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  • DIY: Converter Lock Up with Brake Pedal Release

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    Torque Converter Lockup Switch with Brake Pedal Release System


    What it will do


    This system can keep the torque converter locked in 3ed or 4th gear.  With a modification to the valve body 2ed gear can be locked up.  When driving normal freeway speed the torque converter can be locked up with the momentary switch and stays locked up.  The transmission stays in direct drive even when the accelerator pedal is released, there is no freewheeling, RPM level is maintained and torque converter unlock is done with either pushing the momentary switch again or pressing the brake pedal.  


     When going up long grades select 3ed gear, overdrive locked out, then lockup the torque converter with the momentary switch.   I have found that by doing this I see very little rise in the transmission temperature with a decrease in exhaust temperature of 200o F.  Unlocking the torque converter is done again by pressing the momentary switch or brake pedal.  The trans mission will up shift from 3ed to 4th  but will not down shift from 4th  to 3ed with the torque converter locked. 


    When go down a long or steep down grade the locked up torque converter will help in slowing but without the added benefit of an exhaust brake.  Another switch* is incorporated in the system which will lock up the torque converter and stepping on the brake pedal will not disengage the lock up.  


    How it works


    The system uses three switches, two relays and a light.


    The first is the momentary switch.  This switch is used to signal the transistor in the switching relay to either power the coil and close the contacts allowing power to flow between pins 15 and 87 or stop the power to the coil and open the contacts. 


    The brake light switch is three switches in one: brake lights, cruise control and anti-lock brake system.  The anti-lock brake system grounds through this switch, white/pink wire, and is closed circuit until the brake pedal is depressed making it perfect for grounding terminal 85 of the switching relay.  When the transistor loses its ground it turns off the power to the coil and the contacts between pins 15 and 87 open stopping current flow to the grounding relay.   


    The 3ed switch* can either be floor mounted or dash mounted.  This switch is used to energize the grounding relay and light. This keeps the torque converter locked when using the brakes.  I use a floor mounted head light dimmer switch to turn it on and off.


    The switching relay is used to control the power to the grounding relay coil with the use of the momentary and brake light switch.  This relay is used in 1981-1988 Volvo models 240 and 740 that had 5 speed manual transmissions with the overdrive 5th gear is a Laycock overdrive unit and provided power to the hydraulic solenoid.


    The grounding relay is used to open and close the circuit that grounds the torque convertor solenoid via the orange/black wire at PCM connector B11.  Since this relay is used as only a grounding switch its power rating can be minimal. 



    There is a light add to the system that is on anytime there is power supplied to the grounding relay and the torque converter is locked up.  I used a green LED light so that the color isn’t annoying and power usage is low.



       Parts needed


    1 overdrive relay for a Volvo manual 4 speed w/od (M46)   

        IPD.com  part# 102250


    1 Bosch type/mini ISO relay terminal 87 normally open (NO)


    1 12V LED light, Linrose Superbright LED

        Frys.com  part# B2191L5


    1 push button momentary switch, Phillmor Push Button green

         Frys.com   part# 30-12634



    1 headlight dimmer switch

        O’Rielly.com  part # DS109


    1   ½ watt 33ohm resistor  NTE HW033

          Frys.com  part# 999026


    1 fuse holder with 1-2 amp fuse


    6 Scotch Lock connectors


    2 #8 X 1½” self-taping sheet metal screws 




    Heat shrink tubing


    1 central lock motor harness from a 1981-1993 Volvo model 240.  The wire harness is found behind the center of dash.


    1 overdrive relay harness from a 1982-1993 Volvo model 240 with either manual or automatic transmission.  The wire harness is found above left front kick panel for manual trans or behind right center of dash for automatic trans.


    1 shift lever from a 1998-2002 Dodge Ram 1500, 2500, 3500, Dakota or Durango.


    If you’re making the wire harness


    11 solderless insulated female spade connectors .25” sized for wire gauge


    3-4 solderless ring terminals sized for wire gauge and grounding screws.


    18-20 AGW  stranded  (16 AGW will work if you can’t find smaller) in different colors. Try Home Depot or Lowes electrical department.





    Putting it all together


    Study the wiring diagram and have all of the parts in hand before starting the installation.  Most of the wire length is from 6” to 2’.  The wires for the light and the floor switch will be 4-5’ depending on where you put them.  The wire from the grounding relay to the PCM will be about 8’.  The power lead with fuse can be attached to any wire that is hot when the key is turned to the “on” position.  The power draw should be between 1 and 2 amps; with the system having its own fuse, there should be no problems.  Install the ½ watt 33 ohm resister between pin #87 of the grounding relay and ground by cutting the wire and soldering the resistor in place.  


     I used the wire harnesses and relays from old Volvos that were in a wrecking yard. I modified the wire harness and added extra wire for the longer runs.  An extra shift lever can be obtained at the wrecking yard for a few dollars also. 



    Installing the momentary switch: refer to article written by Me78569

    DIY- Lockup Switch install into Gear Selector Arm. 

    This is a great how-to article on installing a momentary switch in the gear selector.  If putting the switch in the gear selector arm is a bit difficult then try installing it on the steering column cove or some were on the dash board bezel that’s easily reached.




    You will need to remove the panel below the steering column, the dash bezel and the head light switch for the relay installation and wire routing.  The left A post cover will need to be removed if the light is going to be installed there.  Take your time and identify what wires are going where, think two or three times before cutting any wire.  You should not have to cut any of the truck factory wires.  The only wires that need to be cut are the ones you are adding.  





    Find where you want to put the relays and LED light.  I put my relays behind the bottom panel under the steering column and worked out from there.  I have my LED light mounted next to my transmission temperature gauge.  It’s at eye level and I just have to glance at it to see if the torque converter is locked or not.  The light on JAG1’s truck was installed in the dashboard bezel between the headlights switch and instrument cluster.  You will need to drill a hole through the plastic then slide the light housing into the hole and secure it with the supplied clip.  Once the light is secured the wires can be connected and the bezel refitted.




    The 3ed switch* for energizing the grounding relay is mounted on the floor left and forward of the brake pedal in about the same spot the headlight dimmer switch was located back-in-the-day.  I mounted this by putting the switch on top of the carpet and drilling through the floor pan with the self-taping sheet metal screws.  

    A toggle or push button on/off switch could be used and installed on the dash bezel if the floor mounted switch is not to your liking.



          * Caution:  coming to a full stop with the torque converter locked will stall the engine and could cause damage to the flex plate, input shaft or other driveline parts.



    Prepared by:  J. Daniel Martin / Martin’s Mobile Maintenance

    AKA: IBMobile





    • Like 5
    • Thanks 4

    User Feedback


       1 of 1 member found this review helpful 1 / 1 member

    Very good write up. A tremendous amount of work went into this article. I appreciate also the work Daniel did on my truck while accomplishing this Mod. It's nice when hauling heavy on mountain curves to be able to stay locked up and not need the brakes much. It affords a time too, reminiscent of my younger days running my old first gen I drove for many years and loved the feel driving a real truck with its 5 speed transmission.


           One must consider also that if your getting a bit older when coming to a stop. even though I'm getting used to Daniels beautiful two switch system, I use it with caution because having a green lite does not always remind you that your locked up. Esp. when the system is first installed its easy to forget.

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    Thanks for the detailed write up, I've been wanting to do this for quite sometime, this detailed description sums it up well. going to move this up on the priority list.

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