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Torque Convertor Lock-up Revisted *UPDATE ORG Post

badmix

badmix

1/2 ton status
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Well, my last thread gained some info. But here is the latest. Just got done with a 2hour interstate run. The convertor at one point did lock up, my RPMs dropped 200rpm and the tranny temp gauge dropped a good 10degrees. I tapped the brakes to see if it would unlock, it did, only to never lock up again for over an hour I eagle watched the gauges, it never locked. So, I know it is capable of locking but why wouldnt it?

I need to know what to check, change, look for etc etc.

If its the solenoid, how hard is that to change? Anyone have a diagram as to where it is and how to access it? I have no idea how to check the firewall vacuum pressure switch. and the switch under the dash that the brakes activate.

Is the switch under the dash strictly to Dissengage the Cruise and the TCC? It has a long threaded body, how is this suppose to be adjusted or setup properly.

Im sure someone has to had this problem on their K5 at some point. Just trying to figure where to look before I end up down at the tranny shop.

The truck is '84, 305cid, 700r w/ 137k miles. Could the solenoid just be wore out, could the convertor be worn out?

***UPDATE***

Well, I hooked up my lil LED light to the 12v wire at the tranny. That was interesting. Its amazing when that thing lights up. But Im guessing me monkeying with the connection at the tranny and under the dash Ive got it working. I just drove 2 hours and it locked and stayed locked. I did unlock it on the freeway and it took a few minutes to lock up. Also itll lock up at low speeds which surprised me. So, im going to clean up the connections better at the tranny and may just wholesale replace the TCC / CC cancel switch under the dash, Im sure its OEM stuff and probably getting wore out. I plan to service the transmission, I got a nice billet pan with drain hole. Might as well change the fluid and filter and put in the new plan. NOW. should I replace the solenoid in the tranny or leave well enuff alone?

thanks for all the help, I do sincerely appreciate it. You guys are a wealth of knowledge.


Thanks
 
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Sounds like the solenoid has an intermittant problem. The solenoid threads into the valve body inside the trans pan. It could also be a bad wire going to the solenoid as well. There are quite a few different style of solenoids so if I were you I would take it to a trans shop and have them take care of it for you.
 
My '81 G10 van's torque converter refused to lock up when I first bought the van,and I discovered the stop light switch was way out of adjustment and was preventing it from locking up...it also has a vacuum switch on the firewall that is used in the circuit to disengauge the converter clutch when engine vacuum falls below a certain spec too,your truck may also have that switch,and if it fails or doesn't get a good vacuum signal it might not let the converter lock up...I would try rigging a hot wire and a switch right to the wire on the tranny that activates the solenoid and go for a test ride and see if it'll lock up that way using the manual switch first,before taking the pan off the tranny and blaming the solenoid myself..(but then,I'm a lazy cuss!)..
 
Ok, but which wire. its a 4 prong plug with only 3 prongs being used in the plug, so which one do I hook 12v hot to
 
I cant tell you,never having had a 700R4 myself I had to test that way..but someone here will likely be able to tell you..my van has a TH350-C (MV4) tranny and its only got one wire on it for the TC lockup..I looked in my automatic tranny rebuild manuals and they dont show a schematic for the wiring so I'm unable to tell you which one to put the juice too..
 
On the 700 the wire furthest to the front and outside of the connector is the 12 volt source for the solenoid, it is referred to as the A terminal.
 
Ok, so if I hook up a lil light to that wire and put it in the cab, Id know if everything OUTSIDE the tranny was working properly to get the TCC to lock up, correct? If it lights up and nothing happens, than we are talking solenoid INSIDE the tranny or the TCC itself. COrrect?

Thanks
 
The light will let you know that you are getting voltage to the connector, and if the wiring is in place internally, then it should get 12 volts to the solenoid. The solenoid will also need a ground , whether internally or externally through the TCM.
 
The button/switch under the dash is not actually threaded, just indexed. Just push (with some force) the switch closer to the brake pedle.
 
The Lockup has several controls and devices that make it all happen.\

As mentioned, the brake switch is one, then there is the valves in the VB itself.

Does the truck have the original tranny or has it been replaced.

Inside the tranny is a series of switches and also a temp switch too.

If any of the pressure switches are bad, the system will not work.

The temp switch must be working or the clutch will not opperate either.

The solenoid is also suspect.

You can install a Kit from Transgo called a 700LU this kit eliminates all the extra crap and can be adjusted (springs in the VB) to lock the thing at your chosen MPH.

I like to set these to lock at around 50 MPH.

The Converter on the 700 is fairly small anyway and with the factory equipment, the clutch is always fooling around, on off, on ,off and such.

This sort of stuff and the 4th gear in town locked up at 35 MPH just beast the clutch up.

Below 50 you really dont need it.
The clutch is not really strong enough to handle 2nd gear stuff.

The Clutch is fine for 50MPH and up Cruising at Light throttle.

Personally if the tranny is in good shape, I would install a 700 LU Kit and be done with it.

Or have it done. Be sure they set it to lock no lower than 45 MPH


Hope this helps.

Snowy
 
Ok...

Man, this sux..too much to contend with on this stupid thing.

Someone I was talking to mentioned the TV cable maybe too tight. That is easy enuff to adjust. Ill check it. Ill try the lightbulb on the wire at the Tranny connection. not much else for me to check cuz Im limited on what im doing.
 
If you have the pan off you may as well replace the TCC solenoid, they are bad about cracking at the base of the neck where the plunger seats that controls flow through the stem, and being an electro magnet they have a tendency to draw contamination to the solenoid and bind it eventually.
 
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