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4WD Relay affect TCC Lockup?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by aandpman, Jan 19, 2003.

  1. aandpman

    aandpman 1/2 ton status Premium Member

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    I have been looking over schematics of 1985 K-10 (thanks to whoever posted that on webshots!) troubleshooting lockup on my 700R4 TCC.

    I found that it wasn't locking up in 3rd because the EGR Bleed Solenoid was disconnected.

    I find a little gizmo that the drawing called a "4wd relay" under the dash bolted to the column. It's hard to make out, but it looks like it has to do with lighting the 4wd indicator light (never seen it) and <font color="green"> my question is does it prevent the 700r4 from going into lockup mode when the truck is in 4wd? </font color>

    Looks like the blue wire to term B on tranny is the main power to TCC for 4th gear lockup.
    Looks like the yellow wire to term D on tranny is for controlling the 3rd gear lockup
    <font color="green">What does the green wire on terminal A do? </font color>

    I've searched and read the posts on 700R4 and looked at 700R4.com and got some good ideas for a lockup manual switch, but I wanted to know what the stock stuff really does before I waste my time doing something the truck does stock.

    Truck is 85 K10 /forums/images/graemlins/truck.gif,305 /forums/images/graemlins/rolleyes.gif without ECM. Mine had only ESC with basic knock sensor and harness to dist which I converted to old style HEI.
    700R4 whick I drive in 3rd all the time due to 3.08's and 33's (but my 14FF is going in soon with 4.10's Detroit and caddy calipers /forums/images/graemlins/cool.gif /forums/images/graemlins/cool.gif /forums/images/graemlins/cool.gif /forums/images/graemlins/cool.gif)
     
  2. Blue85

    Blue85 Troll Premium Member

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    Good eye. You are correct. When you shift to 4WD, it lights the lamp and disables lockup. But IIRC, lockup still works in 4th gear.
     
  3. aandpman

    aandpman 1/2 ton status Premium Member

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    Thanks for the info. I'm still not really sure if the lockup is working in 3rd gear. I've wired a toggle switch to manually supply +12 to pins A &amp; D to ensure lockup and I just can't seem to tell any differrence.
    I know I am getting +12 to the Connector on the tranny.

    Duhh /forums/images/graemlins/crazy.gif also - I found that the fuse panel conncetion that supplies power to the brown wire on the 4wd relay didn't even have a fuse in it. Been running this thing for a long time without even a CHANCE of lockup.....
    I put a fuse in and now I'll see if there is any change in feel or RPM etc.
    Makes me wonder if the fellow I bought the truck from had a non lockup TC installed or something.

    Is there any physical way to tell what kind of TC is in the truck?
     
  4. imiceman44

    imiceman44 1 ton status

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    The only way you can tell is taking it all appart.
    There is a valve in the pump itself, at least in the 350C, I didn't notice if yours is the 350 or the 700.
     
  5. aandpman

    aandpman 1/2 ton status Premium Member

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    Mine's the 700
     
  6. Blue85

    Blue85 Troll Premium Member

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    I would be surprised if someone put a non-lockup converter in. The price of a rebuilt converter is similar either way and if you don't want lockup, it is easy enough to disable electrically.

    There are two things that control lockup in the 700.

    -First, there is lock-up selection valve. This is different from the lock-up relay valve or whatever it's called (I forget all of the correct names), which just acts to trigger engagement. This valve selects whether or not lockup is appropriate based on the governor (vehicle speed) and T.V. pressure (throttle position) signals. If this valve is stuck, you might never get lockup.

    -Secondly, there is the lock-up solenoid. This is one of the things you are powering through the connector. This thing connects between the pressure going to the lockup clutch and the pan. When it is open, the pressure is vented to the pan and no lockup occurs. When it is activated, it is closed and if pressure is present (based on the above valve) then the lockup clutch in the torque converter is engaged. These solenoids do have a high failure rate after enough miles have gone by. You should hear a clicking noise inside the tranny when you apply power to the two pins in the connector, although it may be really faint when the oil pan is on and full of fluid.

    If you truly are applying power to both of the appropriate pins and you don't get lockup, I see three likely culprits:
    1) The TCC is bad or doesn't hold pressure (or likewise, is actually a non-lockup type). This can be checked at any transmission shop, but it has to be removed from the vehicle /forums/images/graemlins/frown.gif You pretty much want to rule everything else out first and if none of them are the problem, it's time to get this checked.
    2) You have a stuck valve. Usually, the first one to stick is the throttle valve, but you could have one of the two valves related to lockup stuck. To fix this should only require removing the valve body and cleaning the appropriate valves. This should only be an hour job for a tranny shop. If you do it your self, have diagrams on hand showing the valve assembly and by all means, do not lose any of the checkballs!
    3) The solenoid could be bad. If you drop the pan, you can see the solenoid up near the front of the transmission. If you apply 12V to it and it doesn't make a clear, consistent click each time you apply and remove 12V, it should be replaced. These can be oredered from a dealer or a tranny shop should be able to sell you one for $20-$50. For troubleshooting purposes, you can bypass the solenoid. It's easy. Just remove the solenoid and put a check ball down in it's neck. Then reinstall it. This will always block off the pressure, just like the solenoid was always engaged. Then you will get lockup based only on the hydraulic signal. This is bad for long-term, though, since it will not disengage based on engine load or when you hit the brake pedal. If you do drop the pan, the first thing you should check is that the solenoid is actually getting 12V from your setup. If it is like stock, you will need to be in 2WD and then use a jumper wire to bypass the vacuum switch mounted near the brake booster.

    I hope some of this helps. Running a 700 in 4th gear without lockup can make a lot of heat. You should probably flush all of the fluid if you haven't already.
     
  7. aandpman

    aandpman 1/2 ton status Premium Member

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    Thanks for really good info. /forums/images/graemlins/thumb.gif

    I definitely want to get this totally ironed out soon. Right now I never use 4th due to 3.08's and 33's. I'm almost finished building a D-44 and 14Bff with 4.10's, detroit and disc brakes and I'll probably run 33's or 35's with that combo.

    4.10's ought to give me roughly the same RPM in 4th as the 3.08's in 3rd, and lockup is going to be a must.
     
  8. Blue85

    Blue85 Troll Premium Member

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    I used to have 3.08's and 33's, but I still used OD and lockup on the freeway. It was like 1600 rpm! Acceleration was not too impressive. Then I went to 4.10's and it was great! Best modification I've ever done. Now that I run 35's, it is still good, but 4.56 would be good too. But that's another whole thread...
     
  9. PWagon

    PWagon 1/2 ton status Premium Member

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    Can you guys supply the link to the wiring diagrams for the 4wd relay (that's mounted to the steering column)? I no longer have an EGR valve, and I'm guessing I need to check/modify those wires. Plus, I do not have power at the fuse block for the relay. My guess is the fuse is bad, but I have no idea which one it is. I've pulled all fuses on the block, and they are good. My guess is that there's one missing on the block (and it's not labeled anything meaningful). Suggestions? My goal is to get my 4wd indicator light working again.
     
  10. paratrooper307

    paratrooper307 1/2 ton status Premium Member

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    Don't forget to check the switch on the transfer case. If it is inoperative your indicator light will not work.
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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