baxsom

ok so for the second time my th400 quit going into passing gear.
i crawled under the dash with the key on and pushed the switch by hand. no click from the tranny.

i thought ok the switch is bad like last time.

i unplugged the switch and jumped the terminals from the wire.
still no click from the tranny

i got out my voltmeter.
one wire has 12v with the key on like it is supposed to.

i reconnected the plug to the switch. i put both ends of the voltmeter on each terminal and turned on the key and get a constant 12v with the switch in the up position. if i press the switch to the engaged position the volts go to 0.

any ideas on what could be wrong. it seems i get 12v going through the switch with it in the up position but no voltage with it in the down position like the pedal is to the floor.

if i take the switch out and wire it into a simple battery to light circuit
the light is off with the solenoid switch in the up position but the light goes on in the WOT position so i know that the switch itself works.

'75

It sounds like the switch is working properly. When you hook the test leads to both switch terminals you are reading the voltage from the fuse and the solenoid coil in the trans is your ground. When you close the switch, you are basicly hooking both your test leads together and should not see any voltage reading.
The solenoid in the tranny may have a problem.

TimAT

Switch your meter to OHMS. Disconnect the switch, put one lead on each terminal and see what happens. Should show open with the switch in the normal position and then "O" with the throttle at WOT.

Also check that wire to the trans has not either come off the trans or is burned and broken.

glassman74

Mine had a broken wire.

baxsom

a little troubleshooting update.

i checked under the car
there is a two wire plug going into the tranny.
one orange
one black.
the orange is the same wire that connects to the fuse box at the kickdown switch.
when i activate the switch the orange wire into the tranny is hot. when i let go of the switch the orange wire is no long showing voltage at the plug.

i can only assume that the black wire is ground. i cant get a contuity test on this wire. my voltmeter beeps if i have connection. when i connect the black wire going into the tranny to the - side of the battery i get no beep.

if that is the ground to the switch that may be the problem. but i traced the two wire harness all the way back to the firewall and cant find anything wrong.

tomorrow i am going to try and splice an temp ground into the plug and see what i get.

'75

I gotta ask, have you made sure the pedal is moving the switch at WOT?

7T1vette

Check the resistance (ohms) between the two leads going into the tranny. They connect to a solenoid valve which is activated to dump pressure so that the tranny will downshift. If you find some level of resistance,,,a few hundred ohms or so...then the coil in the solenoid valve is still OK. If it reads very high resistance or "overlimit", then the coil is open and it is 'junk'. The solenoid is easy to get to if you drop the tranny pan....held on with two small bolts. If you need to replace it, find a replacement before you go to the trouble of opening it up. Those valves were really cheap junk; I think they cost GM less than $2 each! I can't imagine what they cost now.

21boy

I have a question about the kickdown and want to save some forums space. My orange wire has been melted and broken by the muffler so I don't have a kickdown, but what does it do? Sorry for question just curious.

TimAT

When you apply power to the orange wire, (kickdown) the power opens the solenoid and dumps 3rd gear oil back to the pan causing the 2-3 shift valve to drop to the 2 position.

(just a rough description off the top of my coconut- I don't have the hydraulic diagram here)

Bax- don't forget when/if you need a new solenoid- don't forget the seal for it!

21boy

Neat thanks.

baxsom

good to know about testing this thing. autozone has them for like 30 bucks or so.

i took it out a year or so ago when i installed the transgo shift kit.
god i dont want to go through all of that again.


i did figure out that the black wire that goes into the plug is not grounded. maybe the wire broke into the harness somewhere.

i get 12v on the orange wire if i ground my multimeter on the frame.
if i stick the neg pole of my multimeter onto the black wire at the plug i do not get 12v.

(i removed the kickdown switch and am using a pushbutton switch jumped across the switch plug to connect the orange wire to the fuse box.

7T1vette

The two wires go to the solenoid coil. The black is supposed to be connected to the housing of the solenoid..and that is mounted to the channel plate in the tranny. Either the black wire is broken or the tranny is not connected to a good ground source. You would have to drop the pan to diagnose your problem.

baxsom

i am not at that point yet.
if the black is ground then it should have continuity with the frame.

right now the black wire outside the tranny isnt showing on the continuity checker that it is connected to the ground on the battery.
that is an outside the tranny problem. now if i put a dedicated ground and power to the solenoid that i know is good and it still doesnt click then i need to take off the pan.

baxsom

orange and black wrapped together all the way back to the firewall.
i put an ohmmeter on the terminals of the solenoid.
it read 1.83

is that good or bad

baxsom

fyi
i put the ohmmeter across the terminals on the tranny solenoid.
it read 1.83 whatever that means.

7T1vette

Sounds like the solenoid coil is still OK. Put 12vdc to the orange (+) and black (-) leads and listen for a click from the tranny pan area. If you hear the solenoid actuate, you know that part of the unit is still good. Next, check to see if you get 12vdc at the connector that mates with the wires coming from the tranny. With voltmeter attached to that connector, turn on your ignition key (engine OFF), then push accelerator to the floor. If you have 12vdc at the connector, then the kickdown switch is still working. If all that works, you likely just have a plugged up solenoid valve in the tranny. You could probably just get it loose from the valve body plate and use some alcohol or mineral spirits (not brake or carb cleaner) to rinse out the opening on the bottom plate. If you get that far, you can test the valve functionally by powering it up and seeing if you can blow through the orifice (gee, that sounded bad, didn't it...). Good luck if you decide to check it out.

TimAT

Here is a picture of the solenoid and the wiring inside the tranny. I've never seen a 400 with more than one wire to the solenoid. Not saying GM never did that, Just that I've never seen one since i've been playing car. Somewhere around 1965?

baxsom

ok here is what happens.
the wires off of the tranny.

scenerio 1

voltmeter red connected to orange wire
voltmeter black to black wire
push gas pedal and no voltage readings.

scenerio 2

voltmeter red connected to orange wire
voltmeter black connected to frame
push gas pedal and i get 12v on the meter

scenerio 3

+hot wire to + plug on solenoid
- ground wire to - plug on solenoid
no clicks

so it is almost beginning to look like i have two problems

the first one is the ground wire is not grounding anymore.
ok thats an easy fix. worse comes to worse i just reattach the ground wire to the frame and call it good. a little bubba but at least a temporary fix.

the second problem is that even with a known 12v and ground on the solenoid i am still not getting a click.

(i can wiggle the terminals on the tranny a bit too if that helps)

so i am going to drop the pan and test the solenoid out of the tranny and see what happens.

god i hate dealing with stuff like this but the tranny shop wants 200 bucks to drop the pan and replace the solenoid.
thats a lot of money for a 30 dollar part

7T1vette

If you are going to drop the pan, go to NAPA and, for very few $$, pick up an aftermarket oil pan drain plug. You just drill a hole in the pan and it has gaskets to seal it off. I chose an area about half-way up on the back face of the pan just to the left side of center [didn't want it to show underneath..and you have to find an area where the inside portion won't interfere with the valve body]. Then you can drain enough of the fluid out to not slosh over everything for future 'activities'.

baxsom

ok dropped the pan.

i already had the drain plug in it but even after letting it drain overnight i still spilled maybe a pint when i dropped the pan out.

of course it went right on my chest. but i digress. there were technically two wires inside the case. one was the + wire to the solenid. the other explained why there was no connection to the ground. it was clipped at the terminal. i guess it used to have an extra ground.
now the solenoid grounds to the tranny valve body i guess.


anyway the wire to the solenoid was almost broken. bare wire was showing. the case to the solenoid was cracked and loose.

i grounded the case straight to the neg pole of the battery and touched the actual wire to one side of a light bulb test wire and the other wire from the light bulb to the + side of the battery
the light came on but no click from the solenoid.

i guess its bad. new one is on order