700r4 locking up in 2nd also locking too fast. Vac switch?

[SirRobyn0]

Is the vac delay valve the little check valve looking thing in line to the vac switch. How would i test that. I took it off and it seemed like air only went through it one way

Yes that's it. If you have a vac pump and put vac to it, it should be a few seconds of vac application before vacuum will go though it.

If you don't find anything external make sure to check the switches in the pan like some of the other guys have suggested.

Yeah it helps. Im pretty sure ive got 3-4 lockup setup. I have the vac switch and delay valve,brake switch with no external 4th gear pressure switch. Its an 84 as well with no tcm,ecu etc. Pretty sure its 3 wire as well. I plan to mess with it tomorrow and see what else I can find. I cant find a replacement vac switch anywhere...even online. Im gonna try a few things that will help track down the culprit tomorrow.

I'll see if I can find the wiring diagram this morning at work at post it up, no guarantees I'm going to be able to locate it though. I will try.

FWIW- My 1986 will only lock the TCC in 4th gear if there's no vacuum to the switch. That happens right after the 3-4 shift at 45+mph. I'm having some issues with vacuum lines and delay valves, so have had the switch connected directly to manifold vacuum. In that case, the TCC will engage in 3rd after I'm above 45 or 50mph, and will in 2nd if I'm holding it in that gear and exceed 45-50mph (fairly easy with 3.08 gears). Without the delay valve, the TCC will lock a bit sooner under light loads and unlock a bit earlier if manifold vacuum drops. My semi-educated guess is that the delay valve is there in part to keep the TCC from locking and unlocking rapidly under on throttle/off throttle driving conditions, though I need to check the color code on my delay valve to see what the actual time delay period is. Either way, it only fine tunes the lock and unlock a bit, and doesn't contribute hugely to the road speed at which things happen in my application.

Mine is Federal emissions with no computer (save for ESC).

That is exactly how my 84 works. 2nd and 3rd are vac controlled, 4th is any time it's in 4th.

 

[SirRobyn0]

FWIW- My 1986 will only lock the TCC in 4th gear if there's no vacuum to the switch. That happens right after the 3-4 shift at 45+mph. I'm having some issues with vacuum lines and delay valves, so have had the switch connected directly to manifold vacuum. In that case, the TCC will engage in 3rd after I'm above 45 or 50mph, and will in 2nd if I'm holding it in that gear and exceed 45-50mph (fairly easy with 3.08 gears). Without the delay valve, the TCC will lock a bit sooner under light loads and unlock a bit earlier if manifold vacuum drops. My semi-educated guess is that the delay valve is there in part to keep the TCC from locking and unlocking rapidly under on throttle/off throttle driving conditions, though I need to check the color code on my delay valve to see what the actual time delay period is. Either way, it only fine tunes the lock and unlock a bit, and doesn't contribute hugely to the road speed at which things happen in my application.

Mine is Federal emissions with no computer (save for ESC).

That implies that there is something governing the TCC from locking below 45 mph or so is that true? Will your truck really not lock 3rd or 2nd at lower speeds? I ask because that sounds nice but mine will lock 3rd and 2nd quite a bit lower, under the correct vacuum conditions obviously.

 

[Swearbody]

Guarantee that you’ve got constant power being sent to the 4 pin connector at the transmission. I’ve got a manual over ride switch on my 82 so I can let the factory switches do their thing, I can manually unlock the converter and I can manually lock the converter as well. If I forget the switch in manual lock. The instant I hit 2nd gear, the converter locks and stays locked through overdrive. So, if your brake switch is good, it must be since the converter unlocks when you step on the brakes. I’d suspect a stuck vacuum switch or a possible short in the harness. Unplug the vacuum switch and see if the converter still locks. If it does, I’d check for power at the 4 pin connector at the transmission for power all the time the key is on. Shouldn’t. If you do then you need to find the wiring problem. If you have no power there, and the converter still locks even with the 4 pin connector unplugged. Then you’ve got internal issues. Possibly a stuck solenoid.

Ben

SO to unwrap this a bit more.... I did a thing. I interrupted the pin "a" green wire of the 4pin connector with a toggle switch. When off it no longer locks in 2-3 but immediately after 3-4 shift it locks 4th. That lead me to believe you were right about the constant power short on 'A' pin. That wouldn't be so bad but my motor has a cam that prefers over 2k and a 2200ish stall so when cruising in town it chugga luggas when locked. I have to assume I interrupted the wrong wire to accomplish the goal of Manual lock of the converter and that I instead should have interrupted the "d" pin. However this would have accomplished nothing with the "a" pin being shorted somehow so I kinda got lucky I think. I am going to install the switch on the "D" pin and leave the "a" disconnected so as to control the lockup only on the highway....everything seems as though if I just swap the toggle switch to "D" ill have lockup only in 4th and only when I want.

 

[Swearbody]

Has the OP hooked up a pressure gauge to the port on the trans? I would be wondering if your TV Cable is adjusted right, if the fluid is DEX III or DEX VI (not anything else, unless a custom racing ATF but it sounds like yours is a standard unit?), and what your fluid looks like on the dipstick. Im wondering if the internal pressures arent just enough they overcome seals or force their way into the tcc solenoid chamber or whatever it uses. basically, if your immedetialy following a shift it to me would make sense the line pressure is high and slamming into the gear with high pressure its passing anything and everything and applying, but its fluid path is such that it bleeds off elsewhere in 1 and r. Idk. Or that the TV cable is being screwy with its adjustment and combined with this other stuff I mention to give the unique behavior. I dont think failed trans, failed torque converter, etc.

hows the fluid cooler lines? right diameters and free flowing?

It has been traced to a likely short somewhere on the "a" pin or green wire. The short may be internal but a bypass has shown it to be a constant voltage to pin "A" of the 4pin connector. Trans has less than 5k on it. TV cable is new and recently adjusted. Trans temp and functionality are flawless other than lockup.

 

[Swearbody]

You must be registered for see images attach

the switch with the blue connector is the 4th gear switch if that switch is bad (stuck closed) or the black wire attached to it is shorted to ground the trans can go into lock up any time there is power to the transmission.

That may very well be the case. I did some digging today and found that if the pin "a" of the 4pin connector is interrupted then it only locks up in 4th...no more 2-3. I traced the wires and found no shorts externally. I also drove it with a toggle switch on the pin "a" wire and could get lockup in 3rd with continuity. My proposed solution is to interrupt pin "d" with the toggle switch and leave pin "a" disconnected allowing me "manual" control of the TCC. I dont believe this to be ideal but its cheap and verified,LOL

 

[Swearbody]

Yes that's it. If you have a vac pump and put vac to it, it should be a few seconds of vac application before vacuum will go though it.

If you don't find anything external make sure to check the switches in the pan like some of the other guys have suggested.


I'll see if I can find the wiring diagram this morning at work at post it up, no guarantees I'm going to be able to locate it though. I will try.

That is exactly how my 84 works. 2nd and 3rd are vac controlled, 4th is any time it's in 4th.

I put the mighty vac on it today and there was about 3 seconds of delay.
No need for a diagram...at this point ive had hands on all the external wires,LOL

 

[Swearbody]

FWIW- My 1986 will only lock the TCC in 4th gear if there's no vacuum to the switch. That happens right after the 3-4 shift at 45+mph. I'm having some issues with vacuum lines and delay valves, so have had the switch connected directly to manifold vacuum. In that case, the TCC will engage in 3rd after I'm above 45 or 50mph, and will in 2nd if I'm holding it in that gear and exceed 45-50mph (fairly easy with 3.08 gears). Without the delay valve, the TCC will lock a bit sooner under light loads and unlock a bit earlier if manifold vacuum drops. My semi-educated guess is that the delay valve is there in part to keep the TCC from locking and unlocking rapidly under on throttle/off throttle driving conditions, though I need to check the color code on my delay valve to see what the actual time delay period is. Either way, it only fine tunes the lock and unlock a bit, and doesn't contribute hugely to the road speed at which things happen in my application.

Mine is Federal emissions with no computer (save for ESC).

My truck has been modified enough that im not sure the factory setup would even function properly if it were all new parts. I have a cam thats right before needing a vac pump, a 2200+stall, 3.90 gearing. Im not completely sure how all of that ties in but im sure it changes the parameters GM used to set up the lockup. Thank god I dont have a computer reading rpms VS wheel speed...or speedo cause its waaay off.

 

[SirRobyn0]

I put the mighty vac on it today and there was about 3 seconds of delay.
No need for a diagram...at this point ive had hands on all the external wires,LOL

Ok, sorry I didn't get you the diagrams when they could have been useful. I know they are here at work someone but the question is where?

A couple of thoughts on the cam / vac readings affecting operation. You can order delay valves with a longer delay, that would just make it take long to engage in time. The other thing is you can get adjustable vacuum switches and in that way you can set it to come on at whatever vacuum you want. In that way you could still have it work like it was from the factory. Here is just one https://www.amazon.com/dp/B00BZODN9A/ I have no personal experience, but always wanted to get one so I could tune when my lockup comes in.

 

[SirRobyn0]

FWIW- My 1986 will only lock the TCC in 4th gear if there's no vacuum to the switch. That happens right after the 3-4 shift at 45+mph. I'm having some issues with vacuum lines and delay valves, so have had the switch connected directly to manifold vacuum. In that case, the TCC will engage in 3rd after I'm above 45 or 50mph, and will in 2nd if I'm holding it in that gear and exceed 45-50mph (fairly easy with 3.08 gears). Without the delay valve, the TCC will lock a bit sooner under light loads and unlock a bit earlier if manifold vacuum drops. My semi-educated guess is that the delay valve is there in part to keep the TCC from locking and unlocking rapidly under on throttle/off throttle driving conditions, though I need to check the color code on my delay valve to see what the actual time delay period is. Either way, it only fine tunes the lock and unlock a bit, and doesn't contribute hugely to the road speed at which things happen in my application.

Mine is Federal emissions with no computer (save for ESC).

Just for everyone's FYI it is not just year based. If I am recalling correctly the basic options were 4th gear only lock via vac switch. 3rd & 4th gear lock via vac switch. 2nd - 4th lock via vac switch. 2nd & 3rd lock via vac switch, 4th gear always locked, (I know this one is a fact as it is how my truck is wired and it's factory wiring). I have no idea how common one setup is over another.

 

[Ellie Niner]

That implies that there is something governing the TCC from locking below 45 mph or so is that true? Will your truck really not lock 3rd or 2nd at lower speeds? I ask because that sounds nice but mine will lock 3rd and 2nd quite a bit lower, under the correct vacuum conditions obviously.

I'm not 100% sure on the 2nd and 3rd gear speeds, as my speedometer is way off... do know that the 3-4 shift will happen at exactly 45mph if I briefly lift my foot off the gas. The TCC always engages right after the 3-4 shift. But yeah, it only seems to lock in 3rd once you're around 50 mph... I don't get in many situations where I'm holding 2nd up to a high enough speed for the clutch to lock up, but it does sometimes when I'm on hilly secondary roads. Best guess for that is 40-50mph. One other interesting detail is that the TCC doesn't lock at all when I'm in 4wd.

I've never been deep enough into a 700R4 to know exactly how everything is controlled internally, but am guessing that there's a governor that monitors road speed (output shaft speed) along with the TV cable... and the base calibration of the transmission is probably in the valve body? Either way, I'm sure there are a ton of different variants depending on type of vehicle, engine, final drive ratio, vehicle weight and GVW, emissions class, altitude, what market they were being produced for, model year, etc.

@Swearbody If your original powertrain was set up anything like mine, yeah, the factory calibration will probably suck with what you're running now. Just curious... are your shifts happening at the right time, or are they coming too early as well?

 

[SirRobyn0]

I'm not 100% sure on the 2nd and 3rd gear speeds, as my speedometer is way off... do know that the 3-4 shift will happen at exactly 45mph if I briefly lift my foot off the gas. The TCC always engages right after the 3-4 shift. But yeah, it only seems to lock in 3rd once you're around 50 mph... I don't get in many situations where I'm holding 2nd up to a high enough speed for the clutch to lock up, but it does sometimes when I'm on hilly secondary roads. Best guess for that is 40-50mph. One other interesting detail is that the TCC doesn't lock at all when I'm in 4wd.

I've never been deep enough into a 700R4 to know exactly how everything is controlled internally, but am guessing that there's a governor that monitors road speed (output shaft speed) along with the TV cable... and the base calibration of the transmission is probably in the valve body? Either way, I'm sure there are a ton of different variants depending on type of vehicle, engine, final drive ratio, vehicle weight and GVW, emissions class, altitude, what market they were being produced for, model year, etc.

@Swearbody If your original powertrain was set up anything like mine, yeah, the factory calibration will probably suck with what you're running now. Just curious... are your shifts happening at the right time, or are they coming too early as well?

I'm definitely not a tranny guy so I can't answer much where it comes to inside the tranny. When I got my truck it would only lock in 4th and the vac switch was not hooked up to vacuum. And I just didn't understand how the outside controls worked so I went though a lot of research finding out how it was wired.

There is a glaring difference between how my trucks TCC and yours behaves. Mine will lock up at lower speeds. Honestly I don't notice it locking in 2nd unless I'm at a steady speed in 2nd, like under the conditions you mentioned. 3rd will definitely lock at lower speeds than 45mph. It'll shift into 4th and lockup like with your truck at about 45 MPH if I lift off the pedal. But for example I regularly drive a road that has a 45mph speed limit with curves and small hills. The curves require slowing down a bit. If I slow down to a little under 35 just coasting, when I step on the gas slightly coming out of the curve it'll down shift to third and that's all well and fine, but if I'm stay a little over 35 like 38, just below the 40 mark it'll stay in 4th locked up, and lug pretty hard, necessitating a manual downshift. So my question is have you ever noticed your truck doing that? I'm starting to think though the conversation here that I might have a pressure switch issue on the valve body. So wondering if your truck will do that.

 

[Ellie Niner]

I'm definitely not a tranny guy so I can't answer much where it comes to inside the tranny. When I got my truck it would only lock in 4th and the vac switch was not hooked up to vacuum. And I just didn't understand how the outside controls worked so I went though a lot of research finding out how it was wired.

There is a glaring difference between how my trucks TCC and yours behaves. Mine will lock up at lower speeds. Honestly I don't notice it locking in 2nd unless I'm at a steady speed in 2nd, like under the conditions you mentioned. 3rd will definitely lock at lower speeds than 45mph. It'll shift into 4th and lockup like with your truck at about 45 MPH if I lift off the pedal. But for example I regularly drive a road that has a 45mph speed limit with curves and small hills. The curves require slowing down a bit. If I slow down to a little under 35 just coasting, when I step on the gas slightly coming out of the curve it'll down shift to third and that's all well and fine, but if I'm stay a little over 35 like 38, just below the 40 mark it'll stay in 4th locked up, and lug pretty hard, necessitating a manual downshift. So my question is have you ever noticed your truck doing that? I'm starting to think though the conversation here that I might have a pressure switch issue on the valve body. So wondering if your truck will do that.

No. Mine always unlocks and drops back to 3rd a soon as you drop below 45mph, so it never lugs. It does make it a little harder to maintain a dead nuts 45, so I usually just step it up to 50 on those kind of roads. It also does part throttle downshifts without having to be prodded. The only thing that occasionally trips the transmission up is when I stick it to the floor while rolling at about 20 miles an hour... sometimes it will sit there with its finger up its butt for a few seconds before downshifting to 1st, or just stay in second until I manually stuff it in low gear. Doesn't happen that often, so I live with it.

I've driven a few older GM vehicles with 4 speed autos that seem to try too hard to hold on to a higher gear, but it's usually been a front wheel drive or other passenger car and not a 3/4 ton pickup. I think that was a trick used in the early CAFE era in an attempt to eke an extra few hundredths of a mile per gallon out of something, but that wouldn't be applicable to a 3/4 ton truck, or so you'd think.

 

[SirRobyn0]

No. Mine always unlocks and drops back to 3rd a soon as you drop below 45mph, so it never lugs. It does make it a little harder to maintain a dead nuts 45, so I usually just step it up to 50 on those kind of roads. It also does part throttle downshifts without having to be prodded. The only thing that occasionally trips the transmission up is when I stick it to the floor while rolling at about 20 miles an hour... sometimes it will sit there with its finger up its butt for a few seconds before downshifting to 1st, or just stay in second until I manually stuff it in low gear. Doesn't happen that often, so I live with it.

I've driven a few older GM vehicles with 4 speed autos that seem to try too hard to hold on to a higher gear, but it's usually been a front wheel drive or other passenger car and not a 3/4 ton pickup. I think that was a trick used in the early CAFE era in an attempt to eke an extra few hundredths of a mile per gallon out of something, but that wouldn't be applicable to a 3/4 ton truck, or so you'd think.

Thanks for the info. At this point I'm well use to the way my tranny operates, but at the next fluid service when I have the pan off I'll check the electrical switches on the valve body.

 

[AuroraGirl]

That may very well be the case. I did some digging today and found that if the pin "a" of the 4pin connector is interrupted then it only locks up in 4th...no more 2-3. I traced the wires and found no shorts externally. I also drove it with a toggle switch on the pin "a" wire and could get lockup in 3rd with continuity. My proposed solution is to interrupt pin "d" with the toggle switch and leave pin "a" disconnected allowing me "manual" control of the TCC. I dont believe this to be ideal but its cheap and verified,LOL

as long as braking still unlocks it as you had said previously, then I dont see the issue other than convenience and just be sure to be on top of that especially if cruising. If you drive in such a way your truck wouldnt naturally lock up as much , you may lower your temps by leaving it off than to toggle it on and off, per se.

I've driven a few older GM vehicles with 4 speed autos that seem to try too hard to hold on to a higher gear, but it's usually been a front wheel drive or other passenger car and not a 3/4 ton pickup. I think that was a trick used in the early CAFE era in an attempt to eke an extra few hundredths of a mile per gallon out of something, but that wouldn't be applicable to a 3/4 ton truck, or so you'd think.

some of this may be the behavior of a fuel injected engine vs a carbureted engine. There was a TSB from GM about behavior or TBI and peoples learned feel for older engines, with less speeds, and possibly the lack of lockup, etc. all that could combine. My first car had a 440t4 and sequential port fuel injection 3800 (LN3) and there was definitely a "line" when it came to the downshifty behavior, but the TV cable probably was due for adjustment, and the shift points were off. the vacuum modulator probably could have went for replacement too, because after it got running well, it seemed more on point, but if I go tug on the tv cable right now, its probably a little loose or not riding nicely in the plastic sheathe.
Though, that transmission had electronic switches inside that signaled when the car was in each gear, and the engine would adjust things based on that , so its not entirely like a late 80s truck with a 700r4 because I dont think the computer was aware of its gear and used Speed density, not MAF.

but the idea is worth a thought. There is definitely a difference in how a vacuum/hydraulic 440t4(4t60) operates compared to the hybrid electronic/vacuum of a 4t60e, then compared to a 4t65e. I cant speak to the 700r4/4l60/4l60e to any great extent since ive only owned one high mileage 4l60e vehicle and havent driven it much. vortec 350 engine, too.

 

[Rusty Nail]

Well, 2400 is too high anyway, it'll never be great light to light and prolly gonna kill it anyway.
700s got no modulator those functions are controller via the throttle valve cable - which has gotten no other mention in this thread.

Huh.