changing rear end ratio from 4.11 to 3.23(or close)

[steeeeeve]

Hi fellas,
Need advice. Please explain this to me like i'm a child.
I currently have a 4.11 rear end and i'm looking for better cruising rpms. I will not be doing any burnouts or towing anything heavy.

I'm going to have my mechanic do this job, but I still want some insight.

If i'm going to a 3.?? ratio do I need to have the carrier changed also? And if so which carrier? A type 3? Can someone show me a link or ebay (used would be great $$$) item that would be the correct one? It's pretty confusing. (for me- tired of ordering wrong parts)

Or are there shims? I've read than new 3.9 and lower will work with type 4 carriers.

I don't know if any of this is true.

thanks,
steve

[A1971Blazer]

the carrier changes because the higher the ratio (3.23, 3.42,3.08 etc) the larger the pinion gear is...
to accommodate the larger pinion, the ring gear must move further away
The carrier break is usually 3.73 and up (4.11 4.56 etc)
look here https://www.randysworldwide.com/diff...dentification/

[jayoldschool]

You can probably score a complete rear with higher gears (lower numerically) for around the same price as a gear and bearing set. There were soooo many of these sold. Easy to bolt in...

[factorystock]

There are a lot of factors that need to be taken into consideration before altering the mechanicals. What is the hp of the engine at given rpm. What is the torque of the engine at given rpm. What is the weight of the vehicle. What is the terrain vehicle will be in. IMO, i would go with an automatic overdrive trans will work great with an already low 4.11, it will allow you to keep the present performance in drive, and get the higher cruise rpm in overdrive. Changing the rear gears will alter performance at all speeds. The key is not to alter the gears too much with the present engine. 4.11 to a 3.73, 3.73 to a 3.54, 3.54 to a 3.23, 3.23 to a 3.07 etc.

[gmc684x4]

What year is your truck ?

What diff does your truck have ?

2 or 4 wheel drive ?

1/2 3/4 or 1 ton ?

Do you ever tow a trailer?

https://www.differentials.com/techni...io-calculator/

https://www.randysworldwide.com/diff...tification-gm/

I have mainly seen 4.11 in 3/4 and 1 tons 3.08 and 3.73 in 1/2 ton trucks

For asking carrier change recomendations need to know your diff id
And are you looking for an open carrier or posi or locker i do like the eaton posi locking diffs are great on a 4x4 that gets off road lots
They do not like hard corners on city streets

[KQQL IT]

Me personally a 3.08 and 28 inch tire is a great combo.
Edit: without an overdrive transmission..

[steeeeeve]

Originally Posted by gmc684x4

What year is your truck ?

What diff does your truck have ?

2 or 4 wheel drive ?

1/2 3/4 or 1 ton ?

Do you ever tow a trailer?

https://www.differentials.com/techni...io-calculator/

https://www.randysworldwide.com/diff...tification-gm/

I have mainly seen 4.11 in 3/4 and 1 tons 3.08 and 3.73 in 1/2 ton trucks

For asking carrier change recomendations need to know your diff id
And are you looking for an open carrier or posi or locker i do like the eaton posi locking diffs are great on a 4x4 that gets off road lots
They do not like hard corners on city streets

here's some info on the truck

1968 c10 1/2 ton
2WD
Mild 350
diff id? not sure i'll have to check. but by doing the wheel/driveshaft count it's a 4.11 ratio.

no towing -I have a modern truck for towing

just looking for a bit less revs while cruising to our cabin 75 miles away.

probably just an open carrier

[toolboxchev]

I think you can go with the 3.08 gears, you would need to know exactly which rear carrier you have.

I have heard those work real good with the other items you listed.

[cj847]

I have a 3.08 with a GM crate 350. It is enough power. It will spin the tires, but is not a hot rod.

If you are driving it 75 miles at a stretch, I would recommend just changing to an overdrive transmission. Even with a 3.08 the RPM's are high at hi-way speeds without overdrive. And you'll still have a tire ripping first gear.....

Options depending on budget:
-Have your mechanic change gears - $500-$800
-Buy a used 3.08 rear and have your mechanic put it in - $200-$400
-Buy a used 3.08 rear and you and a buddy change it - $100- $200 +beer
-Change to an overdrive transmission - $800-$1800

The wide range on the trans is because you don't say if it is auto or standard.

[Mike C]

You will need a carrier change if going from 4.10 to 3.40 or less if you have a truck 12 bolt with factory gears.

I had some thick 4.10 gears in my Jimmy installed on the original 3.07 posi carrier. So if the gears have been changed it could be anything. Need to find out what you have first.

[steeeeeve]

Originally Posted by Mike C

You will need a carrier change if going from 4.10 to 3.40 or less if you have a truck 12 bolt with factory gears.

I had some thick 4.10 gears in my Jimmy installed on the original 3.07 posi carrier. So if the gears have been changed it could be anything. Need to find out what you have first.

Okay. I'm sure my mechanic knows all of this but I thought i'd mention some of this to avoid surprises.

I would like an overdrive tranny, but i've been quoted (from a transmission guy) $3400 for a 700r4 installed.
I'm willing to go that route, but my new mechanic who's treated me right so far said I'd be happy with a 3.23ish rear end. I don't drive 75 miles all the time. Once a month approx. I also forgot to mention I think the rear end has too much play. so have to address that anyway.

But I guess what i'm getting at is If i'm going to start from from a point where the carrier ring and pinion are shot, what parts do I need to have buy?

also turbo400 is the tranny.

[cj847]

I think you need;

-Ring and pinion
-Master install kit
-A new carrier (they are only 50-75 for an open carrier; 500 for a Detroit locker).

[mr48chev]

I'd go with hunt down and finds a complete rear in good shape with the gears you want.

They are out there you just have to hunt for them. That should get you going for around 400 if you pay your mechanic to do the work and he doesn't piddle pot around racking up hours on it.

Having someone swap gears and set them up in your housing or another housing might eat up a thousand bucks real quick.

I've got a 71 GMC 3/4 ton but a couple of years ago picked up a 3.5 Posi Dana 60 for 150.00 for it from a guy who backed out on putting it under a Jeep. Picked up a 3.55 Limited slip 9 inch Ford rear for my 48 (has to be narrowed) a few months ago for 100.00 I didn't know that it was limited slip until I got home with it. They are out there if you do some hunting.

Problem for you is that the 68 rear is a tad narrower than the 70/71 so you are pretty well stuck with 67/68.

[gmc684x4]

A tad wider diff wont make a difference unless you have some oversized non stock wheel tire combo that will move the wheel out a bit the box never changed width
Does your truck already have disk front upgrade ?

If you got a diff from 73 up 12 bolt that will work as well with a bit of work on the mounting points and add a panhard bar mount if you have coil rear end

71 72 rear diff are more sought after due to wider and already 5 bolt wheel pattern
67 to early 70 are the skinner rear late 70 up is the wider diff
The wider diff will also take the 73 up 12 bolt axles if you want to swap to 5 bolt wheels

[Old Truck Man]

My 66 GMC long Bed half ton has a 250 six , SM 420 granny 4 speed and a Dana44 with 336 rear gears. tall 16inch rear tires. and it will run 70 all day long and not guzzle gas. with the 4 speed it will pull also. Rough old truck I aint afeared to load it!

[HO455]

Here is a rear end local to you. Might be worth a trip to pop the cover and see what ratio it is.

https://austin.craigslist.org/pts/d/...154483863.html

[gmc684x4]

Worth it for spare diff at the least
Take off the cover and look at the ring gear for a set of numbers like 41 11 which are 3.73 gear set
3.08 should be 40 13