This original article was written by Dan the Gear Man around the turn of this millennia, but still holds true today. We have copied the original content from our first website, quad4x4.com. In addition to valuable content, it also is a "blast from the past" to one of our original website designs, and shows a common website format for that era. *copied in 2024, updates to original content are: images have been transferred to our current website, and links have been updated to current pages and available products* -The Torque King Historical Product Data Team
Causes of Catastrophic Manual Transmission Failures
By Dan the Gear Man™, 4x4 Tech, Inc.
|QUAD 4x4 is home to one of Americas top 4x4 drivetrain specialists, our own Dan the Gear Man™! Dan has over 30 years experience in maintaining and repairing 4x4 drivetrains and chassis components. Dan is a frequent contributor of tech articles for the Turbo Diesel Register and other national publications. He also wrote "Living in Pleasant Valleys Life in Carbon County Montana", a 170 page book that was a local best seller with five printings.
Catastrophic manual transmission failures are an expensive headache you can happily do without. Blowing your transmission apart while towing a heavy trailer at 70 mph is dangerous and very, very inconvenient. As you walk home or wait for the tow truck, you can ponder the sad fact that most catastrophic failures are easily preventable.
The worst killer of manual transmissions we see on Dodge Turbo-Diesel trucks is a small, often overlooked, $10 part that is not even part of the transmission. The pilot bearing or bushing is pressed into the flywheel. It’s function is to support the forward end of the transmission input shaft, keep the clutch disc centered on the flywheel, and allow the input shaft and flywheel to rotate independently of each other when the clutch is disengaged. Dodge used a thin bronze pilot bushing on 1989-1993 trucks and a small, needle type pilot bearing from 1994 on.
When a pilot bushing/bearing gets worn oversize or disintegrates, you may experience erratic clutch performance and/or shifting problems because the front of the transmission input shaft is essentially free floating. With a failed pilot, your transmission input shaft is no longer held in rigid alignment with the mainshaft and counter shaft. The gear on the input shaft transmits full engine power to the countershaft in all gears except direct (4th on a 5speed, and 5th on a 6 speed) so any misalignment will cause that power to be transferred from gear to gear with inadequate tooth contact. Given time, metal fatigue will weaken the gears until a catastrophic failure occurs.
Over the years we have tried various types of metal bushings, Kevlar bushings, needle bearings, and ball bearings in an effort to find the “permanent fix”. None of the metal or Kevlar bushings we tried consistently performed satisfactorily in Montana and Wyoming due, I believe, to dust, dirt, and grit getting between the bushing and shaft. The original, single seal pilot bearing Dodge introduced for the 1994’s quickly lost it’s lubricant and many failed within 50,000 miles. About 1998, Dodge started using a wider bearing with a seal on either side. This bearing appears to have at least twice the life of the original single seal bearing, but it is still less than the life of most clutches. We then tried boring the flywheels to accept standard 3/4” ID ball bearings. Much to our surprise, the thin inner race of standard series ball bearings quickly broke apart. Finally, when we were about ready to admit defeat, one of our suppliers sent us some ball bearings with thicker races. These special bearings (p/n QU51010) have performed flawlessly in every truck we installed them in.
Refilling the transmission with the wrong lubricant is becoming more common all the time. Part of the problem is the plethora of manual transmission lube choices. The G360, NV4500HD, and NV5600 all use radically different lubricants. Fortunately, using the wrong lubricant usually causes shifting problems (particularly with the NV4500HD) long before total failure occurs. Regular automatic transmission fluid may work great in your buddy’s Ford Ranger 5 speed, but it will probably make your Dodge, Ford fullsize, or GM truck transmission self destruct.
|Full Size Transmission Model
|GM & Dodge NV4500 5 spd
|Castrol SyntorqLT 75w85w
|Dodge NV5600 6 spd
|Texaco STF or Pennzoil Synchromesh
|Dodge Getrag G360 spd
|5w30 (Synthetic preferred w/Diesel)
|Ford ZF42 & ZF47 5spd
|Synthetic Mercon/Dexron III
|Ford ZF-650 6spd
|6.4 qts w/cooler
|Ford Mazda M50D LD 5 spd
|GM ZF S6-650 6 spd
|GM Synthetic 12378515
Over the years, we have worked on many transmissions that were run out of oil when the transmission oil level wasn’t checked periodically. The G360 and NV4500HD have a common problem with leaking rear seals, while the NV5600 seems to have an affinity for losing oil from the input seal. These types of leaks are usually rather minor, but the fluid loss can become very significant over time. A loss of a couple of quarts or more will stop you about as quick as a landmine because no 5 or 6 speed manual transmission is very forgiving of high loads and low oil levels.
Oil from leaking NV5600 input seal collected at bottom of bellhousing
One of the laws of vehicle preventative maintenance states “changing oil is cheaper than changing iron”. Over the years, I have found few Dodge owners violate that rule with their Cummins engine, but many never apply it to the transmission. How often should you change the transmission oil? For most years, Dodge does not even have a recommended manual transmission oil change interval. However, back in 1993, Dodge did recommend changing the Syntorq LT™ transmission oil in NV4500 equipped trucks at 18,000 miles for severe service and 36,000 miles for normal service. Those intervals are what we recommend for all manual transmissions bolted behind a Cummins engine. If you use a manual transmission filter kit like our QK1000, which has powerful magnets combined with a simple, but astonishingly effective filter to cleanse the oil of both magnetic and non-magnetic particles, the oil change interval can be extended by 6,000 miles for severe duty, or 12,000 miles for normal service. Filtering the oil is especially important on NV5600 transmissions to remove bronze particles worn from the synchro rings.
Debris caught by QK1000 manual transmission oil filter on NV4500HD. Transmission was run with low oil after stock tailshaft housing shown above cracked from extra weight of auxiliary transmission.