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03-23-2005, 08:21 PM
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#1 |
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Senior Member
Join Date: Jan 2005
Location: LAX area, So Cal
Posts: 499
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Diff ratio help (again!)..very confused!!!
OK...everything I've read in my searches on this board says that my 'corporate diff' should be 4.10:1 or lower (up to 5.x by some accounts).
I need to send my PCM for the 99 suburban engine for reprogramming so I checked the diff for accurate ratio. Here is what I got: For every one revolution of the wheels, I get about 3.4 revolutions at the driveshaft. Wouldn't that give a 3.x :1 diff ratio? Anyone have any ideas? I want my PCM to get as accurate a speed signal as possible. Thanks, Tim
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1972 Suburban C20 454/TH700R4, eaton-corporate 4.10 (looking for 3.7) Sold: 71 Cheyenne 20 Installed a 99 5.7L L31/4L60E from Suburban 1500 (2005) |
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03-23-2005, 08:28 PM
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#2 |
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Senior Member
Join Date: Apr 2000
Location: Delta,Pa
Posts: 14,950
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y not just pull the cover and count the teeth no other way is truely accurate. its about time for new gear oil anyways especially if it hasnt ever been changed
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Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member. |
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03-23-2005, 08:48 PM
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#3 |
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Senior Member
Join Date: Jan 2005
Location: LAX area, So Cal
Posts: 499
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Well....I could but I would need to wait for the weekend. I will do that anyways, but I thought I would see what the brain trust here had to say on the subject...
If it was almost 4 turns at the input, I would just assume a 4.1, but it isn't even close....
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1972 Suburban C20 454/TH700R4, eaton-corporate 4.10 (looking for 3.7) Sold: 71 Cheyenne 20 Installed a 99 5.7L L31/4L60E from Suburban 1500 (2005) |
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03-23-2005, 08:49 PM
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#4 |
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Registered User
Join Date: Nov 2003
Location: Alexandria, VA
Posts: 1,534
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3.42:1
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'72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction.   
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03-23-2005, 08:53 PM
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#5 |
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Watch out for your cornhole !
 
Join Date: Jun 2003
Location: Azle, Texas
Posts: 14,162
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If you only have one wheel off the ground, you need to turn the wheel 2 turns and count the driveshaft turns.
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I'm on the Instagram- @Gearhead_Kevin Last edited by Tx Firefighter; 03-23-2005 at 08:56 PM. |
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03-23-2005, 08:54 PM
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#6 | |
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Senior Member
Join Date: Jan 2005
Location: LAX area, So Cal
Posts: 499
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Quote:
I will definitely open the Diff this weekend..... 
__________________
1972 Suburban C20 454/TH700R4, eaton-corporate 4.10 (looking for 3.7) Sold: 71 Cheyenne 20 Installed a 99 5.7L L31/4L60E from Suburban 1500 (2005) |
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03-23-2005, 08:59 PM
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#7 | |
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Senior Member
Join Date: Jan 2005
Location: LAX area, So Cal
Posts: 499
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Quote:
 thanks for that tip.....4.1:1 Sorry for the rookie mistake......I'm better than that...really I am 
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1972 Suburban C20 454/TH700R4, eaton-corporate 4.10 (looking for 3.7) Sold: 71 Cheyenne 20 Installed a 99 5.7L L31/4L60E from Suburban 1500 (2005) |
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03-23-2005, 09:16 PM
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#8 |
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Watch out for your cornhole !
Join Date: Jun 2003
Location: Azle, Texas
Posts: 14,162
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It's a common mistake.
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I'm on the Instagram- @Gearhead_Kevin |
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