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it's not fast enough
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Discussion Starter #1
i notice on the thunderracing.com web site they have a 7.5 and an 8.5 rear end housing. i know little to nothing about rear ends, therefore this is where my question comes in.
what size rear end does a "STOCK" 2001 gmc sierra come with?
i noticed that the 05 ram 1500 came with a 3:90 gear ratio...
what gears should i buy considering i want street/strip..
my truck is a daily driver, i want to get out the hole...but at the same time dont want to run out of gear come the long run...i do a lot interstate running, and chasing cars that are speeding faster then me...
3:73 / 3:90 / 4:10

thanks for your help

im looking to buy gears by the end of may, along with a good posi lock
 

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Mayhem, Like Me
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3,087 Posts
a 91 should be an 8.5 rear...

some 3.90's should be a nice upgrade and still keep you in a civilized RPM range on the hwy...
 

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He's got an '01. Is your truck a 4x4? What size tires? Your options are going to be 3.73, 4.10, 4.30, or 4.56.
 

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it's not fast enough
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1,677 Posts
Discussion Starter #4
no, it's 2wd...on 285-55-18 i think they are 29" tall..
im about to put my flip kit on...can't find 2 inch drop coils right now...
i'd like 1" drop coils and drop spindles for 17" rims or bigger.
 

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That calculates out to a 30.3" tire. I'd think a 3.73 should do you fine. I'm not sure if anyone makes a 3.90 or not. 4.11 would be too low. I'd also recommend a Detroit TrueTrac posi. They have no clutches to wear out, are smoother in operation, and are slightly more positive than like an Auburn. I just installed one in my truck.
 

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Mayhem, Like Me
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3.90's will make it a little nicer around town but still keep something for the hwy...

if you want strictly hwy... go with something like a 3.23... 100mph 2-3 shifts LOL...
 

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"That calculates out to a 30.3" tire" man, i programmed my truck for 29" tall tires....reckon i should program it to a 30" would that make a difference in the speedo?
It sure would.
 

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it's not fast enough
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Discussion Starter #9
i stand corrected, i WAS LOOKING at the 285-55-18s, but i bought the 255-55-18s so my speedo is correct, they come out to 29" so i was right...sorry for the wrong tire size.
 

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What gears do you have now?
 

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it's not fast enough
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Discussion Starter #11
GU6....so im guessing 3:42s limited slip aka granny spin.
 

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Mayhem, Like Me
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if you are wanting to keep top end pull.. leave the 3.42's and get a better diff to put them on IMO...
 

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it's not fast enough
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Discussion Starter #13
hum....then im torn...because i love the pull..but at the same time i want the 1/4 mile pull...i'm just torn.
 

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I have a brand new set ( 2000 miles ) of Richmond 4.10's 8.5 that were in my 2001 Silv.. Bought my brother in laws 4.30's so they are in the box.
125.00 plus shipping
 

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it's not fast enough
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Discussion Starter #15
im going to build a 6.0 now, and put a built 4L60E behind it, so i'll probally drop down to a 3:90 to give me some kind of pull on the road..with just a locker. but there are a lot of ppl telling me to stay with the 3:42s....for the highway.
 
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