KLDE/KLZE Transmission Conversion

Project Goals:

  • Find suitable replacement for the OEM G-Series 5-speed manual transmission for the KL based cars
  • Find replacement that has extended horsepower handling capabilities (500+ hp) over the G-series
  • Design parts in CAD to simplify the fabrication and installation of the alternative transmission
  • Rigorous testing of the installed transmission to show the feasibility of the conversion
  • Cost study to determine if the gains out-weigh the design and fabrication costs as a stronger alternative to the G-series.

The Candidate:

  • 2006 Pontiac 3.9L V6 F40 6-speed FWD transaxle
  • Three-axis design is approximately 124 lbs
  • Triple-cone sintered bronze synchronizers are used in 1st and 2nd gears increase ability to transfer the torque more smoothly from one gear to another.  Double-cone synchros are used in 3rd and 4th gears.
  • The rated torque capacity was advertised as 245 lb-ft for the 2006 G6 which had  a 240 hp 3.9L V6 engine
  • Pontiac had originally prototyped the G6 with a 275 HO 3.5L and the same F40 tranny.
  • Pontiac Fiero enthusiasts have been installing Corvette V8 LS7 engines into the Fiero using the F40 transaxle since 2005 and running huge amounts of power through them.

Ratio Comparisons:

The data below is based on 3,000 lb Probe with approximate drag coefficient of .34, frontal area of 39.23 sq. ft. and OEM size tires of 225 x 50 x 16 and 25.1" diameter.

  G-Series F-40
  Ratio Resultant Speed
@ 7000 RPM
Ratio Theoretical Speed
@ 7000 RPM
1st Gear 3.307 36 3.77 39 mph
2nd Gear 1.833 66 2.04 72 mph
3rd Gear 1.310 92 1.32 112 mph
4th Gear 1.030 117 .95 155 mph
5th Gear 0.795 152 .76 194 mph
6th Gear N/A N/A  .62 237 mph
Final Drive Ratio 4.388   3.55  
Reverse 3.166      

Theoretical speed is assuming that you have the required horsepower to attain the given speed.  For this theoretical Probe to attain these speeds a few speeds and horsepower requirements are listed below. Note that hp requirement increases exponentially.

Target Speed Horsepower Required Target Speed Horsepower Required
160 mph 382 190 mph 634
170 mph 456 200 mph 738
180 mph 540 250 mph 1435
I have purchased a new F40 transmission for the purpose of engineering pieces to enable this transplant.  I will be doing a scale 3D CAD model which will help to identify the modifications that are needed.  By modeling it in 3D this will allow me to visualize the assembly and accurately measure from any point to another and design flawless pieces before any money is spent on actual materials or machine work.  The model will also help to identify problem areas or potential stress points.  Below is a photo of the F40 next to the stock Mazda G-Series transaxle:
Design Work:

After some extensive research on the possibility of using an adapter plate and spacers for the flywheel I decided it would be much better to modify the transmission for a direct fit.  So I have been modeling up the pieces in CAD to determine how to make the modifications to the transmission.

The model will provide very critical measurements for machining and accurate alignments.

The most optimum outcome would be for the F40 to use the OEM flywheel, readily available clutches and throw-out bearing assembly rather than having to special order replacement pieces or have something custom made when something wears out or fails.

Clutch / Pressure Plate:

I did a lot of research and found that you could get a custom made clutch disc from Spec for around $200.  But I still wanted cheaper with similar quality.  After nearly exhausting all my search efforts I found that a 1995 Ford Ranger 3.0L with manual transmission has a 1" input shaft with 23 splines (same as F40) and a 225mm clutch disc outside diameter.

In this photo to the left -the Ford Ranger friction disc is shown on top of a stock KL flywheel.  It will work with the Fidanza or MX3 flywheel as well.

And here is a view of the insides of both transmissions for comparison.  Note the difference in size on the secondary gears, shafts and bearings.  They are quite a bit more substantial than the KL -G series transmission.
To the right are the ring gear carrier assemblies for comparison.

I ordered the Pontiac G6 shifter and cables but I am not fond of the shifter because it is made entirely from plastic.  So I found another shifter (brand new) for a European model Dodge Stratus as seen in the photo to the right.  It has almost the identical throw and pattern as well as linkage ball joints.


To the left is a photo of the KL jackshaft compared to the SAAB jackshaft.  I am using a 2003-2007 SAAB 9-3 Turbo Jackshaft because they also had the F40 6-speed.  The SAAB axle is hollow which will allow me to shorten or lengthen it to the desired length for this install.

To the right are the custom made chromoly  CV shafts from RCV Performance (a custom axle manufacturer).  They have a lifetime warranty against breakage.

Below is an assembled axle next to a stock one.

These axles will plug right into the F40 trans while still working with the stock Probe hubs.  The shafts are splined for SAAB CV joints on the inboard end and Probe/Mazda KL CV joints on the outboard end.  The only weak point in this assembly is the stock outboard CV joint.

After a thorough modification design analysis I have determined that the cheapest method of performing this swap would be to modify the F40 bellhousing by machining both the F40 and a flange cut from the G series transmission for welding the two together.  The photo to the right shows the pieces after machining and prior to welding.

To align the F40 input shaft perfectly with the crankshaft center - I had an alignment dowel machined to bolt to the crank that lines up perfectly in the F40 input shaft bearing race.  With the flange bolted to a KL block.

Here is the transmission pieces and alignment dowel bolted into place on a block for welding.  

Here is the initial welding.  The welds may appear a bit crude at the moment but it is more important to get a good weld than concerning with cosmetics.  My intention is to clean up the exterior weld and either polish the casing or powdercoat/paint when done.

I had the welder weld the inside and outside to get a better weld.  I am not concerned with the starter mounting at the moment because I have not designed out a good layout for it yet.

Here is the inside weld.  I will not be doing any kind of clean-up on this inner weld to preserve the strength.  It will never show anyway so it is better off -untouched.

The bolt holes where the new rear tranny mount will go are very substantially reinforced as seen in this photo.  I do not think breakage in this area will be an issue.

The flange was bolted to the engine block to preserve the straightness during the heating and cooling of the welding process.

Seen to the right here is where I have begun the post-welding clean-up process.  I have dremel cut down and contoured  most of the exterior welds and then took it back to the machine shop to have them face the bolt bosses with a 1-inch flat-bottom end mill  to make clearance  for a 17mm socket.

After I have cleaned it up like this then I will take it back to the welder once again for re-touching any areas that may have not taken well and to fill holes left by the welding.  If it is not suitable after the re-weld job for polishing then I will likely fill the holes with lab-metal putty and then either powdercoat with silver or spray it with engine enamel.  It will look like a one-piece production piece when done.  It will not look fabricated or welded externally.


Here is the mock-up engine with the transmission bolted in place.  I have installed a Quaife torque biasing differential to get maximum power transfer to both wheels.

This is quite an expensive addition but from everything I have heard - it is well worth it.


Here is the front view of the combination.
Here is half of the finished case after a good clean up and polish.

I will continue to post the progress on this project so be sure to check back regularly.