torque converter lockup in any gear

[anwat]

Can someone explain to me the advantages of wiring a torque converter that can be locked in any gear? Specifically, I just bought a truck that has the 700r4 wired so that it will lockup in any gear with the flip of a switch. Other than being able to stall the truck just by stopping, why would someone want to lock the TCC up at a low speed? If I understand correctly, you're physically mating the engine to the trans when you're locked. So, unless your wheels are turning at a speed that's compatible with your engine rpms, which is unlikely in any gear except maybe 3rd, it is going to take the engine out of the ideal powerband. I think I'm missing something, because the PO paid a fair amount of money to set the trans up this way, I just don't understand what the advantage is...why and when would this be helpful? I looked and have found kits which allow this to be done, so obviously there's a reason someone would want it. Can someone enlighten me?

 

[6872xtc]

The heat source is mostly eliminated when the converter is locked. I didn't know that there was a way to lock it in 1st, but I have 2 that will lock from 2nd on up. But I didn't pay anything to make them that way, just hooked them up to a toggle switch.
But it isn't really practical in 2nd unless towing or in my opinion. To me it's more of a toy in 2nd.

 

[centexk5]

Used to do it when I was racing diesels. Eliminated the slip and put the torque to the ground just like a manual trans clutch. Hard as hell on parts though. It also helps slowing a trailer down since the locking clutch would stay engaged and you could take better advantage of engine braking. But again it's hard on parts if they aren't designed for it.

 

[anwat]

So, it would seem that what you're doing is making your auto a manual, minus the buffer of a clutch. I won't be towing anything with this truck, ever. Since mostly I'm slow speed in the rocks and I'm not all that hardcore, I think I would be better served setting the R4 up so that the TCC locks in OD like most, and taking advantage of the cushion the soft coupling provides for the trans. Sounds like maybe he set it up that way for more consistent/predictable power when crawling, since I don't think he towed much, either, there's no trailer brake or light wiring installed and the receiver doesn't show any wear. There's certainly nothing I would do that would need me to be in second gear at a high rpm with everything locked up. I usually am barely off idle in second and 4 low.
Thanks for the info, and unless someone else chimes in with a good reason to leave it alone, I'll be doing some rewiring next week.

 

[6872xtc]

It would be beneficial to be able to lock the converter in 3rd also when you are driving at a speed that is below where you could use overdrive. Less heat from the torque converter with it locked. This isn't a requirement of course, but would be a benefit at times. The last version of the TH350 had a lock up converter because the factory was trying to get a little more fuel economy. And the 700R4 could have originally had a switch to lock the converter when the oil temperature got to high. I have seen that in some.
But it wouldn't be practical to have it locked while offroad very much, only certain situations. I just have a good auxiliary cooler on mine for offroad because of how much time the converter spends slipping at idle and just above that. It doesn't get above the stall speed and stay there like driving down the road.

 

[centexk5]

Being locked off road while crawling would be a horrible idea. It would be like trying to drive a manual and never putting the clutch in. You'll stall the motor out or break something for sure.

 

[dyeager535]

So, it would seem that what you're doing is making your auto a manual, minus the buffer of a clutch.

No, you have a clutch, it's just not designed to take that much load. It's the TCC, last C being "Clutch".

It was/is a popular mod with folks running the 200-4R in the Buick Grand Nationals, I'm not sure under what conditions they were shifting, but the comments then were that locking the converter helped their times, but definitely wore out the converters faster.

Will be worse in trucks, the weight seems to be a significant factor in how parts last, especially on components that were used nearly interchangeably, mainly the 700-R4 that was initially very poor in the trucks but seemed to last fine in cars, and the 10 bolt, which has a much better track record in cars than trucks, although that may be the difference between limited slips in cars, and gov-locks in trucks. Plus larger tires, potential towing, and again, vehicle weight.

 

[anwat]

It would be beneficial to be able to lock the converter in 3rd also when you are driving at a speed that is below where you could use overdrive. Less heat from the torque converter with it locked. This isn't a requirement of course, but would be a benefit at times.

As in a long steep uphill or one of those 60 mph headwinds on the 395?. Would I need to manually downshift to third/second or would the slowing speed and higher MAP or TPS cause it to downshift as it normally does even though it is locked? Is it hard on the trans to downshift while locked? Just wondering why they wouldn't have made it this way from the factory...or maybe they did as part of a tow package?

 

[Greg Ducato]

If you are pulling a long grade it is advantageous to have the converter unlocked so it can provide torque multiplication as it was designed to do. The 700 can be locked up in any forward gear except first, oil for the TCC comes off the 2nd gear shift valve. It is unwise to shift with the converter locked, the 700 is not a strong trans and the shock can break the input shaft or the input clutch drum. There is a damper on the converter clutch that helps but it is still not advisable. Factory lockup strategy was unlock under heavier throttle or off throttle, that gave the best performance results and longevity to trans components.

 

[centexk5]

Unlocked on a hill can send trans fluid temps through the roof so keep that in mind. Honestly, just let the transmission do what it was designed to do.

 

[frankin5]

@centexk5
You might want to listen to the one, who said unlocked was advantageous, as he is the person that builds transmissions.

 

[6872xtc]

As in a long steep uphill or one of those 60 mph headwinds on the 395?. Would I need to manually downshift to third/second or would the slowing speed and higher MAP or TPS cause it to downshift as it normally does even though it is locked? Is it hard on the trans to downshift while locked? Just wondering why they wouldn't have made it this way from the factory...or maybe they did as part of a tow package?

As stated by Greg, don't shift up or down with the converter locked, it's too harsh. I have shift kits and larger boost valves in both of mine, and it can get kinda wicked.
The factory had to please anyone who may purchase a vehicle, so comprises are the name of the game. And anemic TBI engines with emission controls couldn't pull decent down low and need RPM to keep going.

I would bet that you have more modifications in that transmission, so it will do things differently and better than a factory unit. Use your common sense as you learn how it responds.

Unlocked on a hill can send trans fluid temps through the roof so keep that in mind. Honestly, just let the transmission do what it was designed to do.

He has a modified transmission and it probably won't work as originally designed by GM.

And my comments about running one locked are influenced by how Allison locks the converter under load to prevent overheating. Yes, these aren't Allison units.

 

[centexk5]

Locked or unlocked? I'm not a trans builder but been around the block long enough that you are the first person to ever recommend pulling unlocked whether uphill or not.

 

[Blue85]

On the TBI trucks, you really can lock at any speed and it's easy to add a switch to do so. You can even stall the engine coming to a stop. So maybe yours is 87+. It could be handy to lock it in 3rd, but I would want an override to kick it out in case you forget, perhaps using a pressure switch on one of the test ports.

On earlier 700s there is a valve in the valve body that doesn't put pressure to the lockup solenoid until certain conditions are met. Depending on the year/config, those conditions are some combination of speed, gear, load. The solenoid vents the lockup pressure until you power it. If there is no pressure there to begin with, the solenoid doesn't matter.

So it would take a valve body mod for the early-mid 80's models. I don't know who makes such a thing.

There's also an old mod of putting a check ball above the solenoid (like the solenoid is always powered), but the effect depends on the transmission you have. Likewise, a wiring mod can effect the lockup characteristics, but not to "always locked" unless you're talking 1987+.

 

[Wes Harden]

I have a driver selectable switch that allows 2nd and 3rd gear lockup. While switch is powered and torque converter is locked, if I step on brake, enough to activate brake light switch, the torque converter unlocks.
I tried locked and unlocked towing selecting manually 3rd and 2nd, the temp and engine effort didn't seem to be much different.

 

[anwat]

Unlocked on a hill can send trans fluid temps through the roof so keep that in mind. Honestly, just let the transmission do what it was designed to do.

This is my goal. I just don't know what it was designed to do!

It sounds like I've got a few experts here now, so I probably should have been more specific in asking this question. I didn't realize the modifications would make that much difference. The transmission I am talking about is a BTO stage 2 behind a 454 with FI tech injection. It is wired with a switch on the floor shifter, when that switch is "on" the TCC will lock in 4th, it seems at the same time it would in a stock trans. It will then remain locked as you slow through 3rd, and second, and unlock when it drops to 1st. When you are in any gear other than 1st.flip the switch to the "Off" position, the TCC will lock and remain locked through whatever up and downshifts you manually direct, or the usual up/downshifts based on speed. This doesn't seem right to me. I took it to the trans shop, and I was told just drive with the switch in the "on" position. Took it to a different trans shop, and they said they've never seen anything like it and suggested i take the switch out and rewire it like a stock 700, which is what I'm sort of leaning towards at this point. I do see the advantage of being able to lock manually in 3rd, possibly even 2nd, so I kind of would like to keep the option, however I want to make sure it's set up correctly. It doesn't have a brake light/pedal disconnect, though, so it would seem it is not wired correctly. It seems to me it should function like a stock trans and unlock when it drops out of 4th when the switch is one way, and the other way it locks manually in 2, 3, or 4, and stays locked until you manually unlock it. The brake switch should override everything and unlock it under any circs. Am I right ?

 

[Blue85]

What year trans is it? How many wires going in? Have any pictures of the wiring inside the pan? There are lots of threads here about lockup options.

 

[anwat]

What year trans is it? How many wires going in? Have any pictures of the wiring inside the pan? There are lots of threads here about lockup options.

Sorry, between the rain and the family I haven't had a chance to check. The trans was purchased in 2016 from Bowtie, I don't know what year it originally was. There are three wires going in, two blacks and a red. There's a black and red going to pin A, and the single black goes to pin D. That black wire goes to the manual lockup switch. The other black goes to a dash light that indicates when the TCC is locked. The red is a keyed power source. I don't have any photos, 'cause I'm trying to avoid dropping the pan unless I need to. I know it could be internal wiring, but I want to rule out something on the outside first. If it came from bowtie the way it is, I would bet it's OK inside, it's something wired wrong or set up wrong.
The only thing that's really bothering me is that it doesn't unlock when it downshifts out of fourth. and that it doesn't have a brake light disconnect, that's easy enough to add, though. From what I'm reading here, though, if it were locked and it downshifted, I would hear and feel something bad. I don't, it just feels like a hard shift.

 

[Wes Harden]

Bowtie has the schematic on there web site. My trans lock up was done by bowtie, D should be operator switched hot, for 3rd and 2nd lock up. 1st should not lock up.
I have never seen 2 wires on terminal A, red should be key hot. The brake light switch should interrupt/open the power circuit.

 

[anwat]

With the switch off, will it automatically lock in 4th and then unlock when it comes out of 4th? That seems to be the issue I'm having, once it locks, it stays locked, no matter which way the manual switch is set. I'm going out to trace the wires right now, I'll compare to the schematic you mentioned and should be able to find the difference.