Converter slippage still causes big problems Many requests have been called into the TCRA newsletter asking for any known ‘fix’ for that annoying code (converter clutch slip) on many Chrysler 518/618 trucks. It seems that after rebuild, the code may appear. As the converter rebuilder, you are the likely candidate. After verifying the correct clutch clearance, proper assembly, correct finish on the mating clutch surface, quality seals, and new friction liner, it cannot slip, right?
Well, let’s back up. Correct clutch clearance can vary in what the exact measurement will be. Most experts say .035-.05 is good. Any more and excessive clutch travel occurs. Then how about the finish on the mating friction surface; how smooth should it be? To prevent argument, a little rougher than a vinyl record is the proper surface roughness. Okay, find an old vinyl record in the basement and take a notice that it has approximately a 25 micron finish on the RM scale. And of course a new high coefficient of friction liner. Does that sound right? Yes, a high coefficient friction liner. In case you do not know which liner to use, most successful rebuilders will use a Sonnax red line, Raybestos tan liner, or Tri Component’s similar liner. Stay away from carbon or graphite liners, in these cases, because they do harbor a lower coefficient of friction.
Once this is done, the converter has been covered, and everything that can be done has been done. The converter is perfect, it is installed behind a stock Cummings diesel Dodge, and still the converter manages to slip under the throttle. Give your customer another one, same thing. The customer insists you do not know shift from shaft, and the customer hangs up on you. I know you all are smiling because you’ve been there.
After countless phone calls and the input from many experts, it has been determined there are multiple areas to direct your attention.
First, thank-you Dennis Weigle from Weigle’s Transmission in Dixon, IL, for telling us to install the appropriate replacement switch valve from Sonnax. Second, drill out the clutch release orifice located on the valve body separator plate. Use the correct high quality transmission fluid. To explain the why and what of these repairs could be quite lengthy. We will make it brief.
At the time of rebuilding, the valve body is disassembled and the aluminum relaxes to a normal state. After many heat cycles, the body shows some warpage. If not corrected, leakage internally is guaranteed. Clutch apply pressure is compromised and converter slippage occurs. By drilling the clutch bleed hole no larger than .062, pressure balance between apply and release is achieved.
Finally, the ATF must be checked because it is a factor that can easily be overlooked. When the old fluid in the transmission was used, it tends to thicken with age. Friction modifiers wear out and a much higher coefficient of friction is present. Changing to a new fluid alone can cause slippage. And when asked how the shop tried to fix this slip they say many times they added a ‘friction modifier.’ This compounded the problem. Stick with a high quality, not just a popular brand, ATF. If you must use an additive, use one that provides increased extreme pressure lubricants and viscosity stabilizers without a friction modifier. Over 21 additives make up the additive package of the average Dexron III and Mercon IV. We will cover more on correct fluids next month with information from leading ATF blenders/suppliers.