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Greg Davis CDL Linkage   -   2003/10/13Viewed 437 times this month, last update: 2005/08/31

Greg Davis designed a DIY center differential lock for those Land Rover discovery II's made in 2000 and 2001 which still have the locking differential in their transfer cases. The design utlizes 3/8inch socket driver extensions and U-joints, plus a hand-made end piece. He published this design in the Tech section of Discoweb, where I saw it several months ago.

I really liked the simplicity, elegance, and low cost of the design, and have been thinking about doing it myself for a while. This last weekend, I started the project. I created the first version of my linkage, and test-fit it in my truck.
This required a complete dissasembly of the center console, but I managed to get it in place without having to completely remove the transmission tunnel cover. I did this by threading a wire through the hole, out the path I wanted the linkage to go, and pulling it back up with the wire. Thus, I avoided taking the cover off, and even more importantly, without having to dissasemble the delicate pieces of the main shifter.
Here you can see where the socket driver extension comes up through the transmission tunnel cover. It's held up by a pipe clamp, on top of a washer. Below the washer is a rubber grommet which completely seals out the noise of the engine and transmission.
That patch in front of the shaft is a cover over the first hole I made, which turned out to be too far forward. It would have interfered with the operation of the high-low shifter. I covered the hole with a piece of galvanized steel sheet, and pop-riveted it in place. Some 'goop' sealant makes it waterproof and quiet.
This is only the test-fit. Now I need to remove it, cut the shaft to put the shifter knob just above the console floor, and paint the welds on the linkage to prevent rusting.

Here is the linkage I made. The key is the 10mm X ~15mm hole at the end, which fits around the flats on the CDL control. I used a spark-plug socket for the end, instead of a seperate joint and socket, just to save cost and complexity. I also cut the socket down do about 3/4 inch. It's got to be as short as possible to clear the fuel lines which run right over the transfer case. This does clear, by about 2 inches, but just to be sure, I rounded all sharp corners.

After sizing the upper shaft, and adding three divits for the set-screws of the knob, I rustolium'ed and oiled it, then with the help of Vanessa, installed it, and replaced the center console. As described in the tech section of Expedition Exchange, everything went together very easily.

And after the installation, the knob works perfectly, actuating the center differential locking mechanism with some, but not too much force. Actually, it's just perfect. It takes too much force to do it by accident, but not so much you need to worry about breaking anything.

Now I need to take it out to the desert for a real trial!

Update: 2004/11/08
I've been on two good off-road trips with the CDL, the Borrego and the Mojave. The CDL makes a HUGE difference. When one wheel is off the ground, ETC (electronic traction control) just doesn't cut it, but a locked center diff pulls me up and over.

Alex (2005-12-07): I am thinking about putting this on my 2000 disco but have heard that the traction control will cause considerable damage to the drive shafts and transfer case over time - is this true?

Erik (2005-12-07): A CDL does add additional stresses to the driveline, but the CDL that
you are trying to actuate is exactly the same one as on the D1 models,
since the transfer case is the same model, and actually the D2 prop
shafts and axle shafts are stronger than the D1, so you should be in
good shape.

However, if you are going to be racing your truck across boulders, you
could still break stuff, but so would any setup.

If you want to discuss this with some pros, (and people who pretend to
be pros, like me) check out www.discoweb.org

Rich L (2006-02-16): go to www.ashcroft-transmissions.co.uk/part_17.html#pa2 which have a full description and parts to do the official Land Rover modification and this site explains how the ETC is compatable with the centre diff and what wires to cut etc. a really excelent website on this subject.

Erik (2006-02-17): Rich, thanks for the link. Yes, that is a very nice alternative to the somewhat hacky project above.

Steve (2006-11-29): This is the best diy job I have seen yet and am going out to the shed to begin manufacturing one now. There's no way I'm parting with $600.00 for a kit just to enable the CDL. Great work.

Erik (2006-12-04): Thanks Steve!

brian (2008-02-25): i know its 2008 and this post is old but do you have any pics of exactly where the CDL control is on the disco 2? thanks for any info....briandmozy@hotmail.com

Erik (2008-02-25): Brian, it's in a very hard place to photograph. It's on top of the t-case, up in the transmission tunnel. If you put your hand up and over the front output flange of the t-case, if you have the CDL nipple, it'll feel like a 1/2"-3/4" threaded rod, with a square base.

Will (2010-01-23): There is a pneumatic controlled CDL available from C&M Manufacturing. You can get it through Great Basin Rovers. It is controlled by air like an air locker and it is around $200. I have some pictures if anyone is interested.

Lynx S (2010-01-26): Hey I would like to see some pix and get more info on that air locker kit.

Blake (2010-02-10): Thanks for the design spec's; great job, brilliant actually. Intuitive and functional. Much less to break or fail, and even if it does, you are intimate with the simple design and could fix it in 15 minutes in the hardware store parking lot. I think I'm going to cut a groove so I can use a circlip to maintain the position of the shaft and put a fixed 90-degree in it near the top so the respective CDL status is known at a glance. (fore/aft=un-locked and rotated = locked.) I might also Plasti-Dip/Plasti-Cote the entire linkage once finished for protection and stock appearence. Great idea and execution. Thanks again.

Will (2010-02-21): The web address is cm-mrg.com where you can get the kit. There is a nice video for install and it is quick...like 30 mins to install.

Will (2010-02-21): Correction the the web address for the Pneumatic CDL shifter. cm-mfg.com

Patrick (2016-02-15): I get this thread is ages old, but I was wanting to know if you remembered how long the extensions were. TIA.

Erik (2016-02-15): I don't remember, but from the picture it looks like a 6in and a 10in extension.


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