"Check Brake" light on and Torque Conv. Not locking up.

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by shum1, May 13, 2001.

  1. shum1

    shum1 1/2 ton status

    Oct 8, 2000
    Likes Received:
    \"Check Brake\" light on and Torque Conv. Not locking up.

    This may be a little technical but I thought Id give it a try. I have a 1990 with a 700r4. I just installed a new tranny due to some warranty issues. On the old one I had a "stock" wiring harness. I did have a swich which allowed me to ground the "F" terminal on the ALDL, thus providing manual T.C. lockup in any gear. Anyways, this new tranny they sent me has a little diferent wiring set up in the tranny itself. I know this company has 2 different wiring setups for stock vs retrofit 4 spd applications. When I first hooked up the new tranny the T.C. would lockup. I could tell because when I applied the break under light acceration, my RPMs shot up about 300 rpm. My problems began when I tried my manual lockup, I smelled a burning wire smell and the "check brake light is now on and the T.C. dosent lock up. What can cause a Check brake indicator on a 1990? Thanks
  2. Blue85

    Blue85 Troll Premium Member

    Jul 26, 2000
    Likes Received:
    Grand Rapids area
    Re: \"Check Brake\" light on and Torque Conv. Not locking up.

    I don't have a '90, so I'm kind of guessing on this, but somebody has to reply to you, right? First you should check all the fuses to see if you popped any. The burning wire smell means that your grounding of the "F" terminal caused a short. In other words, with the new wiring setup, the F terminal must now be tied hot. I would guess that the old setup was for the ECM to provide a ground path to the solenoid for lockup and for the hot line to be through the brake switch. The polarity on the solenoid should not be reversed, so that's probably not what is causing this problem. You must have blown the fuse or taken out a wire that powers both of your brake switches or the lockup brake switch ans the proportioning valve. On older models, at least, that brake light is tied to a switch in the proportioning valve that indicates when you are bottoming it out in one direction (i.e. loss of pressure on one circuit). You should start there. You will need to change the wiring of your switch or the tranny to try to use manual lockup again, or just live without it. Until you get the lockup fixed, don't be using 4th gear or you are very likely to overheat the transmission. You won't hurt anything going down the highway in 3rd gear anyway, some trucks of the same year only had 3 gears anyway. Find out what wiring is in your new tranny and then this can all be solved.

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