Nine times out of 10 if you hear us talking about traction-adding devices here, we are talking about lockers or maybe a spool. We generally give limited-slip diffs the cold shoulder, but that’s not to say that they cannot give us the satisfaction we desire in certain applications. Limited-slip differentials afford more traction on- and off-road than open diffs, and that’s always good. And they do it without many of the drawbacks of a locker or spool. For a mildly built rig that spends lots of time on the road and little on the rocks, like Dino the 1970 Chevy Suburban, adding limited-slip differentials will give us all the off-road traction we would ever need as simply as simple can get.
While Dino has most likely seen more off-road miles than most other 4x4s ever will, it has gone its entire life with a pair of open diffs. The time was right for more traction to help keep the lumbering, nearly fossilized beast out of sticky tar pits and the like, but we didn’t want the drawbacks that can sometimes come with lockers, like twitches and bangs on corners. We also didn’t want lockers, because if we got into a position where they were really necessary we would be driving Dino somewhere it really should not be.
Not surprisingly, limited slips come in a few different flavors—some new, some old, and some more desirable than others. We ended up selecting the Dura Grip Positraction Differential from Yukon Gear & Axle for four reasons. First, the Yukon diff is rebuildable. Second, the aggressive four-spring clutch uses Raybestos composite materials to supply traction to both of the axles wheels. Third, the Dura Grip is competitively priced. Fourth, adding these diffs gave us a great reason to upgrade to an open-knuckle, disc-brake, Dana 44 front axle and Yukon chromoly axleshafts all the way round. That means stronger parts for Dino, more traction, and improved stopping power for our old beast. Follow along with the install, and we’ll give you tips and tricks along the way.
Our upgraded parts came from Yukon Gear & Axle, the junkyard, and our local parts store. Unfortunately one of those vintage Warn locking hubs on our junkyard open-knuckle Dana 44 was junk and the brake calipers were filled with rust, so our swap wasn’t as easy as it could have been.
We pulled the axleshafts, knuckles, steering linkages, and diff cover and cleaned up the junkyard axle before adding the new bearings and diff. With the cover off we checked backlash and ran a pattern on the used gearset. Dino has 3.73:1 gears from the factory, and by some miracle the junkyard axle also had 3.73s. Since Dana 44 carriers split at 4.10 and numerically up, and 3.73 and numerically down, we decided to retain the junkyard 3.73s rather than swap in an entirely new gearset since they were in good shape.
These are original Dana gears. The “41/11” shown here confirms the axle ratio and represents 11-teeth on the pinion and 41 on the ring-gear. If you need to regear your axles be sure to get quality parts like those from Yukon Gear & Axle. We dabbled with the idea of swapping to 4.10s but finally decided that with Dino’s SM465 transmission and 33-inch-diameter Toyo Open Country M/T tires, we would be better off keeping highway rpm down with the 3.73:1 gears.
Almost every axle we have ever seen has had the bearing caps marked when we disassembled them. Here this cap is marked with a capital R. the opposite side cap was marked with a horizontal R. Maybe the guy who set up the ring-and-pinion at the factory was named Roger. Either way, if your caps are not marked be sure to mark them so you can keep them on the correct side and retain the correct orientation. The caps are machined with the housing and cannot be interchanged.
Like most junkyard parts, most of this axle was coated in grease and dirt. One of the easiest ways to clean things up is to drop them in a bucket of Purple Power cleaner and let them soak a few hours or overnight. Wear gloves to remove the parts—you don’t want the cleaner to come in contact with your skin. Once they’re soaked, you can wash the parts off with a pressure washer.
We cleaned up the outside of the junkyard Dana 44 using spray-on degreaser, patience, and a pressure washer. The best is a big old parts washer, or a heated pressure washer, but we don’t have either. Cleaning out the inside of the axletubes is a job best tackled with parts cleaner and a rag or a wire brush tool welded to the end of a length of small tubing.
We bought this seal and bearing driver from the local parts store some time ago. It makes installing bearing races and seals true and straight easy.
Inner axle seals are pretty easy to install; the problem is they are the first part in a new axle and the last part out of a used axle. You have to pull practically every part out of the axle to change them, so if you do anything in an axle be sure to replace them. Remove them with a long, thin piece of pipe. We were able to install them using the seal driver and our trusty hammer.
We bought this bearing puller tool from Yukon Gear several years ago, and it was well worth the price. The clamshell design helps pull bearings without damaging them the way a three-jaw gear puller can. If you plan on doing axle repairs do yourself a favor and get one.
With new Timken bearings from the Yukon master gear install kit on the pinion and Yukon Dura Grip Positraction carrier, we started the dance of setting the backlash and re-creating the pattern. You want to keep things the same because this ring-and-pinion are already lapped together.
We used the same pinion bearing specifications that came out of the axle upon disassembly. That gave us the correct pinion preload for new pinion bearings. Preload is checked with an inch-pound torque wrench like this, another specialty tool needed for ring-and-pinion setup.
Next, install the new pinion seal after you are sure you have the correct pinion depth and preload. Again, a proper seal driver helps ensure the seal goes into the bore squarely and without damaging the seal surface.
Use plenty of red thread locking compound on the pinion nut and torque it to spec. Ideally, torque it to spec. Mostly we just gun ’er down with the old impact wrench.
With the ring-and-pinion set up on the Yukon Dura Grip Positraction, we slid the axle under Dino and mounted it to the leaf springs and shocks. We still have to add the ball joints, outer knuckles, axleshafts, spindles, brakes, hubs, rotors, locking nuts, and locking hubs. Installing the axle now makes it easier to move (because it’s lighter), and having it securely mounted helps with installing certain parts like the ball joints.
These chromoly axleshafts from Yukon with new Spicer 760X U-joints are generally best used for 4x4s with big tires, or those that see high stress and strain in locked axles. We want to keep Dino around for another 50 years or more, so we don’t plan on wheeling it too hard. However, the limited slips we are installing in Dino will be harder on the front axleshafts than the factory open differential. Also, according to our friend (and general GM 4x4 nut) Stephen Watson from Offroad Design, most if not all 1969-1972 open-knuckle Chevy Dana 44s had smallish 260X-sixed U-joints. After 1972 these axles went to larger 297X/760X joints like those used in the Yukon chromoly axles you see here. That is another strength upgrade over Dino’s original closed-knuckle axle and the (pre-1972) junkyard-fresh shafts out of our replacement open-knuckle axle.
For size comparison, here are the new and open-knuckle Chevy Dana 44 old axleshafts (and U-joints) next to the new stuff. We also painted the new Yukon shafts and Spicer U-joints to add a little flash and protect them from surface rust.
Installing the axleshafts into the axle housing after the outer knuckles and ball joints have been installed is pretty easy. We like to add plenty of grease to the axle splines to help the axleshaft slide through the inner axle seal and into the differential’s side gear. Without grease the splines can cut the seal, causing a leak. As we said, changing the seals is easy—except everything has to come off and out of the axle housing to get to them.
Three seals and spacers have to go on the axle stub shaft before the spindle can be installed, and they go on like this. First, the large rubber seal goes on the tin dust shield that is fitted to the stub shaft. Then the plastic bushing goes on the stub shaft with the bevel facing towards the center of the vehicle. Lastly, the small sweeper seal goes inside the grove of the spindle with the open lip facing in. lots of grease on the spindle and axle shaft will help these parts do their job and keep dirt and moisture out of the spindle and hub.
Next the spindle slides on the six studs on the knuckle and then the caliper mounting bracket. Then six new lock nuts should be used to hold the spindle and caliper mounting bracket to the knuckle.
Next we attached the new rotors to our cleaned-up junkyard hubs, installed the bearing races, and packed the bearings. Between the inner and outer wheel bearings you want to build a wall of grease as shown. As the grease in the bearings gets worn and the hubs get hot, the wall of grease flows into the inner and outer bearings and keeps them lubricated . . . or something like that.
Dana 44s have two spindle nuts and a special lock washer that keeps everything from spinning on the spindle and loosening the nuts. The inner nut has a small metal dowel that indexes into the washer, which is keyed to the slot in the spindle. Then an outer nut jams everything together to keep it all in place. The tightening sequence and torque specs are specific and can be found on the internet or in any service manual. Once the hub is installed you can add brake pads, calipers, caliper slide bolts, brake hoses, and locking hubs. It is also important to upgrade to a disc/drum-specific brake master cylinder and proportioning valve. We will hit upon that in another article on Dino later, after we gather a few more parts.
When we opened up Dino’s rear axle it was apparent that the gear oil in the diff was very old and well used, the consistency of grape jelly. It was high time for a fluid change at the very least, but we have more planned for Dino’s original GM 12-bolt rear axle.
We fully removed Dino’s rear axle and took a backlash measurement and ran a gear pattern on the ring-and-pinion. Once the rear axle was totally disassembled we followed a procedure to clean it similar to how we cleaned the front axle. Namely, spray with degreaser, wait, and then pressure-wash it until the housing was nice and clean.
There is a strong chance that these two Timken bearings were made at least 47 years apart. We only use the best bearings to rebuild any axle, but it’s always a good idea to make sure the part numbers of the bearings match before you try to assemble anything. Both bearings have the same part number and say “USA” so there’s no confusion about where they were made.
We moved Dino’s original 3.73:1 ring gear from the factory open differential to our new Yukon Dura Grip Positraction. The ring gear will be a tight fit on the new carrier. We like to use two bolts to line up the bolt holes and then use a brass drift to tap the ring gear onto the differential. Use the included new ring gear bolts and high-strength thread locking compound on all the new bolts, and torque to spec.
The GM 12-bolt is similar to the Dana 44 but for two major differences. One is that the carrier is located side-to-side with shims that go outside the carrier bearings (while the shims on a Dana 44 go between the housing and the carrier bearing). We used our shop press to install the new Timken bearings that came with the Yukon Truck 12-Bolt Master Install Kit. The install kit also comes with special outside shims, but we ended up reusing the factory shims since we were reusing the factory ring-and-pinion.
The other difference between the GM 12-bolt and the Dana 44 is the former uses a crush collar to set pinion bearing preload. Once you have established pinion depth, set the backlash, and gotten a good pattern, it is time to set the pinion bearing preload. Yukon makes a crush collar eliminator kit that comes with a spacer and a solid spacer that makes gear installation slower but, in the end, much less frustrating. Since we were reusing the factory ring-and-pinion we went ahead and used one of the two crush collars that came with the Yukon Truck 12-Bolt Master Install Kit. The kit comes with two because they are easy to screw up. One trick we have heard but not yet used was to precrush the crush collar ever so slightly using our shop press prior to install. This should make getting the preload easier, but you have to be careful not to crush the collar too much. We used the old crush collar as a guide. The new one has to be longer than the used one before installation or else the collar is junk and you could damage the bearings.
With the ring-and-pinion installed, we slid the axle housing (without wheel bearings, seals, and axleshafts) back under Dino. We temporarily installed the diff cover to keep any dirt out of the housing, but it will have to come back off so the 12-bolts shafts and C-clips can be installed. Still, installing wheel bearings and seals is much easier with the axle firmly attached to Dino. These seals and bearings were included with the Yukon chromoly axleshafts. We greased up the wheel bearings and seals to make sure they would not be damaged when we installed the new rear axles. The wheel bearings are bathed in gear oil when Dino is running down the road, but this little grease helps lubricate the bearings initially.
Dino’s factory axleshafts were just about totally worn out after 47 years of stops and starts mostly off-road. We also enjoy the added confidence of having the Yukon chromoly rear axleshafts and the included new wheel bearings and seals. The wheel studs were not included, but the parts store up the street had them. We used a few bits of steel and our shop press to install the new studs in Dino’s new axleshafts.
Not sure if these axle splines could be more worn without the axle possibly spinning in the differential side gear. That’s a lot of wear.
Since the GM truck 12-bolt is C-clip style, one of the last parts you have to install into the differential is the center pin and its corresponding lock bolt. We like to mark the center pin to indicate which way the lock bolt goes through the hole. If the center pin is rotated even a few degrees one way or another, the lock bolt will not go in its home. That can be very frustrating.
Dino’s new chromoly axleshafts add a lot of strength to a pretty decent yet well-used medium-duty rear axle. Unfortunately the fancy Yukon stickers on the ends of the axleshafts will be covered up by a set of patina’d vintage-era dog dish hubcaps.