Stupid question about differentials - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Raven Lunatic · 03-14-2004, 02:54 AM

I think I have a 12 bolt rear end... question (I'm embarassed to ask)... does 12 bolt refer to the number of bolts holding on the dif. cover?

What is the advantage to running a 12 bolt?

1969 GMC · 03-14-2004, 02:56 AM

you are correct, sir.

12 bolt axles are fairly strong as far as half ton suspension goes. parts are plentiful, and they came under a lot of different cars/trucks (different types, though).

Sweet72 · 03-14-2004, 02:59 AM

Actually the "12" refers to the no. of bolts holding the ring gear to the carrier. Confused yet? Ironically the 12's do have 12 bolts holding the cover on.

Raven Lunatic · 03-14-2004, 03:16 AM

Thanx guys, 'preciate the info... do you think I'd be safe to run the 12 with a 409/700r4 combo?

Russell · 03-14-2004, 03:44 AM

Hopefully that 409 doesn't rip that 700r4 to bits, lol

Being a 3/4 ton guy myself, I think you should get yourself a full floater and convert it over to a 5 lug disc brake setup, that would be one wicked rear end

(doubt its possible though, lol)

I'm running a 14 bolt full floater with 3.73s, I like it

Another thing I like is this weather we've been getting (minus Friday night... got like a foot and a half of snow out here east of the city, much fun playing in it with the bobcat this morning)

1969 GMC · 03-14-2004, 04:17 AM

Quote:

Originally posted by Sweet72
Actually the "12" refers to the no. of bolts holding the ring gear to the carrier. Confused yet? Ironically the 12's do have 12 bolts holding the cover on.

Are all corporate diffs like that? A buddy of mine has a late 70s K/20 with a 14bff rear and 10b front. The 14bff has 14 bolts on the diff cover, and the 10 bolt has 10. I always use the diff cover bolt method to ID corporate axles.

Russell, I don't think you can convert 3/4 ff axles to 5 bolt pattern because of the massive hub that protrudes thru the center of the wheel. You could prolly use a spacer but that doesn't sound safe. You can covert sf 1/2 ton axles to ff, I have seen this mod done in 4x4s, to gain extra strength and eliminate c-clips without swapping axles. I have even seen some with this mod that put locking hubs on the rear axle of their vehicle, but they complain about pranksters unlocking all 4 of their hubs so when they go in gear the truck cannot move on its own. That would be a good one to pull

Bowtie67 · 03-14-2004, 07:42 AM

Quote:

Originally posted by Raven Lunatic
Thanx guys, 'preciate the info... do you think I'd be safe to run the 12 with a 409/700r4 combo?

I'am in the process of building a 413SBC and it will be connected to the already TCI 700R4 in my 67, the last little powerplant had no problem. The rear ins't the issue, the trans is, The better 700R4 trans are from 87up and if your goona throw some heavy stuff at it I would make sure it is well built with quality parts. I also run a 2200stall in mine.

Blazer1970 · 03-14-2004, 09:36 AM

Quote:

Originally posted by Sweet72
Actually the "12" refers to the no. of bolts holding the ring gear to the carrier. Confused yet? Ironically the 12's do have 12 bolts holding the cover on

Quote:

Are all corporate diffs like that? A buddy of mine has a late 70s K/20 with a 14bff rear and 10b front. The 14bff has 14 bolts on the diff cover, and the 10 bolt has 10. I always use the diff cover bolt method to ID corporate axles.

Actually, it is the number of bolts holding the cover on. A 14 bolt ff axle has 14 bolts on the cover, but only 12 bolts holding the ring gear to the carrier. Also, there are about 5 or 6 different versions of the "10 bolt" that have been used in cars and trucks. GM uses ring gear diameter to ID the axles.

Sweet72 · 03-14-2004, 11:38 PM

Thanks for the correction on the "bolt" issue Blazer1970. I guess that goes to show ya, don't believe everything you hear or see in print.

Blue_71 · 03-15-2004, 12:01 AM

are you sure blazer? ive always heard that its the number of bolts on the ring gear but usually the cover is the same? i dont know im just asking

Blazer1970 · 03-15-2004, 09:46 AM

Quote:

Originally posted by Blue_71
are you sure blazer? ive always heard that its the number of bolts on the ring gear but usually the cover is the same? i dont know im just asking

Yes, I am sure. The numbers do happen to be the same some of the time (like on a 12 bolt IIRC). That thing about the ring gear bolts is something that some magazine writer mistakenly wrote once, and a lot of people started repeating it. Sort of like the supposedly "bad" Vortec head casting.

Also note that General Motors (and most aftermarket parts suppliers) does not use the "10 bolt, 12 bolt, 14 bolt" terms at all. Since there are several different types of 10 bolts, 3 kinds of 14 bolts, and at least 2 distinct types of 12 bolts, it would be chaos to try to buy parts using those descriptions.

Raven Lunatic · 03-15-2004, 05:45 PM

Just one more question on the diff, and I'll go away guys... thanx for the info so far, it's invaluable...

ugh... actually two questions...

How do I figure out the gear ratio in the rear end?

What's a "full floater"?

Guess I'm "removing all doubt", but there's only one way to learn...lol...

Oh, and Russell, ya this weather has been great... although some little pr*ck broke into my s-10 on friday night, right in the driveway, and stole my skates and weight belt... can always tell when it's a young person, they never touch my cds, lol... guess they don't like my taste in music...

Raven Lunatic · 03-17-2004, 07:03 AM

ttt

**JIMs70GMC** · 03-17-2004, 08:33 AM

How to figure gear ratio- several ways- count the number of teeth on ring and pinion devide ring# by pinion#.
What's full floater- basiacally the rear has a hub w/ inner and outer bearings like the front and these bearings along with the spindle and hub support the load, not the axle shaft i.e the axle "floats" and only has to transfer power not support any weight.
In your 12 bolt rear the axle supports the weight of the vehicle by the bearing it rides in on each side. i.e the axle transfers power and supports weight.

By the way in the above axle refers to the actual shaft turning by the differential.

Tx Firefighter · 03-17-2004, 09:41 AM

There are plenty of 60s era muscle car rearends with 12 bolt covers and the smaller 10 bolt internals. A Chevelle guy will know that one. The 10 or 12 refers to the ring gear bolt count.

03-14-2004, 02:54 AM	#1
Raven Lunatic On the Hillbilly Highway Join Date: Nov 2002 Location: Edmonton, Alberta Posts: 90	Stupid question about differentials I think I have a 12 bolt rear end... question (I'm embarassed to ask)... does 12 bolt refer to the number of bolts holding on the dif. cover? What is the advantage to running a 12 bolt? __________________ Does anyone else smell smoke? 1967 GMC 910, rolling frame coming soon!

03-14-2004, 02:56 AM	#2
1969 GMC Registered User Join Date: Feb 2003 Location: The Rubber City Posts: 5,498	you are correct, sir. 12 bolt axles are fairly strong as far as half ton suspension goes. parts are plentiful, and they came under a lot of different cars/trucks (different types, though). __________________ 1969 GMC K2500 1996 Honda Accord 2007 Kawasaki KLR 650

03-14-2004, 02:59 AM	#3
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	Actually the "12" refers to the no. of bolts holding the ring gear to the carrier. Confused yet? Ironically the 12's do have 12 bolts holding the cover on. __________________ '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.

03-14-2004, 03:16 AM	#4
Raven Lunatic On the Hillbilly Highway Join Date: Nov 2002 Location: Edmonton, Alberta Posts: 90	Thanx guys, 'preciate the info... do you think I'd be safe to run the 12 with a 409/700r4 combo? __________________ Does anyone else smell smoke? 1967 GMC 910, rolling frame coming soon!

03-14-2004, 03:44 AM	#5
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	Hopefully that 409 doesn't rip that 700r4 to bits, lol Being a 3/4 ton guy myself, I think you should get yourself a full floater and convert it over to a 5 lug disc brake setup, that would be one wicked rear end (doubt its possible though, lol) I'm running a 14 bolt full floater with 3.73s, I like it Another thing I like is this weather we've been getting (minus Friday night... got like a foot and a half of snow out here east of the city, much fun playing in it with the bobcat this morning) __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)

03-14-2004, 11:38 PM	#9
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	Thanks for the correction on the "bolt" issue Blazer1970. I guess that goes to show ya, don't believe everything you hear or see in print. __________________ '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.

03-15-2004, 05:45 PM	#12
Raven Lunatic On the Hillbilly Highway Join Date: Nov 2002 Location: Edmonton, Alberta Posts: 90	Just one more question on the diff, and I'll go away guys... thanx for the info so far, it's invaluable... ugh... actually two questions... How do I figure out the gear ratio in the rear end? What's a "full floater"? Guess I'm "removing all doubt", but there's only one way to learn...lol... Oh, and Russell, ya this weather has been great... although some little prck broke into my s-10 on friday night, right in the driveway, and stole my skates and weight belt... can always tell when it's a young person, they never touch my cds, lol... guess they don't like my taste in music... __________________ Does anyone else smell smoke? 1967 GMC 910, rolling frame coming soon! Last edited by Raven Lunatic; 03-15-2004 at 05:49 PM.*

03-17-2004, 07:03 AM	#13
Raven Lunatic On the Hillbilly Highway Join Date: Nov 2002 Location: Edmonton, Alberta Posts: 90	ttt __________________ Does anyone else smell smoke? 1967 GMC 910, rolling frame coming soon!

03-17-2004, 08:33 AM	#14
JIMs70GMC user # 2756 Join Date: Jun 2001 Location: Chesapeake, Virginia Posts: 4,612	How to figure gear ratio- several ways- count the number of teeth on ring and pinion devide ring# by pinion#. What's full floater- basiacally the rear has a hub w/ inner and outer bearings like the front and these bearings along with the spindle and hub support the load, not the axle shaft i.e the axle "floats" and only has to transfer power not support any weight. In your 12 bolt rear the axle supports the weight of the vehicle by the bearing it rides in on each side. i.e the axle transfers power and supports weight. By the way in the above axle refers to the actual shaft turning by the differential. __________________ 1970 K25, 8' stepside bed 350/465/205 44 up front, 60 in the rear 4.10s rolling on 33" Dunlop MTs 1986 K5, 350/465/208 Dana 60/14 bolt from a cucv 36" Super Swampers TSL/SX 1983 K20 w/ CUCV axles, 350/700R4/208 sitting on 37" Goodyears 1986 M1031 6.2 diesel, TH400/NP205 locker in the rear and a LS in the front, all stock for now..... 1986 K30, 350/400/205 dana 60 and 14 bolt. I kept the drivetrain. Body/bad and chassis are gone. 1981 K30, 350/465/205 dana 60 and dually 14 bolt. Has a G80, and a flat bed. Going to replace the flat bed. 1985 K20, 350/400/208 10 bolt and SF 14 bolt. I wonder where I can find some 1 tons. Hmmmmm

03-17-2004, 09:41 AM	#15
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	There are plenty of 60s era muscle car rearends with 12 bolt covers and the smaller 10 bolt internals. A Chevelle guy will know that one. The 10 or 12 refers to the ring gear bolt count. __________________ I'm on the Instagram- @Gearhead_Kevin



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