Torque Converter Rebuilders Association

September 2010Issue 12, Volume 8

tcranewsletter@comcast.netwww.tcraonline.com

PLATINUM SPONSORS: Monthly publication of TCRA newsletter provided by Melissa Hall

TransmissionCertified

In last month’s article, technicians found that centrifugal force acting on oil trapped be-

tween the TCC piston and cover in the 722.6 converters was applying the clutch on cold start up. They also learned that the cold stall issue could be eliminated by forcing the oil out of the cavity between the piston and cover. Finding the root cause of the cold stall issue - and the subsequent fix - solved many other customer complaints and symptoms, including downshift shudders and tugging sensations. Several other customer complaints and symp-toms also are related to the same problem of oil becoming trapped between the piston and the cover. Brendan Patten at Jasper Engines & Transmissions in Willow Springs, Mo., was seek-ing the cause of complaints involving several Sprinter vans. Symptoms varied from flares on upshifts to vibrations around 15 MPH (especial-ly noticeable on slow U-turns) and to shrieking noises coming from the transmission pan. The noises proved to be caused by restricted filters, and were eliminated when the filters were replaced. The upshift flares were monitored on a scan tool, revealing that the TCC slip was increasing as much as 500 RPM on each shift. The TCC so-lenoid was then checked to determine whether it was being turned off or modulated during the shifts. The Solenoid remained on during all of the shift cycles. These diagnostics ultimately pointed to the integrity of the TCC apply circuit or to the converter itself. When the converter was inspected, exces-sive wear was found on the TCC frictions. The clutches did not visibly show the wear, but on the frictions it measured as much as .040” per clutch. (Figure 1) This created extra clearance that allowed the TCC piston to come into contact with the clutch hub, reducing TCC clamping force. (Figure 2) The vibrations caused by the TCC dragging at low speeds also contributed to excessive clutch wear. This wear was allowing TCC slip, felt in this case as flares on the upshifts. The material that was worn from the TCC frictions was responsible

for restricting the transmission filters. In short, all three Sprinter issues ultimately lead to the same TCC concerns. Although many of the mysteries surrounding the 722.6 converters were being cleared up, a few questions remained. The main one was: If the oil trapped between the piston and cover was causing the cold stall issue, why did install-ing different clutches seem to solve the prob-lem in some units? It helps to understand what’s going on if we compare what’s happening with the TCC apply piston to what happens to a disc brake system with a defective or out-of-adjustment wheel bearing. When a disc brake is working properly, there is a minimal amount of clearance between the brake pad in its released position and the brake rotor. In this position, the brake is ready for immediate apply. If the bearings which the rotor rides on become damaged, worn or out-of-adjustment, however, the rotor will not run true. Any wobble of the rotor creates extra clearance between the rotor and brake pad as the pad and corresponding piston are forced away from the rotor. This extra clearance will cause the brake pedal to travel further and possibly need to be pumped to complete the brake apply. There is a vast difference in the thickness uni-formity and parallelism of friction plates. A fric-tion plate with good thickness uniformity and parallelism will be more likely to have a cold stall issue if all other parameters are equal (no wobble effect). A friction plate that does not have good thickness uniformity and/or parallel-ism will have the same effect on the TCC apply piston as rotor on the disc brake piston. Special thanks to Wayne Russell, Russell Auto, Manchester, N.H.; Rick Morris, Professional Transmission, Marcy, N.Y.; Brendan Patten, Jas-per Engines & Transmissions, Willow Springs, MO; Milt Zemanek, A-1 Transmissions, Salem, OR, and Bob Warnke as well as Maura Stafford from Sonnax for helping to resolve this critical issue.

Ed Lee©2010 Sonnax

Mercedes 722.6: Cold Stall/TCC Shudder, Part 2

Figure 1 Figure 2Piston Contacts

Hub Here

Mystery converter returnsOnce again we have a converter that needs identifying. All submissions can be made by contacting any board member or by email-ing tcranewsletter@comcast.net. Thank you to Marcin at Florida Torque Converters for supplying this converter.

Pilot:1.376OA/HT:5.427Bolt Circle:10

Hub Height:1.944Pads: 3 with 2 holes

Torque Diameter: 8 3/8Hub Diameter: 1.692/1.688

Torque Converter Rebuilders AssociationPO Box 2546Reno, Nevada 89505

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Gold Sponsors:

Jeff Stuck ........................Presidentjstuck@certifiedtransmission.comEd Lee ..................... Vice President

ejl@sonnax.comKen Kelly ........................Secretary

kenktsi@comcast.netRick Morris .....................Treasurer

rick@professionaltran.comMartin Brooks

martin@aceomatic.co.nzRob Hans

robjdhans@hotmail.comChris Mann

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jmstimmel@yahoo.comLen Wack

lenw@embarqmail.com(973) 293-8925

The torque converter in-dustry has noticed a con-

tinuing increase of torque converter clutch piston crack-ing. Our first experience with converter clutch piston crack-ing was back in the early 1990s with the troublesome E40D piston. Since that very early learning experience there have been several other converter clutch pistons with cracking problems. We believe this problem will continue to escalate. Checking the pistons though vi-sual inspection is virtually impossible since most pistons are stamped out in a die and are subjected to imperfections. We have de-signed several fixtures to check the pistons for cracks. With a few things that you may have around your shop you can put a test fixture together. We used some old bonding dies. This saves you a lot of time because the dies are usually very close to the size of the piston you may want to check. For example, this is how we built a 4L80E test fixture: Cut a ¼ inch wide groove into the top of the die and approximately 1/8” deep. Glue a 1/4 inch O-ring into the groove. You may have an O-ring kit splicing kit to make your own O-rings, if not you can

Tech Tip: Clutch Piston Cracking

pick a kit up from MSC industrial the item number is 09270034. Drill and tap a hole into the side of your fixture and install an air pressure gauge and air regulator. Drill and tap three holes into the bottom on the outer most part of the fixture for the pur-pose of legs so that you have clearance un-derneath the fixture. The size of the legs is your prerogative. Drill and tap a hole in the bottom of the center of the fixture to accept ½” threaded rod. Install threaded rod into hole to approximately 3 -4” in height. In-stall flat washers and nuts on both sides of the die to secure threaded rod. Make your-self a ½” wing nut so that you can tighten your piston onto the fixture quickly. Install a turbine spline with O-ring in the center of the fixture over the threaded rod and se-cure with fasteners. Your spliced O-ring on the top of your fixture seals the bottom or outer most part of the piston and the tur-bine spline O-ring seals the center of the piston. We check the pistons at 5 psi with a little transmission fluid mixed with mineral spirits brushed on the outside of the piston. Cracks are easy to detect and you will also find a lot of rivets that also leak.

Rick MorrisProfessional Transmission