Chevy Car Questions & Answers - Performance Q&A

Kevin McClelland May 1, 2009 0 Comment(s)

The nine-bolt cover rearend you have was considered the Aussie rearend (they were built by BorgWarner of Australia). They debuted in the '88 Camaros and '85 Firebirds. The reason GM swapped these differentials into the Camaros was the weak 7.5-inch 10-bolts in the F-cars. The nine-bolt featured a 7.750-inch ring gear; 2.77:1, 3.08:1, 3.27:1, or 3.45:1 rear gears; bolt-in axles instead of the C-clip-style retention of the 10-bolt; and 28-spline axles. Another major strength increase was a reduced carrier bearing spacing. The 10-bolt diff had a spacing of 7 inches, and the nine-bolt came in at 6.125. This was a major reduction in carrier deflection. And finally, the differential uses a four-pinion spider gear arrangement verses the two-pinion in the 7.5-inch diffs. The rears were offered in both open and posi configurations, with the posi being a cone type.

The failure points of this diff were from excessive backlash from either excessive ring/pinion clearance or worn posi cones creating excessive clearance between the side gears and the four-pinion gears. Keeping the clearances correct keeps these rearends happy.

Finally, the General doesn't support these rearends any longer. Any parts and components needed for service will need to come from the aftermarket. Check with Differential Solutions for largest selection of hard-to-find parts for the nine-bolt: rebuild kits for both open and posi carriers, used ring-and-pinions, and mini spools. Check out the condition of your nine-bolt and get on the rebuild. Parts will only get tougher to get as time goes by. Enjoy your '82 Z28, and keep your eyes peeled for the other drivers.Source:9bolt.com

Stay Between The Lines
Q I'm trying to find someone who sells bent transmission cooling lines for a '90 Chevy Impala. The car only has 49,000 miles on it, but the Wisconsin winter caused them to rust through. I'm sure they're out there, but where? Thanks.
Mike Lefeber Via e-mail

A Now that is some tough winter! Rusting through galvanized plated steel tubing is hard to do. There must have been places where the galvanized plating had been compromised, which allowed the nasty, salty snow melt to reach the steel tubing. Nothing is offered by the General; however, the aftermarket has come to the rescue.

Fine Lines offers bent tubing for all your restoration needs, lines from fuel systems, brake systems, trans cooler lines-almost any bent hard lines. They're available for the most popular musclecars and some of the late muscle into the early '90s. Note "muscle." Fine Lines doesn't view the late B-body GM cars as muscle! However, it does have an extensive library of patterns of original lines from cars it doesn't offer as regular production items (or you can supply your car's original lines if there's no pattern), and they can be custom-made for you. Another really nice feature is that Fine Lines offers the original galvanized steel tubing or, as an upgrade, stainless steel tubing. This sounds like the perfect option for your nasty winters to prevent this problem again. Good luck and take care of that Imp!Source: finelinesinc.com

The Mystery 350
Q I bought a '74 El Camino to part out. The guy I bought it from told me the engine was a 350 that he bought from an engine remanufacturing company. The price was so good that I didn't even check the casting number on the block until after I bought the car. The casting number on the block is 3932373 with a late-'68 casting date. All my research shows it to be a '68-72 307. A little disappointed, I pressed on and tore the engine down. This is where it gets interesting. The first thing I noticed when I removed the heads is that all the pistons were stamped "40," indicating that they were 0.040-inch oversize. So I took my inside micrometer and measured the bores. To my surprise, they all measured 4.040 inches! Is it possible to take a 307 block with a stock bore of 3.875 inches and bore it 0.165-inch over? I'm not sure if this block can handle this much overbore.

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