Building a performance machine is all about making more power and thenuncovering the weak areas that inevitably show up as a result of theupgrades--and usually at the worst possible moment. We've been beatingon our mule '65 Chevelle for more years than we care to count, so itwasn't a big surprise when an axle broke right at the flange. We'vesubjected our Chevelle to much more than just high torque andsticky-tire drag launches; we've also abused the stock 12-bolt axle withyears of 1g lateral laps on the road course. So the snapped axle made itclear it was time for improvements.
This is what happens when you try to road race on stock, 40-year-oldfactory axles. The axle broke just outboard of the axlehousing. Luckilyour Baer rear-disc-brake caliper mount kept the wheel from tearing upour rear wheelwell.
Previous experience had taught us that while a C-clip eliminator kit isa popular axle upgrade choice, we discovered that our Baerrear-disc-brake kit would not work with the pillow block that mounts thebearing. So we went looking for a better solution. Moser has beenbuilding brand-new 12-bolt housings for Chevelles, Camaros, Novas, andother Chevys for several years now. The company is also well known forits bolt-in 9-inch Ford housing conversion. We wanted to stick with our12-bolt for several reasons, including its reduced weight, better geararrangement, and also because we have a whole shelf of 12-bolt gears andparts to choose from.
We noticed that Moser equips virtually all of its new 12-bolt housingswith forged-steel, CNC-machined housing ends that retain the stock 10-and 12-bolt backing-plate bolt pattern but allow the use of a muchlarger axle bearing. When we compared the size of this new bearing tothe stock 12-bolt bearing, we knew this was the way to go for our12-bolt. This larger axle bearing combined with a much strongeraftermarket axle will add the strength and durability we need to stopworrying about breaking an axle when diving into a corner at full song.While accommodating the larger bearing, this new housing end also allowsus to retain either the stock rear drum brakes or use a Baerrear-disc-brake caliper bracket.
Here is a comparison of the old 12-bolt axle bearing (in the housing)next to the Moser aftermarket 9-inch Ford bearing we will use. Thelarger bearing is capable of handling much more abuse without tearing upaxles.
The premise is pretty simple--cut off the stock housing end, weld onthis new Moser end, and line everything up so there is no bind on theaxles once everything bolts back together. While the theory may besimple, its execution requires serious housing modifications that arebeyond our backyard bolt-on abilities.
Since we already had a 12-bolt that had been modified for a C-clipeliminator kit, which removes the stock 12-bolt axle bearing pressedinto the housing, it was a simple decision to go ahead and modify thisexisting housing. Of course, if you don't have a 12-bolt, Moser offersthese housings in various levels of assembly depending upon your needs.
Once we had the housing ends and new axles from Moser, we took ourpieces to Ed Sutton at Sutton Engineering in Industry, California.Sutton carefully cut the housing ends and welded on new ends using afixture to ensure the housing was straight after all the welding wascompleted. This was also a great time to have the tubes fully weldedinto the centersection to build a little more strength into the housing.
To complete our 12-bolt conversion, we also added a Detroit Truetracgear-style limited-slip unit from Tractech. The gear-style limited slipoffers several advantages over clutch-type units, including moreconsistent performance over a much longer period of use and abuse.
Since this move required a complete disassembly of the rear gears, wealso decided to upgrade our abused Eaton clutch-type Posi with a newTractech Detroit Truetrac gear-style limited slip. The gear-stylelimited slip is designed to apply maximum torque to the wheel that canhandle the additional power without spinning. This will allow us toapply much more power coming off the corner on an autocross or roadcourse without spinning the unloaded tire.
We also decided to improve our 12-bolt's durability with a Ratech solidpinion spacer that replaces the crush sleeve. This solid spacermaintains a more accurate preload on the two opposing pinion bearings,which makes life easier on the pinion gear. We also used a completeRatech ring-and-pinion installation kit.
We also decided to upgrade our 12-bolt with a couple of other extras,including an installation kit from Ratech that includes new bearings,seals, and shims to set up both the pinion depth and the backlash. Wealso use a Ratech solid pinion spacer instead of a crush sleeve toestablish a more consistent pinion position relative to the ring gear.This requires a little more setup time, but the increased durability iswell worth the additional effort.
This conversion will radically improve the stock 12-bolt's strength andaxle retention when combined with a stronger Moser aftermarket axle. Nowthat Moser has pumped a bunch of strength into our 12-bolt, it's time tohit the track and start abusing our Chevelle all over again.
