Shop Talk - September - 2019

Touch Your Nose with Your Tongue and Wiggle Your Ears

Math problems can be a challenge for many. You know the ones: Mr. Jones is traveling north on the Pike express traveling at 60 mph. Mrs. Smith is traveling south on the Fargo Flyer traveling at 70 mph. They’ve both been traveling 20 minutes on their 200 mile journey. How long before they can wave hello to each other? This math problem is about as clear as the GM clutch clearance procedure for the 8L90. In fact, it’s so confusing that you might just skip it entirely, or worse… get it wrong.

Using the idea that “Just about everything meaningful can be put in a pamphlet,” we’re going to strip away the confusion and make this process simple. First, you’ll need some special tools. Figure one shows the tools for the various procedures and figure two shows the part numbers, description and cost of each tool. There’s also an item number shown which is just for reference. We’ll use those numbers as we cover the procedure. There’re a couple of good things to know: You won’t absolutely need every one of these and it’ll be apparent as we proceed. The dial indicator is probably something you already have so there’s no point in spending $250 on the one they use. And finally, you can find great deals online from people who have given up trying to follow GMs instructions. The cost for all of the tools through Kent Moore is about $1,300 but depending on what you decide to use and the deals you can find you can keep it under $500 to get through this.

There are four drums with selective snap rings and procedures. Once you understand how to do one you can figure out the others pretty easily. For this example we’ll cover the 2-3-4-6-8 clutch clearance. For this you’ll use tools 1, 2, 3, 4 and 7 from the chart.

Let’s begin. Assemble the drum and tools as shown in figure two. We’re using the 2-3-4-6-8 clutch since it’s a bit easier to see the tools in use but there’s another clutch that’s deeper in this drum (4-5-6-7-8-Reverse clutch) and you’d follow the same procedure for it.

Where the factory procedures fall short right away is the process for checking the wave plate. When you consider that the wave plate is part of the clearance factor there’s an easy solution – replace it every time. The cost of a new wave plate is well worth the time and aggravation for checking it.

Next, make sure the three feet of tool #2 are resting on the pressure plate. Now, adjust the fixture screw until you achieve 80 lbs. of force to the pressure plate. This procedure will compress the wave plate and clutches to a specific point. Place your dial indicator on the pressure plate while it’s still compressed. Then zero the indicator.

Release the force on the pressure plate. Now you have two options: blow air into tool #4 to lift the pressure plate up against the snap ring and check the reading on your dial indicator. If you don’t have tool #4 you can reach in and lift the pressure plate up against the snap ring to get your measurement. The tool is pretty reasonable and works great for air checking so I think it’s worth the cost.

From here, just look at the clearance specifications and select the right ring to get the proper clearance (figure 4). There are two tools we didn’t use #’s 5 and 6. They’re used for checking the 1-2-3-4-5-Reverse and the 1-3-5-6-7 clutch, respectively.

Like most everything, it’s easy once you figure out the instructions and what the authors wanted. And as far as Mr. Jones and Mrs. Smith? They were waving at each other 72 minutes later.