What front diff do I have? (it was swapped from a 2004)

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soonrfish

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I am in the unfortunate predicament of needing a new rear end in my 2005 z71 tahoe. I know the front diff was swapped out with one from a 2004 z71, but I dont know what the ratio was. Since I need a new rear end, I need to match it and I cant trust the RPO code because it may have been swapped too. Is there any other way to identify the front diff other than the RPO code? What did GM typically put in the 2004 z71 tahoes?

thanks for your help!
 

swathdiver

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I am in the unfortunate predicament of needing a new rear end in my 2005 z71 tahoe. I know the front diff was swapped out with one from a 2004 z71, but I dont know what the ratio was. Since I need a new rear end, I need to match it and I cant trust the RPO code because it may have been swapped too. Is there any other way to identify the front diff other than the RPO code? What did GM typically put in the 2004 z71 tahoes?

thanks for your help!
There are codes on each axle. Of course, if someone changed the gears then there's another, easier way.

Spin the yoke or wheel side and count revolutions of the opposite. If it makes about 3 and a half turns, 3.42 gears. If it turns 3 and 3/4 turns, 3.73 gears. Just over 4 turns, 4.10s.

The top of the axle tube on the passenger for the rear differential is where the codes reside. The top of the front differential where the two halfs bolt together, passenger side of the case is the codes reside.

1680630223644.png

Your generation also had cars with 3.23 gears but I do not know those codes.
 
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soonrfish

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There are codes on each axle. Of course, if someone changed the gears then there's another, easier way.

Spin the yoke or wheel side and count revolutions of the opposite. If it makes about 3 and a half turns, 3.42 gears. If it turns 3 and 3/4 turns, 3.73 gears. Just over 4 turns, 4.10s.

The top of the axle tube on the passenger for the rear differential is where the codes reside. The top of the front differential where the two halfs bolt together, passenger side of the case is the codes reside.

View attachment 396069

Your generation also had cars with 3.23 gears but I do not know those codes.
Ok, thank you for the info. I looked as best I could from underneath the vehicle, but did not see a code on the case that resembled any of these. May just have to jack it up.
did most 04 z71s come with a certain ratio or did it vary?
 
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swathdiver

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Ok, thank you for the info. I looked as best I could from underneath the vehicle, but did not see a code on the case that resembled any of these. May just have to jack it up.
did most 04 z71s come with a certain ratio or did it vary?
I'm speculating but I think the most popular were 3.42s and 3.73s.

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I had a 2002 LT that had 3.73 gears and I liked that ratio. Then I bought my 2005 Z71 and I was surprised that it had 3.42 gears. I loved the rig but was not happy with off the line and sudden accel performance. Then I won a "traditional tune" from Black Bear Performance and that engine came alive. I no longer miss my 3.73 gears. If you have a GU6 RPO code you have 3.42 gears and a GT4 is a 3.73 gear ratio.
 

Sam Harris

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I had a 2002 LT that had 3.73 gears and I liked that ratio. Then I bought my 2005 Z71 and I was surprised that it had 3.42 gears. I loved the rig but was not happy with off the line and sudden accel performance. Then I won a "traditional tune" from Black Bear Performance and that engine came alive. I no longer miss my 3.73 gears. If you have a GU6 RPO code you have 3.42 gears and a GT4 is a 3.73 gear ratio.
But he says the diff was swapped. Just have to find the code on the actual hardware..
 
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soonrfish

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But he says the diff was swapped. Just have to find the code on the actual hardware..
yes it was, I need to figure out what it is because Ive got to get a rear end to match. Its possible that the front and rear in it right now dont match because of that. Thankfully I havent tried it in 4wd.

crawled under and didnt see a stamp, tag, or anything from my view that identified it.
 

Sam Harris

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yes it was, I need to figure out what it is because Ive got to get a rear end to match. Its possible that the front and rear in it right now dont match because of that. Thankfully I havent tried it in 4wd.

crawled under and didnt see a stamp, tag, or anything from my view that identified it.
There should definitely be an indication on both the front and rear, as @swathdiver detailed. Or, get the front, then rear up off the ground, and rotate a wheel and count revolutions, as he also advised.
 

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