old Clutch Lines

New Brake Pads, Rotors, Bushings, and Caliper Cleaning

I even engineered and built my own clutch slave cylinder bleeder out of parts from Lowe's.

I was feeling really good about my hack mechanic skills.

If you don't care about cars and you are sill reading don't give up on me yet, here's where the story gets interesting.

Enter Fletch and his 2001 M Roadster. Fletch had found a perfect example of an M Roadster. It was Estoril blue over an Estoril blue and black interior and a hardtop. With 21,000 miles it still smelled like new. He asked if I would replace his clutch line along with a few other things. Always happy to help out another Z3 enthusiast I obliged. Everything went smoothly and we were on track to go to a meet up with some other enthusiasts that night. All that was left was to bolt the slave cylinder back up.

Fletch's M Roadster

Hydraulically Actuated Clutch 101: The slave cylinder bolts to the outside of the transmission behind the bell housing. It has a piston that pushes against a release lever. When you push in on the clutch pedal this piston pushes against the release lever disengaging the clutch and the transmission from the engine.

Clutch 101

Actual Release Lever (item #3)

Bell Housing (the slave cylinder bolts to the part labeled #1)

The end of the release lever has a "cup" shaped indent that the clutch slave piston fits into. If the piston isn't aligned correctly into this cup then when the clutch is pushed in the hydro-mechanical advantage of the system will force the slave piston, spring, and clutch line fluid into the transmission bell housing. Think of it like blowing a dart out of a blow gun. It was August and Fletch's transmission was scolding hot. As a result I couldn't hold the slave against the transmission for very long before my hand would burn. A pair of mechanics gloves would have fixed this, but alas I'm the Hack Mechanic (i.e. no gloves). The slave felt good, but I didn't know any better.

With it all buttoned up we were ready to go. All that was left was to test the clutch a few times to make sure it was bleed correctly and lower the car. I sat in the driver's seat, pressed in on the clutch and... (long dramatic pause) ...with a bit of a pop it went straight to the floor. "That is odd"; I thought. I climbed underneath and saw hydraulic fluid dripping ominously out of the bottom of the bell housing.

Let's consider the situation for a moment. In my garage is a collector vehicle, that originally retailed for over $55,0000, leaking hydraulic fluid out of the transmission and it's my fault. To make matters worse, I've known the vehicle's owner for a total 2 hours and have no clue what I did wrong. It was an awkward moment. Doug and Jonny V were there, but the silence was deafening.

I went through several stages of denial, anger, fear, and frustration before I figured out what happened and, even worse, the only way to fix it. I spent an hour desperately trying to fish the slave cylinder piston out with a cheap grabber tool, but it was fruitless. The transmission, factory fresh with only 20,000 miles on it, had to come out.

It was getting dark. I gave Fletch a ride home and we pondered our options. The thought of pulling a stranger's transmission in my garage was terrifying, but in my gut I knew I needed to do it. It was the only way to make things right. The problem was it wasn't my decision to make. To pay a BMW mechanic to pull the tranny, clean out the slave cylinder components, and reinstall it all would cost anywhere from $3000 to $8000. The thought of all that money only made it more awkward between us. We collectively worked through the decision process and decided to pull it. While it was out we could replace the shift pin bushings, a known defect in ZF transmissions.

A week later after hours of research, gathering a long list of replacement parts (one time use nuts, etc), and a few special tools we set to work. The first part of the job was removing the exhaust, heat shield, driveshaft, transmission mounts, and disconnecting the shifter. It was drama free except for a clip on the shifter assembly that is called the "Bitch Clip". It took over two maddening, hand cramping hours picking at it to get it off.

///M Exhaust Mmmm

The Bitch Clip

Finally we can get to the Transmission

To get the transmission out it has to be unbolted from the engine and very carefully slid rearward to avoid damaging the pilot bearing or input shaft. Sounds easy right. Remember that part about "shoe-horning". The only way to get to the top bolts is to rotate the front of the engine up (clearances are millimeters) and lay under the rear wheels with 3 feet of socket extensions. It's arduous, but will be much easier next time now that I've done it. When we pulled the tranny out the clutch slave piston and its spring were sitting in the bottom of the bell housing. Luckily when it exploded into the bell housing no hydraulic fluid got on the clutch.

The Slave Piston and Spring in the Bell Housing

The Clutch was Clean - Thank God!

The stress wasn't over when we got the tranny out. The next order of business was replacing the shift pin bushings. ZF transmission of this era had a run of bad shift pin bushings. The result was that the shifter would stick to the left or right instead of returning the center underneath 3rd gear. Incidentally the ZF company was formed from the remnants of the Graf Zeppelin Company, makers of the Hindenburg.

Getting the old shift pin bushings out requires slide hammering out the covers, removing the springs, and carefully prying out the bushing which was pressed in at the factory. You have to be careful not to etch the wall of the transmission. I made a special tool by grinding a jeweler's screw driver flat on one side. After stressful prying and picking I got the old bushings out. I irrigated the holes with gear box oil to flush out any metal shavings. A special drift is needed to hammer the new pins in, but anticipating my shift pin bushings would fail someday I had acquired a set when I got my car.

Shift Pins Disassembly

My Homemade Tool

Hammering the New Bushing In

Done, Only 4 More to Go

With the tranny serviced and the slave piston recovered it was time to put it all back together. It went smooth except for 1 bolt on the top of the bell housing, which look no less than 6 hours to get the right angle. When I reinstalled the slave cylinder I did it with the attention of a brain surgeon. When it came time to test the clutch my stress level was through the roof. I gathered all the bravery I could, got in the car, took a deep breath and pressed on the clutch pedal. It responded with a satisfying linear pressure. The job was done. What started as a two hour job finished 2 weeks later with 5 solid working days. Fletch got his shift pin bushings serviced, CDV deleted, and a few other odds and ends done. I garnered a wealth of knowledge and earned the title of Hack Mechanic. We both worked together to solve the problem and became friends in the process. With the hard work over it was time to go for a victory drive.

Victory Shots