I just realized here recently that the vacuum switch has been unplugged since before
I bought the car back in late 2008, So I would say the torque converter has not been
locking up since I have owned the car. Does this hurt anything?

The car runs great at any speeds, high or low, freeway or in town. What am I
going to experience with the vacuum switch reconnected, What have I been missing?

The only thing I am not happy with is the down shifting, when you are trying
to get it to kick down when aggressively accelerating, this should be fixed by adjusting
the TV cable, Right?

Thanks for any info that you can give.

Riggs.

 

When the torque converter "locks up" you will experience a drop in rpms of several hundred, like shifting into another gear...internal clutches actually physically connect the tranny and the engine, like a manual trans...This is usually accomplished with a speed sensing switch, or anytime you shift into 3rd or 4th (varies with the tranny). The vacuum switch is usually there to unlock the tranny in the event of acceleration or load on the motor. The vacuum switch senses a drop in vacuum, and unlocks the tranny, raising your rpms, giving a little more power. When the vacuum builds up again, say at cruise (foot off the pedal!), the switch closes, allowing the converter to lock up...

Locking up lowers tranny temp and gives you better fuel economy. Driving at higher speeds "unlocked" will lessen tranny life, due to the heat.

Confused???

 

Simply put, cooling. In addition to the lower RPM and better economy, when the TC locks up the cooler pressure jumps to 120 PSI or thereabouts. The extra pressure thru the cooler = more volume and more cooling.

 

The only loss is in fuel mileage and the extra wear & tear on the engine from doing more work than it needs to. That extra work will result in more engine heat.

 

A couple of years ago I had a problem with my 700r4 in my 85. I messed with it for a long time - months.

I'm not a guru but I dont recall that there are any vacuum lines controlling anything in the 700r4. The TC is controlled by a relay in the pan. The relay is not controlled by vacuum.

The 85 TPI motor has a lot of vacuum lines for the emissions and the fuel pressure regulator but nothing extends down to the trans. Do you have some kind of aftermarket TC lockup device? If so, do you know makes it?

 

Tim ko,

The vacuum switch monitors the vacuum and controls a contact
that sends power to the solenoid in the trans, at least this is how
my set up is.



With this switch being in active, is this why the car would not down
shift when heavily accelerating, when most transmissions down shift?

Thanks,

Riggs.

 

your vaccum switch is just one of the ways to get to LOCK UP... it is not part of the 700r4 just an aftermarket set up, on mine i have the brake relay and a manual toggle switch. the vaccum switch is good stuff

 

Hey Riggs,

Are you saying that now that the vacuum is hooked up, that it doesnt downshift when at wide open throttle?

Was it downshifted at wide open throttle when the vacuum was not hooked up?

I know there is a failure mode in the trans for a "no downshift" condition. I'll check the diagnostics section and see if "TC didnt unlock" is one of the possible causes. I'll let you know.

 

Tim Ko,
No the vacuum switch is still disconnected. I couldn't understand why
someone unplugged it, the way this plug is made, it wouldn't come unplugged
by it's self. I won't get to drive this car for several more weeks for many
reason but most of all, there is still lots of salt on the roads and I need to
align the front end before I drive it.




So is the lock up meant to redirect more of the fluid to the cooler to pull the temp
down or is it meant to make the car stay in which ever gear it gets locked into, 3rd
or 4th.

The down shifting problem (passing gear) I have is in 2nd, 3rd,and 4th so I'm pretty sure that the down shifting
or the lack of down shifting isn't caused by the vacuum switch, probably the TV cable
adjustment. The car runs really well while driving it normal, it shifts through all the gears
and runs at a very low RPM at highway speeds. When I slow down to a stop from highway
speeds the car seems to have no problems with down shifting to the appropriate gear.

I have traced the wires from the vacuum switch connector and they do run to the transmission,
So this appears to be the only lock up system in place, but disconnected.

Riggs

 

VACUUM UNPLUGGED:
Yikes. My guess is that the person who put it in didnt like something that was going on and thought it ran/shifted better unplugged. You know, you get better performance in 1-2-3 when the TC is unlocked. So, maybe his seat of the pants dyno told him to unplug it.

You should track down the vendor of the vacuum switch/transmission supplier and read their claims as to performance and see what they say about what they did and why they did it. There are gazillion ways to rebuild 700's and a gazillion claims as to power capacity, and reliability and parts used. If you locate the road test procedure which is in the GM corvette manual, you get a matrix of things to look for. That would help isolate any kind of a problem.

LOCKUP/COOLER:
No,... nothing like that. Think of it as a clutch/pressure plate, When engaged (locked), it doesnt slip. When it is semi engaged, it slips. When it slips, it creates heat. Heat is bad, and reduces lifespan.

When mine upshifts to 4th and the TC locks, it stays locked even if I slow down and it downshifts to 2nd or 3rd as long as I havent touched the brake pedal.

DOWNSHIFTING:
After I got mine rebuilt a while back and had a shift kit put in, I could be driving at 60, mash the pedal to the floor and it would downshift to 2nd and burn the tires. It downshifted instantaneously.

TV Cable:
Yeah, you nailed it. There is a lot written on the TV Cable adjustment because when retrofitting the 700 in an earlier model (carburetted) that cable has got to be adjust properly or you can burn the trans in the first 5 miles. Its a very easy adjustment and plenty has been written about it.

Diagnostics:
NO PART THROTTLE OR DELAYED DOWNSHIFTS
1. External linkage not adjusted
2. 2-4 Servo damaged or misassembled
3. Govenor Assembly - weights binding or valve stuck
4. Valve Body Assy - valves stuck, TV sleeve turned in bore, 4-3 channel blocked, #5 check ball omitted from valve body.

There is nothing about the TC locking/unlocking

You might want to do a 700r4 700-r4 search in the C4 section. There is a bunch of stuff in there. Pete is "the man".

 

Thanks guy's,
This gets me headed in the right direction. With all the work that I have done to this
car I don't remember seeing anything tied to the brake light circuit. I am going to look
through the whole system and see what might be missing.

Thanks again Guy's

Riggs.

 

Hey Riggs,
The 85 is computer controlled car. The signals are all sent to the computer and out pops a wire for the TC solenoid ... I know there are a bunch of people have retrofitted these into non-computer controlled applications. You need to find the vendor (or a vendor) and get information from them on how they make it work. Personally, I dont know. If you "set" the TC to lockup with a low vacuum; how & when does it unlock? The vendor would know.

Let us know what you find.

 

It should be set to UNLOCK at low vacuum, as when you are in 4th and push the gas to pass or accelerate. If your acceleration is not enough to drop it down in to 3rd, then the drop in vacuum when you push the accelerator will UNLOCK the converter, raising your rpms...when you let off the gas, the carb butterfly starts to close, raising the vacuum, the TC locks up again....

There are adjustable vacuum switches available to do this...the GM switch has long since been discontinued, though a few dealers still have one on their shelves, but they want a mint for them ($100!)