Dorman Driveshaft Assemblies

“I have [a] 2006 Sprinter 2500. A mechanic tells me that I have u-joint problems which means I have to replace the whole unit all the way back since the u-joints are welded.” This quote from a forum thread is referring to original equipment (OE) driveshafts with non-serviceable universal joints. If a u-joint fails, then the entire driveshaft and all the parts attached to it must be replaced. This can be expensive, especially for a high mileage commercial vehicle that may go through several sets of u-joints in its lifetime.   

RockAuto’s selection of driveshafts now includes complete driveshaft assemblies by Dorman. Dorman driveshafts are engineered with serviceable universal joints. This means if a u-joint ever fails in the future, the owner can simply replace the u-joint instead of again facing the expense of replacing the entire driveshaft assembly.

New Year's Resolution

Now take an even closer look to verify that a part is the one you need. Adding a zoom feature to many part images on the "Info" pages was one of the catalog improvements RockAuto started implementing in 2014. Making the catalog better for customers is RockAuto's ongoing New Year's Resolution. Watch for more catalog upgrades in 2015!

Forum of the Month

Established in 2006, SN95Forums.com is a forum dedicated to 1994-2004 Ford Mustangs. The forum offers informational discussion on topics ranging from the engine and drivetrain to all things tech-talk, to race and performance. If you have a question regarding a 1994-2004 Ford Mustang, look no further than SN95Forums.com for your answer. If you are not already a member, register and get involved today!

Repair Mistakes & Blunders

In 1973, I got my first "real" mechanic job working at a local brake and muffler shop. I was happy to find out that I was under the tutelage of an old family acquaintance that I used to race slot cars with when I was youngster. Being the senior mechanic, John would delegate more complex jobs to me as my skill set improved. One day, a 1968 Cadillac Coupe De Ville came in with rusted mufflers (a common thing in New Jersey), and so he instructed me to "cut down that exhaust..." while he went for lunch. So, with the acetylene torch in hand, I promptly obeyed and proceeded to remove every bit of exhaust: hangers, mufflers, tailpipes, cross pipes etc.

When John got back from lunch he was horrified to see what I had done, since most of the hangers were special order from the dealership only.

The moral of the story: be very specific when dealing with a young apprentice and a torch.

Joe in California

Tell us about your most infamous auto repair blunder or unconventional fix. Use your woe to help others avoid similar mistakes or share off-the-wall solutions that worked (at least for a while!). Please e-mail your story to flamur@rockauto.com. Include your mailing address and if you would like a RockAuto T-Shirt (please let us know your shirt size) or Hat if we publish your story. See the T-Shirts and Hats under Tools & Universal Parts in the catalog. The story will be credited using only your first name and your vague geographic location (state, province, country, continent, etc.) so you can remain semi-anonymous!

Automotive Trivia

The Ford Model T came from the factory in which of these colors?

A. Black
B. Blue
C. Drake Green
D. Royal Maroon
E. All of the above


Answer below

I Will Just Call Them All 4WD

The tires on my wife’s ’93 Ford Tempo have three different tread patterns, tread depths and brands. This two-wheel drive (2WD) car is mechanically happy as long as the same tire size is printed on all the tire sidewalls. However, running a similar hodgepodge of tires on a modern four-wheel drive (4WD) or all-wheel drive (AWD) vehicle might seriously damage the transmission or other costly parts. With many modern 4WD systems, it is very important to replace tires as a set of four and to regularly rotate the tires so they wear evenly.

Tires worn to different tread depths or even new tires of the same size but made by different manufacturers will have slightly different outside diameters and rotate at slightly different speeds. Tires also turn at different speeds every time a car turns a corner so it is hard to understand why a relatively small difference in tire rotations per mile could cause problems for a 4WD system.

Mom often helps when I am confused about something, so I will start with my mom’s first 4WD vehicle, an ’86 Ford Bronco. I knew when the Bronco’s 4WD was engaged because I had to move a lever and climb out of the truck to manually lock the front hubs. When turning a corner, all four of the Bronco’s wheels were rotating at different speeds. The front and rear differentials allowed wheels on the same axle to safely rotate at different rates. But, in 4WD the front and rear axles were also connected to each other via the driveshafts and transfer case. During a turn, the wheels on the front axle wanted to move faster than those on the rear, but the front driveshaft could only rotate as fast as the rear driveshaft. The driveshafts prevented the front wheels from rotating as fast as they needed to.

This binding up of the drivetrain did not cause problems in the dirt, rain or snow because the Bronco’s tires could slip slightly on the slick surface. But, driving the Bronco on dry pavement meant the front wheels would hop and extra strain would be put on the drivetrain during turns. Driving the Bronco on dry pavement for a few car lengths was not a problem, but driving it in 4WD on a dry freeway at 60 mph (100 kmh) would have damaged the u-joints, differentials, transfer case or other drivetrain parts.

Jump forward to vehicles of this century. Both cars and trucks are now likely to have 4WD systems that are always engaged. Part-time 4WD like that on the ’86 Bronco is harder to find. The differences between many modern 4WD and AWD systems have become murky, so I will just call them all “4WD.”

Today’s always-on 4WD systems must avoid binding up during cornering like that old ’86 Bronco did, and they must send power to the wheel(s) that still have traction. One common way to do that is to have a transfer case or center coupling filled with clutch packs, viscous fluid or some other components designed to compensate for tire slippage and prevent drivetrain bind-up. The energy of spinning tires or binding parts is often converted to heat. For example, if one tire is spinning then a viscous fluid heats up, thickens and pushes together a clutch that directs the power to another tire that still has traction.

Tires with slightly different diameters moving at different RPMs can damage these 4WD systems by overheating the center coupling. Always-on 4WD systems are designed to drive long distances on dry pavement. However, they are not designed to handle thousands of miles of non-stop tire slippage or thousands of miles of left or right turns, and that is what tires with different diameters simulate.

There may be some modern 4WD systems with center differentials and computer systems designed to safely compensate for tires with larger differences in diameter. 4WD systems vary greatly between manufacturer, model and model year. Following what the specific owner’s manual says about tires is a good idea, but it is always safe to have a set of four matched tires. Anti-lock brake systems (ABS) and limited-slip differentials found on 2WD vehicles also work better with tires of the same diameter. Even my wife’s Tempo would probably handle a little better if all four tires were a little more alike!

If this article came too late or if you are ready to upgrade your car or truck, then find new differentials, transfer cases, u-joints, axles and other 4WD parts under “Drivetrain” in the RockAuto catalog.

Tom Taylor,
RockAuto.com

To read more of Tom's articles, click this link and choose from story titles on the Newsletter Archives page.

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