70 BB automatic question

[Andrew Strauss]

I am looking for the origin of the wire that goes to the solenoid on the l/side of the trans [400].I can find it nowhere in the aim or the wiring diag I own.It is a one wire pin on the trans.Does it go to the blk/pink wire that is on the harness at the firewall?

Thanks Andrew

[Chuck S.]

Re: 70 BB automatic question

Andrew, automatic transmissions are not my bag, and like you, I found next to nothing in the AIM or the service manual on wire colors. Maybe someone with M40 will help you out with the colors.

The transmission solenoid you mention must be the throttle kick-down solenoid. You can check the kick-down switch on the accelerator pedal rod support (UPC M40, Sheet A8) for wire colors, but they will probably be different colors than the solenoid wire. Wires for the kick-down switch should branch out of the engine wiring harness, or the same harness that goes to the starter. I would expect the solenoid wire to the transmission to also come out of the same harness.

One way to confirm that the blk/pink wire is the correct wire for the kick-down solenoid is to connect one voltmeter lead to the blk/pink wire and the other to a good ground. With the ignition switch on (engine off), check the voltmeter to be sure the wire isn't already hot, then operate the kick-down switch at the firewall. The voltmeter should register voltage when the kick down switch at the firewall is activated if the blk/pink is the transmission wire. If the needle doesn't move when the switch is activated, then the blk/pink is probably not the transmission wire.

The above assumes that there is no problem in the switch circuit up to the transmission wire. Even if you identify the transmission wire, you may still have a problem...Bubba didn't cut that wire off because it was working. You may have to back up to the switch and use an ommeter to confirm continuity between the switch and the wire.

[Andrew Strauss]

Re: 70 BB automatic question

Chuck,

Thanks for the response.I just replaced that harness and found a home for every connector except the blk/pnk and a 2 wire connector that is orange and black.Blk/pnk is hot at all times with ignition on.the orane and black may be it except never has voltage even if the switch is operated,the switch tested good.I am confident I can fix this if I could just find a GOOD wiring diagram.Does anybody make an updated diagram with componenet location?were can I find the function descrition of this circuit/system?

Thanks again

Andrew

[Chuck S.]

Re: 70 BB automatic question

Andrew, I have frequently set out with great confidence and resolve to fix electrical problems with wiring diagrams...only to get knocked in the dirt. My belief is: if mechanical-minded guys are from Mars, then electrical guys are from Uranus.

I think you best bet is to find another 70 auto and check out the wire colors if someone doesn't ante up some help here. As for as updated wiring diagrams, I think what you see is what you get. I know of no other source.

Options cloud the wiring diagram picture. Does your car have C60? One 14 ga orange wire in the engine harness is not used for the blower motor when car has air; the blower motor wiring is in the AC harness. Further, the case wiring connection on the THM seems to be shown with two terminals in the service manual...the second terminal is for a pressure switch which is associated with the TCS. The wiring diagrams are particularly inadequate for dealing with the TCS.

[Jeff A.]

Re: 70 BB automatic question

My 70 th400 has a onw wire connection coming up to the kick down switch. I found help in the AIM but in the appendixes on transmissions. Does the car kick down when you get on it ? My switch was bad and I was able to get wone from the local Chevy dealer and use the guts of th "hecho in Mexico" new switch to fix the old one.

[Andrew Strauss]

Re: 70 BB automatic question

My trans does not have 3rd gear.2 overhauls and 3 valve bodys later still does not have 3rd.someone on this baord mentioned that the detent solenoid may be the cause.He said his had 2 wires.I have found a connector that has 2 wires [1 orange & one black]that has continuity with a wire wich goes to the switch on the gas pedal,but the plug in point on the trans ony has a single pin connector.This could have been incorrectly installed previously.I think what is happening is that the detent solenoid is staying open and allowing fluid to pass when it should be closed and only opened when told to do so by the gas pedal switch.I was looking for varification that this is how this circuit worked.

Thanks Andrew

New Years resolution=3rd gear

[Roy B.]

Re: 70 BB automatic question

You are right ! in my post I think I did say two wires, but one is correct to the trans detent (orange). And as you stated the detent is open or closed.? I cant remember? old age you see. But like I said , I think the detent is keeping it from going to third.Black should be ground.You should get the answer from a trans. shop or chevy dealer trans man.Sorry about that!

[Chuck S.]

Re: 70 BB automatic question

Andrew, from the service manual:

"The detent solenoid is activated by an electric switch on the carburetor or accelerator linkage. When the throttle is fully opened, the switch on the carburetor is closed, activating the detent solenoid and causing the tramsmission to downshift at speeds below approximately 70 MPH."

This indicates the kick-down switch is normally open, and energizes the solenoid on closure. Your problem sounds like it may involve a weak/missing return spring or a solenoid mechanically failed in the extended position.

The overhaul manual shows the vertical terminal of the case connector as the detent solenoid terminal, and the horizontal terminal appears to be the pressure switch terminal. Both the solenoid and the pressure switch are single wire connections. The pressure switch (Closed in Drive, open in reverse) probably completes a ground circuit to activate TCS.

[Chuck S.]

Re: 70 BB automatic question

Andrew, check the VIN stamp on the left side of your transmission just above the pan flange, and between the shift lever shaft and the speedometer cable connection; you may find that the trans has been changed to one from a model year without TCS and having only one connector terminal. Or, maybe in one of those overhauls, someone has replaced the case connector with an incorrect part number. Your case connector should have two spade terminals in an "L" layout; one vertical and one horizontal. Single pin connectors were not used in 70.

Also, how long is the harness branch with the orange and black wires? Who manufactured the repro harness? Lectric Limited's catalog shows the 68/69 harness requiring an additional jumper harness to reach the transmission, and the 70 harness does not. If your orange and black wired connector is not obviously long enough to reach the transmission, then it sounds like you could have been sold an incorrect harness.

[Andrew Strauss]

Re: 70 BB automatic question

Chuck,
The black and ornage connector reaches to the switch and is what I have been looking for.The case is out of a 72.So I need to find 2 pin connector.Once installed is the detent solenoid the same?Are there any componenets inside the trans that are rtelated to the tcs?I purchased a new detent solenoid from the dealer today.It looks as if the part has been updated,but should work.

Thanks again

Andrew

[Chuck S.]

Re: 70 BB automatic question

Andrew, the two terminal connector may be only one of your problems as far as TCS goes. The case connector can be easily changed to the two terminal connector...BUT...If the case originally had a one pin connector, then there may be no provision for the TCS pressure switch.

The pressure switch should be located on the right side of the transmission, across the valve body from the detent solenoid, and aft of the rear servo cover (round "can-like" cover with three depressions). The switch should be mounted horizontal in the case, with the electrical wire coming out of the forward end of the switch. If there are no switch-like devices there, then look for a threaded plug in that area, maybe allen socket head variety. Maybe you'll get lucky.

As I said earlier, the second (horizontal) connector terminal should be for the pressure switch, which is closed by fluid pressure in "Drive", and open in "Reverse". A black wire (ground) connecting to this terminal would make sense because the pressure switch would complete a ground circuit to activate the TCS in forward gears.

You can decide if the TCS is important to you; unless the car is being judged you could probably care less. You'll probably decide based on how much has to be done to set the transmission up for the pressure switch. If you intend to have the car judged, then the TCS will be checked for proper operation...for sure in a PV, perhaps (not sure) in the operations check prior to flight judging. Transmission VIN stamps are typically not judged since they are too hard to see on the judging field.

[Jim T.]

Re: 70 BB automatic question

Andrew the two wires from my full throttle kick down switch in my 70 has a orange wire and a black wire that go through a gourmet in the firewall. There is also another orange wire with a black stripe that shares this gourmet through the firewall.
On my turbo 400 drivers side is a connection that has a orange and black wire. This wire is wrapped and goes up the front of the firewall and under the windshield wiper.
Connected to the TCS solenoid on my intake is a connection with two wires, one blue and one black. The blue wire is of a smaller guage.
The temp unit wire on the passenger side has double black wire and a green wire in a two wire connector.

[Andrew Strauss]

Re: 70 BB automatic question

The tcs being operational does not realy matter to me.I am more interested in having 3rd gear.Thanks for all the advice,this has been a great learning experience.I hope to put the new detent solenoid on this weekend and go for a drive>

Thanks Andrew

[Chuck S.]

"Great Learning Experience." Yeah, Me Too...

Fore daze uh'go, Eye kud'unt evan spel Terbo-hidruh-matick. Now, I know more than I ever wanted to know about automatics.

Andrew, I would start by adjusting the kick down switch as specified in the AIM (UPC M40, Sheet A8). You may have already done that by now. Then, with the ignition switch on (engine off, DO NOT TURN TO CRANK POSITION), check to see if there is voltage at the orange wire when the accelerator pedal is depressed, and none otherwise.

After changing the detent solenoid, confirm that the solenoid is activating before closing up the transmission. With the ignition on (engine off), I think you will be able to hear an audible click when the throttle is opened to the WOT position. If there is still a problem after the kick down switch has been properly adjusted, and the solenoid is confirmed to be working, then the problem has to be in the transmission.

Let us know how you come out. Good Luck.