12 Bolt Differential Mystery
 

OK,
I am in the midst of 3 builds at once and I am pulling my hair out on one of them.:waah:
I have a 62 GMC that is a ground up deal going. :metal:
The original differential was broken. I got a diff out of a 70 and tried to install it but the trailing arm perches are in the wrong place. :confused:
The owner decided he wanted to go 5 lug so I ended up getting another "good" diff off C/L ... :uhmk:
This diff started leaking from the axle tubes the minute I put fluid in it.. the center section casting is cracked!!! :devil:
I pulled the posi carrier and pinion out, all in good shape.. but the axles don't match any other 12 bolt I have??
I have the axles out of the 70 diff but the axles out of the leaker diff are longer...
Anyone know how many length 12 bolts were put into Chevy trucks and what years had what lengths???


:5150:

Re: 12 Bolt Differential Mystery
 

The 1962 perches will weld outside the 1970. I know mine are that way. Just get new ones and weld on. The 60-62 x frames are wider than the 1963-1966 hince bed bolt issues and such.

Re: 12 Bolt Differential Mystery
 

Being a GMC you might ask Barry over at the GMC boards
He's had his hands on more rear ends than richard simmons. Just for different reasons :D

Re: 12 Bolt Differential Mystery
 

Yes, I am aware of the differences, thanks.. :metal:
I need a 5 lug and wanted to swap in the 5 lug axles but they are too long for the "70" diff.. :(
Now I am looking for a housing for the parts out of the unknown year leaker diff or I may just need to find a 5th complete differential.
(I left out the 86 10 bolt that is noisy):waah:
At this point I don't believe the "70" diff is a 70, I think it is a 64-69 possibly...
I'm freaking confused now...


:5150:

Re: 12 Bolt Differential Mystery
 

Thanks Brother :metal: but being a GMC is pretty irrelevant at this point since I am just trying to hang a 12 bolt in the truck with 5 lug axels and not using the original in any way.
If someone knows what length axles fit what housings I will be miles ahead...
Thanks for the tip tho..



:5150:

Re: 12 Bolt Differential Mystery
 

Let me say it different - if you wanna swap something under a GMC, he can answer it in 10 seconds or less without consulting anything other than experience. Interchanging parts is what he does.
:D

Re: 12 Bolt Differential Mystery
 

So I used CPP axle kit 6to5 70RACK at 31.5" and cost $329

Re: 12 Bolt Differential Mystery
 

Old ones.

Re: 12 Bolt Differential Mystery
 

I posted the info you need in the thread in the 'Engine and Drivetrain' section that you posted in.

You can not install a set of factory 5 lug axles into a '63 to early '70 12 bolt, they are too long. I guess you can as others have, but it is not correct. You would also have to change the backing plates and drums to the ones for the 2-3/4" wide shoes, but then your bearing surfaces aren't in the right location.

Re: 12 Bolt Differential Mystery
 

Fetch.. gotcha thanks

LV, thanks, I have the axles and all I need, I just need to find the correct housing.

Cap.. just saw that post, thanks. With that info I will have to say that the 70 diff must be an earlier than 70 diff because it is shorter.. my axles and parts from the leaker 12 bolt must be later.

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