Another 700r4 question? TC lockup...

[N2TRUX]

Ok here's my situation. I need a TC lock up kit for my 700r4. My bro-n-law built the tranny and he recommends going with a factory style set up that has a vacume switch "and" a brake switch to unlock the convertor.

So far I have found that Bowtie Overdrives kit is brake unlock only. Painless wiring sells a kit, but it includes the internal solenoid, pan gasket, etc for the internal mods that I don't need and it's 129.00

The only other one I have found is from TCI. I think it has everything I need, but it's like $80.00 from Summit.

Can anyone recommend any other options that will allow both brake "and" vacume unlock....

[Jonboy]

I wussed out and used the Painless kit.

[beaterC10]

Have you tried a search on the net? I was considering dropping a 700 in my truck a while back, in my search I found a sight that detailed the instructions to do it yourself on a factory style set up. Didn't seem like very much was involved. A 12V source to a vacuum switch, through the brake light switch, to the solenoid.

You prolly already have and I'm wasting server capacity.

[N2TRUX]

Originally Posted by beaterC10

.... Didn't seem like very much was involved. A 12V source to a vacuum switch, through the brake light switch, to the solenoid.

Yeah, I already know what to do. I'm just trying to locate the parts to do it with. I guess I could try to find what I need from a donor truck, but I never have time to hit the junk yards...

Jonboy- What Painless kit did you use? I need a part number if you have it. The only one I can find is what Summit carries for 129.00. Do they offer a kit with just the harness, and switches?

[Jonboy]

I bought the one from summit. It came with a new Brake pedal switch, the vacuum switch, a new pressure switch and servo for the valve body, and wiring.

I am pretty sure that there are instructions and part numbers on Jeff's site. I found that after I bought the Painless kit
http://www.73-87.com/7387garage/drivetrain/lockup.htm

[N2TRUX]

Looking at the parts list on Jeff's site it looks like the TCI kit is the way to go. It's 76.88 which is about the same price as the GM parts listed in the article....

[plumbcut]

its my personal opinion that you wont really want the TC to unlock at low vacuum situations.. i sorta think that its a driveability thing from the '80's to absolutely minimize any sort of un-smoothness of tranny operation before it starts... Mine is only foot-brake unlock and I usually have it manually locked anyways. the more lockage, the better. my 2¢

pc

[DOOBZ]

N2TRUX, I've used the TCI kit before, infact im still using one on my 85 and i think they work as good as a factory lockup on 700r4 trucks. I also used the B&M "adjustable" lockup kit on my chevelle that worked pretty good once you found your happy medium setting between 30 & 90 mph but it didnt operate off vacuum and the control panel is kinda hard to hide. Lotsa different options out there, but that TCI unit works pretty sweet.

[N2TRUX]

PC- I guess it's just me being anal again. I figure if the factory did it that way I may as well do the same. Yeah I know that's not a good example, but it's the best excuse I have for being wierd.

DOOBZ- Thanks for the confirmation. I was starting to realize this would be the best route to go to get what I wanted. I know I could scrounge used parts from another truck, but I would like to get everything new. From the looks of the parts list that Jonboy directed me to on Jeff's site, I wouldn't save much money and would spend a lot more in time trying to duplicate the kit with new GM parts....

[7T7]

Ken here is another lock up kit.
It's the one that came with my 700r4 from TPI.
http://www.tpiperformance.com/noncomlockit.html
It's very simple. Works on trans pressure.
Just another option to look at.

[N2TRUX]

Frank,
That looks like a good option too. It's currently priced at 69.50 which puts it at price of the TCI kit. I think I prefer the TCI kit, but I will ask my bro-n-law if he thinks this will do the same thing with less install hassle...

[JustOneTruck]

Here come the dumb question.

When rebuilding the tranny didnt it come with a kit to do this operation. Or is that a up grade if it didnt work right in the first place.
I have a 700r4 in my 84 and it seems to lock up at about 35 36 ish if Im easy on the fuel.{Diesel} and if Im hard on it it locks in when I let up and stays locked untill a hill or braking. Just wanted to know maybe what it wasent doing or was missing the lock up part.

Are these trannys {700r4}known for shifting hard from 1st to 2nd and a little less between 2nd to 3rd. This thing feels like I rebuilt it like my T-350 with a 3000 stall with rv shift kit in it.

1984 GMC 6.2l Long Bed just 31,000 miles .

[plumbcut]

Originally Posted by N2TRUX

PC- I guess it's just me being anal again. I figure if the factory did it that way I may as well do the same. Yeah I know that's not a good example, but it's the best excuse I have for being wierd.

n2trux, no explanation needed Im not saying you SHOULDNT install it, just giving another point of view.. I figure swervin would be quick to shoot my theory down but as we now know, hes been in hiding...

86-C10-V6 makes a good point about spark knock, I hadnt considered that.

pc

[Jonboy]

there is also a way to use a fluid pressure switch and not have an electrical connection at all. My cousin built one for me about 10 years ago that locked up that way, but I can't remember how he did it. I would have had him help me with this one but he is 500 miles away now.

[RockHQ]

the difference in shift harshness between the 700R4 and the 350 is largely caused by different gear ratios. The 700R4 shifts from 3.06 1st to 1.62 2nd gear, or ~47% reduction in gearing, while the TH350 shifts from 2.52 1st to 1.52 2nd, or ~40% reduction.

[8t5Silverado]

Since all the 700R4 experts are together, here's my question.

I am considering rebuilding my 700R4 with the help of my father-in-law. He has rebuilt T350's before. Does this seem reasonable or am I out of my league? I want to basically do a slightly beefed up factory build, nothing expensive.

[7T7]

Originally Posted by Jonboy

there is also a way to use a fluid pressure switch and not have an electrical connection at all. My cousin built one for me about 10 years ago that locked up that way, but I can't remember how he did it. I would have had him help me with this one but he is 500 miles away now.

Good one Jon!
I’m glad you mentioned that.
A buddy of mine has the same TC mod done on his 700r4 in a 1936 Chevy Rat Rod.
He has driven that thing thousands of miles and never had any problems.
I’ll try and get the details tonight and get back to ya’ll.

[SanitysBane]

I personally neve saw the problem with just using a toggle switch, but I plan on washing my hands of 700R4's soon. Oh and on the low vacum thing, at WOT you have very little if any vacum.

[86-C10-V6]

The vacuum switch allows the TC to unlock under modest loads like going up hills without having to down shift from overdrive. It reduces the likelyhood you will lug the engine and cause spark knocking as well.
The vacuum source should be connected to a TVS on the manifold that will not allow the TC to lockup when the engine is cold.
This is the way the factory setup works.
If you want you can put a manual dash switch in line with the vacuum switch that will allow you to force the TC to unlock, but the 700R4 does not like to be run very long with the TC unlocked, it will overheat the TC. This is why when you are pulling loads or operating in hills it is best to run it in Drive. This will allow the TC to stay locked under heavier loads than when running in OverDrive.
JMHO

[boxrodz]

N2TRUX-

In what gear are you planning to lock the TC? I understand that in the early models, the factory TCs locked in second gear and the later models in third. When I had my 700R4 rebuilt, they tried to change the lockup from second to third. After many blown fuses and spending a full day checking the wiring, they reverted the lockup back into second gear.

[N2TRUX]

Originally Posted by boxrodz

In what gear are you planning to lock the TC? I understand that in the early models, the factory TCs locked in second gear and the later models in third......

Mine should lock in third gear and OD. It was built from an 88-89 truck core.

86-C10-V6- Great input. I am learning all these things as I go. I'm really don't care to have a manual over ride switch just so I don't have to worry about over heating. That why I am determined to get the lock up to work as close to the factory design as possible.

[boxrodz]

Originally Posted by N2TRUX

Mine should lock in third gear and OD. It was built from an 88-89 truck core.

... Thanks

[Bob Gervais]

I have a possible solution as well. A friend of mine, Paul Nimz, has made some devices for another car club I belong to. He named them the "VAK", Vacuum Accessory Killer. Basically, it switches at about 2" of vacuum and kills all the accessories (alternator, AC, etc). The cars these were originally designed for, Taurus SHO's, do this at WOT, however this device allows the car to kill the accessories sooner.

I'm thinking that this type of vacuum switch arrangement is what is used to control the converter lock/unlock function, and that Paul may be able to make the switches needed for trans swaps, for a lot less money. In fact, he's told me he could make vacuum switches for around $25. I'm not sure if it would work or not, I don't know what level of vacuum this needs to switch at, because I have not swapped a 700R4, but I figured it's worth a shot.

Paul is a great guy to deal with, and probably has done more electronic modifications to his own vehicles, and others in the club, than he probably cares to remember. He has a great deal of knowledge about the subject, we'd just need to tell him our needs.

For anyone interested, his email address is pnimz@v8sho.com. He's told me that anyone that is interested can contact him, and specifics can be worked out.

[Grande Rojo]

Ken, I ran a 700 for about a year and never even used the lock up. My tranny builder said I would only gain about 200-300 rpm in lock-up. So unless you are doing alot of hiway driving I would not use it.
What rear gears are you using?? 308's ?????? what the cam specs in your new motor??

high gears+overdrive+big cam = not good
you need to find your cruise RPM

I just got a th400 "built" I did not want to blow the 700 behind my new 454 bigblock!!

[Bob Gervais]

I thought running without the lockup would fry the TC? I've done a little looking around though, and it seems you can get a non-lockup TC as well, maybe that's the way to go?