MikeP

A bud of mine owns a 1986 C4 with the 4+3 manual trans. His trans started to stop coming out of overdrive (pushing the overdrive button and no response from the trans) and stay there. In the begining the car would shift to overdrive as normal when shifting to 2nd and would stick in overdrive, then after the car would "warm up" the shift **** buttion would become operative and allow you to disengage the overdrive function. Eventually the button stopped working and the trans would stick in overdrive continuously to include shifting to overdrive in 1st gear!!! The overdrive button is inop completely and the car is a sled!! This car sits alot (garage queen) and has leaked some trans fluid on to the garage floor but would stop when driven (not a substantial leak). What is the problem? Is it the switch sylnoid or pressure switch?

Any help with this would be great because a dealer here in town has told us these parts are discontinued. What are the part numbers and where can you get them to fix it if that is the
problem? :confused: :confused: :confused: :withstupid:

ductape

A couple a things this could be. Before I bat it around, you really need to post this in the C4 Tech/Performance section. There you will hook Scorp. He'll bite hard on this and tell you where to go and what to do when you get there. He is THE MAN on these OD's. :yesnod:

lilblackvette

It sounds to me like that stupid $180 switch at the base of the shifter, same thing was happening to mine, don't go to GM for the part. Radio shack has it for $2.99 PN#275-1549A SPDT-Momentary switch. All you need is a soldering Iron and continuity tester make sure you solder one wire to the center pole and the other wire to the normally open pole. When your done soldering take a hot glue gun and seal the connections. save yourself $177 for something worth it.

MikeP

Thanks for the intel. Where exactly do you find this bad switch at the base of the shifter. What do you need to remove and what does this little thing look like. If you could explain more in detail that would be great. Thanks. :iagree:

MikeP

Thanks for the intel. I have posted this on the Tech forum, but no bites I will search for Scorp.

Thanks again. :cheers: :_dupe:

lilblackvette

You need to remove the shifter **** first, pry the button up carefully from front, once you remove the **** you'll see a black t-rod, unscrew this count how many turns so you can put it back in the same position, then pry the retainer wedge out, unscrew the ****, then take out the reverse lever. Now you have to take the dash apart, start with the insrument bezel then the radio/information center bezel, and finally the center console. You will see a white teflon piece attached to the switch, leave it attached until you get the switch out. There is a nut on the switch, loosen the nut and the switch will slide out. Now you have to take the teflon piece off to use it on the new switch, just push the pin out that is holding it to the switch. Now follow the wiring loom to the connector and unplug it. There is 2 wires atached to the switch you'll have to cut them as close as possible to the switch. Now on the new switch check to see which post is the normally open (should be one of the posts on the ends). You can check this with a conitinuity tester, just put one of the leads on the center post and one on one of the outside posts, you'll need to use the one that does not complete the circuit. Solder the wires to the center post and whichever post is the normally open one. Oh before I forget the switch you buy at Radio Shack will have a red plastic **** on the end, you will have to remove this for the switch to work, just pulls right off.

86_RedRider

it's probably not the switch, or at least there is more to it then that. if OD stays on in 1st, the switch has nothing to do with it.

the system works like this:
if the car is below 117 degrees, the OD won't come on. it will come on by default in 2nd gear once the temperature reaches 118 and shut off in 1st regardless if the switch is working or not. it will also shut off if you slam the gas down. the switch does nothing more then turn it on or off manually and doesn't effect the rest of the way the system works.

MikeP

Do you feel we should tear the trans pan off and seek the solenoid and pressure switch to replace them. And where can we get these parts as they are discontinued.

MikeP

Per our discussion, do you think it is the solenoid switch and the pressure switch in the trans? And should this be replaced? Where can I get the parts? They are discontinued?

scorp508

It isn't that cut and dry. 85 through 88 all had different variations in how things worked.

1986 requires 122* (F) (just like 87-88 too) to be seen by the ECM before overdrive will be available. This temperature reading is the one registered by the coolant sensor in the front of the intake manifold also, not the one in the engine block. The one in the block is just for display on the dashboard.

Overdrive IS available in 1st gear when downshifting while O/D is engaged. It will only turn off in 1st if you apply throttle or slow to under 4mph. If O/D is on in first and you are over 4000 RPM it will NOT turn off when you apply throttle.