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Differential and Gears Upgrade.
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Differential and Gears Upgrade.
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Submitted By:
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Mark42
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Date Created:
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12-04-2009
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Description:
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The open differential and 3.08 gears are being replaced with a performance gear ratio of 3.73 and an Eaton Truetrac positive traction differential. This change runs about $550 in parts, and $400 in install. Estimates for the install of gears and carrier ranged from $200 to $800 for labor, so shop around. The best price came from a trans rebuilder/speed shop who does rear gears regularly and knows how to set the lash properly. Avoid the local shop, they don't do this often and mistakes are expensive.
The PCM (Power train Control Module - the cars computer) was sent out to PCMforless.com for reprogramming so that the speedometer will register correctly with the new gear ratio. They also modified fan speeds to match a lower temperature (180*) thermostat, shift firmness, and adjust fuel/air/timing to give about an additional 15hp boost to the car. Strongly recommend them.
It is important to note that if a PCM from a different car is re-programmed and installed in your car, the "CASE Learn" procedure needs to be done on the PCM after its re-programmed. (CRANKSHAFT VARIATION RELEARN aka CASE Learn). Basically it tells the PCM what the variation in the crankshaft position sensor is in your particular engine. It is a fine tune of the timing. Not needed if the PCM from your car is reprogrammed.
Update: 06/10/2010 (6 months later). No leaks, no bad noises, everything works perfect. The Summit brand gears do make a little noise. My passengers didn't even notice until I pointed it out, its that minor. After tracking fuel economy for a few thousand miles, there is no noticeable loss in fuel economy. The car averages 27 mpg, and can still get 30 mpg on a strictly highway trip. The car is much faster, passing is a breeze, and the firmer shifts are nice. Punch the throttle and the car leaves rubber for about 60 feet. Wheel hop was much worse after the gear change. Had the "hollow star" bushings in the rear control arms replaced with Moog solid rubber bushings. Problem solved. I recommend having the bushings upgraded when the rear is done.
Update 01/12/2011: Still no problems or leaks after about 20,000 miles. The Truetrac works great in the snow and rain. About 120 lbs of weight added to the trunk really helps in the snow, especially on steep hills. An aluminum drive shaft from a LS1 Trans Am was added and the gear noise has all but disappeared. I'm guessing that the aluminum does not transmit sound as well as the steel shaft so noise from the rear is reduced. Towed my boat a few times, the gears and Truetrac make the trip easy. Same with launching and retrieving the boat. It pays to buy quality parts and pay for qualified mechanics.
BTW, avoid Newgmparts.com. They messed up my order for a Reluctor Ring, and would not pay return shipping or give full refund even though they sent the wrong part. I even specified the part number in my order. Go figure. Very bad merchant.
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Related Projects:
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1998 Pontiac Firebird Coupe
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(Differential and Gears Upgrade.)
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LS1 Aluminum Drive Shaft
Cold Air Intake
Cat-Back Exhaust
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Eaton Truetrac
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3.73:1 Gears
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PCM Update
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Install Done
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Add Drain Plug
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Fill with Lube
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Buttoned up
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Need bushing Upgrade
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All projects on Shareaproject.com are user-submitted and should be used for reference information only. The projects are not intended to be complete "How-To" articles. Use the information contained in these projects at your own risk. Projects are not checked for completion, accuracy, or safety and therefore cannot be guaranteed in any way.
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