Need Some Input

[chevjayfsd]

I am looking to upgrade the 3.08 12 bolt in my truck.
What am I looking at in terms of money to change out the gears to a 3.73 posi?
What Brands do I need to look at?

[bigcdawg99]

I'm in the process of doing the same thing. I've found that most Eaton posi units (new) run around $400-$500. I haven't checked out Auburn, because I've heard so many good things about Eaton. A nice set of gears from Richmond seems to run around $150-$170 but I've seen them new in the box on Ebay for a little over $100. Let me know if you find any good deals. Good luck.

[sleepyboy]

I want to do the same thing but am a little confused. My 69 has 6 bolt lugs. Yesterday, I read a post that it should be 5? Would like to know what is best setup to run at 75 less than 3,000 rpms on a 350 motor 1:1 final ratio 4 speed muncie.. 373/305? Not to steal the thread, just getting different stories?? Finding 6 bolt rims are more of a challenge.

[69 Short Fleet]

sleepy. The 6 bolt setup on your truck is stock from the factory. They didn't switch over to 5 bolt until 1971 both Chevy & GMC with the 1/2 tons (if memory serves me). You could go with a 3:42 setup for your rearend but I'm not sure if the gears are available for your aplication. I would like to change my gearing also (sometime) I'm running a muncie SM265 (granny 1st gear) with a 4:10 rear end.... the thing is so low in first you could prolly pull a mobile home with it (LOL). Doug

[chevjayfsd]

Alright here is another question,

I only drive the 72 on weekends, and not every weekend. So basically not hardly at all, I don't want too many miles on it...
So, that said, what gear should I go with? It's almost never on the freeway, so top speed isn't a problem, I just want something that will throw you back in the seat HARD!!!
Question: 3.73 or 4.10?

Jason

[69 Short Fleet]

Jason. With your turbo 350 & 4:10 gears it might be what your after... you might want to go for a spin in someone elses ride with the same setup first. As you know changing rear end gears is time consuming & tricky (backlash) so you want to try and nail the ratio first time. With my set-up my truck only does 55-60 MPH flat out (lol). I'm seriously considering a T56 tranny upgrade (later on) and keeping the 4:10's, for what I want I think it would be an ideal set-up. Doug

[70c10]

My truck already had 3:73's which is a great all around gear. I bought my 4 series Eaton posi unit from www.tomsdifferentials.com for $280 about 2 years ago. They also sell gears but I don't know their prices on them.

[70GMCer]

I don't know that much about rears, but correct me if I'm wrong. Isn't there and issue with different carriers in regards to changing rear gears. I have a 4.10 in mine and there was a thread on here awhile back stating that you need a bigger carrier if you're going from 3.08 to a 3.73 or 4.10. Just a thought before you dig into this and find out the taller gears will not fit your carrier....

[chevjayfsd]

Thats what the posi unit is for.

[alf1096]

I dont know what I think about 373s. I have a mild 350 with a turbo 400 and 373 posi. I do not have a tac but at 70 it sounds like the engine is reved high. I like the gears for in town becase it hauls. But if you want to take it on a road trip it is loud and I will only run about 60.

[Dual quad]

70GMC'r, you are correct. Regradless of weather the carrier is posi or open, the series of carrier must be appropriate for the ring gear. As the ratio gets numerically higher, the pinion gear gets smaller, andthe ring gear must be placed closed to the pinion. This is accomplished with a thicker carrier flange.

On trucks, I believe that 3.73 and above ratios require a 4 series carrier and ring gear. Ratios of 3.42 down to 3.08 I think are 3 series, and below that is a 2 series. Some manufacturers make a "thick" ring gear to allow use of a 4 series gearset with a 3 series carrier (not a good idea to shim the ring gear).

[70short/step]

If you plan on buying the gears and new carrier and then having it setup for you I bet you will spend over $1,000. Ask 'Chevy-Dude' he just had his all setup with new posi and gears, berings ect.
Dual Quad is correct about the 3:73 and 4:11 needing seris 4 carrier and 3:42 and 3:08 using the 3 series.
If you want to get set back into your seats then go for the 4:11. But they sure make your engine whine going down the freeway at 70 mph! I have 327/350! and damn it kicks butt around town and getting up on the freeway but if your crusing for a long ways, it kinda sucks!

[pjmoreland]

I originally had 3.07 gears in my truck. I bought a set of 3.73 gears made by Richmond that bolted right up to my series 3 carrier. Here's a link.

http://store.summitracing.com/defaul...=egnsearch.asp

[70short/step]

Originally Posted by pjmoreland

I originally had 3.07 gears in my truck. I bought a set of 3.73 gears made by Richmond that bolted right up to my series 3 carrier. Here's a link.

http://store.summitracing.com/defaul...=egnsearch.asp

Thats a New one on me! I have never seen that before. It was just common knowledge that 3:73 needed series 4 carrier. Good to know that you dont have to change carriers then!
Thanks for the info!

[69 longhorn]

I beleive you can also get 4.10, & 4.56 gears to fit a 3 series carrier.....if you already have a 3 series posi, that would be the cheapest route to go. you might consider tire height before swapping gears, the 4.10's really "spin' the eng on the hyway! I pulled the 4.10s out of my 69, & went back to the stock 3.40 gears(75 12 bolt). on a 28" tall tire, 400 turbo, the 4.10s reved my 383 right @ 4000 to keep pace with the 18 wheelers on the interstate(they run 78mph through Illinois). IMO, 3.73 is a better all around gear, & still has some good kick on takeoff. I run a 29" tire with the 3.40 gears, & tach 3000 rpms @ 73 mph. it lost a little kick on takeoff, but the 383 pulls hard from 2500-5500. it runs easy on the open hyway tho(5000 will put the speedo needle straight down). the 4.10s, & the Richmond trans are under the bench for another project.......69L