Rear axle question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

MDFarms · 10-07-2021, 06:25 PM

Good evening, I have a 1972 k10 that had a 3.07 ratio want to switch to 3:73 ANYONE KNOW IF THIS WOULD BE TYPE 3 OR 4 CARRIER WITH ORIGINAL 3:07 RATIO? I NEED TO FIGURE OUT CARRIER INFO FOR ORDERING PARTS

STAMPED GM 56 ON ONE SIDE OF HOUSING

**LockDoc** · 10-07-2021, 06:42 PM

Quote:

Originally Posted by MDFarms

Good evening, I have a 1972 k10 that had a 3.07 ratio want to switch to 3:73 ANYONE KNOW IF THIS WOULD BE TYPE 3 OR 4 CARRIER WITH ORIGINAL 3:07 RATIO? I NEED TO FIGURE OUT CARRIER INFO FOR ORDERING PARTS

STAMPED GM 56 ON ONE SIDE OF HOUSING

Ratio should be stamped on the metal tag fastened to the top bolt. If it only has the tooth combination stamped on it go to the red chart in post #2 in this thread to look it up.

http://67-72chevytrucks.com/vboard/s...d.php?t=578793

I can't help you on the series.

LockDoc

Bigdav160 · 10-07-2021, 07:18 PM

K10? Are you changing the front gear too? Figure the need another differential case

Your 3.08 is a 3 series and the 3.73 is a 4 series.

**HO455** · 10-07-2021, 08:05 PM

The 3.08 gears are on a 3 series carrier from the factory. If you want to go to 3.73's on the 3 series carrier you can use a "Thick" gear set. That is what I did with my Burban.

Do you currently have a posi?

https://americanpowertrain.com/shop/...-a-3-73-ratio/

https://www.differentials.com/techni...arrier-breaks/

MDFarms · 10-07-2021, 09:05 PM

the tag said 3.07 i believe and its all correct for year as the date is on ring gears. Yes switching both from 3.07 to 3.73 frnt is a Dana 44.

I thought 3.73 is a series?type 3? I see I have two different opinions here so far.

**kwmech** · 10-07-2021, 09:21 PM

Do not go by the tag after 40 years, look at the gears and get numbers off of those. You can use the same carrier in the front

**CMars45000** · 10-07-2021, 09:48 PM

Quote:

Originally Posted by HO455

The 3.08 gears are on a 3 series carrier from the factory. If you want to go to 3.73's on the 3 series carrier you can use a "Thick" gear set. That is what I did with my Burban.

Do you currently have a posi?

https://americanpowertrain.com/shop/...-a-3-73-ratio/

https://www.differentials.com/techni...arrier-breaks/

Correct. The carrier "split" on the 12-bolt is at 3.73. 3.73 and numerically higher are 4-series. But they do make "thick" gear sets that would allow you to use your 3-series carrier, if it was in decent shape.

**HO455** · 10-07-2021, 10:34 PM

Quote:

Originally Posted by MDFarms

the tag said 3.07 i believe and its all correct for year as the date is on ring gears. Yes switching both from 3.07 to 3.73 frnt is a Dana 44.

I thought 3.73 is a series?type 3? I see I have two different opinions here so far.

Sorry I didn't make my point very well. The factory carrier for a 12 bolt truck axle with 3.73 gears would be a 4 series carrier. As stated above.
I wanted to point out that there was a way to go to 3.73's without having to get a new carrier for the rear axle. See the first link I posted above.
Fortunately for you the Dana 44 carrier is 3.73 and down so you can use your current carrier for the new 3.73's. See the second link I posted.

**ohboy321** · 10-08-2021, 06:15 AM

You may want to pull the cover to be sure. I thought I had a standard 3.07 axle because of the "spin the wheel" test, but was surprised to find it was a posi when I took the cover off. The clutch plates from one side fell out when I pulled the cover. I installed a new clutch kit and all is well.

MDFarms · 10-08-2021, 07:57 AM

Quote:

Originally Posted by CMars45000

Correct. The carrier "split" on the 12-bolt is at 3.73. 3.73 and numerically higher are 4-series. But they do make "thick" gear sets that would allow you to use your 3-series carrier, if it was in decent shape.

Oddly enough my gears on front and rear along with carriers look like new, meaning not smooth and shiny but still look like new condition. I don't think this truck was used very hard other than a daily driver. It was originally a step side so I don't believe it hauled much in bed. Not sure about trailers and such though. Tough to have a short bed stepside as a work truck.

So.it seems I need wide gear set for my carrier. I had cover off and it was not a diff lock unit. Wouldn't mind one though.

MDFarms · 10-08-2021, 08:03 AM

Anyone have a good 3.73 posi lock carrier for a GM 12 bolt rear-end they would wanna part with?

burnin oil · 10-08-2021, 08:58 AM

Depending how you use the truck I would suggest a detroit locker in the rear. Posi rears will lock in after approx 1.5 tire rotations to push you forward but if there is to much torque applied to one wheel they will disengage. Street use is not a big deal but off road it becomes apparent. Pulling a hill on loose gravel is enough for the tire to unlock. I would also not use a govlock type limited slip. They act the same but tend to unlock when you feather the gas. Detroit keep both rears locked together under normal driving and then unlock the tire for turning. I have all 3 types of these units and my gravel driveway let's you know quickly how well each type work.

We have a jeep that we use for the driveway since the 2wd vehicles usually can't make it up the hill. The rear-end was swapped to the ford explorer axle with a factory limited slip. I rebuilt it with the mustang clutches that are stronger and that rear has some odd behaviors. You can feel it lock in all the time and gives a push feeling to the jeep. It tends to get you going at a slight angle. The Detroits don't give me that since they were already pushing the truck forward. Just food for thought since regearing is expensive and you want to get it right the first time.

60case · 10-08-2021, 08:28 PM

I just switched from 3.73 to 3.07 I have 3.73 dana 44 gears and 3.73 12 bolt gears and open carrier if you are interested

MDFarms · 10-08-2021, 08:45 PM

Quote:

Originally Posted by burnin oil

Depending how you use the truck I would suggest a detroit locker in the rear. Posi rears will lock in after approx 1.5 tire rotations to push you forward but if there is to much torque applied to one wheel they will disengage. Street use is not a big deal but off road it becomes apparent. Pulling a hill on loose gravel is enough for the tire to unlock. I would also not use a govlock type limited slip. They act the same but tend to unlock when you feather the gas. Detroit keep both rears locked together under normal driving and then unlock the tire for turning. I have all 3 types of these units and my gravel driveway let's you know quickly how well each type work.

We have a jeep that we use for the driveway since the 2wd vehicles usually can't make it up the hill. The rear-end was swapped to the ford explorer axle with a factory limited slip. I rebuilt it with the mustang clutches that are stronger and that rear has some odd behaviors. You can feel it lock in all the time and gives a push feeling to the jeep. It tends to get you going at a slight angle. The Detroits don't give me that since they were already pushing the truck forward. Just food for thought since regearing is expensive and you want to get it right the first time.

Could you send me some pics? How did gears look? Mine seriously looked amazing but too high for 35's

MDFarms · 10-08-2021, 08:47 PM

Quote:

Originally Posted by 60case

I just switched from 3.73 to 3.07 I have 3.73 dana 44 gears and 3.73 12 bolt gears and open carrier if you are interested

Sent you a pm requesting pics

60case · 10-08-2021, 09:07 PM

I will get some pictures on Saturday

burnin oil · 10-09-2021, 09:12 AM

Quote:

Originally Posted by MDFarms

Could you send me some pics? How did gears look? Mine seriously looked amazing but too high for 35's

What do you want pics of?

MDFarms · 10-09-2021, 10:05 AM

Quote:

Originally Posted by burnin oil

What do you want pics of?

wrong guy sorry

10-07-2021, 06:25 PM	#1
MDFarms Registered User Join Date: Apr 2021 Location: Mount Pleasant, Michigan Posts: 477	Rear axle question Good evening, I have a 1972 k10 that had a 3.07 ratio want to switch to 3:73 ANYONE KNOW IF THIS WOULD BE TYPE 3 OR 4 CARRIER WITH ORIGINAL 3:07 RATIO? I NEED TO FIGURE OUT CARRIER INFO FOR ORDERING PARTS STAMPED GM 56 ON ONE SIDE OF HOUSING Attached Images Last edited by MDFarms; 10-07-2021 at 06:32 PM.

10-07-2021, 07:18 PM	#3
Bigdav160 Registered User Join Date: Apr 2011 Location: Klein Texas Posts: 3,852	Re: Rear axle question K10? Are you changing the front gear too? Figure the need another differential case Your 3.08 is a 3 series and the 3.73 is a 4 series. __________________ My Classics: '72 K20 Suburban + '65 Dodge Town Wagon '72 Corvette Roadster +'67 Corvette Roadster '73 Z-28 Camaro '63 Ford SWB Uni Pickup '50 Ford Coupe

10-07-2021, 08:05 PM	#4
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 11,469	Re: Rear axle question The 3.08 gears are on a 3 series carrier from the factory. If you want to go to 3.73's on the 3 series carrier you can use a "Thick" gear set. That is what I did with my Burban. Do you currently have a posi? https://americanpowertrain.com/shop/...-a-3-73-ratio/ https://www.differentials.com/techni...arrier-breaks/ __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

10-07-2021, 09:05 PM	#5
MDFarms Registered User Join Date: Apr 2021 Location: Mount Pleasant, Michigan Posts: 477	Re: Rear axle question the tag said 3.07 i believe and its all correct for year as the date is on ring gears. Yes switching both from 3.07 to 3.73 frnt is a Dana 44. I thought 3.73 is a series?type 3? I see I have two different opinions here so far. Last edited by MDFarms; 10-07-2021 at 09:13 PM.

10-07-2021, 09:21 PM	#6
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,678	Re: Rear axle question Do not go by the tag after 40 years, look at the gears and get numbers off of those. You can use the same carrier in the front

10-08-2021, 06:15 AM	#9
ohboy321 Senior Member Join Date: Aug 2015 Location: Dunbarton, NH Posts: 289	Re: Rear axle question You may want to pull the cover to be sure. I thought I had a standard 3.07 axle because of the "spin the wheel" test, but was surprised to find it was a posi when I took the cover off. The clutch plates from one side fell out when I pulled the cover. I installed a new clutch kit and all is well. Attached Images __________________ Steve/NH 1967 K10 327 Short Bed Stepside

10-08-2021, 08:03 AM	#11
MDFarms Registered User Join Date: Apr 2021 Location: Mount Pleasant, Michigan Posts: 477	Re: Rear axle question Anyone have a good 3.73 posi lock carrier for a GM 12 bolt rear-end they would wanna part with?

10-08-2021, 08:58 AM	#12
burnin oil Registered User Join Date: Jan 2013 Location: Eastern TN Posts: 1,921	Re: Rear axle question Depending how you use the truck I would suggest a detroit locker in the rear. Posi rears will lock in after approx 1.5 tire rotations to push you forward but if there is to much torque applied to one wheel they will disengage. Street use is not a big deal but off road it becomes apparent. Pulling a hill on loose gravel is enough for the tire to unlock. I would also not use a govlock type limited slip. They act the same but tend to unlock when you feather the gas. Detroit keep both rears locked together under normal driving and then unlock the tire for turning. I have all 3 types of these units and my gravel driveway let's you know quickly how well each type work. We have a jeep that we use for the driveway since the 2wd vehicles usually can't make it up the hill. The rear-end was swapped to the ford explorer axle with a factory limited slip. I rebuilt it with the mustang clutches that are stronger and that rear has some odd behaviors. You can feel it lock in all the time and gives a push feeling to the jeep. It tends to get you going at a slight angle. The Detroits don't give me that since they were already pushing the truck forward. Just food for thought since regearing is expensive and you want to get it right the first time.

10-08-2021, 08:28 PM	#13
60case Registered User Join Date: Feb 2015 Location: friendship WI Posts: 174	Re: Rear axle question I just switched from 3.73 to 3.07 I have 3.73 dana 44 gears and 3.73 12 bolt gears and open carrier if you are interested

10-08-2021, 09:07 PM	#16
60case Registered User Join Date: Feb 2015 Location: friendship WI Posts: 174	Re: Rear axle question I will get some pictures on Saturday



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