Well...it's a 12 bolt - The 1947 - Present Chevrolet & GMC Truck Message Board Network

67Blacksheep · 03-25-2002, 09:33 PM

Just found out today that my donor is a 12 bolt! Any chance that that means a certain ratio? Fast told me 3:08 or 3:73 before. Does that apply to both ten and twelve bolts? Fast if you are listening....still need the pan hard when you find one. Due to the economy, my company is ready to revoke our company trucks! Looks like my 67' will be seeing a lot of miles here real soon. Enough pressure to keep me out in the garage cleaning and preparing the new rear. Oh well...I needed to get her done anyway!

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67 Chevy C20 LB Stepside,
350 4-bolt with goodies.

71402BB · 03-25-2002, 09:39 PM

nope it dosen't mean that you have a certain ratio! depending on what it came out of it could be 3.08's 3.73's or in a rare case a 4.11's! I have 4.11's in my 68 burb! you'll know what you have as soon as you start driving it! If it sounds like it's reving high at 55mph you have 4.11's, if it sounds like your reving high at 70-75 you have 3.73's anything higher is prolly 3.08's or higher! Good luck wit the install!

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71 SWB Stepside, was a 250, now is a 402 Big Block with 4 speed and 3.73's

72 LWB 4x4 350 4-speed 3.08's posi wearing army olive drab green (SOLD!)

68 BURB 50TH LOOKALIKE with built 350 4-speed 4.11's and posi

67Blacksheep · 03-25-2002, 09:45 PM

402-
Thanks, when I got it from the yard I didn't care what it was. I have an Eaton in my C20, it's geared so bad that 55 MPH is a stretch. I was glad to see the twelve bolts just for bragging rights....are they really that much better than 10?

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67 Chevy C20 LB Stepside,
350 4-bolt with goodies.

71GMC 4x4 · 03-26-2002, 11:42 AM

In cars, some of most of the early 70's novas (and other cars too) had the 8.5 10 bolt their just about as strong as the 12 bolt. But the early 7.5 10 bolts were weak, that's why alot of people put the 8.5 under thier camaro (12 bolts for camaros are getting hard to find & expensive). I don't know if the trucks 10 bolts are bigger than a car 10 bolts maybe their the same?(I think they are different) Anyway the 12 bolt is usually stronger than the 10.

[This message has been edited by 71GMC 4x4 (edited March 26, 2002).]

*Fast68Chevy* · 03-26-2002, 12:48 PM

actually the 8.5" axle can be considered stronger if you examine the pinion gears of one and of a 12 bolt 8.875" axle,.
the diameter of the pinion gear where the bearign rides is only 1.425 on the truck 12 bolt comparted to 1.625 on car 12 bolt and 8.5" 10 bolt and most all other axles out there. also lower ratios like 3.73 and 4.11 are weaker in that there is alot less tooth contact patcxh area in existence on lower rtatio gear sets compared to on 3.07 and 2.73 and 2.56 and 3.40 and such, reason being is because the diameter of the pinion gear is alot larger on the higher ratio gear sets. Technically an 8.5" 10 bolt or a dana 44(also 8.5") with 3.07 can take alot more aplied torque than a 12 bolt truck axle of 3.73 or 4.11 or 4.88 or 4.56 ratio.

Im gonna try and see if I can figure out what i done with all the other pan hard bars, will keep digging around, sorry
good luck

67Blacksheep · 03-26-2002, 06:36 PM

Thanks once again. I did get the old u-bolts cut free last night and now have the new arrival resting comfortably in my garage! I will keep everyone posted on the progress.

------------------
67 Chevy C20 LB Stepside,
350 4-bolt with goodies.

03-25-2002, 09:33 PM	#1
67Blacksheep Registered User Join Date: Mar 2002 Location: Ohio Posts: 135	Well...it's a 12 bolt Just found out today that my donor is a 12 bolt! Any chance that that means a certain ratio? Fast told me 3:08 or 3:73 before. Does that apply to both ten and twelve bolts? Fast if you are listening....still need the pan hard when you find one. Due to the economy, my company is ready to revoke our company trucks! Looks like my 67' will be seeing a lot of miles here real soon. Enough pressure to keep me out in the garage cleaning and preparing the new rear. Oh well...I needed to get her done anyway! ------------------ 67 Chevy C20 LB Stepside, 350 4-bolt with goodies. __________________ '94 GMC Seirra Ext. Cab '67 Formula Firebird '89 GSX-R 750

03-25-2002, 09:39 PM	#2
71402BB now thats a true COON DOG Join Date: Nov 2000 Location: Franconia, NH Posts: 1,977	nope it dosen't mean that you have a certain ratio! depending on what it came out of it could be 3.08's 3.73's or in a rare case a 4.11's! I have 4.11's in my 68 burb! you'll know what you have as soon as you start driving it! If it sounds like it's reving high at 55mph you have 4.11's, if it sounds like your reving high at 70-75 you have 3.73's anything higher is prolly 3.08's or higher! Good luck wit the install! ------------------ 71 SWB Stepside, was a 250, now is a 402 Big Block with 4 speed and 3.73's 72 LWB 4x4 350 4-speed 3.08's posi wearing army olive drab green (SOLD!) 68 BURB 50TH LOOKALIKE with built 350 4-speed 4.11's and posi __________________ current project 67 402BB stout th350 3.08's with a locker. Plan on tubs 18.5's out back! (thanks Burnsman!) 71 SWB Stepside, was a 250, now is a 402 Big Block with 4 speed and 3.73's ( was crushed by a tree, bed sold, motor pulled) was my first truck!... oh well... 72 LWB 4x4 350 4-speed 3.08's posi wearing army olive drab green (SOLD!) 68 BURB 50TH LOOKALIKE work in progress, soon to have 250-I6 with a 3-speed on the tree 4.11's and posi ( currently sitting in back yard tarped awaiting time, $$$, and lots of love!) 67 1 TON- work truck 396 sm 420 4-speed, flat bed 4.57 gears "big red" (my first landscape truck, very rusty and crusty! but still gets the job done when needed!)

03-25-2002, 09:45 PM	#3
67Blacksheep Registered User Join Date: Mar 2002 Location: Ohio Posts: 135	402- Thanks, when I got it from the yard I didn't care what it was. I have an Eaton in my C20, it's geared so bad that 55 MPH is a stretch. I was glad to see the twelve bolts just for bragging rights....are they really that much better than 10? ------------------ 67 Chevy C20 LB Stepside, 350 4-bolt with goodies. __________________ '94 GMC Seirra Ext. Cab '67 Formula Firebird '89 GSX-R 750

03-26-2002, 11:42 AM	#4
71GMC 4x4 Registered User Join Date: Mar 2002 Location: Redway,Ca. U.S.A Posts: 37	In cars, some of most of the early 70's novas (and other cars too) had the 8.5 10 bolt their just about as strong as the 12 bolt. But the early 7.5 10 bolts were weak, that's why alot of people put the 8.5 under thier camaro (12 bolts for camaros are getting hard to find & expensive). I don't know if the trucks 10 bolts are bigger than a car 10 bolts maybe their the same?(I think they are different) Anyway the 12 bolt is usually stronger than the 10. [This message has been edited by 71GMC 4x4 (edited March 26, 2002).] __________________ [IMG]http://mustangmods.com/publish/topless99/truck2.jpg[IMG]

03-26-2002, 06:36 PM	#6
67Blacksheep Registered User Join Date: Mar 2002 Location: Ohio Posts: 135	Thanks once again. I did get the old u-bolts cut free last night and now have the new arrival resting comfortably in my garage! I will keep everyone posted on the progress. ------------------ 67 Chevy C20 LB Stepside, 350 4-bolt with goodies. __________________ '94 GMC Seirra Ext. Cab '67 Formula Firebird '89 GSX-R 750

03-26-2002, 12:48 PM	#5
Fast68Chevy Account Suspended Join Date: May 2000 Location: IL Posts: 0	actually the 8.5" axle can be considered stronger if you examine the pinion gears of one and of a 12 bolt 8.875" axle,. the diameter of the pinion gear where the bearign rides is only 1.425 on the truck 12 bolt comparted to 1.625 on car 12 bolt and 8.5" 10 bolt and most all other axles out there. also lower ratios like 3.73 and 4.11 are weaker in that there is alot less tooth contact patcxh area in existence on lower rtatio gear sets compared to on 3.07 and 2.73 and 2.56 and 3.40 and such, reason being is because the diameter of the pinion gear is alot larger on the higher ratio gear sets. Technically an 8.5" 10 bolt or a dana 44(also 8.5") with 3.07 can take alot more aplied torque than a 12 bolt truck axle of 3.73 or 4.11 or 4.88 or 4.56 ratio. Im gonna try and see if I can figure out what i done with all the other pan hard bars, will keep digging around, sorry good luck



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