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Author Topic: Question about installing 3.42 gears in 10 bolt  (Read 3407 times)

Offline JBerryhill

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Question about installing 3.42 gears in 10 bolt
« on: March 03, 2009, 02:18:54 pm »
As some may know I have an 87 GMC, I recently bought a complete posi rear end from a salvage yard that was supposed to have 3.42 gears in it. Well turns out it doesn't, and I have been told that 3.42 gears will not fit in all applications. I do not know the ratio that is in it now, can someone tell me how to tell if 3.42 gears will fit in this rear end. It there a code or something on the rear end housing? Thanks again for helping an idiot.......................Jerry
« Last Edit: March 03, 2009, 02:26:18 pm by JBerryhill »
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Offline Blazin

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Re: Question about installing 3.42 gears in 10 bolt
« Reply #1 on: March 03, 2009, 02:31:15 pm »
Its not the housing, its the carrier that some gears wont fit on. The ring gears are different thickness, for some ratios. So the carrier is thicker or thinner to make up for the space.
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Offline VileZambonie

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Re: Question about installing 3.42 gears in 10 bolt
« Reply #2 on: March 03, 2009, 07:25:43 pm »
what gears are in the one u bought? Why not return it?
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Offline JBerryhill

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  • 1987 GMC Sierra Classic SWB
Re: Question about installing 3.42 gears in 10 bolt
« Reply #3 on: March 03, 2009, 08:18:44 pm »
The one I bought is a limited slip which is good but I was told and it was tagged a 3.42 but it is a 3.08 by the numbers on the ring gear.
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Offline Captkaos

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Re: Question about installing 3.42 gears in 10 bolt
« Reply #4 on: March 04, 2009, 05:39:50 pm »
The carrier Break on a 10bolt (stock for an 87) is 2.56 and down or 2.73 and up. so a 3.42 will fit on there as it is the same carrier.
For reference a 12bolt Truck is 2.73 and down, 2.76 - 3.42 or 3.73 and up.
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Offline JBerryhill

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Re: Question about installing 3.42 gears in 10 bolt
« Reply #5 on: March 22, 2009, 08:02:54 pm »
Well I got my rear end all finished, 3.42 gears, limited slip 12 bolt, all new bearings, seals, brake shoes, hardware and wheel cylinders. I did everything myself except setting up the rear end. I have done a few Ford 9 inch chunks but never a GM. I paid a tech at the local Chevy dealer 100 bucks to do it and was so pleased with the seat of the pants feel after I installed it I went over and bought all the guys lunch. My truck feels like a totally different vehicle!! No more sluggishness and more important no more converter locking and unlocking at 55-60, it feels like another 50-70 HP has been added to the engine. Thanks for answering all my questions regarding this swap guys. Well on to the next project.
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