Axle swap - The 1947 - Present Chevrolet & GMC Truck Message Board Network

70GMCer · 04-30-2005, 07:07 AM

I thought I read on here a while back that you could just swap out the 6 lug axles for 5 lug axles in a leaf spring 12 bolt. If you can do this, what year truck axle should I look for. Mine is 70 GMC......and has a really sweet "rear", lol, and would hate to change it.

thanks.....

krue · 04-30-2005, 07:26 AM

In the middle of the 70 model year they started using wider rear ends. If yours is the wider rear you should be able to swap 5 lug axles out of 71 and up to 80 or 87 (I can't remember how far it goes). If yours is the earlier (narrower) rear end the axles will be about 3/4 inch too long. I am told you can make spacers to make up for the difference.

Bamm · 04-30-2005, 07:45 AM

Yeah, what Krue said. I had guys tel me that they were direct swaps when I bought a '70 posi rear. Then the axles wouldn't fit and I had to swap the internals..........Jerry

70GMCer · 04-30-2005, 08:45 AM

So, mid model year or later, assuming that was when my truck was made, I should have the narrow rear. Again, assuming that the rear has never been changed. Is there any place where I could get the specs, length size on those 2 differant rears so I can measure?

thanks......

Billy G · 04-30-2005, 01:40 PM

How do you tell when you have the "70 1/2" rear end? Serial #s? Measurements?
This would be good info.

Thanks in advance..
Billy G

flip66 · 05-01-2005, 03:04 AM

67-70 6 lug is 3/4 of an inch longer on both side then the mid 70-72 I have put 5 lug axels in a 69 you have to space the backing plate out about a 1/2 inch on each side and use the 72 brakes and drums

Billy G · 05-01-2005, 10:17 AM

What about 77 GMC rear axles??? I have what I THINK is a .308 rear end in my parts truck for the 76 that I dont know what Im going to do with. Would these somehow fit??

70GMCer · 05-01-2005, 10:32 AM

I learned yesterday, that all truck 12 bolts were the same from mid year '71 thru mid year '81. Then they went to 10 bolt. This according to the "Hollander" manual I was looking thru.......

HugrOrang71 · 05-01-2005, 08:21 PM

Why not take some measurements of your axles and have Moser or Dutchman build a set to your specs. Then you get brand new ones (maybe even HD alloys). Or if you have access, have yours redrilled.

04-30-2005, 07:07 AM	#1
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	Axle swap I thought I read on here a while back that you could just swap out the 6 lug axles for 5 lug axles in a leaf spring 12 bolt. If you can do this, what year truck axle should I look for. Mine is 70 GMC......and has a really sweet "rear", lol, and would hate to change it. thanks..... __________________ 1997 GMC Sierra Ext 1965 Mustang

04-30-2005, 07:26 AM	#2
krue Designated A-hole! Join Date: Mar 2003 Location: South Mississippi Posts: 36,448	In the middle of the 70 model year they started using wider rear ends. If yours is the wider rear you should be able to swap 5 lug axles out of 71 and up to 80 or 87 (I can't remember how far it goes). If yours is the earlier (narrower) rear end the axles will be about 3/4 inch too long. I am told you can make spacers to make up for the difference. __________________ "If it ain't broke, fix it 'til it is!" Being stupid ain't illegal. We're Still Debt Free Except for the House!!! www.daveramsey.com 70 GMC SWB Stepside project "Green Booger" soon to be 6.0l/4l80e 93 S-10 "Poppaw's Truck"

04-30-2005, 07:45 AM	#3
Bamm Cowboy Fan for Life!!!!!! Join Date: Apr 2002 Location: Amelia, Virginia Posts: 2,921	Yeah, what Krue said. I had guys tel me that they were direct swaps when I bought a '70 posi rear. Then the axles wouldn't fit and I had to swap the internals..........Jerry __________________ 1967 ShortBed Fleetside 3/4 Drop 350/700R4 Tilt wheel 18 x 8 Torque Thrust II's Future mods: All new gauges & wood bed My Zip is 23002 I ship UPS, USPS

04-30-2005, 08:45 AM	#4
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	So, mid model year or later, assuming that was when my truck was made, I should have the narrow rear. Again, assuming that the rear has never been changed. Is there any place where I could get the specs, length size on those 2 differant rears so I can measure? thanks...... __________________ 1997 GMC Sierra Ext 1965 Mustang

04-30-2005, 01:40 PM	#5
Billy G Registered User Join Date: May 2003 Location: Dayton, Tx (in Old River) Posts: 286	How do you tell when you have the "70 1/2" rear end? Serial #s? Measurements? This would be good info. Thanks in advance.. Billy G __________________ My FAMOUS LAST WORDS...."Ima Gonna!!" - 1970 GMC 1500 swb/step 250 I-6 3 spd - "The GEM" - 1976 Chev Scotsdale swb/step 350/350 - "The JEWEL" - 1982 Chev C-10 swb/step 250 I-6 3 spd - - 2001 Chev Silverado LT -

05-01-2005, 03:04 AM	#6
flip66 Registered User Join Date: Jan 2004 Location: Garland TX Dallas area Posts: 658	67-70 6 lug is 3/4 of an inch longer on both side then the mid 70-72 I have put 5 lug axels in a 69 you have to space the backing plate out about a 1/2 inch on each side and use the 72 brakes and drums __________________ 1998 Pontiac Grad Prix GTP 1969 C10 396 TH400 3.08 posi

05-01-2005, 10:17 AM	#7
Billy G Registered User Join Date: May 2003 Location: Dayton, Tx (in Old River) Posts: 286	What about 77 GMC rear axles??? I have what I THINK is a .308 rear end in my parts truck for the 76 that I dont know what Im going to do with. Would these somehow fit?? __________________ My FAMOUS LAST WORDS...."Ima Gonna!!" - 1970 GMC 1500 swb/step 250 I-6 3 spd - "The GEM" - 1976 Chev Scotsdale swb/step 350/350 - "The JEWEL" - 1982 Chev C-10 swb/step 250 I-6 3 spd - - 2001 Chev Silverado LT -

05-01-2005, 10:32 AM	#8
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	I learned yesterday, that all truck 12 bolts were the same from mid year '71 thru mid year '81. Then they went to 10 bolt. This according to the "Hollander" manual I was looking thru....... __________________ 1997 GMC Sierra Ext 1965 Mustang Last edited by 70GMCer; 05-01-2005 at 10:34 AM. Reason: mispelling

05-01-2005, 08:21 PM	#9
HugrOrang71 Bite me, import boy Join Date: Apr 2005 Location: Eagle Point, Oregon Posts: 102	Why not take some measurements of your axles and have Moser or Dutchman build a set to your specs. Then you get brand new ones (maybe even HD alloys). Or if you have access, have yours redrilled. __________________ Jason '71 C-10 Deluxe-under construction '69 C20, 396,T400-donor truck, '65 C10 project "Facts are meaningless, You can use facts to prove anything that's even remotely true."



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