1971 Pontiac Firebird - Driveshaft U Joint Replacement - Tech

QUESTION
I have a '71 Firebird that sees a lot of street/strip action. It's got a hot 400ci V8 with a TH400 trans, 2500-stall converter and 3.73:1 rear gears. After cruising it for the past year or so, I've noticed that each time I put the car in gear, I hear a clang coming from somewhere underneath. Sometimes I even hear it clanging while I drive. The trans and converter are new, so what could the sound be? Lee Kerr Oil City, PA

ANSWER
By John Kiewicz

The loud "clang" noise is probably coming from the driveshaft universal joints. The noise is generated because the U-joints are severely worn and are moving around within the driveshaft yolk assemblies. This is extremely bad and potentially dangerous. The U-joints are shot and need to be replaced. If Lee's engine is as hot as he says, one good launch at the dragstrip will likely destroy the clanking driveshaft assembly. And if the Firebird doesn't have a driveshaft safety loop, a nasty crash will likely occur when the U-joints break.

Being that U-joints are an overlooked hop-up amongst street machiners, chances are that the units in Lee's '71 Firebird are stock. The stock units were medium-duty U-joints at best, which were not designed to handle the rigors of stout street/strip use. Upgrading the driveshaft with new U-joints is a step in the right direction, but what really should be done is an upgrade to heavy-duty units that can handle the hard-launching abuse inflicted by today's high-horsepower street machines.

Here, we follow along as the driveshaft experts at Wenco Industries show us how to install new heavy-duty Lakewood U-joints in Car Craft's project Cheap Street Chevelle. At the dragstrip our rig runs low-13-second times on slicks and 12.20s on nitrous. Our U-joints weren't making noise yet, but we wanted to replace them with heavy-duty parts before they started acting up. We advise that the driveshaft be balanced and checked for straightness while it's out of the car, and that's just what Wenco Industries did to ensure that our driveshaft performs properly for years to come.

1. We ordered new driveshaft universal joints (PN 23013) from Lakewood Industries to replace the stock units in our project Cheap Street Chevelle. The Lakewood U-joints are made of high-strength alloy and have heat-treated needle bearings made of high-carbon steel. Lakewood performance U-joints are not cross-drilled, which helps them withstand the rigors of harsh racing conditions. Lakewood U-joints are available for most O.E.M. uses as well as for non-O.E.M. drivetrain conversions.
1. We ordered new driveshaft universal joints (PN 23013) from Lakewood Industries to repla
2.Begin the U-joint swap by removing the driveshaft from the vehicle. Be sure to support the car with a sturdy set of jackstands--don't just rely on a floor jack to hold the car's weight.
2.Begin the U-joint swap by removing the driveshaft from the vehicle. Be sure to support t
3. Use an old piece of pipe or a large-diameter socket as a low-buck U-joint removal tool. Place it under one end of the driveshaft. It will support the yolk assembly but allow the U-joint cap to be pushed out.
3. Use an old piece of pipe or a large-diameter socket as a low-buck U-joint removal tool.

4. Using a pair of needle-nose pliers, remove the snap rings that hold the U-joint caps in place. Then use a punch (or even a socket extension) and a hammer to drive the U-joint downward. As the U-joint moves, it will push the U-joint cap out of the yolk assembly and into the pipe/socket support. Rotate the driveshaft 180 degrees and remove the other U-joint cap in the same way. With both caps removed, angle the U-joint slightly and remove it from the driveshaft.
4. Using a pair of needle-nose pliers, remove the snap rings that hold the U-joint caps in
5.Once the U-joint is removed, carefully inspect the driveshaft end for cracks and/or damage. Use a small metal pick or a thin screwdriver to remove any gunk buildup in the snap-ring retainer groove.
5.Once the U-joint is removed, carefully inspect the driveshaft end for cracks and/or dama
6.Carefully remove the U-joint caps, making sure you don't knock any of the small needle bearings out of position. Then angle the new U-joint and slip it into the driveshaft yolk. Install one of the U-joint caps and slowly tap it into position with a hammer. Only tap the cap far enough to clear the snap-ring retainer groove.
6.Carefully remove the U-joint caps, making sure you don't knock any of the small needle b

7.Use a pair of needle-nose pliers to install the new snap-ring retainer clip. Rotate the driveshaft 180 degrees and tap the other U-joint cap into position (as shown earlier). Now install the other snap-ring retainer.
7.Use a pair of needle-nose pliers to install the new snap-ring retainer clip. Rotate the
8.To remove the front U-joints from the transmission yolk, begin by supporting the driveshaft with a brace. (We used a scrap piece of iron.) Remove the snap-ring retainer clips from the driveshaft and yolk. Hold the end of the snout and tap on the yolk with a hammer. As you tap, the U-joint cap will push itself out. Rotate the driveshaft 180 degrees and do the same for the other side.
8.To remove the front U-joints from the transmission yolk, begin by supporting the drivesh
9.With the two U-joint caps pushed up, angle the yolk slightly and remove it from the U-joint. (The U-joint will remain in the driveshaft.) Then remove the other two snap-ring retainer clips and use a hammer to tap out the remaining U-joint caps (as shown with the other end of the driveshaft).
9.With the two U-joint caps pushed up, angle the yolk slightly and remove it from the U-jo

10.Install the new Lakewood U-joint into the driveshaft (as shown with the other end of the driveshaft). Secure the U-joint in position with the supplied snap-ring retainer clips, then angle the yolk and slip it onto the new Lakewood U-joint.
10.Install the new Lakewood U-joint into the driveshaft (as shown with the other end of th
11.Position the new U-joint end caps in the yolk and carefully tap the cap downward until it clears the snap-ring retainer groove. Install the new snap-ring retainer clips and you're done. Move the yolk and new U-joints to make sure that everything actuates smoothly and nothing binds.
11.Position the new U-joint end caps in the yolk and carefully tap the cap downward until
12.Whenever you do driveshaft service work (such as installing new universal joints), it's an extremely good idea to have the driveshaft checked for straightness and balanced. Even if you install new U-joints, if the driveshaft is bent or out of balance, the new parts will wear prematurely. In addition, your car will experience weird vibrations at various road speeds. The folks at Wenco Industries perform full driveshaft service, including driveshaft straightening and balancing. Balancing usually costs about $35, straightening is roughly $15 and U-joint installation is $7.50 per unit. If your driveshaft needs to be shortened, Wenco can usually perform the work in one day for about $35.
12.Whenever you do driveshaft service work (such as installing new universal joints), it's

13.Just as your wheels do, driveshafts use add-on weights to achieve proper balance. However, unlike wheel weights that clip on, the driveshaft balance weights are welded into place. This ensures that they will remain in position when the driveshaft spins at high rpm.
13.Just as your wheels do, driveshafts use add-on weights to achieve proper balance. Howev
14.While the driveshaft is out, it's a good idea to use a center punch to mark the position where the yolk aligns with the driveshaft. By doing so you'll know where the original yolk-to-driveshaft alignment was in case driveshaft service is needed at a later date. If for some reason the driveshaft needs to be shortened or a new driveshaft end needs to be installed, the marking will serve as a reference point for alignment. Maintaining proper alignment will ensure the correct phasing of the driveshaft ends, which is critical for reliable, trouble-free operation. (Out-of-phase driveshafts wear U-joints at an accelerated rate and can add harmonic vibrations to the drivetrain.)
14.While the driveshaft is out, it's a good idea to use a center punch to mark the positio
15.Carefully inspect the end of the driveshaft yolk that slips into the tailshaft of the transmission. If it is heavily scratched or gouged, you should replace it. Many times, if the end has minute scratches or a built-up glaze on it, you can use a piece of emery cloth as a low-buck micropolisher. Just be sure not to sand so much that you reduce the outside diameter of the yolk snout.
15.Carefully inspect the end of the driveshaft yolk that slips into the tailshaft of the t