Throttle Position Switch Operation - 700R4

[rhill2901]

I've recently replaced my tps for my 83 sub w/6.2 and 700R4. I don't know how its suppose to operate, but I do know it is causing me problems. My new switch reads closed from some throttle position to max throttle. I don't see how that will work. Isn't it suppose to close at some throttle position and open again if I pass that throttle position to full throttle? The reason I ask is because I get early lockup when I accelerate moderately to heavily. And it will drop out of lockup when I reach just under cruising speed (less then 50 mph) and then it will lock up when I exceed 50-55 (depending on throttle pressure). For giggles I took it to the transmission shop and they told me that it will cost me $150 to open the transmission up and see what was wrong. They wouldn't listen to my topic about the tps. Yea right.... Their jaws dropped when I left, showing them that a 83 sub diesel can burn rubber (I know it was childish). In the mean time, I have the tps disabled and manually switch into overdrive. There are no other problems with this transmission. Any help would be greatly appreciated.


1983 GMC Suburban 6.5L - Banks Turbo & Exhaust, 4911 w/6.5 hiflow injectors, dual crossover mod, modified 700R4 & weird acting tps.

[oldiesel]

I had my IP replaced last August, 2 months after my tranny was rebuilt. I immediately noticed increased rpm for a given mph plus my mpg dropped from 18 at 70-75 to 13. I drove it like this until April, approx. 12000 miles when I noticed my tranny fluid was brown, not pink. Took
it to the tranny shop, they said the problem was a wiring problem at the IP and rebuilt my transmission again. I drove it home and the lockup/rpm still did not look right. I drove it back to the tranny shop (120 miles away, and they replaced a connector on the IP pump (assume it was the TPS connector), rebuilt the tranny again and now have no problems and my mpg is where it used to be. My van has 340000 miles on it. Incidentally, the tranny shop rebuilt the tranny the two times under warranty.

[BC Clark]

Well, a couple of things: First the TPS is not a switch. It's really a center tap potentiometer, and with it disconnected you should read increasing/decreasing resistance with rotation depending on which lead you are measuring. If you are really reading an on-off type response then your new TPS is bad too. However you need to be measuring that with a good ohm meter that's sensitive enough. In operation the computer supplies a 5volt reference signal to the center tap and reads the increasing voltage on one side and the decreasing on the other. Which means the center point must be acurately set. This is done by utilizing the Voltage ratio listed on your emissions tag and a gauge block between the throttle and stop. Late models used a .686 block. Some folks have had success by trial and error until they like the shift points and Torque Converter Lock points. Secondly, as Old diesel found the 700R-4 will die a quick death if driven in OD without TCC lockup. You mentioned disconnecting the TPS and using a switch for OD. Hopefully you are actually activating the TCC Lock solenoid. The 700R-4 derives most of it's shift points from the the TV Cable on your throttle and an internal governor, But needs the TPS for correct TCC lockup.

[britannic]

You can also modify the 700R4 to dispense with the TPS altogether, so that it uses just the governor and the TV cable. A pressure switch takes care of the OD lockup and the rebuilder can set the tranny to lockup at a set speed when 4th is engaged.

I had this done for mine and it worked great.

[rhill2901]

My older style sub doesn't have any electronic control (no computer) except the tps. This tps is nothing more than a switch because the transmission is looking for lockup voltage only when a certain throttle position has been reached. After close inspection of the old one, It is nothing more than a switch being operated by a cam that is controlled by throttle position. But I have learned more since my post that something is in fact wrong with the transmission. Even though the tranny is receiving the lockup signal from the tps, the torque converter is suppose to rely on internal pressures inside the tranny to determine when to lockup. My problem is that when the tranny receives the +12volts, it wants to lockup immediately, even in 2nd gear at 15mph.

[G. Gearloose]

I concur, the TPS dedicated to the 700R4 is indeed a switch that closes at 10% throttle.

I'm not saying there are no potentiometers on the pump, depending upon CA emmisions and other options;
But on an '83, the TPSwitch goes to the tranny, in series with a secondary brake switch.

There is a gauge block tool of precision thickness to set both devices.

Aparently, your tps is set higher than your typical cruise throttle setting. Upon depressing the accel, it is also allowing RPMs to flare before locking and pulling the rpms back down.

Is this a factory tranny?

Some are set up common ground, other common hot. Causes lots of inoperability unless things are carefully planned.

My TCI 700r4 locks at 2,3,4 gear, yes even at 15 mph, if over 10% throttle; when in 2wd.

Factory wiring disables lockup in 4wd until 4th gear. Intercepting that wire in the harness let me disaable the 2 & 3 gear lockup with a dash switch.

I used to have similar fun with my 83 K20, Twin walker turbo tubes and the TCI chirping 35" mudders. quite a spectacle.

[ 06-12-2004, 11:04 AM: Message edited by: G. Gearloose ]