65 Riv pitch switch

[Guest Vetter]

Probably a stupid question but is there an easy way to tell if it's working correctly? Mine has been sitting for for a while and I don't remember how it feels driving it anymore. I've driven it with the electrical plug disconnected and plugged in and don't feel a difference which leads me to believe it's bad but I've been told that leaves it in overdrive (or whatever). The windshield wiper fuse was blown and replaced.

Edited October 8, 2010 by Vetter (see edit history)

[Lapham3]

Hopefully, you have the service manual where there is coverage of this area. I've usually found the throttle linkage/microswitch adjustment as the problem area. You can hear the solenoid in the transmission enerigize/deenergize with the key on, but engine off while on/off with the foot feed-good luck-Dan

[Guest Vetter]

I've disconnected the plug on the switch next to the carb and didn't hear anything. I haven't tried disconnecting the plug at the tranny yet. Maybe the internet and my local mechanic has completely confused me on how the pitch switch works. The car noticeably slows down when getting off the gas, almost like it isn't in high gear. It does drop down a gear when passing.

Edited October 10, 2010 by Vetter (see edit history)

[JZRIV]

With key on - engine off with no background noise; Grab the throttle linkage rod close to where it comes out of the firewall, before the activation switch on the linkage (do not confuse the kickdown switch with the smaller activation switch) and pull the rod back barely enough to just start moving the linkage to carb. Do this motion back and forth while listening for the small switch clicking on the linkage, and also the solenoid inside the transmission clicking.

If you can not hear the solenoid, carefully listen for the switch clicking on the linkage. If no noise investigate the switch for proper operation and adjustment.

If the switch is clicking on the linkage, then test to be sure it is transmitting power down to the terminal going into the tranny.

If the solenoid is clicking in the tranny. Find a spot where there is just enough of an incline to prevent the car from moving when you put it in drive. Barely touch the gas pedal enough to activate the switch but not move the throttle linkage on the carb. You should be able to feel the car want to move forward a slight amount and/or hear the engine rpm change each time the switch is activated. Some might consider this a crude method but it works for me once you get the feel for it.

You can also wire a temporary switch you can operate from the driver seat and take the car out on the road and get it to cruising speed and operate the switch and see if you can feel a difference in the car.

Usually the problem is with the wiring/switch adjustment. The converters and solenoids are typically very reliable but I did have a converter go bad and had to replace it.

[Guest Vetter]

Pretty sure I can hear the solenoid working while engaging the micro switch on the linkage. At rest the switch is not engaged and there is a .010-.012 gap between the switch's contact point and the bearing in that U shaped bracket. Pulling back on that rod to remove all the play in the linkage and that gap is over .030.

[NTX5467]

From what I understand of the switch-pitch set-up, there is an "idle switch" and a "kickdown switch". The idle switch, when depressed with the carb at base idle, puts the converter in "high stall" mode to reduce creeping in gear. Once the carb linkage is moved away from the base idle enough, the switch is no longer depressed and the converter goes into the "tighter" "low stall" mode for highway cruising. When "Passing Gear" is used at WOT, the kickdown switch is depressed (at the other end of the linkage travel) and the converter then goes back to the "high stall" position for more torque multiplication and power. It may well be that the kickdown switch also serves as the "WOT High Stall" switch, but I don't know that for sure. I do know that all THM400s have the kickdown switch even if they are not a switch-pitch transmission . . . sometimes on the back of the carb and other times under the instrument panel on the firewall.

As mentioned, having an applicable model year Buick sevice manual can be a help. Similar year Oldsmobiles also had the switch-pitch feature, but it was "gone" by '68, but could be retro-fitted if desired.

Keep us posted on your findings!

Just some thoughts,

NTX5467

[gungeey]

Not unusual to have a frayed or separated wire from the dog dick (drivers side of carb). Unplug it at the transmission and trace the wiring back up to the switch looking for defects. S