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I rebuilt my 91 700R4 with a kit from Pro Built Automatics from Dana and a TCC lock up kit from Painless. The vacuum line for the TCC is connected to port vacuum. When cruising at 60 mph 1900 rpm if I keep the gas pedal steady and touch the brake pedal the TCC unlocks, rpm goes up a little and then it locks back up rpm comes down again. That part works good. If I step down on the pedal a little to get it to unlock it sounds like it is unlocking then locking then unlocking and repeat. Stepping down a little farther it stays unlocked, stepping down further it down shifts as supposed to. All up/down shifts are good. Ideas? Go to my facebook page, take out the spaces, I had to add spaces so I could post it here.
So do you think you are right on the edge of vacuum to activate/deactivate the vacuum switch at part throttle? If so, is that vacuum switch adjustable, or are switches with different values available?
So do you think you are right on the edge of vacuum to activate/deactivate the vacuum switch at part throttle? If so, is that vacuum switch adjustable, or are switches with different values available?
As far as being on the edge of vacuum to activate/deactivate the switch, I don't know, maybe. I am running 5/32 hose from the carb to just before the switch then 1/4" to switch. Would 1/4" all the way from carb to switch make any difference? I don't think it is adjustable and I don't know if they have different switches.
As far as being on the edge of vacuum to activate/deactivate the switch, I don't know, maybe. I am running 5/32 hose from the carb to just before the switch then 1/4" to switch. Would 1/4" all the way from carb to switch make any difference? I don't think it is adjustable and I don't know if they have different switches.
I've gone through this tuning process and from the sounds of your setup, you're experiencing what's known in electrical terms as "toggling". You reach a vacuum setpoint, the engine load unlocks the converter, the engine load changes again, the lockup is reactivated. Lather. Rinse. Repeat.
Somewhere, someplace I've got a P/N for an adjustable vacuum switch for my DIY'd TCC lockup circuit.
FWIW, I've a 4th gear apply switch in the valve body (TCC only in O.D. in this case), in series with a vacuum switch and the brake pedal switch. It took some experimenting to dial in the vacuum part of it.
It takes a little back and forth to dial it in but the range of 6" to 22" of vacuum is broad enough to cover most applications.
Do yourself a favour and have a vacuum gauge in the cabin as you test and tune. It's immensely helpful.
But it wouldn't be hot rodding without that would it?
When I had my 700r4 in my 91 I didn't use any vacuum switches I used a relay on a ground trigger from my Holley HP to lockup the converter.
Why not just do the same thing here with a manual toggle switch?? No vacuum to worry about just shift into 4th and flip the switch to lock it up
Not my thread however the objective on this side is to have it perform "automatically". While I do have a manual switch to engage the TCC when operating conditions exist, the idea is to have it happen just as if the Holley ECU was running the show.
The manual switch is handy (which I failed to mention is also a part of my TCC circuit) but for me it serves another purpose.
FWIW: Other models in GM's lineup had exactly the same switch arrangement as I described earlier. There's an 82 Monte Carlo in the fleet that has an all GM engine management system that's all analog with no ECU involved. It works superbly with the vacuum switch mounted to the LHS inner fender.. The GM switch might still available although it's not adjustable and is designed to work within OEM parameters. I may still have that OEM switch in my parts bin.
Can you explain how the pressure switch is integrated into the circuit and compensates for engine load?
I've a 4th gear applied switch in the valve body which will prevent TCC apply unless O.D is engaged. Very OEM. But there are still a couple of running parameters which have to be monitored. Engine load being one.
BTW, mine is not computer controlled.
EDIT: Having just had a look at the Monster kit, it provides what the 4th gear apply switch I've described does (with Monsters 4th gear apply port availability) however it doesn't indicate what other bits you have to have in play to make it work.
In your case, how does it compensate for engine load? Are you analog or ECU controlled?
As far as being on the edge of vacuum to activate/deactivate the switch, I don't know, maybe. I am running 5/32 hose from the carb to just before the switch then 1/4" to switch. Would 1/4" all the way from carb to switch make any difference? I don't think it is adjustable and I don't know if they have different switches.
You need a vacuum switch with more hysteresis. Don't know if one is available or not. The reason for the lock/unlock, rinse and repeat is that when the TCC unlocks (low vacuum), the engine RPM goes up which increases the vacuum. This causes the switch to flip and re-lock the TCC.
Then the RPM drops along with the vacuum and the switch again unlocks the TCC. RPM and vacuum go up and the switch locks the TCC.
So need a switch where there is enough 'distance' between the lock and unlock vacuum levels to prevent this. The following graph shows this hysteresis, although in a stock ECM which uses the TPS%. Just replace the TPS% axis with the word vacuum and reverse the TPS% scale, no difference:
Not my thread however the objective on this side is to have it perform "automatically". While I do have a manual switch to engage the TCC when operating conditions exist, the idea is to have it happen just as if the Holley ECU was running the show.
The manual switch is handy (which I failed to mention is also a part of my TCC circuit) but for me it serves another purpose.
FWIW: Other models in GM's lineup had exactly the same switch arrangement as I described earlier. There's an 82 Monte Carlo in the fleet that has an all GM engine management system that's all analog with no ECU involved. It works superbly with the vacuum switch mounted to the LHS inner fender.. The GM switch might still available although it's not adjustable and is designed to work within OEM parameters. I may still have that OEM switch in my parts bin.
The way I had it in my Holley HP ECU was as basic as it could possibly get. As soon as you hit 4th gear it would lock the converter and hit the brakes to unlock
It's an automatic so I want it to be automatic. I just got off the phone with Painless. It is adjustable. Yaa hoo. Thank you for all you comments. We have fresh snow this morning so my gravel road may be several days before it's dry again so it will be a few days before I can take it on the road.
It's no longer ECM-controlled, hence the need for the Monster kit. Engine load is a non-issue. It is controlled by the oil pressure in the transmission. It locks the TC in overdrive and un-locks at a predetermined PSI. The brake pedal switch overrides the lock-up whenever the brake pedal is applied. Later model 700R-4 transmissions don't have the external 4th gear pressure port, so an internal kit is required...
Which kit do you have?
The painless 60109 shows both a vacuum switch and the valve body mounted 4th gear applied switch.
Got it.
What I see then is that the TCC disengages when the transmission downshifts. That would be the TV valve doing it's job. Fair enough.
What the vacuum switch will allow (whether it means anything to anyone else but me) is that the TCC will disengage without downshifting. That is, it'll kick the clutch off but remain in O.D. If I apply more throttle, then like all good transmissions it'll drop down a gear. Mine kind of behaves a bit like a 5 speed although there's only a few hundred RPM between clutch on and clutch off. My late model Chevy truck is the same in function.
I also have the manual selection switch.
I wasn't aware that there was externally available port for the 4th gear applied function (thanks for bit of tech as it's always good to know).. Mine is all in the valve body. There's also a temp switch that'll prevent the TCC from applying until the transmission is warmed up.
So with the Monster kit you manually turn it on & off?
You have the option of manually turning it on or off.
On would have the TCC come on when you hit O.D.
Off is off.
As I mentioned I have a manual selector as well and there have been be a few times on a highway tour that I'll have forgotten to switch it on.
Harmless enough although with a high stall converter, there's a little extra heat getting pumped into the transmission.
An Adjustable Vacuum Switch that is properly tuned for your Engine/ Vehicle will ONLY improve Operation.
I consider this Mandatory for these Transmissions.
The Vacuum Switch allows the TCC to Operate More So like a Control Module was actually being used...
The TCC Automatically Locking and Un-Locking dependent upon Engine-Load.
When properly done; all the Switches combined allow for a more modern feeling TCC.
The "Feel"/ "Behavior" is very much the same as an Electronically Controlled TCC of a 4L60E (Circa 1996 - 2008).
I have adjusted the vacuum valve from all the way in to all the way out. The only thing it changes is the amount I have to step on the gas pedal to get it to toggle: lock/unlock. I read about some setups need putting a DSV31 vacuum delay valve inline. Or a Dorman 47149 check valve. I don't know if one works better than the other. I have 3 feet of vacuum hose from carb to switch. Would it make any difference where the valve is installed, closer to the carb or closer to the valve.
No check valve in my setup.
Are you able to describe the wiring circuit in it's entirety?
It makes no difference how far the switch is from the vacuum source (within reason of course). And speaking of vacuum source, you'll want full manifold vacuum for this.
Have you used a vacuum gauge as part of your tuning process? I find it gives a better insight into the load the engine is seeing and how it translates to shifting.
OE 700r4s lock the torque converter in 2nd, 3rd and 4th. The early models lock off the ported vacuum switch in 2nd and 3rd and the 4th gear pressure switch in 4th gear. There is no TCC hunting in 4th.
No check valve in my setup.
Are you able to describe the wiring circuit in it's entirety?
It makes no difference how far the switch is from the vacuum source (within reason of course). And speaking of vacuum source, you'll want full manifold vacuum for this.
Have you used a vacuum gauge as part of your tuning process? I find it gives a better insight into the load the engine is seeing and how it translates to shifting.
The OE vacuum source was ported and it ran through a TVS. 2nd & 3rd gear TCC were controlled by vacuum and 4th was via the 4gh gear pressure switch. Many advantages to setting it up in this manner.
Power wire goes to brake switch, to vacuum switch to trans. Inside trans wire goes to solenoid then to pressure switch. All parts are supplied in the Painless kit. Instructions say vacuum is to be supplied by port vacuum so when cruising you have lockup, throttle applied to increase speed, vacuum drops, unlock. When I'm having the lock/unlock problem vacuum is less than 3 lbs (according to my gauge and that's manifold vacuum, I guess I should change that to port vacuum for proper testing) and does not change from lock to unlock. I saw on a different site that some set ups need the vacuum delay valve to prevent the problem I am having. Some say it helps a lot. Some add a timer delay so it doesn't lock back up right away, maybe 3-5 seconds (adjustable).
I can't recall having had a TH700 that locked the converter in anything other than O.D. Then again, all of my stuff has been worked over in one way or another. I did have a couple of stock 700's , (the 86 IROC comes to mind) although I can't recall how that transmission behaved. It and ECM didn't stay around long as the 305 TPI got sold and the 350 hot rod journey began (25 years ago)
Simple circuitry. In no particular order (but everything in series) Power through the brake switch, vacuum switch then to the valve body where there's a 4th gear applied switch (closes when 4th is engaged) then on to the TCC solenoid.
Vacuum was manifold sourced although at cruising RPM's I've found that in my case, there's little to no difference. Part throttle in OD would release the TCC and it would re-engage once the vacuum came back.
And you lost me on TVS?
I'll be revisiting all of this as the transmission is getting a rebuild and I'll have the valve body and related components in hand. Unfortunately, I wasn't present when this latest trans was on the bench (2017) and the valve body pressure switches are a bit of a mystery.
Power wire goes to brake switch, to vacuum switch to trans. Inside trans wire goes to solenoid then to pressure switch. All parts are supplied in the Painless kit. Instructions say vacuum is to be supplied by port vacuum so when cruising you have lockup, throttle applied to increase speed, vacuum drops, unlock. When I'm having the lock/unlock problem vacuum is less than 3 lbs (according to my gauge and that's manifold vacuum, I guess I should change that to port vacuum for proper testing) and does not change from lock to unlock. I saw on a different site that some set ups need the vacuum delay valve to prevent the problem I am having. Some say it helps a lot. Some add a timer delay so it doesn't lock back up right away, maybe 3-5 seconds (adjustable).
Parallel posts it seems. Our circuits are largely the same.
I'd contemplated the delay switch or a pressure switch that has a delta between on and off (like a water pressure switch for a well pump) as I have a similar difficulty as you're experiencing.
It turned out that with some vacuum switch tuning, the issue was resolved.
Obviously that's not working for you so those parts you mention might be needed.
And that's interesting. What could be the other variable here? Engine vacuum at cruising speed?
Seeing as the installations are slightly different there could be something in how the parts work together.
That said, engine vacuum is the trigger so knowing that value in real time while you are are testing I think is key.
It's been a while since I set mine up but I do recall going through three different vacuum switches until I settled on the OEM unit (IIRC). Two were from Superior with ranges of 1"-6" and 6"-22". The OEM value I don't recall.
I used a hand held vacuum pump and a mutlimeter to test each switch's operating range. Then the vacuum gauge in my dash gave me an indication of cruise RPM Hg". Eventually I came to a workable combination.
OR...you could just use a kit like mine. Vacuum is not an issue. Lock-up only in Overdrive...
Sure. There is that option. And I can appreciate the success you've had.
My question is: does your TCC only disengage when the downshift occurs?
That is, OD and TCC are as one and no OD occurs with a free wheeling converter?
Without deselecting the clutch manually via a switch I should add.
The transmission will not engage into lock-up until transmission is in 4th gear. Transmission will automatically disengage lock-up switch when it down shifts to 3rd gear (or when brake pedal is applied) and re-engage when transmission shifts back to 4th gear. If you include the switch (I did not), you can bypass the lock-up altogether...
I'm glad this 4th gear TCC engagement setup has worked for you. My concern would be part throttle cruise, pulling up a grade that does not require a downshift. Your passing a lot of increased load through that TCC that it was not designed for. A vacuum input helps eliminate this concern. In factory trim, my TCC kicks out pretty quickly with increased load.
I'm glad this 4th gear TCC engagement setup has worked for you. My concern would be part throttle cruise, pulling up a grade that does not require a downshift. Your passing a lot of increased load through that TCC that it was not designed for. A vacuum input helps eliminate this concern. In factory trim, my TCC kicks out pretty quickly with increased load.
This follows along with my earlier comment referring to my 4L60 behaving somewhat like a 5 speed. The 10" converter does exaggerate the RPM split between TCC on and off but as just stated, it takes the load off of the clutch. That said, if the transmission kicks down, then the load is relieved. So that point is moot.
Now, further to that, and something I'm unfamiliar with is the TCC being engaged in gears other than O.D. I can see that there'd be some benefit to that but there again, that little clutch is being put to work. I'm not talking WOT mind you, so it may be a point not worth discussing.
FWIW, I've a Yank converter in the works. It'll be part of the transmission package when I've another rebuilt ready to go in the spring. For an additional $500 (USD) I can have a three-disc clutch that'll be suited to WOT. That would certainly be handy on the chassis dyno or, as I hope to do some day, an open road event or standing/flying mile event where lockup would gain some MPH. Or in the case of the dyno, perhaps a greater recorded output.
12-16-2023, 02:48 PM
