TH700 r4

[adey]

can someone please exlain how the th700 works in overdrive please. i have one fitted as standard to a 1984 k20 silverado, i have a brake switch with 4 terminals on it, and a shifter on the dash with an overdrive position.
i thought the th 700 where / did not have an overdrive position on the shift lever, but was electric controlled?
i have fitted a new brake light switch , but the brake light on the dash stays on all of the time, as it did with the old switch .
can someone please explain how this is wired up so i can chase through the wiring? could this be something to do with the auto not always shifting into fourth gear.
i have ordered a chilterns manual , but that has to come from america to me here in the united kingdom, and i think they must of sent it by sea.

many thanks adrian

[NH2112]

The brake warning light on the dash indicates that either the parking brake is applied, or that there's a loss of pressure (leak, worn linings, etc) in 1 or both of the brake circuits.

4th gear in a 700R4 is selected by fluid pressure just like the other 3 gears, but torque converter lockup is electrically controlled through the connector you mention.

[britannic]

The extra terminals on the brake switch are/can be used to deactivate the locked TCC, so you won't stall the truck when you stop.

[DmaxMaverick]

On a 700R4, you can't stall it, if it's working properly. The TCC hydraulic circuit internally dumps pressure below a set output speed, regardless of electric input. Depending on year model, it will be between 30 and 42 MPH in high range, and accordingly lower in low range. The 4L60/80's will allow the TCC to stay locked below this speed, but those are different animals.

[Robyn]

Maverick
I am going to pull the lockup converter out of my 700 when it goes from the Blazer into the Hummer project and replace it with the larger non lockup unit to give better torque multiplication and better service life. There is a kit to redirect the lube oil flow with the converter change.
This is a real great addition. The innards on the 700 converter are very small with the clutch in there.
I have a fellow here locally that builds converters that makes some fine units.

[DmaxMaverick]

That may work out well in your situation. Those big converters put out a LOT less heat with the same/more output (while unlocked). Keep that 700 cool, and it'll be rock solid with a non locker.

[britannic]

The way mine was set up, I did stall it a few times due to an electrical fault that kept the TCC circuit engaged.


On a 700R4, you can't stall it, if it's working properly. The TCC hydraulic circuit internally dumps pressure below a set output speed, regardless of electric input. Depending on year model, it will be between 30 and 42 MPH in high range, and accordingly lower in low range. The 4L60/80's will allow the TCC to stay locked below this speed, but those are different animals.

[DmaxMaverick]

There were a couple aftermarket valve bodies that did allow it, but those had other issues. IIRC, it was a "country of origin" thing. AAMCO was notorious for replacing valve bodies with inferiors, rather than properly servicing the OEM's.

[Robyn]

Late 700's without the hydraulic valveing to control the converter were locked and unlocked with the computer via the lockup electrical valve in the front of the unit.
These will stall if the electrical switching is not working right.
Mine has the valveing in the valve body and have a check ball stuffed into the snout of the lockup electric solenoid and it runs without any power to it.
Its anoying though in that it locks up at about 35 and stays there untill you drop the speed way down or really mash it. The 3-4 shift is nasty due to the converter being locked.
Dont do it that way. use the hydraulics but also use the electric solenoid.
The valve bodies were made both ways so you have to check to see.
The ones that dont have the valves usually have aluminum slugs pluging the valve bores.

[Robyn]

Maverick
I really think that is the best way to go.
That Hummer kit does not need any extra crap to go sour.
I am told that those non lockers really slip very little at higher road speeds.
Sure rids one of a lot of worry for sure.
If I dont go that way I am going to install one of those B&M lockup control units that allow you to adjust the lockup speed. Its a unit that goes in the speedo cable and sends a signal to a controler. It can be adjusted from 30-50 mph sounds sweet to me. I do like the ability to use compression down to 25 with the converter locked.

[ZZ]

I have my TC controlled with a toggle switch. It won't stall my truck at stops. It somehow unlocks the TC when it drops to low gear.

[Robyn]

Your tranny has the hydraulic valving and the TCC is operated like the rest of the shift valves. The TCC generally drops out about 25 give or take.
You can see where by engaging your switch and then allowing the rig to drop on compression in second gear and see when the TCC falls out.

[ZZ]

I thought it had to be something like that. But with mine, it if it's shifted out of low then it's locked.