3.08 gears are worrying me - The 1947 - Present Chevrolet & GMC Truck Message Board Network

70Chevy4x4Nut · 08-03-2003, 06:41 PM

My 70 4x4 has 3.08 gears. What I've read is that they're not worth having. I have a posi in the front and open diff in the back. I am thinking I might just put it all back together as it is and look for some different gears later when I can afford it. How much trouble it is to change out later once everything is back together?

This is one area I feel I need to let someone else do, which will mean big bucks I'm sure.

86k10 · 08-03-2003, 07:37 PM

What exactly is it about them that worries you. I've run them before and thought they were just fine. Just wondering.

70Chevy4x4Nut · 08-03-2003, 08:42 PM

I want to run 33" tires and by what I've read that combo would make the RPM's too low. And by the way I do not have posi in the front like I thought. I spun it at the pinion and they both turned the same way, but I can grab one side and the other keeps turning. This was on a 71 donor axle I want to use for disc brake setup. I guess I got too excited too soon.

I tried to take off a disc rotor on that 71 4x4 dana44. I got to the nut that has a bunch of little holes all the way around. What tool is needed to get in there and break that loose? Need to replace the rotor.

Class of 69 · 08-03-2003, 09:42 PM

You need a spindle nut socket for that axle. May be available at better auto parts stores.. For sure thru Snap-On, Matco, Mac. Been a while since I worked on that specific model, but I thought the rotor fit over the center hub, and studs...didn't need to remove front hub to remove rotor. They get very rusted on, so it may seem as one piece.

1969 GMC · 08-04-2003, 12:59 AM

someone on this board had a chart about tire size and gear ratio correlation, but i have no idea where it is now. 3.08's probably would be too high to use with 33" tires, IMO. I have 3.73's with 32" OD tires right now, and it seems to be a good medium between performace and fuel efficiency (lol).

Prerunner1982 · 08-04-2003, 01:36 PM

there use to be one on the 4wheel parts website, but i guess they rearranged as i cant locate it.........

bouncytruck · 08-04-2003, 01:37 PM

I have 4:10's with 35's on my '69. My old '72 had 3:73's with 35's and it was a little to high a gearing. The 4:10's are much better. For 33's, I'd think you'd need a minimum of 3:73's. I would also think you'd be able to find them used fairly easily from someone going with higher gear set. Check on CK5.com or Pirate4x4.com for some 3:73's

wildwood · 08-04-2003, 03:07 PM

.373s work good with 33s in my opinion. .308s are a little tall for 33s. The chart found here is good but they like their RPM. I'm running .373s with 35s and it works OK with the 4 speed even though it's off the charts here:

http://www.4wheelparts.com/tirel_gear_ratio.asp

I'm assuming you have a 12 bolt rear end. If so you will need a different carrier for .373 and up (numerically). I'm also assuming you have a Dana 44 front in which case you can use the same carrier you have now which is for .373 and down. When changing the carrier you will almost definately need to "set" the gear pattern. A new gear set should come with a helpful instruction sheet. You might want to get this done professionally if your spending $ on a new set. If you buy used and don't mind a slight howl you could set it up yourself. In the front end you may not need to set anything as your reusing the carrier. Make sure to check with gear marker. You should be able to find all these parts no prob new or used. If not I could supply them for you at decent prices (used) but you'll have to pay shipping from Canada. I can get used posi diffs for both.

70Chevy4x4Nut · 08-04-2003, 07:24 PM

Thanks for the input. After much thinking about it, I think I may keep the 3.08's and my 31" tires for now. After I get it on the road, I will have a feel for this combo. If I like it then great. If I want to change, then I will rebuild the other front and rear axles that I have and just make a complete swapout. That way the truck does not sit for too long. I will do a lift and bigger tires all at the same time. Less money now and on the road quicker. Some may not like that idea, but I can see lots of more spending on the way.

**MJN** · 08-05-2003, 11:36 PM

I've got 3:08 posi in my '72 Blazer with 35's and it sucks. Great mileage on the open highway but it really drinks the gas going up hills and through town and in the mud you can't get enough power to the ground. I would love to upgrade to 4:10s.

blazerboy72 · 08-07-2003, 07:36 PM

I have 3.73 with 38's so you should be fine with 3.08 and 33's

08-03-2003, 06:41 PM	#1
70Chevy4x4Nut Registered User Join Date: Dec 2002 Location: TX Posts: 311	3.08 gears are worrying me My 70 4x4 has 3.08 gears. What I've read is that they're not worth having. I have a posi in the front and open diff in the back. I am thinking I might just put it all back together as it is and look for some different gears later when I can afford it. How much trouble it is to change out later once everything is back together? This is one area I feel I need to let someone else do, which will mean big bucks I'm sure.

08-03-2003, 07:37 PM	#2
86k10 Registered User Join Date: Feb 2003 Location: Bertrand, Nebraska Posts: 355	What exactly is it about them that worries you. I've run them before and thought they were just fine. Just wondering. __________________ 98 Neon 97 Grand Prix GT 02 Grand Prix 40th Anniv. 86 GMC 5.0 77 Olds 98 6.6 REAL AMERICANS, DRIVE AMERICAN

08-03-2003, 09:42 PM	#4
Class of 69 Registered User Join Date: Mar 2003 Location: Stillwater MN Posts: 1,166	You need a spindle nut socket for that axle. May be available at better auto parts stores.. For sure thru Snap-On, Matco, Mac. Been a while since I worked on that specific model, but I thought the rotor fit over the center hub, and studs...didn't need to remove front hub to remove rotor. They get very rusted on, so it may seem as one piece. __________________ 69 GMC K10 ..some restoration required....still..

08-04-2003, 12:59 AM	#5
1969 GMC Registered User Join Date: Feb 2003 Location: The Rubber City Posts: 5,498	someone on this board had a chart about tire size and gear ratio correlation, but i have no idea where it is now. 3.08's probably would be too high to use with 33" tires, IMO. I have 3.73's with 32" OD tires right now, and it seems to be a good medium between performace and fuel efficiency (lol). __________________ 1969 GMC K2500 1996 Honda Accord 2007 Kawasaki KLR 650

08-04-2003, 01:36 PM	#6
Prerunner1982 Registered User Join Date: Oct 2002 Location: Edmond, OK Posts: 5,906	there use to be one on the 4wheel parts website, but i guess they rearranged as i cant locate it......... __________________ Jon 1982 Chevy Silverado 350/th350.... RETIRED 1993 Jeep XJ 2 door(Cherokee) 4wd 4.0ltr/AX-15 (5spd)/NP231 .... Oklahoma Roll Call

08-03-2003, 08:42 PM	#3
70Chevy4x4Nut Registered User Join Date: Dec 2002 Location: TX Posts: 311	I want to run 33" tires and by what I've read that combo would make the RPM's too low. And by the way I do not have posi in the front like I thought. I spun it at the pinion and they both turned the same way, but I can grab one side and the other keeps turning. This was on a 71 donor axle I want to use for disc brake setup. I guess I got too excited too soon. I tried to take off a disc rotor on that 71 4x4 dana44. I got to the nut that has a bunch of little holes all the way around. What tool is needed to get in there and break that loose? Need to replace the rotor.

08-04-2003, 01:37 PM	#7
bouncytruck SKINNY TIRES RULE! Join Date: Sep 2001 Location: Bothell, WA Posts: 11,049	I have 4:10's with 35's on my '69. My old '72 had 3:73's with 35's and it was a little to high a gearing. The 4:10's are much better. For 33's, I'd think you'd need a minimum of 3:73's. I would also think you'd be able to find them used fairly easily from someone going with higher gear set. Check on CK5.com or Pirate4x4.com for some 3:73's __________________ bouncytruck 1972 K5 The Hauler 1994 K1500 Suburban The Daily2010 Kia Soul Wife's Ride2014 Fiat 500L

08-04-2003, 03:07 PM	#8
wildwood Registered User Join Date: Jun 2003 Location: Calgary AB Posts: 110	gear ratio chart .373s work good with 33s in my opinion. .308s are a little tall for 33s. The chart found here is good but they like their RPM. I'm running .373s with 35s and it works OK with the 4 speed even though it's off the charts here: http://www.4wheelparts.com/tirel_gear_ratio.asp I'm assuming you have a 12 bolt rear end. If so you will need a different carrier for .373 and up (numerically). I'm also assuming you have a Dana 44 front in which case you can use the same carrier you have now which is for .373 and down. When changing the carrier you will almost definately need to "set" the gear pattern. A new gear set should come with a helpful instruction sheet. You might want to get this done professionally if your spending $ on a new set. If you buy used and don't mind a slight howl you could set it up yourself. In the front end you may not need to set anything as your reusing the carrier. Make sure to check with gear marker. You should be able to find all these parts no prob new or used. If not I could supply them for you at decent prices (used) but you'll have to pay shipping from Canada. I can get used posi diffs for both. __________________ You can't get out if ya don't get in

08-04-2003, 07:24 PM	#9
70Chevy4x4Nut Registered User Join Date: Dec 2002 Location: TX Posts: 311	Thanks for the input. After much thinking about it, I think I may keep the 3.08's and my 31" tires for now. After I get it on the road, I will have a feel for this combo. If I like it then great. If I want to change, then I will rebuild the other front and rear axles that I have and just make a complete swapout. That way the truck does not sit for too long. I will do a lift and bigger tires all at the same time. Less money now and on the road quicker. Some may not like that idea, but I can see lots of more spending on the way.

08-05-2003, 11:36 PM	#10
MJN Registered User Join Date: Feb 2000 Location: Maquoketa, Ia/ Orr, Mn Posts: 2,983	I've got 3:08 posi in my '72 Blazer with 35's and it sucks. Great mileage on the open highway but it really drinks the gas going up hills and through town and in the mud you can't get enough power to the ground. I would love to upgrade to 4:10s.

08-07-2003, 07:36 PM	#11
blazerboy72 Senior Member Join Date: Mar 2002 Location: Temple, Ga Posts: 854	I have 3.73 with 38's so you should be fine with 3.08 and 33's



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