Vacuum switch for 700R4

[dixiepc]

I am trying to find some information about the vacuum valve that is on the IP of a 6.2 that had a TH400 transmission. I read somewhere that it
simulated the vacuum of a gas burner to control the modulator valve on the 400. What I need to know is: will this IP vacuum valve supply the right vacuum to control the vacuum switch that locks and unlocks the torque converter on a 700R4?

Thanks

[DmaxMaverick]

The 700 doesn't use vacuum. None. The electrical switch on the pump throttle shaft is for TCC. The vacuum valve for a 400 is NOT the same. If you have a 400, you have a vacuum valve. If you have a 700, you have an electrical switch. The TV (Throttle Valve) cable on the 700 does the pressure modulation, similar to a vacuum modulator on a 400, but the parts and principals are not interchangeable.

[dixiepc]

I know that the 700 does not use vacuum to control the throttle valve. But the early non-computer 700's used a vacuum switch to unlock the torque converter as the gasser's vacuum decreased under heavier throttle. I want to know if the vacuum valve on the IP would control this switch.

[DmaxMaverick]

None of the TH700R4's had any vacuum control. The TCC is/was electric/hydraulic (it has a solenoid valve). No place to plug in a vacuum line, anywhere. All of the 700's are "non computer". The TCC was electrically controlled by the ECM only late models, for emission system purposes. Early models were strictly non-logic circuits, with later models only relayed from the ECM. Vacuum modulated transmissions died with the TH400.

[dixiepc]

I didn't say the vacuum went to the transmission. On the pre-computer carburated gassers, they used a vaccum switch on the drivers side firewall to control the torque converters locking and unlocking based on the vacuum that was present at the time. I now have my torque converter on a switch on the dash. I am trying to find a way to control it better. I thought that the vacuum valve on the IP might would provide the right signal to this switch so that my torque converter would unlock under heavy throttle. I have put a 6.2 in a 1992 gas Suburban. Just trying to make things work proper.

[DmaxMaverick]

OK. Gotcha. Sounded like you were trying to plug your vacuum into the tranny.

It may work, but I doubt adjustment will be a simple process, or even possible. The vacuum behavior between gas and Diesel is very different. It would be much more simple to just install the correct TPS on the pump. They aren't expensive, or hard to find. You may be able to find one for little to nothing. Ask in the Classified Ad Forum.

[dixiepc]

What I have found out about the IP throttle position "switch" is that it is open only at no throttle and WOT. I don't think that will help me as I never see WOT.

Thanks

[dixiepc]

I talked to a guy at Transgo today about their 700 LU kit. Looks like that may be the way for me to go. Has anyone here had any actual experience with this kit?

[Robyn]

The 700LU kit is a winner.

This is the best overall setup.

You dont need any electrical hookups or computer to have a really reliable lockup.

You can customize the thing to lockup just where you want it to.

My suggestion is to have lockup in 4th only at 45 mph or above.

The 700R is a busy little tranny anyway, so you dont need the lockup bouncing in/out/in/out all the time.

The LU clutch is not a real killer anyway and all the bump bump bump in /out just beats them to death.

Dont even be tempted to go for a lockup in second. It can be done, but I dont recommend it.

The whole concept of the Lockup is to get better mileage at cruise speed.

Now, if you want, you can use the LU700 Kit and also wire in a toggle switch to manually keep the thing from locking up.

The LU kit does require that your tranny have a vavle body with the lockup spools in it. The late 700R (just before they went to the 4L60E series) may not have the spools or even a place to put them.

You can swap in an ealier VB though.

The vacuum switch used on the 6.2 with a TH400 did do a fair job of running the modulator by simulating manifold vacuum.

The vacuum switch that was used on some gassers to lock and unlock the Converter might work with the vacuum switch from a 6.2, not sure.

I would forget that mess and just install the LU700 KIT
Simple, easily calibrated and it works good.

Missy

[dixiepc]

Thanks Missy,

I plan to use 4th gear lock up only, I see no need to lock up in any other gear. I also plan to use a toggle so I can keep it unlocked when I want to. Can you still run the power through the brake switch to unlock when braking? If you have used this kit yourself, does it unlock when you accelerate to go up a hill or when you pass?

[Robyn]

Yes, it will unlock with throttle applications such as passing etc.

Yes you can wire the solenoid in so that it will unlock on braking.

Just have to get creative.

As I mentioned, the kit allows some very good adjustments


Missy