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Project Corvette u-joint replacement

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Project Corvette is finally on the road after 2 years of downtime. The repair list is long and extensive, but only fair due to the fact that after many years of neglect (i.e. not driving consistently), the C3 (1968-1982) Corvette was showing its age.

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Case in point, after removing a leaky transmission in Project Corvette, it only made sense to restore the driveshaft.

Most muscle cars rely on a standard slip yoke, where in quick fashion you can dislodge the differential connection and slide the driveshaft out of the transmission tail-housing with the yoke still attached. This method definitely saves time, but Project Corvette employs straps to secure the u-joint bearing caps to both the transmission yoke and differential. To drop the ‘shaft, you must disconnect the straps. Though it sounds like an easy in and out procedure, the C3 has a tight tunnel clearance which requires some finesse.

For this article we’re concentrating on just the driveshaft. Replacing axle shafts (also called half-shafts) and their corresponding u-joints in the C3 IRS (Independent Rear Suspension) deserves its own in-depth tutorial.

Follow along as we replace the u-joints in Project Corvette…

Beginning
First, disconnect the battery. The C3 positive battery cable runs along the inner portion of the transmission tunnel, right in the work area. For those unfamiliar with C3s, the battery is stored behind the driver’s seat.

Using jackstands will get the job done, but a mechanic’s lift makes the task much more efficient. Whatever method you use, make sure the vehicle is safely supported before sliding underneath.

We've found placing the transmission in neutral allows the driveshaft to turn offering better access to all of the u-joint strap bolts. There are 4 bolts that need to be removed at both ends of the driveshaft. The C3 sports a tight transmission tunnel, but a small socket with an extra long extension will be able to remove the straps over the back u-joint caps. Remove the straps at the front yoke, too.

Once all cap straps are detached, gently pry the rear joint free from the pinion. When it dislodges, slide the driveshaft yoke forward into the transmission. It will travel an inch or so, just enough to clear the differential pinion. Then pull the u-joint away from the front yoke. Drop it down and slide the ‘shaft out through the front. The yoke stays in the trans to keep fluid loss to a minimum.

Again, you can’t slide the driveshaft out with the yoke attached on a C3. That being said, these cars are classics and many have had non-stock parts installed over the years. If your yoke is a solid-style without bolt-on straps for the u-joint caps, you must locate the correct part. Otherwise you’ll never be able remove/install the driveshaft in a C3 chassis.

On the bench
With the ‘shaft out, we could now assess our options.

After a thorough cleaning the factory stencil marks were still present. Though barely visible, we took pictures of the yellow paint numbers along with the small daub of color on one of the forged ends. This documentation could then be used to properly restore the factory stencil codes. However, original driveshafts weren't painted from the factory. We’re also not going the NCRS (National Corvette Restoration Society) route, so leaving it in a natural, soon-to-rust state isn't an option either.

First though, we needed to extract the u-joints. On a side note, an added benefit to the C3 driveshaft is you only have to deal with 2 bearing caps. Remember, both ends of the ‘shaft employ a pair of straps to secure the bearing caps to the transmission and pinion yokes.

What this means: there are only 2 bearing caps per side to deal with. In other words, less work to do.

The process
First off, let’s breakdown what exactly comprises a universal joint. Think of it as a cross with each end a detachable cap. Each cap is lined with needle bearings which ride along a machined pad (or cross end). Each cap has a dust seal to keep the grease in and contaminates out.

The driveshaft is a metal tube with forged ends welded on. These forged yoke ends (or bearing bores) accept pressed-in universal joints, which connect the driveshaft to both the transmission slip yoke and the rear differential pinion (by straps over the bearing caps).

Once pressed into their bearing bores, the u-joint bearing caps are retained by a snap ring.

To simplify matters, we’ll call the yoke bearing bores just “bores.” The transmission slip yoke is more commonly referred to as the actual yoke.

U-joints are a machined part with a precision fit. When you get right down to it, removing and installing is a process of pressing out the bearing caps to be able to shift and remove the center cross part of the joint.

As with any driveline part, years of abuse combined with rust leaves the caps unwilling to back out. Lots of penetrating oil is required. It’s a good idea to squirt the joints well ahead of time to ease the repair process.

Leverage is the key here. A large C-clamp can be successful, but with its more stable foundation and ease of cranking, a vice is more effective. In using either tool, a pair of sockets are placed on opposite cap ends: one is smaller than the diameter of the bearing cap; the other slightly larger than the cap. Basically, as one cap is pressed down into its bore, the cap on the other side is popped out from its bore.

Once a cap is sticking out from its bore, a vice grips can clamp and spin it all the way out. Only then can the cross section be removed from the yoke.

Getting busy
There are 2 snap rings at both ends of the ‘shaft. These clips, which snap into a groove and hold the bearing caps in their bores, can be a pain. Generally they are much easier to remove than install. A needle nose a pliers gets the job done, but be prepared in case they fly with protective eye-wear.

Once the clips were out, we used a combination of devices to press the bearing caps out. Initially we started with a large C-clamp and the pair of sockets. Soon we switched to the bench vice, as it provided a more stable foundation. The vice’s jaws also make it easier to center the sockets on the bearing caps. We held the ‘shaft where it stood out of the vice at about a 45-degree angle; your vice may need a different angle or approach.

Another technique deals with a hammer and socket. Simply put, a hammer is used to pound a socket down into the bearing cap until the other cap pushes out. Though crude and initially a bit intimidating, for removing old parts that aren't being re-used, it won’t hurt a thing.

A few things to consider: Don’t push the bearing caps down too far. If you completely tap out one cap into the center, you may not be able to tilt and extract the universal joint. We were forced to re-install a cap – from the inside-out – to essentially start over. There’s only so much room inside the center or between the yoke bores.

Pay close attention to the extraction process. Knowing how to remove the u-joints is a great reference on how to orient and install the new parts later.

Hopefully everything goes smoothly. It’s when the caps are frozen in their bores that things get interesting.

Like new again
With the u-joints out, all we had left was the ‘shaft. And it was a rusty mess.

We started sanding the scale off using a combination of sanding paper and wire brushes. Once stripped to bare metal, we prepped for paint. Since paint would go everywhere, we decided taping off the cap ends would be a good idea. Surprisingly we spent a considerable amount of time prepping for the glossy stuff. Looking back, we probably went too far in our masking, but at least we were thorough.

We didn't aspire to greatness here, as the factory left it natural to begin with. We also applied the primer and top coat sparingly, not wanting to lay on too many mills in one particular spot for fear it might unbalance the ‘shaft.

At the same time, we cleaned and painted the straps. The black Krylon went a long ways in making both parts presentable and ready for more hardware.

After the paint cured, we fired up the Dremel tool. From previous experience we discovered it helped to polish the insides of the bores in preparation for the new bearing caps. The smooth surface eases the new caps into their bores, with less pressure from the vice needed to accomplish the goal. The Dremel's small wire brush made quick work, polishing the insides to a nice sheen. A file was used to take down some sharp burrs and jagged edges around the perimeter of the bore, too.

We also paid attention to the snap ring grooves. You’d be surprised how much junk can hide in these grooves, even after a thorough cleaning.

Finally we pulled out the yoke from transmission tailshaft. Some ultra fine sand paper was used to polish the surface to make sure there weren't any gouges or nicks that could impair the rear seal. All 4 bolt holes were chased with a tap to ensure accurate torque readings. We wanted to do the same on the rear, but space wouldn't allow it. We did, however, clean all the original bolts.

Local shops
Obviously the easiest and least time-consuming way to have the universal joints replaced is at your local shop. Notice we didn't say the cheapest solution. Originally we looked into getting a custom made ‘shaft, but soon balked at the prices. Local build shops quoted anywhere from $275 to $400 depending on rebuilding our shaft to fabricating a new part. Many recommended and charged extra for re-balancing, too.

Speaking of balancing, we were given all sorts of advice regarding this. Most shops recommended that any driveshaft and u-joint repair should be balanced upon completion. We agreed, but several things swayed us to skip this step. For one, Project Corvette’s original driveshaft had been fitted with new(er) u-joints back in the day and though it wasn't balanced, it performed flawlessly.

Secondly, the cost for just balancing ranged wildly from each shop. We were given different rates and explanations which only added to the confusion. The kicker was finding out that even if we did all the work and supplied a shop with our rebuilt shaft, the balancing approached a hundred bucks. We thought this out of line, especially when there are brand new C3 shafts online for only $200. We didn't go the online route, either, for most are fitted with cheap foreign u-joints (hence the price). Still, it’s hard to beat the budget pricing of online sources selling shafts with u-joints ready to go.

After evaluating our options, we felt performing the R&R ourselves was the way to go. Besides, we wanted to keep some original parts on Project Corvette.

For our application balancing wasn't required. Your project may be different.

Too many choices
There are several different styles and sizes of u-joints available for C3 Corvettes, too numerous to list. These driveshaft unions can vary depending on engine size and intended usage. Adding to the confusion, there are the half-shafts or axle shafts in the IRS to consider, which this article won’t cover.

What is important is that you get the correct size for your particular application. One way to easily assist in choosing the correct parts is to not toss the old u-joints. Keep them on-hand as a reference. Tape the caps so they don’t fall off and stash them in a plastic bag so you can compare them to the new u-joint’s overall size and cap diameter right at the parts counter. It’s a foolproof way to get the right part. Nothing is more annoying than having to make a second trip to the parts store at the last minute.

The u-joints being replaced seemed in decent shape and were probably fine. However, since Project Corvette was getting a freshly-rebuilt TH400 transmission, it only made sense to bite the bullet and do it right. These u-joints had been beat on for many years so it made sense to replace them.We noticed they were a Spicer greasable unit, a strong choice and one of the most frequently recommended upgrades over stock. Though Spicer units weren't available at our local parts store, we were more than satisfied with the high performance options offered. We decided to use non-greasable or solid units, as they are considered stronger and less failure-prone for not having the zerk fitting drilled into the center of the u-joint.

Press on
As a rule of thumb, installation usually takes longer than removal. For one, you don’t want to pound away on new parts. Secondly, it can be difficult to center both bearing caps with sockets being a one-man show. As such, it helps to have a partner. You’ll need to support the driveshaft while performing this repair. Though shorter than most muscle cars, a C3 Corvette ‘shaft isn't exactly light. Holding it in place while messing with the bearing caps is probably a 2-person job, especially for a novice.

A high degree of leverage is required here, so working a vice is the preferred method. The large C-clamp will suffice, but we found the former a better option. Others may choose to utilize a hydraulic press.

Start by installing a bearing cap in one of the forged ends of the driveshaft. Use the jaws of the vice and the smaller diameter socket to push it into the bore. You don’t want to seat the cap all the way down just yet. Release the vice and insert the u-joint (cross section) from the inside or center by sliding it into the bearing cap. For now, the u-joint will appear crooked or shifted more towards one side.

Set the other cap in its bore and hold the u-joint inline. Tighten the vice slowly. If it the cap binds or there is any resistance, stop and release the pressure. As you crank the jaws, both caps should slide and gradually sink into their bores, meaning the ends are accepting the bearings.

The caps need to be perfectly parallel. If the caps get cocked in their bores, it’ll ruin your day. Take your time and don’t be in a rush. If you speed things up, something will shift and the caps won’t line up. Remember, these units are precision-machined assemblies. They aren't supposed to fit loosely. It takes a little skill to seat the caps on both sides.

When the bearing caps are seated, the snap rings must be installed. They fit into a machined groove and keep the caps from coming out of their bores. One hand can squeeze the clip with a needle nose pliers while the other hand uses a small screwdriver to hold it flat against the cap and work it into the groove. It usually takes several attempts to get the snap clips fully seated.

Once both u-joints are installed, you’ll notice the assembly may be stiff or feel as if there is a slight resistance to rotating smoothly. In order to “loosen” or seat the u-joints all it takes is usually a couple whacks on the forged ends with a hammer. You’ll want to make sure the new u-joints are not binding before the driveshaft is installed.

Re-installing the stick
Removing the ‘shaft is one thing, but putting it back is quite another. The hardest part is seating the (loose) bearing caps in the rear differential yoke. There is not much room to spare and both caps need to be fully seated in the pinion grooves before the straps are bolted on.

In order for a perfect fit, you need to thoroughly clean the mating surface. Use a small wire brush to scrub the dirt and grime out the pinion. Pay special attention to where the bearing caps are seated; there are two small raised pads that "lock" the caps in place before the straps are bolted on.

Visibility is limited due to the front differential mount bushing. At times you will be reaching up and working by feel. With jackstands the close proximity makes it harder to see both caps at the same time. Usually it will be a combination of feeling one cap and eyeing the other.

At first we tried holding the loose caps, but one would shift and slide and nearly fall off. Eventually we took some advice and wrapped the caps with some tape. Don’t try to ease in the ‘shaft and expect the caps to stay in place. With all the maneuvering they will inevitably slide off.

Don’t be disappointed if you fail to seat the u-joint on your first attempt. Take your time and eventually you’ll get it right. Once seated in the pinion, bolt on the straps so it can’t fall out of position. You don’t have to torque to specs just yet. Bolting the straps on allows you to temporarily forget about the rear; dealing with only one set of u-joints at a time is hard enough.

Thankfully we found the front u-joint more forgiving to install. There’s far more room to work here than out back. Make sure the transmission is in neutral so the output shaft spins to align the driveshaft to the slip yoke.

Once you are certain both u-joints are fully seated in their yokes, with the straps bolted on, you can torque to spec.

In review
With so much power being transferred through the driveline, universal joints take a ton of abuse.

Project Corvette will be driven hard, so it makes sense to keep the u-joints fresh to be up to the task.

We would recommend this job to anyone confident with a set of tools and the motivation to learn something new. It takes some practice to seat the bearing caps, but it’s easily accomplished in an afternoon.

For more information on Project Corvette and its restoration, check out the links below.

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