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Preparing for Your Installation

Vehicle Preparation

COMPUSHIFT Mini cannot properly operate a malfunctioning transmission. A malfunctioning transmission may damage COMPUSHIFT Mini and void your warranty.

Your transmission must be properly installed and in good mechanical condition before using COMPUSHIFT Mini.

A qualified transmission repair shop can inspect, clean, install, and/or rebuild your transmission as required.

If you have any questions about the condition or type of transmission, please contact a qualified transmission repair facility, HGM Headquarters, or one of our distributors for a recommendation.

Prior to installation, you should ensure that your powertrain, engine, transmission, drive shaft, rear axle, are all in good working condition.

The vehicle's electrical system should be properly maintained and working correctly. Battery voltage should be 14.4 - 14.7 volts while the engine is running.

The transmission should shift smoothly and correctly through its gears, and the shift linkage should be correctly adjusted.

Your transmission must have a properly-calibrated speedometer gear.

COMPUSHIFT Mini uses the industry standard 1000 turns per mile speedometer cable speed to determine speed.

A Word About Adjusting the TV Cable

A properly-adjusted TV cable can make a world of difference in transmission and engine performance.

Two things are important for setting the TV cable:

  1. Removing the slack
    • Proper slack in the cable means that the cable has a little bit of tension with the throttle is closed, but no so much that it changes in the main line pressure.As soon as the throttle starts to open, the line pressure should start to increase.
    • Proper travel in the cable means that the cable extends its full range when the throttle is moved to the fully open position, but no further.
  2. Setting the travel
    • If the cable fails to move the full range, then full line pressure won't be reached, the transmission may slip, and also the shift points may be too low.
    • A cable that moves too much will cause hard shifts that are too soon, can break the linkage in transmission, and can also prevent achieving a fully open throttle.

Getting both of these right means having the right combination of cams and arm length on the throttle linkage. Some accessory kits, like the Bowler Tru-Shift allow full adjustment and correction of TV cable problems.

The COMPUSHIFT Mini is a valuable aid in doing TV cable adjustment because it can display line pressure on screen in real-time. The cable travel and slack can easily be adjusted to their proper limits because:

  • When the pressure starts to increase, the slack has been removed.
  • When the pressure stops increasing, the cable is at its full extension.

GM 700R4 / 2004R

During the years that GM built these transmissions, a number of different combinations of internal switches and wiring looms were fitted. The transmission must have a proper internal wiring harness. It must use a 4th gear pressure switch that is normally open and switches to ground when 4th gear is engaged.

The following are recommended wiring looms:
  • Rostra 350-0045
  • NATPRO 51870U
  • TRANSTAR 54425B

The following are recommended 4th gear switches:

  • NATPRO 51876
  • TRANSTAR 74411B

Chrylser A518 / A618

Your engine must have a throttle position sensor in order to use the controller.  Aside from being in good, working mechanical condition, no specific preparation is required for this transmission.  

Additional Planning

Prior to installation, you'll also need to decide:

  • Where to mount your COMPUSHIFT Mini Controller.
  • Where to install the firewall grommets for your wiring harnesses.
  • How to route the wiring harnesses to the engine and transmission.

Other Considerations

  • COMPUSHIFT Mini can provide an electronic signal to operate an electronic speedometer.
  • Refer to the COMPUSHIFT Mini Quick Install Guide, also included in the packaging, to get an overview of all the components.

Tools You Will Need

  • 1/8" or 3/16" flat blade screwdrivers
  • Drill and small drill bit assortment
  • Socket / open-end wrench assortment
  • Wire cutters / wire stripping pliers
  • Soldering iron and solder or wire crimping pliers
  • PTFE / Teflon sealant or tape

Tools You May Need

Depending on the installation, you may also need:

  • File
  • Tin snips
  • Center punch
  • Sheet metal tools
  • Insulating tape
  • Wire spade lugs
  • Wire crimp connectors
  • 1.1875" hole saw or chassis punch
  • Volt/ohm-meter
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