I've been searching and reading around and have come to the same conclusion. My diff must be a 3-series and those gear sets that are 4.11 and up (numerically) that say they work with 3-series should work for me. This is great news, I thought I was limited to 3.90.

I've also been spending some time with some gear ratio calculators. I think I'll want 4.11 or 4.33, 4.56 is just too crazy. I need to get the car on the road and see if the engine likes being revved up to 6,500rpm and beyond with my new cam before I decide.

 

you don`t, you pull the cover and look at the flange where the ring gear bolts on, I believe the 4 series case is thicker, you can use a 4 series gear on a 3 series case with a ring gear spacer, 65-79 rear ends used an Eaton case.

 

I didn't think about 4.33... maybe a perfect tweener? Not quite as much of a torque monster as a 4.56, but a little more oomph compared to a 4.11??? (Probably still too much with the blower, though my cam is strong in the upper rpm's.

 

How much hp are you pushing that you're talking about these crazy short gears? I'm wrapping up a retro roller cam build with blueprint heads and a T56. Should be close to 400hp and around 430tq. I think that along with some short gears will give me a good street/strip setup that'll keep me happy for a long time. If you're talking about even more HP than that, I just, that'll be interesting!

 

My first gear as yours is a 3.06, with a modified engine first gear is a blink of the eye and your shifting out fast. I can't imagine 4.11's and how fast you'd be shifting. Sounds fun.

 

I should have more than that. Had some ignition issues when I had it on the dyno, but I'm guessing with that fixed it should be around 385-420HP/450+ TQ... but that was before the blower. Just installed a baby Weiand which from everything I've read should be good for another 100 hp, so guessing it'll end up somewhere around 485HP/550TQ give or take.

After thinking about it some more we decided to just go with 3.73's. With the Roots blower and already having a pretty early torque curve, I think 4.11's would likely just be too unruly without slicks and would blow right through the power band too quickly to really enjoy it. It's already quite torquey down low and with the roots blower which produces boost right away, I think it would probably be impossible to hook up.

 

Well yeah and to make things even tougher I have a roots blower which is gonna lay down torque right away. Ended up going with 3.73's. Hopefully that helps me hook up and enjoy the power band a little more. 4.11's would be fun on a drag car with some slicks, but on a street car with a roots blower I think it's just too much. What's your rear gear right now and how much HP/Tq are you working with?

 

The stock diff did hold up decently.... with 165 hp. Stub axle wear and cross shaft wear was a big problem.
If it is the original diff in the car, it is an Eaton. The housing is cast iron. If the housing is aluminum it is a Dana, which never came in a 78 Corvette. Dana'44's were used in 80-82.
The only gears that fit into a corvette are corvette gears. They cost more. There are two types of new gears for a corvette: quality gears and garbage gears. This is not the place to save money. All corvette diffs were built using NDH bearings. They are no longer available. There are several brands of bearings available but if you do not use TimkenUSA bearings you will be rewarded with building it again. And probably replacing the housing.
The new bearings do not set up the same as the NDH. You cannot use the same pinion shim and carrier side shims you took out. This isn't a Camaro. New gears will change the pinion depth .004 just to start with.
You should have a "297" carrier if it is the stock one. There are 4 castings defects that need to be addressed. Also the ring gear flange needs to be trued. New 8620 gears are not as forgiving as the soft OEM gears.
The stock slotted clutches will not handle 400 hp. You need to change to the solids. Your spline teeth are most likely worn out anyway along with the 4 retainers. Does your buddy know how to set up a posi unit? Re-using the stock shims will result in the spider gears hammering everytime you step on and let off the gas. Replace the thrust washers also.
New hardened cross shaft is a must. Along with some decent stub axles. Check the cross shaft bores for "egging".
If you plan on going out and standing on it, you need to consider a steel cap on the left side. Cap stretch is a serious issue with these diffs. Most ring gear failures are caused by cap stretch, not the gears. The stock cast iron cap will stretch like a rubber band with 500hp.
You mentioned putting a truss in. Where? Why? Did you get the .095 or the .134 halfshafts?

 

Lots of great info, thanks Tracdogg. Ugh, you are correct. I found more info on the "Eaton differential" now so it does look like my initial thoughts that a Dana 44 only came in 80 or later was correct. Damn it.

Sounds like there are a lot of very specific needs to be addressed. Going to have somewhwere around 500HP and I'm guessing that all this stuff needs to be addressed even for that much power?

I am not sure of the thickness of the halfshafts. I ordered the Dragvette 3" balanced ones. I'll have to see if I can track down how thick they are as I don't remember seeing that.

With all this info I'm thinking it might be easier/cheaper to just buy one already complete as opposed to dealing with everything. Any opinions on the Duntov Motors ones or do you have any other suggestions? I seem to remember that maybe you rebuild them from other threads? I've dropped a ton of cash into the build already and am trying to keep costs down as much as possible, but I certainly don't want to have to spend more in 6 months because it's not done right now.

 

Also trying to find out what bearings are in the kit I ordered. It's a Ratech deluxe installation kit and on their site it says they supply "INA, Koyo, NSK, SKF, Timken, Torrington" bearings, but it doesn't specify for sure what's in the kit.

 

PM sent.

 

After reading this thread I'm confused on the direction I should take. Looking for some advice.

79 Vette with 388 stroker, just under 500hp and my engine builder said to look for a set up that can handle over 500 torq, with like 390 gears. Currently have stock rear, 700R4 and 3:55 gear ratio, automatic.

Any advice on what companies I should be dealing with to get a setup that is right for my vehicle would greatly be appreciated.

Thank yoiu,

Kevin

 

I have a set of motive 3.70 gears (italian made) for the stock differential.
They are the performance version and would probably work for you. I am doing a 12 bolt conversion and will not be using them. I also have a polished 10 bolt differential case that was the original in my housing. You can send pm if interested and I would also recommend you give Traccdog2 a call.
The 700r4 has 3.06 1st gear combined with a 3 series gear will give great off the line acceleration.

 

The big question here is how do you plan on driving it? Ever plan on putting slicks on?
Mike

 

Definitely talk to Traccdog on here or get with Tom of Tom's differentials.

 

At this point in time I'm not sure if I will do any drag racing with it. Tires now are Nitto's 285/40-18s rear and 255/40-17 front. My biggest concern is that with the power and torq that I am set up that I don't end up breaking something when I do get on it. I want to jump on it just horsing around some, but again, not to break it.

Any ideas?

 

you car is a 78 .. That's an Eaton Differential..not Dana .. The Dana 44 was not used until 1980 .. unless its been replaced by previous owner

 

Contact Duntov Motors. There is no one I trust more with Corvette drivetrain than them. I bought my 4 series diff carrier for my 79 from them, used, but with new posi plates. It was pretty cheap, as I remember. They set me up for my 4.11:1 gears that I use with a 2004R OD trans. I could not be happier, and I have been running this combo for three years now. Great acceleration and only 2200 RPM at 70mph on the highway. What ever you do, DO NOT USE a 3 series carrier with a ring gear spacer for 4 series gears. It will fail if you put any real power through it, and you'll be having your car towed home. Don't ask me how I know! Duntov has the used 4 series carriers for Corvettes in stock most of the time, and will give you solid advice free with purchase. I am running a 421 stroker with over 600hp and 550ft/lbs torque through the 2004R and 4.11:1 diff, and the acceleration is unholy fast! Feels almost out of control! Yeee-Haaa!

 

Used to work for a parts store. I think the 3 series only goes up to 3.73? 4 series is 390+ I believe. I know that yukon makes new gearsets for c3 vettes, but they howl and make noise. I think it could be a gear lapping issue with those though, so you might have to get them worked on to fit properly without howl. If anyone knows a gear manufacturer that doesnt howl when set up right, I'm interested in knowing.

 

There are some used Gm gearsets available for Corvette C2 through C3 that run great. Again, Duntov has them in stock, usually. I don't work for them or anything, I just had a very positive experience buying my diff stuff from them. I can vouch for the fact that my 4.11 makes little or no gear noise. That is, none I can hear over the music coming from my sidepipes!