I recently purchased a’71 Camaro with a small-block and a 700R4 overdrive trans. The guy who I bought it from said the trans has a lockup converter and that everything worked great. But driving it now for a while, I don’t think the converter is really locking up. I have a buddy with a 700R4 with a lockup converter and his rpm drops a lot more than mine does when it shifts into fourth gear. So how do I get the converter to lock up in fourth gear? — T.D.
Jeff Smith: The most popular way to convert a 2004R or 700R4 to lockup is to do so when the transmission shifts into 4th / overdrive.
Several companies, including Painless and TCI, offer kits.
The contents of these kits vary, but before you purchase one, it’s possible the transmission may already have the conversion accomplished and all it needs is a simple 12-volt connection.
The kits add a pressure switch inside the transmission that enables the torque converter clutch to engage when the transmission shifts into fourth. All that’s needed to test this first is to apply 12 volts to the A terminal on the four-pin connector on the side of the transmission. If there is no electrical connection to the transmission, that is a huge indicator that the system won’t work in its current configuration.
If the male plug for the connector is missing, you’ll need to find one. We ran down a Dorman part that will do the trick. The A terminal is the one that needs switched 12 volts while the B terminal will need to be grounded. For a quick check on whether this works, merely connect switched 12 volts from the fuse box to the A terminal on the connector. With the engine running and 12 volts to the transmission, if the trans has already been converted, when the trans shifts into fourth gear this will also engage the torque converter clutch (TCC) to lock up. The rpm drop will be noticeable.
If you try this and the converter doesn’t lock up, then you will need to convert the transmission to one of the above-mentioned kits. The Painless kit costs a little more, but offers an extra feature that you might find worth the higher price.
Most standard kits include the internal components to convert the transmission. The TCI kit for example also offers a relay switch that must be wired into the brake light circuit. This is because when you apply the brakes, this switch disconnects the power to the TCC, which disengages the TCC when you apply the brakes.
If this switch isn’t employed, the TCC remains on until the transmission downshifts out of overdrive. Often this won’t happen until vehicle speed drops below 20 mph. This can begin to lug the engine a bit, which doesn’t hurt anything, but in a panic-stop situation, it’s possible the locked TCC could stall the engine.
That would be bad.
Imagine attempting an aggressive stop only to decide immediately to accelerate (like sitting on the railroad tracks) and then having the engine stall.
This is a very common four-pin brake light switch brake light switch that operates the brake lights normally but also has employs a separate pair of electrical connections. This set is normally closed, which connects 12-volts to the transmission until the brakes are applied. When the brake pedal is depressed, the switch opens and cuts the voltage signal to the transmission and disengages the TCC.
The Painless kit adds a second low-vacuum switch.
This is wired in series with the above wiring and is connected to sense engine vacuum. This switch disconnects the voltage to engage the TCC when the throttle is opened under heavy acceleration (roughly six to eight inches of manifold vacuum).
So when you step on the pedal to perhaps half- to three-quarter throttle, the vacuum switch disconnects the electrical circuit, unlocking the TCC so the converter adds stall speed and allows the engine to accelerate with more power. Assuming you’re still in fourth gear, when the throttle is relaxed, the vacuum rises in the manifold, the TCC re-engages, and you’re back to cruising.
It shouldn’t take much diagnosis to determine if your 700R4 is fitted with one of these kits. If not, it’s probably best to have a professional shop install the kit in the trans since this will require removing the pan and adding some wiring and a pressure switch to the valve body.
This is also a good time to add a new filter and some new fluid.
what in your opinion would cause (causes) a torque converter to stay locked on a 700r4 causing the engine to stall ? i just replaced the torque converter after replacing transmission pump in the transmission. i also replaced the decant cable and reset. i had perfect operation of the transmission for a couple hundred miles then suddenly stated having an occasion hard shift into second feeling as though it was the torque converter engaging. The converter is still locked as i limped home. By reading your article it might highly suggest the this to be as simple as the brake switch ?? in you opinion is this a mechanical issue or a electrical issue …thank you in advance
Your solenoid is bad
Sticking TCC solenoid.
my 700r4 was rebuilt to put in my 31 chev behind a 300 hp 327 cu in evey time I brake the engine slows down and then kills other than at the flywheel thats all that connects the engine and transmission
You don’t mention the dorman part number for the switch pictured. I’d like to get one to run in my project.
Painess PN 80176 will do the job
i have a57 chevy when it shifts in to 4th gear i lose rpm and the car shakes spitz and pops
have a 700r in a 89 s10 2.5l 4 cyl ( all factory) when i drive it
it goes into lock up right away bogging down the little engine , no matter where i position the tv cable its the same
fluid is dark / burnt odor
any suggestions here dont want to overhaul beater pick up
ive drained the fluid and will change the filter
is there a pressure switch thats faulty ? i can chabge while pan is off??
I have a S10 with a 350 700r4 swap and my b and m lock up converter switch quit working one minute it was working and thirty minutes later it wasn’t what I’m wondering is what would it do to the transmission if I was to take it one a 500 mile trip up the highway driving like 70 for hours at a time would it burn it up
I have bought 2 of these kits and still don’t have a
working lockup. They work for a short while and then quit. The box is the bad part and is also the only part not available separately. I am now exploring alternatives.
I have a question I desperately need help with. I have a 92 c1500 pickup with a 383 stroker and a fully built 700r trans with a tci constant pressure valve body. The problem I’m having is when it shifts to overdrive lockup keep coming in and out surging the truck back n forth. The only way I can get lockup to quit going in and out is to very very lightly feather the throttle to gain speed slowly or really mash into it. Anything between that and lockup will engage and disengage. The lockup switch does have 12v power and vacuum is ran to a port on my Holley 750 carb. Any help would be greatly appreciated
I have 1955 chevy with 406 SBC and 700R4 out of a 1992 Caprice wagon, my problem is the transmission freewheel and you have to gas it to make it shift, any ideas?
94 Chev 3/4 ton 4×4, 700 R4 … transmission freewheeling all the time, no compression braking any gear any speed, still runs and shifts fine.
I had to make a very hard stop from about 60 mph, and since then my 700r4 (qjet on a 350) is crawling really low rpm and stuttering through gears like there’s no pressure. TV cable looks normal at carb, I took off the detent housing, and worked the linkage in and out, reinstalled, and it drove great for 10 miles, until I stomped the accelerator a bit, and the problem returned. What exactly could be happening there, in the cable and with TCC setup, if any?
HI Jeff. we installed a 700 R4 GM tranny in our street rod, the tranny didn’t
have a removable plug on the 4th, gear to use come of those lockup
controllers, however we found a total electronic , external type on E-Bay. even has a feature that disengages the lockup when the brake is pushed &
an indicator light to let you know when it is in lockup, works great.
Do you remember the name of the unit that you bought?
My mechanic just swapped my TH350 to a 700R4.
Cruise control used a switch on the brake to disengage if the pedal was pressed.
the new torque converter unlock uses the same switch.
Can we make both work on the same switch?
If so, How?
If not, Whats the solution?
I have read where if you put a check ball in one of the holes in the valve body plate, it will engage the clutch in OD. The 700 that was built for me did that. An interesting thing, though, is that the clutch would disengage when the throttle was fully released (idle), so no need for a brake light switch interrupter. While towing, when you released the throttle in OD and reapplied again, you could hear the engine rev slightly until the clutch engaged, lugging the engine down, and eventually downshifting to 3 due to added throttle.
The transmission is toasted now, we towed with it in a C-30 with a 402, 3:54 gears, and 31″ tires. It would never stay in OD while towing, unless downhill with tailwind. 3-4 clutch pack is wasted. Possibly overheated? Only had the stock cooler in the radiator tank. This set up was fantastic if not towing.
when my 700r4 is in 4th gear and a slight amount of throttle is applied it revs up and down. If i unplug my painless lock-up kit it goes away. I have replaced the stall converter, and all of the lock up kit parts. any ideas.
i have a 69 c10 with a 383 strocker and a 700r4. i have it idleing at about 1100 rpms and when i put it in gear the RPM’s drop to about 900 and can’t hardly hold it with the brakes. it suppose to be a 2000 stall convertor in it. do you think the converter is locked up?
Hi I have a 454 67 chevelle with turbo 700r4 & 3.73 12 bolt rear, I am using a oil pressure switch in 4th gear port to active my lock up converter .
The pressure switch is 50psi , the car moves through the gears good and into 4th easy but because of the ratio and 454 bbc I feel iam in overdrive to early, the motor can handle it because of its torque but I am worried about the gearbox, maybe i should be using a different size pressure switch, or getting rid off it
Can you help
I have a 700R4 that I believe has already had the mods installed in it to operate properly. On ds I have the 2 wire switch which already has black to ground and other wire to ps 2 wire pressure switch which is mounted in servo. Do I possibly just need to wire 12 bolts to other terminal on ps side with relay and cab toggle switch. This Jeep was in a fire and I don’t no how to wire this up right. I’m replacing kick down tv cable because of fire so just needing any info I can get. Thanks
4r44e torque converter stays locked up unless I put it in 1 manual but have to put it in rev for a split second then shift to 1 manual and it will let me stop without diieing If I come to stop in d with or without OD on it will stall out if I break hard while coming to stop in d it will downshift to 1st but will stall out but if coming to stop I down shift manually to manual 1 it will clutch or unlock converter because it doesn’t stall and let me stop and idle no problem so I have to drive it manually into d then cruise no problems so I drive it lick it’s manual stick shift but I can’t pass smog cause tech won’t drive it like a stick I mean I don’t know that this is causing the fail but it couldn’t be helping
Just had a 1988 700r4 rebuilt. I put it in my 1987 Chevy R10 TBI 2wd pickup with 700r4. The old trans from my truck shifted really smooth under cruise. 2nd was starting to slip under harder acceleration. I bought the 88 700r4 just to do the swap faster cause the truck is my daily driver. (Both trans have Vette servo) After installing the 88 trans the shifts good just a little more aggressive. Something I noticed was while Cruising in 3rd gear if feels like a light shift a few seconds after and the rpms drop 300rpm. I know it’s not over drive because when I shift into over drive after cruising at 55mph from 3rd the rpms drop about 700-900rpm. Is my torque converter locking up in 3rd also? Is that what I’m feeling?