Clutch Delay Valve (CDV) Modification

E39 5 Series - 525i, 528i, 530i, 540i (1997-2003)

E46 M3 (Late 2002, all 2003-2006), ZCP Model

E46 3-Series (1999-2005) 320i, 325i, 330i

E53 X5 3.0i (1999-2006)

E60 5 Series  - 525i, 530d, 530i, 545i, 550i (2004-2008)

E63/64 6 Series - 645Ci, 650Ci (2004-2008)

E83 X3 2.5, 3.0 (2004-2008)

E90/91/92/93 3-Series (2005-2008) 325i, 328i, 330i, 335i

Z3 2.5i, 3.0i (1999-2002)

Z4 2.5i, 3.0i, 3.0si (2003-2008)

Z8 (1999-2003)

Theory of operation - What is a CDV?

Benefits of replacing your CDV with a modified unit

Directions for installation of modified CDV

Free CDV modification service by mail

How to order a modified CDV from Zeckhausen Racing

Theory of Operation - What is a CDV?

The Clutch Delay Valve (CDV) is a one-way restrictor installed by the factory between the clutch slave cylinder and clutch master cylinder, as shown in Figure 1.  It "delays" the engagement of the clutch, much like old record players used a damped tone-arm to gently lower the needle onto the surface of a record.

Because of this valve, no matter how quickly you lift your foot off the clutch pedal, the clutch engages the flywheel at a constant (slow) rate.  In theory, it can save the driveline from shock, were an inexperienced (or immature) driver to dump the clutch at high RPM.  But in practice, all it does is prematurely wear out the clutch and turn experienced drivers into people who, despite 20 years of practice, cannot shift gears smoothly.  During parallel parking maneuvers, the delay can be infuriating, causing constant clutch slippage.  And during hard acceleration, the large amount of clutch slippage can greatly shorten the life of your clutch.  During normal, sedate driving, the shift from first into second gear is often jerky, leading passengers to question your skill.  As the driver, you can see your passengers' heads bobbing back and forth during every shift!  Yes, in their minds, they are laughing at you. 

Figure 1.   E39 5-Series CDV, slave cylinder, and hydraulic lines

Figure 2.   E46 3-Series CDV, slave cylinder, and hydraulic lines

Interestingly, BMW did not install a CDV on the E39 M5.  The terrible shifting behavior would be unacceptable to these high performance customers.  For some reason, BMW does not seem to think the rest of their 3-Series & M3, 5-Series, 6-Series, X3, X5, Z3, Z4 and Z8 customers who shift their own gears will notice.  They were very wrong!

Since BMW models have different clutches, they have different CDVs with different valve openings and springs.  In order to reduce the odds of a factory worker installing the wrong part on the assembly line, each CDV has a different number of ribs and may even have a different barrel shape.  (See Figures 3 & 4 below)  The effect on all of these cars is the same.  The driving experience is degraded.

Figure 3.       E39 & E60 5-Series and Z8 CDVs with hex-shaped bases

Figure 4.   Z3,      Z4/E46 3-Series,  E36 3-Series,  E46 M3,  E90 3-Series

The solution is to replace* the CDV with a modified valve which has had the interior parts carefully removed. We do not drill these valves.  Drilling will damage the taper at both ends of the valve.  The male tapered end seals against the female taper of the clutch slave cylinder.  And the male hydraulic fitting seals against the CDV's tapered seat at the female end.  It does not seal via the threads.  Drilling a CDV may cause it to leak under pressure and leave bits of valve material behind, potentially migrating into and damaging the clutch hydraulics.

We have developed a technique for removing the interior valve and spring without damaging the delicate tapered seat at the female end and without touching the taper on the male end.   Zeckhausen Racing provides a free service to modify CDVs which are mailed to us.  Click here for details.

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Benefits of replacing your CDV with a modified unit

After the stock CDV is replaced with one of our modified units, you will be able to shift gears in your BMW just like a "normal" car.  No more vague, inconsistent clutch engagement.  No more jerky 1-2 shifts.  You can actually chirp the tires when shifting from 1st to 2nd gear!  Parallel parking becomes a breeze and your clutch will love you for it and last much longer.  Best of all, your passengers will stop making fun of your driving skills.

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Directions for Installation of Modified CDV

Safety Warning:

Working on your own car can be dangerous.  Even quality jack stands can collapse if not positioned properly, and a floor jack can fail suddenly and without warning.  You can be seriously injured or even killed if you do not follow proper safety procedures.  Please use both a floor jack and a good pair of jack stands to support your car so that a failure of any single support is less likely to result in the car falling on top of you!  Zeckhausen Racing LLC assumes no liability expressed or implied for any injuries or damage suffered as a result of following these instructions.

Jack up the front of the car using a jack point specified in your service manual, and gently lower it onto a pair of jackstands, leaving enough room to crawl under the car just forward of the shifter.  Leave the jack in place to provide a safety backup in case one of the jackstands should fail or slip.  You can be seriously injured or killed if you are careless doing this!

Locate the CDV on the driver's side of the transmission case.

The drawing in Figure 1 and the photo in Figure 5 shows a 540i CDV.  The Z8 CDV is identical.  The replacement of the E39 525i, 528i, and 530i CDVs is slightly more difficult, since a support bracket should be unbolted before the CDV can be easily disconnected.  The E60 5 Series (2004+) requires the removal of plastic underbody panels to gain access to the CDV, so you may prefer to take the car to a shop equipped with a lift.

Figure 5. CDV location for 1997-2003 540i and 1999-2003 Z8

The CDV on the Z4, E46 3-Series, and X3 3.0 models does not screw directly into the slave cylinder.  Instead it is located at the opposite end of the hard line from the slave cylinder, at the junction of the steel hard line and rubber line.   See the drawing in Figure 2 and the photo in Figure 6. 

Figure 6. CDV location for E46 3-Series (M3 shown)

Place a large drip pan under the car, since brake fluid will leak out of the hydraulic fitting as soon as you remove it from the CDV.  Using a hose pinch-off clamp or (carefully) using a small set of vice grips to squeeze the rubber line will minimize fluid leakage and make the job of bleeding the system easier.

Use an open-end wrench (14mm or 17mm, depending on BMW model) to hold CDV steady and an 11mm flare wrench to loosen hard line fitting.  An open-end wrench may strip the 11mm fitting. 

Once you've broken the 11mm fitting loose with the flare wrench, use a stubby, open-end wrench to remove it the rest of the way.  It will go faster.

Install the modified CDV in its place, being careful not to cross thread it.

Use your fingers to start the threads of the 11mm hard-line fitting into the new CDV and make sure it is threading properly before you start tightening it with a wrench.  You may have to wiggle it around a bit before it starts to thread properly.

When you've got the fitting snug, use the 11mm flare wrench to finish tightening it.

Now, crawl out from under the car, dry off your hands with a paper towel and change your shirt!  It's time to bleed the hydraulic clutch.

Tip for E39 5-Series owners:  The challenging part is finding the brake/clutch fluid reservoir.  BMW hides it under the driver's side microfilter housing.  Remove the housing cover and the microfilter.  Then unclip the hood sensor from the wiring harness.  Unsnap the three plastic tabs on the microfilter housing using a large flat-blade screwdriver.  Squeeze the metal spring clip holding the microfilter housing to the post and pull up.  Wiggle it free.  Voila!  You've just exposed the brake fluid reservoir. 

The hydraulic clutch uses the rear chamber of the brake fluid reservoir, which is only about 1" wide (measured front to back).  There is a divider between the clutch chamber and the brake chambers so, in the event of a hydraulic leak in the clutch system, you don't also lose your brakes.  Even though the reservoir looks full, it's possible you've drained the rear chamber.  Use a quality DOT 4 brake fluid, such as ATE TYP 200 or Motul 600, and fill the reservoir, making sure the fluid flows over the divider into the rear chamber.

If you have a pressure bleeder, hook it up to the reservoir and adjust the pressure to 20-25 psi.  Much more than 30 psi and you risk blowing the reservoir apart and that would make a mess!  Brake fluid is not good for painted surfaces.

With your  pressure bleeder set at 20-25 psi, crawl back under the car with a 7mm box end wrench and a plastic tube or a brake bleeder catch bottle.  Remove the rubber cap from the clutch slave cylinder's bleed screw and place the wrench over the end, then attach the plastic tube to the nipple.  Turn the wrench about 1/4 turn and hold it for 4 to 5 seconds as the air bubbles are purged from the system.  Do not hold the bleed screw open much longer or you'll run the reservoir dry.

If you don't have a pressure bleeder, you'll have to do this with an assistant.  It will take longer, especially if you've fully emptied the reservoir and have introduced air into the system while swapping out the CDV.  As before, fill the reservoir to the very top.  Get under the car and follow the same procedure described in the paragraph above, except this time you'll have an assistant push the clutch pedal to the floor repeatedly.  If there is air in the system, the pedal will drop to the floor and your assistant will need to reach down and pump it up and down with his/her hand.  Open the bleeder screw while your assistant is pushing down and close it while he is lifting the pedal up.  Keep testing the clutch pedal to see if it has returned to full firmness.  Once the clutch pedal feels normal, tighten the bleed screw and replace the rubber cap.

Wipe any brake fluid off the CDV and nearby parts and test for leaks by having your assistant push the clutch pedal repeatedly.  If you have a pressure bleeder, simply leave it set at 20 psi and watch for leaks around the base of the CDV or the base of the 11mm hard line fitting.

* An alternative to replacing the CDV is to eliminate it entirely.  However, there are two reasons why you might not want to do this.  On some models, the steel hard line needs to be bent to a new angle if the CDV is deleted.  The bend is slight and there is little risk of damaging the line.  The problem is, if the line is not bent just so, it's difficult to get the threads to line up without cross threading them.  This is made tougher by the fact that the fitting is slippery with brake fluid.

Another reason for not simply yanking the CDV is that some folks are concerned about future warranty issues.  It's not uncommon for an overzealous service writer to try to blame any modification for whatever failure has occurred.  Rather than try to argue with the service department about whether or not the deletion of the CDV was responsible for the air conditioning failure, many folks simply install a modified CDV.  That way, the stock appearance is maintained and the issue of user modifications never comes up.

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Free CDV Modification Service by Mail (USA only)

We do not drill these CDVs, as some have suggested.  Drilling enlarges the openings on the tapered seats at each end, causing leaks. Drilling may also result in loose bits of metal destroying the seals in your clutch slave cylinder.  We have developed a technique for removing the guts of the valve without damaging the tapered seats that allow these valves to seal properly.  To avoid the risk of a hydraulic leak and subsequent clutch failure caused by modifying your own CDV, you can have one modified by Zeckhausen Racing.

Rather than paying us for the modification, you can send us two new CDVs.  We will modify them and send one back to you. The other will be kept for our local CDV customers and to refresh our inventory of modified valves for sale.

Send two (new, not used) CDVs, along with a padded, self-addressed, stamped envelope (US Mail only, please) to:

Zeckhausen Racing

Attn: David Zeckhausen

123 US Highway 46

Fairfield, NJ  07004

You may also purchase a modified CDV from Zeckhausen Racing.

The CDVs are different for each BMW model.  You will need to order the proper part for your car from a dealer.  Pacific BMW is an excellent source for these parts and often charges less than half of what your local dealer wants!  A word of warning: The dealer will have no idea what a "CDV" is.  The BMW parts CD describes this part as a "LOCK VALVE" so that is what you should ask for. To make this process easier for you, the BMW part numbers are listed below, as well as the number of fins and the size of the wrench (in millimeters) required to remove it:

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Modified CDVs Available for Sale

We are often asked if we can sell a modified CDV, rather than have our customer go through the hassle and time delay of sending us a pair of valves to modify.  The cost for a modified CDV is $35 plus shipping.  UPS Ground is standard.  UPS Next Day Air, 2nd Day Air, and 3-Day Select delivery is also available in order to meet your scheduling requirements.

We are implementing an E-commerce system, and the first item to be automated is the CDV.  Simply click on Products/BMW and then select your BMW model.  Scroll down to the CDV description and click the button.

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Free yourself from the evil Clutch Delay Valve today!

CDV clinic participants, Summer 2001

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To order by phone or for technical assistance:

Call (800)222-8893 and press "1" for Sales

International customers may call: 973-761-5054

Hours of operation: Monday-Friday, 10AM - 5PM  (Eastern Time)

We are located in Fairfield, New Jersey

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Send mail to webmaster@zeckhausen.com with questions or  comments about this web site.
Copyright © 2008 Zeckhausen Racing, LLC
Last modified: 08/09/08