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700R4 Torque Conv. not locking

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by will89, Jul 8, 2003.

  1. will89

    will89 1/2 ton status

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    Howdy guys..I should first mention that I am not interested in buying a 400!!! Ha... My 89 has actually been a great tranny for a mostly road tripping & light wheeling guy like me.

    A couple of months ago my TC wasn't locking in overdrive. I got a some good tips from you guys and things somehow solved themselves for a while.

    Now the problem is back and again the TC won't always lock up in OD. Sometimes it will engage once my tranny temp gauge hits about 150. Ive checked the wires and they seem to be tightly connected and also done the brake test on the highway. When it is working and I hit the brake it unlocks immediately and the rpms go up.

    So now Im thinking it is time to get into the pan. From what Ive read the solenoid could be tired or possibly the pressure switch. Im thinking the pressure switch might be a bit off. When Im real light on the throttle (on the highway)in OD and I approach a slight grade sometimes it will decide to lock up?? Seems like an unlikely time for it to lock up???
     
  2. the professor

    the professor 1/2 ton status

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    The probablility is you TC lock-up clutch is history. an 1989 should have an aux. valve body trans.. (4l60), with a small round addition sticking out of the vavle body.. this is the latest design before the 4l60E,,(electric)
    --
    There are several different torque converters, different sized input shafts (27/30) which you don't have to worry about..thats 1986 and earlier.. different stall speeds, and different clutch material.. they all cost about $100-115 to for a replacement...

    This site will give you the code to read from the tag on the front of your converter (if OEM), so that you will be able to replace it with the same as you had stock, if you were satisfied with it.. some people like to use the factory "high-stall" 2000rpm unit, if they have a cam, or the truck is heavy..

    http://www.bulkpart.com/cgi-bin/miva?Merchant2/merchant.mv+Screen=CTGY&Store_Code=MDITP&Category_Code=700R4tc

    A good place to get parts if you know what you are doing..

    It could also be the small special "O" ring on the front of the input shaft has gotten old and hard and is leaking... it should be replaced when you replace the converter...since you have to pull the trans and converter to replace it, replace the converter too...

    Note that some use a "carbon filled" and some a "woven graphite" clutch in the converter... Usualy, and I say usualy, when you pull the pan, you will find a layer of black sludge when the carbon-filled is failing...

    Do not confuse this with black flakes, or "burnt smell" trans fluid, which indicates a failing trans..

    Small additions to you trans to make it more durable, without teardown or great expense.. A Corvette 2/4 servo (about$13.00) change from outside, and a .500 TV boost valve, and larger reverse boost valve.. also use the hi-pressure pump relief spring..All changed at the same time, when you pull the pump relief valve.. a little trickey so maby you shouldn't do it without advice... the Corvette servo is on the outside and easy to change...

    This company has cheap instruction manuals..

    Oh yea, I just ate my TH400 and am building a 700r4 to go behind my 454

    Good luck /forums/images/graemlins/cool.gif /forums/images/graemlins/truck.gif
     
  3. Foy

    Foy Registered Member

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    Here, I dare to follow the Professor, who obviously has forgotten more about auto transmissions than I'll ever know. I wish I'd been reading this board for much, much longer.

    That being said, and despite Will89's "brake test", I wonder if he's having a problem with his Suburban similar to the one I had a couple of years back with my wife's (hated) Jeep Cherokee: sometimes the converter would lock, sometimes it wouldn't. No apparent rhyme or reason. Did so for a couple thousand miles, and immediately following a shop's routine changing of the fluid and filter, and also following a hard-charging interstate run in 95+ degree heat which caused some fluid to puke out of the overflow and onto the exhaust (that was pretty cool--looked like a NASCAR race car blowing an engine on the backstretch at Talladega). Anyway, I assumed some problem with the fluid change job, or at least an overfilling at it's conclusion, so had them do it again, but the torque converter situation was still "sometimes on and sometimes off" Well, I drove the (hated) Jeep for a few days myself and only then noticed that when you tap the brakes enough to get the brakelights to come on, when the converter was locked, she unlocks. I then learned that was the correct mechanism, for bloody obvious reasons, and looked at the brake light switch. Nothing wrong with the switch other than it was loose from its mounting. One cable tie, then two, later, problem solved.

    It sounds like your switch is working like it ought to when it locks up, but is the switch working like it ought to all of the time? Worth a look?
    Foy
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    [ QUOTE ]
    It sounds like your switch is working like it ought to when it locks up, but is the switch working like it ought to all of the time? Worth a look?

    [/ QUOTE ]

    Very good point. Easy enough to check, make sure the brake pedal switch is "set" correctly...outside chance that it could be just on the edge of "correct" and the brake pedal has just enough slop that the problem isn't consistent.
     
  5. Blue85

    Blue85 Troll Premium Member

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    I will agree with the posts above, and add that it is up to the ECM to lock the converter. You can put a jumper wire in the ALDL connector to force a lock. This will help you to troubleshoot where the problem is. If you do a search, this process has been explained a few times before.

    If the problem is inside the pan, my bet is on the solenoid. These things often start to act up with age. It would be strange to get a sticking lockup valve in the valve body without seeing other valves start to stick. Usually the TV is first. It could also be the seal or the check ball capsule on the end of the input shaft. If the culprit is the torque converter itself, it is probably a seal inside. If the friction lining was worn enough not to hold, you would probably get shudder and slipping instead of the intermittent operation you describe.

    I had the lockup clutch go out on a torque converter and basically would just always be unlocked. When tested, the lockup pressure was blowing right trough it. Unfortunately, there is no test for the converter itself without removing it, which pretty much means transmission removal. If you have it out to test it, you should probably replace it anyway.
     
  6. will89

    will89 1/2 ton status

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    I guess I'll start with the brake switch and double check that again...from there I'll take the pan off and see what gives.... Whats a new solenoid cost anyway?
     
  7. the professor

    the professor 1/2 ton status

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    Thanks for the compliments, at my age, remembering things is getting to be a problem..Did my first trans overhaul of a "cast-iron" Torqueflite, followed by a A727 in 1962
    --
    Every post here is valid..Unfortunately, there is not an easy way, except for replacing the TCC solonoid and trying it..then mabye grounding it to test the TCC..

    The symptoms for a failing TCC, a failing solonoid, and a failing input shaft O-ring are all the same...
    --
    Be careful of the NASCAR smoke.. ATF lights of nicely when it comes in contact with a hot cat or exhaust manifold..
    --
    The TC lock-up solenoid runs $15-45 depending on where you buy it..

    Like I said.. drop the pan, need to do it for the solonoid anyway, if the bottom is covered in a black sludge, and the oil seems OK or maby just brown.. You are probably looking at the converter..and a new solonoid is a good idea with a new converter, so nothing lost...

    On a 1989, TBI or Carb..there is no external oil pressure switch..

    the brake switch only signals the ECM....and not on all the systems.... there is a good possiblity of a CE light if it is out of adjustment..

    THe Trottle Position sensor being out or adjustment, would have an effect also.. but again, possibly a CE light..or at least some other drivablilty problem, like a high-idle with at TBI...

    The ECM grounds the TCC solenoid, 12v is supplied from the fuse box.. so if you can figure out which wire it is, you can ground it and see if the converter will stay locked..

    Usualy 4 wires (4L60E's have more), 2 go to the solonoid, 2 to an internal oil pressure switch(s)

    Different years, have different combinations of pressure switches.. at one time the TCC sol was wired through them..

    Your internal oil pressure switch(s) just tell the ECM what gear the trans is in.. The TCC sol is two seperate wires..

    If you do have a 1989, it is an "auxiliary valve body" trans, it has an "extra" small valve body, aluminum, round a couple inches long... sticking off the main valve body (NOT the servo/accumulator cover) ...that controls when the TCC can lock-up. This trans will not engage the TCC in anything but 4 gear... some 3&4th.. so you can ground the wire at a stop without having the engine stall...

    Got to go, have fun..
    /forums/images/graemlins/cool.gif /forums/images/graemlins/truck.gif
     
  8. will89

    will89 1/2 ton status

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    Great suggestions Prof

    Ok.. couple of questions. What is the CE light? And where would I buy a solenoid? Online?

    Im also going to look at the throttle position sensor as well. Did I mention this whole thing really started up after my trip down to the tip of Baja and back??? Over the course of the trip I unfortunatley had to drive over a couple hundred miles of washboard to get to various fishing and surfing spots. All of that vibration could have affected the TP sensor among other things.
     
  9. will89

    will89 1/2 ton status

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    Hey Professor.. does the throttle position sensor go by another name? I wasn't able to find anything like that in the Helm manual. Im guessing it is the rubber diaphram thing next to the throttle cable. Is this correct?
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    TPS is a 3 prong connector that goes into the TB. You can check it for correct operation, so do that, don't replace.
     
  11. 84_Chevy_K10

    84_Chevy_K10 Banned

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    What if it's just as simple as the brake light switch out of adjustment, causing the TCC not to lock? Not to ask a stupid question, but I'd hate for a guy to miss the obvious.
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    Posts 3&4 in this thread /forums/images/graemlins/deal.gif /forums/images/graemlins/tongue.gif
     
  13. Blue85

    Blue85 Troll Premium Member

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    Any local transmission shop will have the solenoid. You just have to find one that sells parts. I got one for about $28, IIRC
     
  14. 84_Chevy_K10

    84_Chevy_K10 Banned

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    [ QUOTE ]
    Posts 3&4 in this thread /forums/images/graemlins/deal.gif /forums/images/graemlins/tongue.gif

    [/ QUOTE ]

    Oops...
     
  15. will89

    will89 1/2 ton status

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    I figured it out.... When I was down in Baja I took out the thermostat because it was running a little hot out in the dessert. Turns out the computer (its an 89) reads the engine temp and won't engage the lock up if its not hot enough. Of course down in baja it was hot enough. When I started heading north around Ensenada where there was coastal fog and it was much cooler, well that was when I first noticed that it wouldn't lock up.

    So Ive put it back and what do you know... it works now. Thanks for all of your responses and I hope my idiocy has at least saved you guys some headaches.
     
  16. dyeager535

    dyeager535 1 ton status Premium Member

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    At least you didn't start throwing parts at it and tearing things out. /forums/images/graemlins/smile.gif

    Glad you were able to figure it out, and that the solution was so "simple".
     

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