It's been a while since I've provided an update about the progress of on the Caddy. Mostly because things have been slow due to a busy work and family schedule. Here's the rundown of what I have gotten done though.
I have rebuilt the carb, and realized that a broken vacuum pot on the carb was actually only used to crack the throttle open a bit and increase the idle RPM when the A/C was running. Since the A/C system is not holding pressure, and looks like it hasn't in many many years, I went ahead and removed this "extra" part. Hopefully this'll fix the hesitation problem that I detected on the few short drives I took.
Now, when I first got the car, I immediately noticed that there wasn't any sort of linkage that I could see for the tranny kickdown. So while I've been staring at the service manual to get my carb back together properly, I've also been trying to figure out how the heck this thing is supposed to get a kickdown signal from the throttle. Turns out there is a switch which is supposed to be mounted on the intake manifold, near the carb which actually sends a +12v signal to the transmission for kickdown!
Even more interesting than that, the transmission in this thing is at least as rare as the engine. I've got a THM400 with "Switch Pitch", which was only offered in the Caddy for like 3 years. Basically the torque converter has two stall settings, one around 1000RPM and another around 3200RPM. It switches between the two with another +12v signal (also sent by the switch which I don't have) which causes the angle of the blades in the converter to change. So, that means two things.
First, instead of just throwing everything back together and hoping the trans "just works" I'm actually going to take the time to yank it out and have it gone over to make sure it'll work well for me. No sense it blowing this thing up since it's a stout and apparently rather desirable piece! I'm hoping to have it yanked out this weekend, and over to Alphonso's Transmission by Monday.
Second, because I don't have the original switch to operate the "Switch Pitch" mode and kickdown I've got to either find one (fat chance) or devise my own. Currently, my plan is to mount up a TPS (Throttle Position Sensor) to the carb and feed that signal to an Arduino Microprocessor which will send the +12v signals to the trans for both the switch pitch, and trans kickdown. There is actually a guy who built a controller for the switch pitch part of the trans back in the mid 80's, and I've actually been in touch with him. His solution uses vacuum, the brake light, and timers to operate just the pitch change of the torque converter. Then a mechanical switch for the transmission kickdown. His name is Bruce Roe (firstname.lastname@example.org) and I've been in touch with him to get some feedback on how his device works. He's been very helpful and encouraging, I can only hope my device is as effective as his.
So, with that I've decided I'm going to nickname my Caddy "Bionic Caddy" in honor of the fact that "we have the technology, we can make it better". It's especially fitting since I'm going to put a CarPC in it, and hopefully put a Megasquirt EFI on it one day. Also, it abbreviates nicely to a personalized license plate *BIONCAD*. Should be good fun.
While my simple project of identifying (and fixing) a mysterious "clunk" has sorta exploded into a much bigger project of getting the engine back together and building a controller for the transmission, I still hope to get it done reasonably soon and keep the complexity to a minimum. Stay tuned for updates!