The Other Side of the Pump - October/November - 2016

Tips for a Successful Converter Installation

When you’re playing a sport, sometimes it’s necessary to go back to basics to achieve your best performance. This applies to other things in our life as well. In this article, we’re going to look at the basics of converter installation. Following those basics will help to prevent the dreaded comeback and possible warranty claims.

The very first step in installing the converter begins before you even open the box: Check the rear face of the engine block where the transmission bolts, to make sure it’s clean and free of any paint or burrs. And check that the alignment dowels are in place and protrude far enough to index the transmission. If you removed the starter, make sure it’s clean and free of oil.

One of the most overlooked areas to check is the pilot pocket in the back of the crankshaft or flexplate adapter. 4L80 and A4LD/4L55 transmissions have had issues in this area. Make sure the pilot pocket is clean and free of wear, and then apply a light coat of grease to the pocket.

Inspect the flexplate for wear at the converter mounting surfaces and check for cracks. Tap the flexplate with a wrench: It should ring like a bell. If you hear any buzzing, the flexplate may be cracked.

Now to the transmission: Make sure the face of the transmission case is clean and free of paint and burrs, and there’s no wear in the dowel pin holes.

With this done, you’re ready to move on to the converter itself. Compare the new converter to the original, paying attention to the diameters and lengths of the pilot and hub. Remove any paint from the pilot, and make sure the mounting pads are the correct type and the threads are in good condition, clean, and free of paint.

You should also check that the fin angles are the same (figure 1). If there are any differences between the two converters, call your supplier to make sure it’s an acceptable change.

Now check the converter’s endplay:

  • Select a shaft or similar piece that’s larger than the input spline and smaller than the stator spline.
  • Invert the converter so the impeller hub faces down and use the shaft to push up on the input spline.

In general, you should have between 0.010” and 0.030” movement. Some converter models can vary, so, when in doubt, check with your converter supplier for the correct measurement.

Now you’re ready to place the converter against the flexplate and make sure the pilot and mounting pads are a good fit.

If everything checks out okay, you’re ready to prefill the converter with one pint to one quart of the fluid recommended for the transmission. Besides lubricating the converter bearings, this gives the clutch lining time to absorb the transmission fluid. Most converter remanufacturers don’t presoak their clutches, due to the many different fluids available. This makes prefilling especially important.

When installing the converter into the transmission, make sure you follow the manufacturer’s procedures, and be careful not to damage the internal seal. Lubricate the pump seal and bushing with fluid; not grease.

In some newer transmissions, such as the 6T70 and 6F50, you need to install the converter with the transmission held vertically. With other units, such as the 45RFE, rough installation can easily damage the plastic turbine hub-to-cover thrust washer.

As you install the transmission, make sure the mating face sits fully against the engine block, with the dowels installed correctly and no gaps between the mating surfaces before you tighten the bolts.

Push the converter all the way in to the transmission and measure the gap between the flexplate and mounting pads. On most units, this clearance should be between 1/8” and 1/4”. On stud-mounted converters, push against the end of a stud to force the converter back into the transmission and then pull the converter forward to the flex plate. You may find that starting a nut on the stud will make this easier.

If there’s too much clearance, you can add spacers between the flexplate and mounting pads. The spacers must be all the same thickness and you must make sure you have adequate pilot engagement.

Start all the converter bolts before final tightening. Never use an impact wrench to tighten the converter bolts; that’s likely to damage the converter. Use a ratchet or wrench. On units with blind mounting pads, make sure you’re using the correct length bolt and never overtighten.
Overtightening or bolts that are too long may damage the reaction surface for the lockup clutch.

When filling the transmission, always follow the manufacturer’s procedures. Modern transmissions have high capacity pumps and small fill tubes or fill ports, so it’s possible to run the pump dry and damage the pump and converter during the initial startup.

By taking a little extra time and care with your installation, you’ll prevent problems and save time and money in the long run.