Turbo Diesel Register

106 www.turbodieselregister.com TDR 75 MR EDITOR – CAN YOU READ? G56 MANUAL TRANSMISSION WOES by Joe Donnelly Mr. Editor, thank you for bringing to my attention a recent thread on the TDR website forum concerning the G56 six-speed manual transmission used in '05 and newer trucks. I had followed the thread, but didn't contribute to it since my recent article in Issue 71 already gave my thoughts on the issues covered in the thread. However, these issues are important to the TDR members, and perhaps you did not search deeply enough in the article to discover them. Otherwise, you would not have asked for my response—again. Let's take this opportunity to summarize the problems with the G56 transmission described by members who have them in their '05 and newer Turbo Diesels. I will also outline solutions, or partial solutions to them. Justin Blackwell has a '06 Ram 2500, 4x4 truck. At around 25,000 miles, he added a programmer, which was later swapped out to the Smarty power-adder program. The South Bend OFE conversion single-mass flywheel and clutch was added at 27,000 miles. At 100,800 miles, his G56 started having a bad tick/rattle in the gears. He has owned the truck since new and changed the transmission lube at 25,000 mile intervals with ATF+4 (the factory recommended lubricant). His truck has about 10,000 towing miles, with about 1,500 of those miles being at 26,000# to 30,000# gross weight. Almost all of those heavily loaded miles were in fifth gear. The details he provided showed that he had not abused the transmission with such modifications as a high torque management setting on the programmer, or by clutchless shifting. His usage seemed pretty typical, possibly excluding the small amount of heavy towing. Maintenance by changing the lube was good. Standard Transmission in Fort Worth, Texas, told him that teeth were broken off of third, fourth, and sixth gears, and the transmission needed a new bearing kit. After the rebuild, Justin reported that the transmission shifted very well. He installed coolers at the PTO locations and added nine quarts of Amsoil. Another TDR member, "Okie-Go," has a '06 Turbo Diesel 3500. He reported that his G56 transmission started howling at 213,000 miles. He took it to nearby Blumenthals in Oklahoma City. The bearings and one of the synchronizers in the G56 were bad. Another member, CKelley1, reported that overfilling the G56 by one quart is essential. He feels that the dual mass flywheel contributes to the G56's problems. He uses Pennzoil Synchromesh fluid because the ATF factory fill gets burnt easily. He often tows heavy loads (44,000 pounds gross combined weight). He also recommends transmission coolers and insulation wrap on the exhaust pipe near the transmission. Eric Nafziger also has a '06 Turbo Diesel. He has a 3500 single rear wheel truck with TST and Smarty power adders as well as bigger injectors and twin turbochargers. His G56 failed at 103,000 miles, losing teeth off of fourth and sixth gears. Eric's analysis of the problem: A large percentage of G56 equipped trucks are having failures not far past the 100,000 mile mark. Failures seem to be 3rd, 4th, and 6th gears, the front mainshaft bearing, and case cracking at the bellhousing. I understand that the heat treating of the gears is too hard, offering wear resistance and hardness, at the expense of toughness. The aluminum case flexes too much, allowing the mainshaft and countershaft to separate, resulting in poor gear mesh and high tooth loading. The stock dual-mass flywheels are known to fail prematurely. The fix is to take it out and replace with a solid flywheel. ATF is different from a gear lube, and a GL-6 specification gear lube would be best. From Member's correspondence on the web and my ramblings in Issue 71, let's see if there is a consensus. Previously I had written: A fairly large number of sixth gear failures have occurred, and it may be that the mild 0.79 overdrive ratio causes more drivers to use sixth gear when towing heavy trailers, when direct drive (fifth gear) should be used. The dual mass flywheel has been problematic. . . Now, five years later we find that the South Bend clutch conversion (see Issue 68, p. 88) is a "standardized" replacement for the OEM dual mass flywheel and clutch. Performance of the G56 has been flawed, according to Charlie Jetton and Richard Poels of Standard Transmission & Gear in Fort Worth, Texas. In lighter duty and moderate towing, the G56 transmission has been adequate. Hot shotters and other owners who do very heavy towing have experienced failures. The G56 transmission often came with too little lubricant, and further that automatic transmission fluid may not be suitable under some driving conditions. A slightly "heavier" lubricant is better at the elevated temperatures that the transmission may experience towing or at higher ambient temperatures. They recommend that lubricants successful in the NV5600 such as Pennzoil Synchromesh be used. My NV5600 did very well with Torco RTF (Issue 67, page 87) and it should be an excellent lubricant for the G56. [Torco "Backfire" is a forum for corrections, clarifications, and further explanation. Yes, you're reading between the lines correctly. "Backfire" is a column where the editor gets to eat crow.

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