OrangeWhite77

Last Saturday my differential came apart on me. There's a big hole in the cover from something important trying to escape.

After getting the tires aligned a couple months ago, I read on this forum somewhere that the tires tilting inward was a sign of differential wear. It was to late for me at that point so I crossed my fingers. A little while after that, it started clunking when making slow turns. Per instructions on this website, I bought the GM additive and changed the oil. The problem went away.

Now I have to consider what to do with my differential. And I would like your input about the best balance between money and reliability. I am also looking for input for gear ratios. I have a 383 crate motor with 460hp and a Tremec TKO600 5-speed... but it seems underwhelming. New gears might be the best option but I do 50/50 highway and street driving. I already get 8 mpg, so running 4,000 rpm at 75 mph isn't my preference.

Here are what I'm considering:
A) A local rebuild shop (without looking at the car) said it would be anywhere from $900 - $1800 to rebuild it.
B) Buy a rebuilt diff online. (Zip has them for $999 but a $500 core and they don't want mine since it has a hole in it.)
C) Buy a new diff online for $1500
D) Mail mine out and have it rebuilt. (I don't know the cost of shipping or the cost of rebuilding.)

If you have any experience with one of these options I would very much like to know where you would recommend going.

Thank you in advance for your input.

zwede

Odds are just about nothing in your old diff is usable so buy "new". I'd then recommend you send it to one of our trusted diff rebuilders (tracdogg2 or gtr1999) for inspection... I've heard of many supposedly ready-to-run diffs having issues due to bad assembly or parts selection.

As for gear ratio I just went 3.08->3.73. I have a TKO II (3.27 1st gear, 0.68 5th). Great combo. About 2300 rpm @ 70 mph.

OrangeWhite77

I have read a lot of good things about tracdogg2's work. The shipping cost is all that scares me. I'm sure I can get it shipped directly to him for free, but then I'll pay for it to get to me. I live in Arizona.

bashcraft

Who sells them new on-line?

OrangeWhite77

Oops. The site where I thought they were new are actually rebuilt. My appologies.

Gordonm

I don't know anyone who sells "new" ones. Since nobody has made a new case for years all you will find is rebuilt ones. Maybe all the inside components are new but that is about it. Since Mike (Tracdog) is close by to you contact him and tell him what you are looking for. He may have some cases already or have access to the cases. No need In sending junk or blown up stuff to him. Seeing you have some power a stock rebuild will probably not hold up to well if you drive it hard. I would have mike build you one and pay the shipping one way from him to you.

Gale Banks 80'

You might start watching Your local Craigs List or here on the Forum. Rebuilders might have enough parts laying around to build you one, and You save shipping one way. For what its worth, I was at the Puyallup Swap Meet in Washington State a couple of weeks ago and sold a 1979 3:55 for $300. A fellow vendor sold a 78 3:73 for $250. We both sold them with one hour left in a 3 day show. There is a Corvette Recycler in Centralia Wa who generally gets $300 for a Pumpkin.

gbvette62

I don't know of any new rears for 63-82 Corvettes, on the market.

The problem is the 3 series posi carrier/center section. GM discontinued them a few year ago, and no one has made a replacement. The 3 series posi units are quite often cracked, and the supply of good ones is drying up.

It's probably not likely, but if by some chance your posi unit isn't damaged, it should have some value. I wouldn't chuck the rear, without checking inside to see what did break.

Silvertone

QUOTE=Gale Banks 80';1589051678]You might start watching Your local Craigs List or here on the Forum. Rebuilders might have enough parts laying around to build you one, and You save shipping one way. For what its worth, I was at the Puyallup Swap Meet in Washington State a couple of weeks ago and sold a 1979 3:55 for $300. A fellow vendor sold a 78 3:73 for $250. We both sold them with one hour left in a 3 day show. There is a Corvette Recycler in Centralia Wa who generally gets $300 for a Pumpkin.[/QUOTE]

I have a '77 also. About 15 years ago I found a '72 big block 3.70 at the Puyallup Swap Meet. Seems like a relatively tough unit with u-joint caps instead of straps, and I'm told the big block cases were hardened. Good in combination with our 3" halfshafts. I also have a 468hp 383 and a Keisler SS700 road race 5spd. In my opinion, it's a nearly perfect gear choice with a 26" tire.

bashcraft

No, they weren't.

Silvertone

Oy, the only thing worse than finding wrong information in these blogs is me spreading it. I duly retract!

lurch59

What's your overdrive dear ratio for 5th?
You will need to upgrade, not just rebuild, the diff to a super 10 etc with that much power and a stick. Traccdogg can help you with this.
Why are you getting 8 mpg? I'm getting 14-15 on the freeway with a big block.

NAmuscle

If budget is a problem, ask locals for rebuilding services. I had mine done by a friend for $500. Even though mine did not have any holes, I'm sure you could find someone who will quote a lot cheaper than 900 - 1800

lurch59

How long the diff rebuild will last is important. This type of work is not easy. The hp numbers alone require a quality rebuild. I've busted up a lot of diffs with a stick and small block.....

OrangeWhite77

Fourth gear is 1.00
Fifth is 0.64

I am pretty sure I have some carburetor issues, that's why the poor fuel mileage. I need to work them out. More on that topic later... And I definitely would rather spend a little extra cash now for something durable rather than do this whole thing again 5 years down the road.

lurch59

I've got the same trans then, with 3.90 rear gears. Even with the overdrive, it wouldn't be bad to be at 3.70. Methinks you'll break the rear diff way before 5 years, if you are driving it like you should!