Entering The Twilight Zone – Strange Problems - Transmission Digest

Entering The Twilight Zone – Strange Problems

Everyday technicians earn their living by solving complex problems. The modern automobile or truck has evolved into a very sophisticated machine in which all parts must function together to perform properly. This means that what used to be a simple three- or four-speed transmission has become entwined with systems that are computer controlled and where an antilock-brake system or suspension system that is not working correctly can have major effects on transmission operations.

Up to Standards

  • Author: Mike Weinberg, Contributing Editor
  • Subject Matter: Manual transmission
  • Units: NP 271, 273; NV 245; G56; 3650
  • Vehicle Applications: Dodge, Ford, Jeep
  • Issue: Diagnosis

Everyday technicians earn their living by solving complex problems. The modern automobile or truck has evolved into a very sophisticated machine in which all parts must function together to perform properly. This means that what used to be a simple three- or four-speed transmission has become entwined with systems that are computer controlled and where an antilock-brake system or suspension system that is not working correctly can have major effects on transmission operations.

Periodically I like to highlight problems that we have solved on the free tech line that is available to only our customers and that do not show up in any factory bulletins or fixes. You can’t make this stuff up, and you can’t find it on a website; it just comes from experience. We deal with a great variety of customers from all over the world. Most of them are professionals who are doing their best in a business that is now more complicated than brain surgery. Lest you think I exaggerate, consider this: The human body has not changed in millions of years, but our industry is changing daily. Brain surgeons NEVER warrant their work, and they can bury their mistakes.

NP 273 transfer case

Because of the huge variety of major weather issues that have occurred in the past several years, we are seeing a rash of electrical issues caused by immersion in water, either salt or fresh. Some epic problems have happened with uncommanded shifts into 4WD ranges, and the cause is damage to the encoder shift motor and the harness that connects it to the computer control module for the transfer case.

The most memorable of these is a 273 in a Ford truck that shifted at speed into low range at road speed. The computer in these vehicles will not allow a shift into low range at speeds above 3 kilometers per hour. What happens is that the computer will send stepped voltage to the encoder motor to regulate how far the motor will move. Saltwater corrosion in this case changed the resistance in the wiring and, unbelievably, the unit made an uncommanded shift into low range.

Even stranger is the fact that the shift to low involves unsynchronized shifting of components in the low-range planetary, which should be impossible at speeds over the design parameters. One way or another the shift was achieved, resulting in the vehicle blowing apart the rear of the transmission. Even more miraculous is that the driver, even though sideways, did not crash the truck and only mechanical damage occurred. In areas that were affected by severe weather or where people routinely back into water to load or unload a boat, it is critical for you to disconnect all harnesses that could have been underwater and check for corrosion, rust or other moisture-related problem.

NV 245 Jeep transfer case

Problem found: The unit will bind up when cold and be all right when up to operating temperatures. The 245 is found in 2005-2010 Jeep Grand Cherokees (WK) and 2006-2010 Jeep Commanders (XK). The solution that cures this problem is replacement of the encoder motor with a new OEM part and re-flashing the final-drive controller module (FDCM). We have yet to find the exact cause, but there is an NHTSA safety recall (Figure 1) on the same units (N23NHTSA 13 V-17S for a problem where the transfer case may unintentionally shift to neutral, making it possible for the vehicle to roll away. This is also strange, as there is no provision for a neutral position in the transfer case. The solution listed on the TSB is to reflash the FDCM, which leads one to believe that there are software issues at the root of both problems.

Dodge and Ford 271-273 transfer cases

These are the same units, with the 271 being mechanically shifted and the 273 shifted electronically. A common problem is the front case cracking from top to bottom between the main case and the front output shaft. Provided that all mounts and the cross member are in good condition, the problem is caused by a bad front driveshaft, with a worn CV joint allowing an out-of-round condition that whips the shaft until the case breaks. These are expensive repairs and a very expensive comeback. Go back to the basics and leave no stone unturned during the initial vehicle inspection. It is much easier to check and inspect U-joints than to examine a CV, but more and more driveshafts are being manufactured with CV joints and you really need to pay attention to every detail when inspecting and diagnosing a customer complaint. Victory loves preparation, and the time you spend on a really thorough vehicle evaluation will prevent comebacks and increase the dollar value of your repair orders.

G56 Dodge six-speed

In 2005 the G56 (Mercedes) six-speed (Figure 2) was introduced in the Dodge 3500 vehicles. The usual complaint is noise in neutral and in gear. The unit gets taken apart and inspected, and although some normal wear and tear is present there is not enough visual evidence to condemn the unit. The problem is usually found in the front countershaft bearing. The cup or race will look OK, but it is difficult to look at the inner race because it is a tapered roller bearing.

Solution: Pull off the front countershaft bearing (special puller required [Figure 3]) and cut off the bearing cage to get a good view of the inner race, which will be ugly. This problem may be caused by electrolysis when the inner race becomes a ground path for electricity through the unit. This can be solved by adding a good ground strap to the unit to prevent recurrence. Sometimes you need to do some destructive testing to discover an unseen problem. Many noise complaints occur because of the inability to see all the areas that can create the noise. Just looking may not solve your problem.

Ford 3650 five-speed transmission

The Tremec 3650 transmission (Figure 4) replaced the T45 in Mustangs. The 3650 is a solid, dependable unit, which has one problem: too much oil. When Ford originally signed off on the design, it placed the fill plug 1/2 inch too high. If you fill one of these units until it spills, there will be too much oil in it, causing notchy, dragging shifts. This happens because the extra oil causes a windage problem for the countershaft. When the clutch is disengaged during a shift the oil over-slows the countershaft, resulting in a timing problem for the synchronizers and causing hard, dragging shifts. The cure is to fill the unit 1/4-1/2 inch below the fill plug. Bend a pipe cleaner 1/2 inch, fill the unit and use the pipe cleaner to measure the fluid like a small dipstick. A lot of surplus 3650 units are being sold into the market, and a little knowledge goes a long way toward solving this problem.

Now, to the weirdest 3650 problem ever: A customer called complaining of a gear rattle between shifts. He had done a lot of work inspecting the vehicle. He tore down the transmission, carefully examined the clutch components etc. and was at his wit’s end. One of our technicians, knowing that gear rattle is usually caused by some form of engine harmonics traveling into the transmission and rattling the gears, asked the guy to check out the engine and the engine oil. Believe it or not, this 4.6-liter engine had only half a quart of oil in it.

By his own admission the customer had beaten this unit like a red-headed stepchild for more than 100 miles trying to figure out the problem. It turned out that the camshaft hydraulic tensioner was leaking. How did this engine not seize a bearing? How did the low-oil condition not show up with an oil-pressure warning? It defies all logic, but when the engine oil was topped off properly, the gear rattle stopped, the engine still performed well and everybody got happy. I thought I had pretty much seen it all, but every day you learn something new.

Yesterday is history and tomorrow is mystery, but one thing is sure: We have to leave no stone unturned in our quest for diagnostic perfection. Assume nothing; make sure you look at everything that can interact with what you are doing.

Mike Weinberg is president of Rockland Standard Gear.

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