04 May Fitting a 901 Porsche Tranny to an IRS Beetle Chassis
Editor’s Note: Many people want to fit their Beetles with a 5 speed tranny. The two most popular methods are to either fit a Berg 5 speed, or to install a 901-based Porsche transmission. To fit a 901 transmission requires the use of an IRS chassis, and a lot of fabrication work. In the article below, Steve Beecher outlines some of the modifications that were required to fit a 901 tranny to his ’52 Cal Looker.
The 68 pan that came with my car was originally a swing axle, and it stayed that way until converting it to an IRS in order to fit the 901/5 in 1986. The changeover wasn’t that difficult, it was just a lot of work. I’ve never written this down so this will bring back a lot of memories for me. 🙂
The original IRS trailing arms and spring plates were used without modification. I had to cut the original front transmission mount off of the pan, and use a holesaw to cut a 2″ hole in the lower side of the pan and modify the hole/pan area for the 901 hockey stick (shift rod). This was done because it’s lower than the stock VW unit. I made the front “cross bar style” mount (similar to the Berg setup for their 5 speed unit) out of stainless steel, and it is mounted to the pan by welding mounting brackets made from 1/8″ steel plate next to the IRS trailing arm mounts (again, similar to Berg’s). I then used Volvo engine mounts to attach the cross mount to the pan brackets, and welded aluminum plates to the transmission housing in order to attach the saddle mounts. Some later 901 boxes have the mounting plates cast into the transmission housing, and the plates therefore don’t have to be welded in.
I had to cut the throw-out bearing arm to add 1″, and angle it toward the front of the car so that it cleared the floor pan horn (driver’s side). This provides a better angle so that you can connect a type3 clutch cable to it. I trimmed the floor pan transmission horn in order to clear the throw-out arm. Remember that the clutch cable comes in the bottom instead of the top like the original VW unit. I manufactured an over cable return spring set up so that the throw-out arm disengages from the pressure plate when released. Use a Porsche 912 bowden tube, move the throttle cable tube in the pan toward the drivers side in order to clear the 901 transmission housing (that was fun… not), and modify the pedal assembly clutch cable hook by adding about 1/2″ into it so that you can get enough travel to disengage the clutch.
You also need to modify the body to clear the 901 transmission housing. I used a really big hammer and pounded the body area under the rear seat until the necessary clearance was achieved. This sounds brutal but it really look fairly sano when finished. Since I used the original 911 shifter I had to cut out the pan and make a plate with 8mm nuts welded into it in order to mount the 911 shifter to the pan. I’ve heard of guys using the Hurst shifter but I’ve never tried it. Next, you need to take an original 911 shift rod and cut and rotate one end 180 degrees in order to get the correct angle for the shifter and transmission. Weld in approximately 8″ of pipe to get the correct length, and use a 911 shift rod hanger and shift coupler.
I had to make CV bearing flanges to mount CV’s to the final drive flanges of the early style 901 transmission. Some later 901 boxes have final drive flanges that stock Type 1 CV’s will mount to. Summer Brother’s in Pomona made the axles, as stock VW axles were too long, and would bottom out when the arms traveled upward. This may not happen when the other style final drive flanges mentioned are used.
I think that’s about it. It works very well! I’ve hammered the car from a dead stop many times and never experienced even the slightest hint of wheel hop. The later 915 style Porsche transmission has a much better shift pattern (much like a Berg 5) and will be allot more user friendly than the older style pattern, and they have the right final drive flanges needed.
Sound like fun?
