Casey72
Well-known member
I finally had some time to address the 23 year old C4 in the '72, replacing it with a PerformanceAutomatic Super Comp C4 and 10" PA converter, adding the Gear Vendors overdrive unit in the process. Bottom line up front: This was a great idea and I'm most pleased with the setup, especially on the interstate, where it shaves off almost 1000 RPM at 65 MPH.
Installing the GV onto the C4 was downright painless, as was the wiring for the unit. Remove tail shaft, bolt it on...with some shims for the shaft end play, so it was essentially a ratchet, wrenches, straight egde and feeler gauge used to get it into place. Once in the car the only tasks were wiring the GV controller and connecting the speedometer pieces. I had the driveshaft shortened to 36.75" to make up for the length added to the transmission with the GV installed.
I ran into a couple minor snags in the process, one being the virtual interference fit of the PA hardened input shaft with the converter. The tight fit is intentional and requires freezing the shaft overnight and using a mallet and some lube to get the shaft seated in the converter. Bill Schmidt at PA was awesome about replying to lots of (stupid) questions and never kept me waiting for an answer. The other issue I had concerned my attempt to use a single signal generator for both the GV and my electric speedometer by tying both devices into a one signal generator. I tried both signal generators and neither worked in that fashion, so I had to use both.
As for wiring, the GV comes with wiring already terminated for plugging into the control box, as well as the switches for operation. Plug the other end of each cable to ignition power (should be cold while cranking), ground, toggle switch, manual switch, signal generator and solenoid. Super easy.
The PA Super Comp ships with a "cut" shift lever, which has all the stock extensions cut off. This is great if you're using, or plan to use, an aftermarket shifter. Otherwise, you'll have to drop the pan and valve body to swap your original linkage for the cut version. PA has an excellent video of the process on their website, so no drama there.
The improvements are noticeable in operation. The 10" converter flashes at 3200 RPM with the slightly warm 351W and doesn't have the "mush" of the old locally procured 3500 RPM converter. The transmission shifts beautifully and the GV kicks on automatically at ~47 MPH and off again around 30 MPH. In manual mode you toggle the OD on/off as desired with the foot switch, but you have to remember to turn it off well before coming to a stop due to clutch wear issues. Still, it turns the C4 into a 6-speed when you want it.
Anyway, if you're in the market for a contraption like the GV overdrive, it's a pretty cool toy.
Installing the GV onto the C4 was downright painless, as was the wiring for the unit. Remove tail shaft, bolt it on...with some shims for the shaft end play, so it was essentially a ratchet, wrenches, straight egde and feeler gauge used to get it into place. Once in the car the only tasks were wiring the GV controller and connecting the speedometer pieces. I had the driveshaft shortened to 36.75" to make up for the length added to the transmission with the GV installed.
I ran into a couple minor snags in the process, one being the virtual interference fit of the PA hardened input shaft with the converter. The tight fit is intentional and requires freezing the shaft overnight and using a mallet and some lube to get the shaft seated in the converter. Bill Schmidt at PA was awesome about replying to lots of (stupid) questions and never kept me waiting for an answer. The other issue I had concerned my attempt to use a single signal generator for both the GV and my electric speedometer by tying both devices into a one signal generator. I tried both signal generators and neither worked in that fashion, so I had to use both.
As for wiring, the GV comes with wiring already terminated for plugging into the control box, as well as the switches for operation. Plug the other end of each cable to ignition power (should be cold while cranking), ground, toggle switch, manual switch, signal generator and solenoid. Super easy.
The PA Super Comp ships with a "cut" shift lever, which has all the stock extensions cut off. This is great if you're using, or plan to use, an aftermarket shifter. Otherwise, you'll have to drop the pan and valve body to swap your original linkage for the cut version. PA has an excellent video of the process on their website, so no drama there.
The improvements are noticeable in operation. The 10" converter flashes at 3200 RPM with the slightly warm 351W and doesn't have the "mush" of the old locally procured 3500 RPM converter. The transmission shifts beautifully and the GV kicks on automatically at ~47 MPH and off again around 30 MPH. In manual mode you toggle the OD on/off as desired with the foot switch, but you have to remember to turn it off well before coming to a stop due to clutch wear issues. Still, it turns the C4 into a 6-speed when you want it.
Anyway, if you're in the market for a contraption like the GV overdrive, it's a pretty cool toy.
