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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: str8bloc on September 11, 2011, 10:10:03 am

Title: 12 bolt
Post by: str8bloc on September 11, 2011, 10:10:03 am

i know this subject has been covered, but what do i need to do to swap a 10 to 12 bolt . my truck is 86 the rear is out of a 75-76 i believe.they both are 2-wheel and i have a set of 3.73 for the 12 bolt. I'm running 2.73 in my truck right now.i just gotta rebuild the 12. any advice and tips?Also whould yall kinda give me a ballpark on the gears in the 12

Title: Re: 12 bolt
Post by: VileZambonie on September 11, 2011, 11:23:44 am

You want us to guess the gear ratio? You need to take the cover off. Reallistically you need a conversion u-joint and that's about it.

Title: Re: 12 bolt
Post by: str8bloc on September 11, 2011, 02:59:46 pm

where can i get the u joint? i know that i have to remove to get the ratio but what gears normally came in them

Title: Re: 12 bolt
Post by: beastie_3 on September 11, 2011, 03:05:22 pm

count how many rotations the pinion spins for one rotation of the wheel

Title: Re: 12 bolt
Post by: str8bloc on September 11, 2011, 03:35:23 pm

ill just have to wait till i crack it open, its kinda heavy lol. my bro gets off and he'll help me take it down

Title: Re: 12 bolt
Post by: 69byrd on September 11, 2011, 04:02:11 pm

Quote from: VileZambonie on September 11, 2011, 11:23:44 am

You want us to guess the gear ratio?

It could be anything. My 12 has the same gears as your 10.

Title: Re: 12 bolt
Post by: str8bloc on September 11, 2011, 05:17:36 pm

thankz hopefully its a good buy gear oil poured in the bed i didnt see no shavings and oil looked clean

Title: Re: 12 bolt
Post by: bake74 on September 12, 2011, 09:27:38 am

     You can get the conversion u-joint at part stores or on line, try rock auto.

Title: Re: 12 bolt
Post by: Captkaos on September 12, 2011, 05:32:19 pm

Autozone, O'riellys, Advanced, any local parts store will have the hybrid joint.

Title: Re: 12 bolt
Post by: muddpuppy01 on September 12, 2011, 09:57:50 pm

you can check your ratio without opening it up just have to keep one wheel still or have them both spinning at the same speed and direction.

If only spinning one wheel mark the pinion position in conjunction to the axle. Mark the tire position to the ground. Rotate the tire two times while counting the amount of times the pinion turns. That will give the gear ratio.

If you have a locker were both tires will turn together. Mark the tire and pinion as described above. This time rotate the tire once and count the amount of turns of the pinion. Again that will be your gear ratio.

Title: Re: 12 bolt
Post by: Irish_Alley on September 13, 2011, 01:25:37 am

cant verify what mudd said about the "open style" test but the locker test i know is right along with how the others said to test it. but i will save you this head ach. dont go to autozone or advanced maybe not even pep boys for the u-joint go to Napa and tell them what you have they will get you the right part cause they know how to use the books. autozone and advanced you will be lucky if you tell them what you need and they try to look it up with them computer. i dont think even if they could their books would tell them or if they know where their books are. i used to work with autozone and if a customer would want a special part they would have to come to me cause i would try or if i could get it i would call someone who could. another thing if you want to deal with advanced or autozone is go to napa and get the part number then the other stores can cross it and get the right part for you

Title: Re: 12 bolt
Post by: muddpuppy01 on September 13, 2011, 04:42:17 am

or try and find the part number online then print it out and take it down there done dealt with that to many times

Title: Re: 12 bolt
Post by: str8bloc on September 13, 2011, 10:05:08 am

well i have 2 guys at autozone who know these trucks they dont even use the comp when im there they walk back and grab off shelf they drive em too daily so i trust them.

Title: Re: 12 bolt
Post by: VileZambonie on September 14, 2011, 08:00:51 pm

I posted the conversion joint info in another thread.

These are carquest part # 3-3131 or 3-3130 or 2-1153

Title: Re: 12 bolt
Post by: str8bloc on September 14, 2011, 10:37:57 pm

thankz vile.gears are 3.40 10:34 on the carrier. should i run 3.42 or put 3.73?

Title: Re: 12 bolt
Post by: muddpuppy01 on September 15, 2011, 04:36:06 am

I would use the 3.42 gear that you got now

Title: Re: 12 bolt
Post by: str8bloc on September 15, 2011, 07:37:36 pm

i have 2.73 in the truck the rear i just got has 3.42, ima go through the rear. all new seals hardware etc. so should i keep the 3.42 or just swap the 3.73?

Title: Re: 12 bolt
Post by: 80stepsideguy on September 15, 2011, 08:25:55 pm

3.73s are good if you got a 4 speed or a 700r4 .Any 3 speed  like a th350 or 400 is not good cause of the aggressive rpms it produces.If you got a 3 speed auto go with the 3.42.

thanks
pat

Title: Re: 12 bolt
Post by: VileZambonie on September 15, 2011, 08:54:39 pm

What size tires are you running and what trans? I agree with Pat unless it's just a toy. If it's a toy go with the 3.73

Title: Re: 12 bolt
Post by: str8bloc on September 17, 2011, 12:43:25 pm

wanna make it a street truck 700r4 i want 4.11 but 3.73 would do for the time being

Title: Re: 12 bolt
Post by: VileZambonie on September 17, 2011, 04:03:35 pm

What size tires are you running?

Title: Re: 12 bolt
Post by: str8bloc on September 17, 2011, 08:10:19 pm

oh my bad they are 205 70 15 for the front and 235 75 15 for the rear. i wanna run 205 70 15 for the front and 295 or 325 50 15 on the rear for daily and  a 28 10.5 radial for the track

Title: Re: 12 bolt
Post by: str8bloc on March 20, 2012, 11:00:56 am

well my buddy wants my 10 bolt he blew his 12 bolt do i use the same hybrid joint?

Title: Re: 12 bolt
Post by: Captkaos on March 20, 2012, 01:26:30 pm

Yes