BSeery

I have a 1980 that I have swapped the 350C automatic out and installed a 700R4 in it's place.
One of the problems with a 700R4 conversion is the lockup on the torque converter.

From what I understood, the 350C in the 1980's had this controlled by means of a switch on the brake pedal and a vacuum operated switch on the drivers side firewall.
What I thought was supposed to happen is this:
12+ volts ran to the transmission unless you pressed the brake pedal or if the engine vacuum fell too low (meaning you were accelerating heavily).

I checked the power line on mine (a green wire coming out of the firewall on the drivers side, near the wiper motor) and it does supply 12+ volts until you press the brake. So that part is working.
However, no matter how much or how little vacuum I put to the vacuum switch, it never breaks the 12+ volt signal to the transmission.

Is mine not working?

If someone out there has a 1980 automatic and has a vacuum pump/gage and a voltmeter, please verify that 12+ volts is sent through this switch when vacuum is applied, and that the voltage stops when vacuum stops.

If your confused by this, post here and I will further explain how to test this.

Please let me know what you find out. I hope mine is just broken and stuck to a closed position.

Ingar, Norway

The vacuum switch is connected to ported vacuum , it's closed in all throttle positions except idle.

Sounds like your switch might be connected to manifold vacuum.
The switch need very little vacuum to close, so I expect it will never open if connected to manifold vacuum.

I have a 700r4 article at my page that has some info on this.

BSeery

mine shows 12 volts even with no vacuum applied to it at all, hose disconnected. It also shows 12 volts with vacuum too.

So, you say it's on ported vacuum ? That would be vacuum above idle only, just like the distributor.
I thought it should be a vacuum source that looses vacuum under hard acceleration, thus allowing the torque converter to unlock.
(scratching my head here). I would think you would want to unlock the TC when vacuum fell below a certain point (say about 7-10). With the TC unlocked you would be able to get RPM's up a little faster.
Then when the throttles closed up a little, and more vacuum is applied, then the TC would lock again.

Maybe mine is shot. But it worked fine with the 350C.

Ingar, Norway

If its closed with no vacuum, then its definitely shot.

Agree that having a manifold vacuum switch to unlock at high loads would be better, but the original 1980 switch is not usable for this purpose as it closes on very little vacuum.
Why GM did it like this I don't understand...

At least the 700r4 behaves differently than the TH350C and you get serious bogging during high loads at low rpm if in lockup. Having a manifold vacuum switch could really help.

But you really need an adjustable switch to dial in the correct opening pressure for your motor.
I think some of the aftermarket kits (TCI?) includes an adjustable vacuum switch.

The ideal setup would be these two switches in series.
Anyone who knows where to find a normally open adjustable vacuum switch?

American Boy

Another happy customer!! :D :D

After reading that post, I decided to look after my lock-up and found that the vacuum source was disconnected. I put it back but it didn't work. So I check if I had 12 volt to the vacuum switch and it was ok but finally I discovered that that switch was not closing with vacuum source. I change it and voilà, the lock-up is now operational.

I'll ad that when you load the engine, the vacuum drop enough to switch off the 12 volts at the switch.

Thanks a lot for the great info. :cool:


[Modified by American Boy, 12:42 PM 9/5/2002]

DaveL82

It's my understading vacuum must be high (cruise condition), the brake pedal not applied, and the trans must be in3rd gear which is conrolled by the govenor in the trans. Only then will power be applied to activate the lockup solenoid.

American Boy

That's correct.

Stephan :cheers:

BSeery

So, yours kills the 12 volts when there is low or no vacuum? That's how I thought it should work. Mine holds vacuum, but at no setting does it kill the 12 volts.
Where did you get your new switch ? How much was it ?

American Boy

Yes, that way at cruising speed when you nail it, the vacuum drop, the switch goes to the off position and the lock-up dissengage to let the converter accelerate the car. And if you let go the gas pedal at cruise, the vacuum from the ported vacuum source stop and the switch goes to off too.

I got the switch from my GM dealer and it was 50$ canadian. You could expect near 25$ US. I have the part number at home and I'll post it tomorow.

Stephan




[Modified by American Boy, 12:22 AM 9/6/2002]

tersian

What about hooking up a manual lockup switch inside the car? I have mine on my 81 completely unplugged because it was locking up too soon and not unlocking soon enough, I believed it was either the valve or the solenoid. Either way, I don't want it working automagically anyway, I would just like the option for lockup if I ever do any long distance driving.

Would it be possible to feed 12v to the switch in the tranny off of a toggle mounted inside the car, then, as I understand it, kill the voltage and then I would have lockup? I guess the only danger would be that if I had lockup on and I came to a stop it may not disengage?

I really don't have the whole picture on this one...

-B

Ingar, Norway

Stephan, is your switch as the same type as the original and are you sure it's connected to ported vacuum?

GM spec for the original switch is to close at only 3inch/Hg, that's how my switch works.
I also thought that ported vacuum was created by air velocity through the carburetor and would be high even at WOT?

At least my switch stay closed at WOT, it's only open at idle.

American Boy

I'm sure it's the original type of switch since I ordered mine from the GM dealer. They found the part number from their computer and when I got it, it was the same as the bad one that was on my car.

As for the ported vacuum, the vacuum connection to the switch wasn't connected so I did take that source on my own. I just put a "T" inline with my vacuum advance which is ported vacuum. The end result are the best they could be.

Do you mean that when accelerating at 60 mph at WOT, the lock-up stay engage? Because if the switch stay close, the 12 volt goes to the solenoid in the transmission.

American Boy

You just have to splice the wire pink/black at your lock-up brake switch and put a switch to control the 12 volts of the circuit. That way you would be using the stock safety feature and wouldn't stay engage in unwanted moment.

FYI, you need 12 volts for the lock-up to engage.

Stephan


[Modified by American Boy, 6:24 AM 9/6/2002]

American Boy

Here's the part number for the vacuum switch:

14014519 Switch

Stephan

Ingar, Norway

That's really weird Stephan.

Sure that your distributor vacuum is ported?
Also, 3inch/hg is very little vacuum, my motor (original cam) never goes that low, even during WOT.

I wish that my system worked as yours as I get sever bogging during WOT with my 700r4 (in 4th gear with lockup).

My idea was to get an adjustable switch (to manifold vacuum) in series with the original.

The original vacuum hookup is at http://iotech.no/corvette/technical/...um_diagram.gif (to large to display here)

The lockup switch connection is at the hose to the canister (8D).

American Boy

I'll say one thing before going further, that's a hell of a vacuum diagram. All of these systems on my car are unplugged beside distributor advance and torque converter vacuum switch.

My vacuum diagram is simple, The carb Port ''J'' is ported vacuum so I hook up the vacuum advance and lock-up vacuum switch. No egr or else.

That's explain why you think my dist advance is on manifold vacuum. Well my car has a Frakenstein vacuum system. :D

I think that if you have 3,07 rear gear with the 0,70 overdrive and you run the vacuum switch that was made for the TH-350C, maybe the lock-up don't come to the same RPM as it should. I woul try to order the vacuum switch for a model with a 700R4. The tricky thing is that all model with injection probably contol it by the PCM. Maybe a camaro between 1982-1986 would have one.

Good luck.


[Modified by American Boy, 3:49 PM 9/6/2002]

BSeery

I thought the 1981's TC lockup was computer / brake pedal controlled? Is there even a vacuum switch on the 1981's ?