700r4 No Lockup

[73L48]

Hi, I’ve got an 88 Silverado with an 88 700r4. It’s not the original engine or the original trans. Over time, I’ve replaced the trans a couple different time, but I have never been able to feel the torque converter lockup.

It doesn’t seem to matter what Soren I’m at, when I take my foot off the accelerator, the rpm’s drop to idle and there’s no drag that one would feel as the trans contributed to slowing down.

The 4 pin plug is plugged in, and the engine is a 75 350 block, so there’s no original throttle body or fuel injection, thus, the computer is not monitoring emissions, etc.

Can this be the/a reason why the converter won’t lockup?

Any suggestions?

Thanks in advance for any/all input

 

[NickTransmissions]

Hi, I’ve got an 88 Silverado with an 88 700r4. It’s not the original engine or the original trans. Over time, I’ve replaced the trans a couple different time, but I have never been able to feel the torque converter lockup.

It doesn’t seem to matter what Soren I’m at, when I take my foot off the accelerator, the rpm’s drop to idle and there’s no drag that one would feel as the trans contributed to slowing down.

The 4 pin plug is plugged in, and the engine is a 75 350 block, so there’s no original throttle body or fuel injection, thus, the computer is not monitoring emissions, etc.

Can this be the/a reason why the converter won’t lockup?

Any suggestions?

Thanks in advance for any/all input

Is your ECM plugged in and receiving power and hooked up to the external transmission wiring harness for the TCC?

You should see RPMs drop by 200-300 or so shortly after your 3-4 upshift. If you're not seeing or feeling that happening then yes, you're not going into lock up. You DO NOT want to keep driving it like that as these (and the 200-4Rs) must have lock up functioning if you have not already converted to a non-lock up package! Otherwise, you'll over heat the transmission and burn your 3-4 clutch pack in relatively short order.

The ECM should be initiating lock up once it detects apply pressure via the pressure switch on the valve body by energizing the TCC lock up solenoid bolted to the case that mounts into the entryway of TCC control valve's bore in the pump. Make sure you have power to that case connector via your external wiring harness and that there's no shorts anywhere in the electrical circuit for the TCC...If power is there, then drop the pan and replace the wiring harness in the trans w/a Rostra brand harness (OEM obviously has long since been out of production).

If you have electrical problems on the vehicle that are preventing you from achieving lock up (or the ECM is shot) then buy a Transgo or Superior Tech TCC mechanical lock up kit and install it into 1982-1986 valve body in the TCC control bore (remove the two aluminum slugs that will be in there from the factory). Then bolt that valve body into place of the existing one and you'll have mechanical TCC lock up without the need for any electrical contribution. Let me know if you need assistance w/this process and I'll shoot you a couple of my Youtube videos on the subject.

 

[Schurkey]

88 Silverado with an 88 700r4.

when I take my foot off the accelerator, the rpm’s drop to idle and there’s no drag that one would feel as the trans contributed to slowing down.

That can't be right.

The 4 pin plug is plugged in, and the engine is a 75 350 block, so there’s no original throttle body or fuel injection, thus, the computer is not monitoring emissions, etc.

Can this be the/a reason why the converter won’t lockup?

No sensors, no injection...no computer. Therefore no lockup.

There's aftermarket fixes, but the better way would be to reinstall the TBI and all the sensors so the computer is functional again.

 

[Scooterwrench]

You have two choices.
Install a non-lock up convertor or wire in a vacuum operated switch to control convertor lock up.
I would go for the latter both for cost and for not having to pull the tranny back out.

 

[NickTransmissions]

You have two choices.
Install a non-lock up convertor or wire in a vacuum operated switch to control convertor lock up.
I would go for the latter both for cost and for not having to pull the tranny back out.

There's a third choice (see my initial post above): swap to an earlier (1982-1987) VB and install a Transgo or Superior Tech lock up kit. No electrical or electro-mechanical set up needed. I do this all the time for resto mods, etc...

 

[Scooterwrench]

There's a third choice (see my initial post above): swap to an earlier (1982-1987) VB and install a Transgo or Superior Tech lock up kit. No electrical or electro-mechanical set up needed. I do this all the time for resto mods, etc...

You got plenty of those early VB's laying around?

 

[NickTransmissions]

You got plenty of those early VB's laying around?

I usually have a few on hand for customers doing retro-swaps into hot rods, muscle cars, pre-OD era vehicles, etc...

 

[Schurkey]

I once bought a "famous name" lockup kit with a vacuum switch and some wiring, to control the converter on a 700-swapped 76 Nova.

This one, I think...but it's been twenty-five years and I don't remember the kit costing anywhere near that much. About $35 is what I'm thinking, plus a brake pedal switch to shut-off the converter clutch under braking.
www.summitracing.com/parts/tci-376600

TCI Auto 376600 TCI 2004R/700R4 Lockup Wiring Kits | Summit Racing

Free Shipping - TCI 2004R/700R4 Lockup Wiring Kits with qualifying orders of $109. Shop Torque Converter Lock Up Kits at Summit Racing.

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Fookin' vacuum switch had no hysteresis. Morons used a cheap 'n' crappy vacuum switch, so that the engage and release vacuum was the same. The switch was adjustable within a certain range, but no matter where it's adjusted, it would engage or disengage at the same vacuum level.

So you drive along in 4th gear, the vacuum increases enough that the converter clutch engages. That drops the RPM and therefore the vacuum, so the clutch disengages. Which raises the RPM and the vacuum enough to re-engage the converter clutch. Repeat, repeat, repeat. At some point, the yo-yo effect made me slam the gas pedal to the floor so that the car would build enough speed and RPM that the clutch would stay engaged when I finally backed-off the gas.

 

[Scooterwrench]

Hmm,thanks Shurkey,
Now I know what hysteresis means.
Now you've made me think that a switch that does work right would operate the TCC better off ported vacumm.
Idle/off the throttle,unlocked
Part throttle,locked
WOT,unlocked
Sounds like the perfect set up to me.

 

[Schurkey]

Seems to me that the "kit" does call for ported (timed) vacuum, shut-off at idle.

Still need hysteresis in the switch, so the "engage" vacuum is higher than the "disengage" vacuum level. That way when the RPM and vacuum drop due to engaging the clutch, the switch keeps the clutch engaged. Opening the throttle farther--reducing the vacuum even more--should still disengage the converter clutch.