I just aquired a 700R4 out of a 91' L98 Z28 with decent mileage.
My question, is the lock-up switch in the 91' 700 compatible with
my 86' LG4 ecm?

 

Probably. The 4th gear switch might be different.

 

Different, meaning that if I hooked it up the tranny wont lock-up?

 

Also, if the switch isnt compatable, can I put an 86' lock-up switch in the 91'
tranny or use the lock-up switch out of my 85 ' Silverado 700? I assume it worked, I never hooked it up so IDK.

 

I believe WOT shifts for a stock 87-92 L98 Z28/IROC is 5,000 RPM.
The WOT shifts in my original 86' LG4 T/A tranny was 4,500 RPM.
I dont plan on doing WOT shifts in my car(It's race days are DUN!!!!!!)
Should I put the 86' LG4 T/A governor in the 91' tranny or will I be okay?

 

I would swap the TCC circuit (solenoid, pressure switches, plugs and wiring) from the 86 to the 91 trans. The 86 is ECM controlled by a signal sent from the trans. There is a number of different setups and pressure switches used in the 700s. Stick with what worked. The governor I would swap as well to keep the shift points the same as B4.

 

Different meaning that instead of a N.C. switch it might have a N.O. switch, so the computer would think you're in 4th when you're in any gear but.

I agree with Mikz86TA's suggestion to swap the wiring over if you're unsure how to check.

 

Is it easy to replace the lock-up switch in these trannies? Tranny work or repair is an ancient dark art to me and I've never attempted to work on one. Where is the governor in the 700's and how hard of a job is it to replace it? Also, my lock-up switch in my 86' T/A 700(the original one) crapped out back in 03'. I had been riding around w/o lock-up for a year before I parked it in Oct. of 04'. Would the lock-up switch in my 85' Silverado 700 be the same as my 86' tranny's?

 

The lock-up wiring is all accessable after dropping the pan.

 

What about the governor?

 

SWap the Gov too. Best thing to do is note the routing and wiring. Take a pic if you have to B4 on both. Remove it all from the 91 and then remove the part by part off the 86 and swap it over in the process. With these checks and balances' you almost cant f-up. If there was a 'known' bad switch, youll need to know which one. Either note all the part #s and color band off the 86 switches and replace them all, or test them. Done with compressed air and a continuity test with a voltmeter. They are cheap, so best insurance is to replace them all. Then when you pick them up, replace them one-by-one when you get back to the car. Again, this is the best way not to get confused. Notes Notes Notes

 

The governor is under the round cover on the drivers side. I wouldn't be too terribly concerned about it.

 

Where can I get a new lock-up switch from, and where is the governor at in the 700?

 

Mikz86TA, where can I get lock-up switches from and are 85' & 86' 700r4's
compatable? My 86 carcass may not be available to reference where everything
is suppose to go, so all I really have as a reference is the 85' Silverado 700.

 

TCC wiring for an 85 or 86 should look like this:

 

Thanks for the diagram Apeiron. I know that 88-up 700's had the aux.
valve body, would the 91' 700's main v.b. look similar to 85' & 86' v.b.?
If yes, I should be able to wire the 91' with the appropriate pressure switches and the 4 pin terminal from my 85' 700 and be done right?

 

It would be somewhat similar, yes.

 

Maybe you guys can clarify for me, so I get things right the first time, I no longer have computer control, and I want to setup the lockup to run in 4th gear only. I understand that if I send key on power to the solenoid, and then ground the 4th gear switch wire, when the car enters 4th gear and closes the 4th gear switch, it will ground and energize the lockup solenoid and lockup the converter. Can somebody clarify if I have that correct? Secondly, I want to just use the wiring that is coming from the harness coming up into the engine bay, I would run key-on power to the red wire (bundle of 3 wires running to the tranny from the ECM) and ground the other wire not colored black (the 4th gear switch wire, I assume the third wire, the ground, will be black) to acheive what I've described above. Does that all sound right? I may rig it on a switch eventually, but right now I'm just interested in regaining some fuel economy, what precious little I might actually see. I appreciate your input.

 

So the aux. v.b. in the 91' is a separate entity from the main v.b.?

 

Yes, somewhere I've got a picture under the pan of a transmission with auxiliary valvebody.

 

Would the 4th clutch switch port and 4-3 downshift port be in the same location on the 91' 700 vs. the 85/86' 700? And the TCC solenoid for all years (83-93)has the same red and black terminals, right?

 

Yes, the locations are the same. The 4-3 downshift switch wasn't used in all years, so don't be too concerned if you don't have one.

 

You can convert your 700 to lock up the converter by vacuum, you can
buy a kit.

 

So I would just need to install the appropriate 4th CL switch from the
85/86 tranny,if that's all that is in the 91' 700? If yes do I still need to swap
out the 4 pin connector plug from my 85' tranny or will swapping in the right
pressure switch from the 85' unit be all I need to do to restore proper
lock-up function with my 86' ecm?

 

It will depend what's already in the 91.

 

If I swapped the entire lock-up harness and pressure switches from my 85'
tranny, would the torque converter lock up like it's supposed to or would I
just completely f*@# up the transmission?

 

Swapping everything over is fine, it's what Mikz86TA suggested above.

 

Sorry I mustve missed a few post. Darkride , I picked up a new switch from Superior the other day for mine. Its a AC Delco part. But you can get them from any GM dealer. Use the above diagram to verify your wiring on your orig tranny is the exact same. Find the switch on the diagram you need. Note its VBody circuit location and its color ID. If its the 4th its the press switch closest to the Accumilator.(plug is Blue, Color ID is White) Accumilator is the round silver aluminum protrusion in the corner. The color ID is the ring around the top where the terminal pin is. The 4-3 circuit is right next to it. (plug is Yellow and the ID is Black) There might be a 3rd switch next one over or a 1/8 plug. The Aux VB is just behind these pressure switches and next to the Accumilator. The Aux VB too is aluminum colored and had a side-mounted round protrusion. Document where they were, how they were wired on a peice of paper and remove them. Take the with you. Also try some tranny shops if the dealer was a bust.

 

Yes, it would work exactly like its suposed to. The TCC solenoind and Tq Converter is all the same. The ECM in your car and the routing of the wiring are the only variables. By swapping the correct CAR-related stuff, will ensure you the lockup is going to properly work as intended for the CAR make and model year. I have a orig LG4 1986 TA with a 1991 tranny. Throw in the mix I no longer have an ECM-controlled vehicle. But as I posted in another section, I was able to wire it up in a non-ecm format (91 tranny) to retain lockup. Yours is way more simple...especially since you still have the orig wiring form the 86 trans availible.

 

Yeah, I'm not interested in a kit, there is no reason I can't just use the 4th gear switch. Does anybody know which color wires on the harness from the ECM to the tranny are what? Will the wiring I described work ok?

 

See my other post on this HOW TO.

 

Here is the link. Scroll down a few post and there is a Bold-Lettered post on how to with pics attached. You can do 2 things to make the TCC work without an ECM. This posted method, there is a 'kit' which is the same as I have posted if you want to spend money on something you can easu=ily do with part of waht you have and a few cheap additional items, or Superior sells a 'Hydaulic Lockup Kit' that does it internally. But its 'year model' limited so ask them and verify your TRANS year B4 getting it. https://www.thirdgen.org/forums/tran...r-lock-up.html

 

The early transmissions had a TCC valve that was biased against a spring to lock the TCC when a certain speed was reached, as long as the solenoid was also powered. Changing the spring allowed the lock-up speed to be changed.

The hydraulic TCC valve from Superior and Sonnax and others goes into the bore that the factory TCC valve went into. The valvebodies in later transmissions don't have this bore.

 

Bingo! I knew there was a difference but couldnt think of it enough to explain it. THX

 

Mikz86TA, the diagram that Apeiron provided was for 85 & 86 700R4's.
I swapped my burned out 86 T/A 700 for the 85 Silverado 700. Apeiron answered this question earlier,but I'll ask again, are 85 through early 87 700R4's TCC wiring and press. switches the same? I know 83-84 700's were different,you couldnt run them w/o lock-up or they would burn up. I'm sorry for asking the same question, but I may not be able to use my original 86' 700 for comparison. All I have for reference or comparison is the 85'
Silverado 700, and it might be an 86'. I know it's definitely not an 83-84 700.

 

700R4s for thirdgens all had essentially the same wiring, which is as shown above. Some L98s used an N.O. 4th gear switch instead of a N.C. one. Some applications also didn't have the 4-3 switch, but it doesn't matter.

The only major difference is for LG4s built for export with non-computer carbs. They use a self-grounded solenoid with a single hot wire, and have no switches. TCC lockup in those cases is controlled by the TCC valve and spring in the valvebody, and a collection of vacuum delay valves and switches.

 

I don't have my 86' F-Body 700r4 to use for a reference point.
The 700r4 that's in my car now is out of an 85 or 86 Chevy Silverado
1/2 ton truck, that's the only tranny I have for reference. Did 700r4's in
mid 80's 1/2 ton pick-ups also have the same or similar wiring?

 

No idea, you'd have to look.

 

My GM Dealer Service Manual for 1985 Pontiac TransAm/Firebird list about 11 different wiring routes in the TCC section.(FYI, the pic above is exactly whar my book shows, but 11 different variations) Notice the one above says Type4 in the lower right box...and list the makes with it. Type 1 = 4.1,5.0,5.7 Gas 2wd C and 4wd T trucks w/emmision except Calif. Type 2 = Any V8 Gas C and T trucks with Calif. Type 3 = 6.2 Deisel C truck and G van Type 4 as above listed Type 5 = another C/T/G truck and van Type 6 = 2.8 Gas S/T trucks w/ Calif. Type 7 = 2.0 Gas s-series truck Type 8 = 2.8 Gas S/T trucks w/o Calif. Type 9 = 2.5/2.8 F-body Type 10 = 6.2 Deisel w/ Calif. Type 12 = 2.8/5.0 F-body or 5.0 B-body Canada Only. As you can see there were quite a few. My 86 was identical to the 85 wiring in this book. So 85 and 86 Trucks should also be alike IMO. 1985 C Gas w/o Calif. Emissions was a Type 1 wiring configuration. Visually there are 2 pressure switches on the F-body Type 4 wiring (4th Clutch and 4-3 Downshift). On the C-Truck Type 1 wiring there are 4 pressure switches (4th Clutch, 4-3 Downshift, 3rd Clutch and TCC signal which is next to the TCC solenoind) The 4th switch on the F-body is WHITE and SINGLE terminal. The 4th switch on the C-Truck is BLACK and DUAL terminal. Wiring is jumped over and layed out totally different. This WILL NOT function correctly with your F-Body ECM. You will not send the ECM the correct info and it will not send the proper signal back. My 1st opinion of what to do remains the same. Put the orig pressure switches (replace needed ones with new ones) and the orig harness in the new transmission.

 

Thanks for the info Mikz86TA, I will see if my buddy still has my original tranny so I can at least get my 4-pin harness back. If I cant, should'nt I be able to get an 85/86 type 4 harness from a tranny shop or tranny parts place? I don't have a problem buying a new harness since I'm going to replace current 91' press. switch/es with new type 4 85/86' press. switches. Also, I can leave the 91' TCC solenoid alone right? Is it the same as the 86' TCC solenoid?

 

This is an off the wall question..so what switch inside causes the motor to stall when it goes bad...it like leaves the converter locked up..onces its reached operating temp..can someone explain that and what happnes to cause it ???

 

Nothing in a properly working 700R4 would cause that.

 

HD I am unsure about that one. Ill have to ponder on it at a sain hour of the day =). Dark No problem. Getting the parts from the orig would be best. But following the above diagram and wiring the newer harness will work too. You might have to cut and cap and mayne splice a wire or 2. I can help you if you get to that point. Just let me know your VIN engine code. Mine was the H 5.0 LG4 orig. Getting your engine letter code will allow me to look up your ECM wiring and see what its doing (where the wires are going/coming and the colors) Then from the inside I can assist you on which pin goes where. The pins are A,B,C and D. C-pin is always usually not used. A-pin would be the Type 4 diagram 12volt input which is wired through the 4-3 switch (NC) and then on to the red TCC solenoid terminal. The B-pin is a grounded signal output to the ECM from the 4th swithch telling the ECM when the trans is in 4th gear. The D-pin is a reference ground for the TCC solenoind. But figure out what you can get 1st and I will help you by listing what goes where and why. TTYL, Michel

 

Apeiron...i would have to totally agree that in a properly working trans ...nothing is wrong......

But..i have seen tranny's where the TC lock up wont unlock after warmup and will stall the engine when you come to a stop...and that would be in a tranny thats not working properly...

 

In a 700R4, the TCC apply circuit is fed by the 2nd gear circuit, so there's no way that the converter can be locked up while the car is stopped, unless there's something seriously wrong with the transmission.

 

Ok..here is the deal..2 times i have seen this happen..once on my 87 buick skylark..which had only 15000 original miles on it...and a 91 chevy 3/4 ton truck about 3 weeks ago..when not up to operating temp u could drive them around and they worked normally...after they warmed up when u came to a complete stop the engine would lug down and die..if u place it in park or neutral it would start right back up..soon as u put it in gear it would die..

example: it was just as if u had a standard tranny and come to a stop without pushing in the clutch...its gonna lug the motor down and die...

anways took it to a tranny shop..say the replace a switch..something to do with the TC...said once it was warm it wasnt doing what it was supposed to...but it wasnt a major deal..cost like $75.00 to fix...doesnt sound to major to me but i am more curious as to exactly what would cause this...i like to learn new things...but i drove the car and it was a bit*h to drive when it acted up...

 

The Skylark would have probably had a TH125C, which is very different from a 700R4 and was notorious for stalling when the TCC failed to unlock when warm.

 

ok cool..what woulda caused the 91 3/4 ton chevy to do the exact same thing??? and if u could explain how and why...i am very courious as to how it all works..

 

Mikz86TA, my T/A is an H-code LG4 std 305. Besides a few splice and
repair jobs, the wiring is all original and not hacked up. I'm going to talk
my friend at work tomorrow and see if he still has my old 700. I think it's just sitting in his garage(he's going to put it in his 72' Chevelle). I don't think he'll
be interested in TC lock-up, so I'll see if I can just swap the 91' harness for my 86' harness. I'll let you know if I'm able to get it.

 

Ok. The 5.0 LG4/H was my orig engine too. So our wiring is the same routing and colors. Just let me know when youre ready and Ill try to assist as much as I can over the net. No worries =)