GOAL: 

The goal for this project is to provide an adapter plate to mate a VQ35DE 6 speed transmission (CD) to an L-Series block. Our Z32 transmission adapters have worked well, but the hardest part for many folks is finding a machine shop capable of modifying the bellhousing at a reasonable cost. A key feature for this design was to come up with a solution that required little to no machining and can be done in the home garage.  

 I have owned a 350z track edition and now run a VQ35DE in my 240z, both of which used the CD transmission.  The transmissions are wonderful to drive, they are very smooth and the shifting feel is direct. The later revision transmissions, CD009, have robust syncros and are capable of handling as much power as most L-Series builds can produce! 

It is a close ratio transmission which gives a short first gear, great for low end acceleration in N/A when matched with a short rear, I run a 3.7 in my car.  Turbo guys may want to opt for a 3.36 or 3.54 to help load the engine down low.  All CD transmissions are interchangeable and can be had used for a reasonable price, especially earlier revisions, new transmissions are also available for under 1700 dollars. 

Gear Ratios: 

  • 1st      3.794 
  • 2nd   2.324 
  • 3rd    1.624
  • 4th    1.271
  • 5th    1.000
  • 6th    0.794

PROTOTYPE DESIGN:

To kick off the project the 6spd bellhousing and block were delivered to a local machine shop with accurate measuring equipment.  A CMM was used to capture the engine block mounting dimensions along with the crank centerline.  The same was done with the transmission bellhousing except a vertical milling center was used for location which allowed us the reach to measure the input shaft bearing surface.   

Profiles for the bellhousing and engine block were transferred by hand and scanned into the computer for digitization.  The accurate bolt and alignment feature measurements along with the perimeter profiles provided the building block for the adapter plate design. 

The first piece of the puzzle is to adapt the mounting patterns between the engine and transmission.  Patterns were clocked in relation to one another to orient the transmission properly and maintaince critical alignment features.  A plate was designed from 3/8" steel which covers the entire perimeter of the bellhousing. This design makes for a stiff, thin plate, with minimal offset aiding in the no-machine design.  The thin plate provides a challenge for thread engagment of the transmission mounting bolts,  to overcome this FHCS where choosen as studs which will be permantient welded to the plate.  

With the adpater plate design complete a few prototypes were made.  The plate starts out as a laser cut blank which is then finish machined in a CNC mill.  THe final product turned out great with the engine and transmission aligning as intended.

The next challange was to properly align the L-Series clutch with the 6spd transmission input shaft and clutch hydraulics.  The stock L-Series and 6Spd share the same input spline count.  However the 350z's dual mass flywheel and clutch assembly is much taller then the L-Series which places the input shaft splines further awap from the engine.  The adapter alos moves the transmission mount further.   These differences require the relocation of the L-Series clutch which can either be accomplished through a flwheel spacer, or an altogether new custom flywheel. 

The spacer route was initially explored as I percieved it as a cheaper option that also allows for the use of any L-Series flywheel, as many people will have already upgraded this as part of their engine builds.  Spacing the flywheel out not only requires a spacer which must be precisly machined but also requires custom flywheel bolts and stator relocation.  Starter relocation was explored both by modifying a tilton stator and buy incorperating the offset into the aapter plate.  Neither proved viable especially is machning of the bellhousing was to be elminated.  

Ultimately it was decided a custom flywheel was the best route and would provide the most value for the kit.  A stock flywheel and 3D printed spacers were used to ensure the new spacing was correct.  The new flywheel maintained the same start ring gear location and center button dimensions.  This allows for the L-Series starter to remain in the same location and for OE flywheel bolts to be used.   

 

As you can imagine the L-Series stater location does not line up with the reliefs on the 6spd bellhousing.   Using a gear reduction starter from a 280zxt the issues is nearly eliminated.  Not only is the starter nice due to the gear reduction but is also does not have a bearing or nose cone outboard of the spur gear making it very compact.  This allows for only a small amount of material removed which can be done using a carbine bur on a die grinder, a 3D printed jig takes the guess work out of the location and size.

While we are working towards a complete bolt in solution I though it would be good to offer some 'DIY' kits for folks that were interesting in being an early adopter installing a kit in parallel with my vehicle developement.  Included is everything needed to bolt the transmission to the engine,  its up to the installer to fabricate a transmission mount and either modify the console for a rearward shifter location or fabrication an alternative linkage!   

A total of 5 DIY kits were made 4 were distributed to enthusist and the 5th was used for my in house installation.  Of the 5 kits ,  2 were sent out to 240z owners (1 beta tester and my shop installation), 2 to 280z owners, and 1 to a customer with a 280zx in Austrailia.  The vehicle we are using for the shop installation came from Dan a local enthusiast with a L28et equipped 240z, I was lucky to have him located so close and interested in being one of the first to test the 6 spd kit.  I used this car to measure for the 240z transmission crossmember and develope the first prototypes. 

The transmission is quite large and fills up the entire 240z transmission tunnel with little room to spare!  The factory transmission mounts must be removed.  This is a messy task but not very difficult.  An angle grinder with a cutoff wheel can be used to remove the mounts, the remaining flanges acan be smooth down to the tunnel sheet metal using a sanding disc.   The pictures below also provide a nice visual of the shifter rod location.

After playing around with a few concepts and taking some lessons learned from our LS kits I decided on a design which mounts directly to the frame rails and utlizes the 350z transmission mount.  

The first mount went out to one of the beta testers,  the Z Car Garage of San Jose.  While putting together the standard beta kits we chatted about getting a 6 spd in their TC24 vehicle for 2017 JCCS.  This was an excited opportunity and I was happy to help with the build.  Due to the DOHC head the engine actually leans the opposite direction of the standard L series so we put together a custom plate for Rob, the timeline was tight but we made it happen.  When the kit arrived they were ready to rock and roll...everything bolted up smooth and they got teh transmission in the car quickly.  With some long hours they finished all the other modifications and made it to JCCS to became the first 6spd L series car to hit the streets!!  These guys are great to work with and I really value there feedback.

With the exicting news of the ZCG vehicle hitting the streets attention was turned back to the shop installation and supporting the other beta testers as required.  With mockup complete and the transmission mount finished the engine was pulled back out for final kit installation.  The block was cleaned up a bit and given a fresh coat of paint to match the shiney bits about to be installed.  

The original dowel pin and bushings were removed from the block.  A new alignment bushing is pressed into the adapter and a new dowel installed in the block.  Next the old pilot bearing is pulled and replace with the new offset version, it is definitly worth investing a few bucks for a pilot bearing puller...the adapter is only 15 dollars and makes removal a snap.  

Before mounting the plate to the engine the transmission bellhousings needs to be modified slightly to provide clearance for the spur gear,  this process the covered in detail further up the page so Ill skip the details here. 

After the bellhousing modification is complete the adapter plate  can be install on the block with 4 M10 FHCS,  these are installed with loctite 242 and torqued to 30ft*lbs.  Thy new flywheel bolts in place like stock, new OEM bolts were used and will be included with each kit.  The starter was installed next, 3 washers are used under the mounting bolts to provide proper thread depth allowing for full thread engagment on the plate without sticking out.  Rounding out the engine prep is the clutch installation, any L-Series clutch may be used and mounted with OEM hardware (not included).  Dan chose a ACT clutch with a 6 puck sprung disc. 

 

 

 

 

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