Drivetrain Q & A

January 1, 2002
Filed under Trailer How To

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Rear-Axle Chatter

Q. We have a 1997 Ford Expedition powered by a 5.4-liter engine. It’s used mostly to tow our 26-foot travel trailer. For the last few months, there’s been a chattering noise that comes from the rear end when I’m turning a corner. It seems worse on tight turns. The rear end has a limited-slip differential. My dealer tried changing the fluid, but it didn’t help much. Do you have any ideas?

- R.M., Fort Lauderdale, Florida

A. Ford has published a Technical Service Bulletin (TSB), no. 98-11-7, dated June 8, 1998, that may apply to your problem. It covers 1997 and 1998 E-150, Expeditions, F-150, F-250 LDs and 1998 Lincoln Navigators. The TSB calls for replacement of the Traction-Lok clutch pack. This may be due to differentials containing clutch packs that have been “gauged” too tightly. Ford will cover this under the provisions of the bumper-to-bumper warranty.

- K.F.

Slammin’ Upshifts

Q. I have a 1997 GMC 1500 pickup with a 4L60E automatic transmission. It’s been having trouble with upshifts from first to second gear. It slams into gear. When the engine is turned off and restarted the problem goes away temporarily. I have had the truck into the dealer three times with no solutions. The transmission fluid and filter have been replaced regularly. Now the dealer is telling me I have to get a new transmission. The warranty is expired-it figures. Do you have any advice?

- J.L., via e-mail

A. When a dealer doesn’t know what to do, he/she often recommends replacing everything. From your description, it seems like the transmission is going into “limp-home” mode. Your truck’s computer has an OBDII self-diagnostic system, which monitors the engine and transmission. If the computer detects a sensor-input signal that is outside of normal parameters in its software, it can put the transmission into a pre-programmed “limp-home” mode that causes harsh shifts (among other things). The fact that it goes away temporarily on a restart is one of the clues.

You didn’t mention if the “Malfunction Indicator Lamp” (MIL) comes on, or if the computer has any stored trouble codes. I suggest that you take the truck to a transmission specialist or a General Motors dealer that has a good reputation and has complete electronic diagnostic equipment. The truck should be driven with a scan tool connected that has a “snapshot” mode that can save the readings taken during a malfunction. I’m sure this will find the gremlins.

- K.F.

Axle Splitters?

Q.
We have a 1996 Dodge Ram extended cab with a V-10 and four-wheel drive. I would like to know if any of your advertisers sell a split rear-end gear system? I am having a hard time finding this information. We tow a 32-foot fifth-wheel and starting out is a big strain on the automatic transmission. I have seen this two-speed rear end before but can’t find it now.

- E.C., Manteca, California

A. A two-speed rear axle won’t work when four-wheel drive is engaged because you would need a two-speed axle at each end. Two-speed rear axles are not available as a factory option on any light trucks nor are they available for them in the aftermarket, to my knowledge. Two-speed rear axles are used on medium-duty trucks with manual gearboxes. When they are shifted, all power must be taken off the two-speed axle by depressing the clutch. Therefore, they don’t work well with automatic transmissions, which would have to be shifted to neutral first, the axle shift completed, engine revs brought back up and then transmission shifted back into drive each time.

What you probably recall is the two-speed auxiliary transmissions, which are also referred to as “gear splitters.” To get a lower ratio in low gear, you would need an underdrive-type gear splitter. Auxiliary transmissions have been written about in Trailer Life a number of times, including a buyers guide in the June 1996 issue. Information on ordering copies may be obtained by calling (805) 667-4366.
- K.F.

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