Installing An 8-1/4 Rearend To A Muscle Mopar
Don't Neglect Your Rear Just Because It's Down and Under
From the November, 2010 issue of Mopar Muscle
By Brad Ocock
Photography by Brad Ocock, Tom Rounds
The first order of business...
The first order of business was to clean up the whole rearend. We had it sandblasted because it's cheap and fast. It's also not a concours car, so we weren't worried about pitting. If we were, it would have been chemically stripped.
The axle flanges were also...
The axle flanges were also blasted to clean them up for painting. Take care to protect the machined bearing surfaces.
This is the complete package...
This is the complete package from Ring & Pinion Service. Everything's included in the kit with the exception of the ring gear bolts and the pinion nut. These are sourced from Mopar Parts.
Here Mike uses a race installation...
Here Mike uses a race installation tool and 5-pound persuader to tap in the front pinion bearing race. An hydraulic press will work well, too, but it's easier to bring hand tools to the rearend than the housing to the press.
Mike presses in the race for...
Mike presses in the race for the inner pinion support. He coated the inside of the differential with Krylon epoxy to seal the inside surface of the differential.
This is a handy little tip...
This is a handy little tip to "cheat" when you set up a new ring and pinion -- mic the shim from the old pinion (the one that goes between the pinion gear and the bearing that regulates the depth of the pinion as it relates to the ring gear) and use this as a starting point when choosing the shim in the new gear set. This one mic'd out to .020. Unfortunately, this doesn't always work due to differences in machining -- we eventually went all the way up to .050 to get proper tooth contact.
This is a bearing press. Note...
This is a bearing press. Note that the press is actually on the "meat" of the bearing, as opposed to being on the edge of the cage. A lot of people will use a large socket to press bearings -- This is why you shouldn't. The points on the inside of a socket will contact the cage that holds the rollers in and damage it as you apply pressure. Use the right tool for the job.
Before pressing the bearing...
Before pressing the bearing onto the pinion shaft, be sure it's well lubed.
This is the crush sleeve....
This is the crush sleeve. By the time you're done setting up the rearend, you may go through two of them. Mike likes to use the old one for the initial setup so he doesn't waste the new one. After he gets everything set up the way he likes it, he puts the new crush sleeve in and does the final assembly.
Once the pinion and bearings...
Once the pinion and bearings are in place, the yoke goes on and is tightened down. You end up doing this a few times while you're figuring out the proper shimming. This is why Mike uses the old crush sleeve first.
These numbers tell you what...
These numbers tell you what the depth of the pinion gear is supposed to be in relationship to the center of the ring gear. A very expensive plunger gauge mounted on a shaft in the differential races will tell you where it's at and how far it's off, but most of us aren't ever going to own one of these gauges. That's where micing the original shim comes in to play. Also, the recommended number is just a starting point, because machined tolerances are going to vary, housing to housing.
This is the stock, open d...
This is the stock, open differential.
This is the Ring & Pinion...
This is the Ring & Pinion Service Posi-style diff. We said "Posi" instead of Sure-Grip because the clutches are behind the spider gears, as they are on a GM and that's what they call it.
Mike installs half the bolts...
Mike installs half the bolts on the carrier and marks them and uses these to draw the ring gear onto the carrier. These dont have Loctite on them, which is why theyre marked. Theyll be removed and Loctite will be applied when the process is over.
Another fun thing to remember...
Another fun thing to remember about Mopar ring gear bolts is they're threaded backwards! This is important to know for two reasons -- so you don't snap them off when removing them from the old ring gear (which a lot of people do, Mike says), and when you torque them onto the new one: Click style torque wrenches only work in one direction! This means you'll need a cheap torque wrench with an external needle, or one of the terribly expensive dial indicator models.
Here are the side adjusters...
Here are the side adjusters and the main caps being dropped into place.
The side of the adjuster has...
The side of the adjuster has holes drilled into it, as well as a large cut-out in the center for a special tool that slides all the way in from the end of the axle housing, much like a very long socket extension. We used an Allen wrench in the smaller holes and screwed the adjuster into place that way.
Mike checks the play in the...
Mike checks the play in the setup. If there's too much or too little, it all comes apart and is adjusted until it's just right. Consult a shop manual or the ring gear manufacturer's instructions for the proper numbers.
After proper backlash is set,...
After proper backlash is set, this paste is spread on the teeth to check the contact between the teeth on the two gears. The paste is supplied in the kit.
Although not what we're used...
Although not what we're used to seeing on a properly set up ring and pinion set, the instructions supplied with the kit indicated this was a good contact pattern on the ring and pinion.
With the diff set up, it's...
With the diff set up, it's time to install the axle bearing races.
To install the C-clips on...
To install the C-clips on the ends of the axles, the pinion shaft in the differential itself must be pulled out so the axle can be pushed forward, exposing the land the C-clip rests in.
Slide the axles into place,...
Slide the axles into place, and install the C-clips on the end of the axle, inside the differential. This is why C-clips are bad -- if the axle breaks, the only thing keeping it in the housing (and your wheel under the car) is luck.
To finish up the housing and...
To finish up the housing and strengthen it internally we installed LPW's Ultimate Cover. The two studs contact the backs of the main caps inside, keeping them from flexing during extreme conditions such as racing. If the caps don't flex, the tolerances inside stay tight on the launch and your rear end lives. The extra holes on the edges of the cover's bracing are in case you'd like to install LPW's Axle Tube Brace(TM). This device benefits by stopping forward movement of the housing tube ends and eliminates case distortion.
Here's the completed rear,...
Here's the completed rear, ready to be put behind a hot small-block.
When it comes to making your car perform better, there's always a set order for performance modifications; front-to-back. We all start under the hood (usually with carb/ intake/headers, often followed by a cam swap). For those who like to row their own, a performance shifter is installed, maybe a clutch; automatic guys modify the valve body and later install a high-stall converter. Last on the list has always been the rearend. A lot of post-muscle Mopars rolled off the line with a standard, "small" not- built-for-punishment 8 1/4-inch rear end. The 8-3/4 is far more popular by virtue of it's easy to set-up drop-out carrier, ease of gear changes (need a different ratio? Just swap the carrier!), no C-clips, stout construction and, of course, the strength of a larger ring gear. If you really want strength on an unparalleled level, you can step up to the legendary Dana 60. Able to handle torque output on the scale of diesel locomotives, the Dana is the last word in rearend strength. During the halcyon days, all it took to get one as original equipment was checking off the right boxes.
If your current street stomper came equipped with an 8-1/4 rear, standard thinking goes something like this -- If it ain't broke, don't fix it. When it breaks, upgrade to an 8-3/4 or Dana. We'll build the engine and trans, but forget about the rearend. When it breaks, we call the car all kinds of nasty names, tow it home, yank the rear and replace it. Most project cars are high-mileage cars, but the engine and trans have at least been gone through, if not outright rebuilt. When's the last time you even changed the fluid in the rearend? Then you get mad when the poor thing breaks after increased horsepower from the front of the car on top of years of neglect.
Truth be known, unless you're building a big-block or a full-race small-block, that lowly 8-1/4 is good enough. There are some guys who prefer a totally built 8-1/4 in drag racing situations because it's lighter and there's less reciprocating mass, so more power hits the tires. And because they're the "cheaper" rear ends, the parts to rebuild and upgrade them are less expensive. Finally -- and this is the real selling point -- it's already under the car! You don't have to pay for a new housing, it doesn't have to be narrowed to fit, you already have brakes on it, even the spring perches are in the right place! The situation we were in with one of our projects was, we had the whole rearend and brake set-up already in the vehicle, but it was an open diff with a highway gear. We thought about replacing/upgrading it, but decided to work with what we had. The engine is going to be warmed over, and the 904 will be upgraded, but it's a daily driver that probably won't see much strip duty. We felt the "little" 8-1/4 would hold up nicely if rebuilt right the first time. We ordered a complete differential, ring and pinion, and rebuild kit from Ring & Pinion Service and a rearend girdle cover from LPW Racing Products (PN 301-10C, fits 8.2 and 8.3 Chrysler 8-1/4). If we were going to put the vehicle on the strip, and especially if we were going to run slicks, we'd have stayed with this rear but purchased aftermarket axles and a C-clip eliminator kit. We had Mike Mott at Pro Automotive Performance Center put together a stout little rear that will survive nicely under an average street car. Certainly less than a full swap and perhaps just right for our needs.
LPW Racing Products, Inc.
632 E. Marion St.
Ring & Pinion Service
11630 Airport Road #300
Pro Automotive Performance Center
1057 US Hwy. 92 West