1969 c-10 rear end question

[HowellKTM95]

I have a 1969 Chevy C-10 with a 12 bolt rear end with 3.73 gears in it. I am wanting to change the gearing to a 3.08 but I understand that I would need to change the carrier to make the 3.08 gears work. Can anybody tell me what vehicles would have the correct carrier that would fit in my rear end to allow the 3.08 gears to work. Would a mid 70 truck have the correct carrier in the rear end? Does anybody have a carrier they would sell for my needs?
Any help would be appreciated.Thanks

[HowellKTM95]

Does anybody have any ideas on which year truck would have the correct carrier I need?

[Fitz]

Originally Posted by HowellKTM95

Does anybody have any ideas on which year truck would have the correct carrier I need?

Carriers for the 12 bolt truck rears are three sizes:
2.73 and numerically lower (Series 2)
2.76 thru 3.42 ratios (Series 3)
3.73 & numerically higher (Series 4)
Since ring gear inner dimension and bolt circle are different, the series 2, 3 & 4 gear sets are not interchangeable.


Your carrier is a series 4. You will need a series 3 to fit a 3.08 gearset.

[ksshane]

Ive been doing a little research and I dont see anywhere that says you cant install 3.08 gears.

Im a little curious as to why you would want to get rid of the 3.73 gears. They seem like the magic number for most builds.

[HowellKTM95]

From what I have been told is that the carrier that's in the rear end now are for 3.73 and up. If I want to go to a 3.08 gearing I need to change the carrier. I believe the carrier in it now is a series 4 and I believe I need a series 3 for the 3.08 gears.

When driving on the interstate the motor is running tight at 65 mph. Like to have it run less RPM at 65 mph and hopefully get better fuel mileage.

[Coley]

Originally Posted by HowellKTM95

From what I have been told is that the carrier that's in the rear end now are for 3.73 and up. If I want to go to a 3.08 gearing I need to change the carrier. I believe the carrier in it now is a series 4 and I believe I need a series 3 for the 3.08 gears.

When driving on the interstate the motor is running tight at 65 mph. Like to have it run less RPM at 65 mph and hopefully get better fuel mileage.

Has your existing carrier been checked to see if it is truly a series 4?
My (loose) understanding is that the series 3 carrier was sometimes used with 3:73's as well as the lower 3:08 ratio although I'm not sure how they defined the 3:73 gear set up to work with both carriers.
If it has not been checked then I would start at that point rather than speculating. As well perhaps some of the other members who have done this particular change can point you in the right direction on the I.d.
My two bits.
Coley

[HowellKTM95]

It has a sb350 in the truck and a automatic 3 speed.

[LockDoc]

-
Depending on what brand of rear end you have It might be easier and cheaper to just change the whole rear end. I just did it on my '69 Suburban. Someone will correct me if I'm wrong but if you have the HO52 you can change the carrier as a unit. If you have a Dana you have to replace the ring and pinion gears. New gears are around 200 bucks and another $100 to install them and set them up. Unless you have experience in gear setup it may not be something you can do yourself....

LockDoc

[HowellKTM95]

Would it be better to change the rim size instead?

[HowellKTM95]

Any suggestion on what year of truck rear end would fit underneath my with 3.08 gears. I currently have 6 bolt lugs. Would like to stay with a 6 bolt lugs so I don't have to change the rims and tires yet.

Thanks

[GASoline71]

There are a lot of 67-72 truck 12 bolts out there with 3 series carriers in them... There might even be 3.08 gears that are made to fit a 4 series carrier.

Need to do a little more research.

What RPM's are you doing at 60? A stock SBC will handle 2,500 to 3,000 RPM's no problem. You're probably just used to modern engines with OD transmissions running at 1,600 to 1,800 RPM's on the highway.

Gary

[HowellKTM95]

I have searched online for a long time trying to find a used series 3 carrier for my rear end with no luck. Summit sells a carrier that will work, but a little high price for my blood at this time.

The RPM's are around 3000 at 60.

[GASoline71]

3,000 at 60 is pretty normal for a SBC. They are made to handle it.

But I'm assuming that gas mileage is your main concern.

90% of the used carriers you're lookin' for are dang near 40 years old. A new one would be a good investment into the reliablitlity of your rig.

Gary

[msgdsrf]

My '69 and most came with 3.08 as standard equipment. So should be easy to locate a salvage. I'm now on 3.73 with a 29" rear tire and spin at 2800 down the freeway around 65mph.

[lolife99]

Call these guys.
They can answer all your questions.
No more guessing.
http://www.ringpinion.com/Default.aspx

[haminator]

Is your truck a coil spring truck or leaf? Changing the complete rear would most likely be the easiest and cheapest if you find a rear reasonably priced. They are not hard to find around here but maybe where you are they are. I generally scrap them, maybe I should rethink that.

[wreckedchevy]

Originally Posted by haminator

Is your truck a coil spring truck or leaf? Changing the complete rear would most likely be the easiest and cheapest if you find a rear reasonably priced. They are not hard to find around here but maybe where you are they are. I generally scrap them, maybe I should rethink that.

that's the problem I'm finding around here there was no market for the taller gears so everyone scrapped them and of course now that I'm running smaller wheels/tires I'm wanting a set of taller gears and can't find them locally either. keep an eye on ebay I just talked to a guy on there last month who had a complete setup for $100 shipped somebody beat me to it before I rounded up the funds.

[HowellKTM95]

My truck has coil springs on it. What year truck would have a 3.08 gears and 6 lug that would fit?

[HowellKTM95]

I have been watching E-Bay for awhile now with no luck. Will continue to watch though.

[HowellKTM95]

If anybody has a series three carrier for a chevy 12 bolt they want to sell please contact me. Thanks

[Fitz]

Originally Posted by HowellKTM95

If anybody has a series three carrier for a chevy 12 bolt they want to sell please contact me. Thanks

Any truck from 1964 through 1982 will use a carrier that fits your housing. Open carriers are easy to find but positraction carriers are not only hard to find but should always be rebuilt before using one. I am not sure that any series 3 positraction carriers were ever built by GM as there are no codes for one in the archives.
Codes stamped on the axle tube for 3.07 are:
3.07=HB, LL, RA, TR, TT (series 3)
3.73=HA, HJ, HQ, MF, TQ (series 4)

[haminator]

My 70 K-10 had a 3:07 posi. Its on the SPID and my folks bought the truck new so I can verify. 4 low brake stands without the hubs locked broke it in half. So much for youth. lol.

[haminator]

Coil springs would be pre 72. Six lug would be 70 and earlier exceopt 4x4 but thats leaf springs anyway. I may accidently have a 3:07 carrier, i'll do some checking. I assume you want a ring and pinion too.

[haminator]

Originally Posted by haminator

Coil springs would be pre 72. Six lug would be 70 and earlier exceopt 4x4 but thats leaf springs anyway. I may accidently have a 3:07 carrier, i'll do some checking. I assume you want a ring and pinion too.

It looks like I have one with 3:07 gears. I'll need to pull it and see what kind of shape its really in.

[WIDESIDE72]

I swapped the 3.73 open that was originally in my 71 GMC 6 cyl 3 ott for a 3.07 posi. A lot of the big block trucks had 3.07 posi rears.