Louis, Like Joel said it's a loaded question. For me, if the money was no object, I would change the trans to a overdrive unit and run a higher numerical ratio differential.  I have a friend of mine that has a '56 Chevy with an 700r4 overdrive unit and a 4:11 ratio differential. He claims the best of both worlds, good acceleration and good top end. I've rode in the car and it feels pretty good in the seat of the pants when taking off from a stop, can lite the tires. Then when he gets to the overdrive, the engine rpm drops off very dramatically. As far as doin the diff work yourself, I wouldn't reccomend it. I have had years of experiance in the automotive and truck world and not afraid to tackel any job, even trans. I have been to Alison automatic school, and have done gm trans's. But the diff presents some daunting points, such as settin the pinion preload, the contact pattern and the backlash. The preload spring pack is another challange to get in correctally. If I were you, I'd go for a rebuilt from a rep. sorce. My '79 has a 3:55 in it, and if I live long enough, I'm gonna go to a o/d trans and a 4:11 diff.

Dave

Hrm... intersting points. If I were to jsut get the kit, with the bearings, races, and seals then I would bring the unit to the same dude who is doing the trailing arms. Hes knowledgable.. but he's always bogged with work. I guess I'm really afraid of having this unit, or the POSi going bad after I put all new bushings, adjustable struts, and the rebuilt trailing arms in. Thats a lot fo work, adn I would hate to have to take it all apart again because my 30 yr old dif or posi fails. Anny suggestions then?

Try this guy, he will even swap gear ratios for free if you don't mind getting used gears.

http://corvetteperfection.com/corvetteperfection001.htm

And for what it's worth, the stampings on the differential that relate to gear ratio ID mean nothing if some previous owner has changed gear ratios. The only way to tell for sure what ratio is in there is count how many turns the pinion has to go to turn the axle exactly one revolution. For example, a 3:08 ratio requires 3.08 turns (barely over 3 turns) of the pinion for one revolution of the rear wheels.

 

The best way to determine the ratio is to count the number of teeth on the pinion and the number on the ring gear. Then divide gear number by pinion number.
Example:
Gear=30 teeth
Pinion=10 teeth
Ratio = 30/10 = 3.00
Of course, you have to be able to see the gear and pinion to do this.

Lewis, If you have your diff rebuilt, get new stub axles for it. They wear on the spyder gear pin, a normal, but regretable condition with the diffs. The half shafts are actually a part of rear tire alignment. I replaced mine with hardened tip axles and a hardened spyder gear shaft pin. I also put an after market cover on it, the stock ones tend to crack.

Dave

Hey guys,

While this thread has been a major learning point for me, my dad pretty much said no. He said to leave the dif alone. Just cleain it up witht he wire brush and paint it. Later on down the road in the next year or so I plan on re doing the car agian anyway. Supercharged demon fed engine, racing suspension, and a 4sp overdrive with a 3.90 dif. Thats my plan. But since I have to go to pamona, and I still ahve to do the interior, and still have to worry about paint... I'm just goign to leave the DIF alone. I need to drive my master piece before I turn 92...

Thank-you a lot guys,

-Louis

I think Dad's giving sound advice. Even though I did a frame off on my L-71, I just cleaned the exterior of the diff. It worked fine before and the car only has 83,000 miles on it.

I would definitely treat it to a fluid change though. Change it before you put the car on the road, and if it's been sitting for a while, I'd put a hundred miles on it and change it again. On the second change, you'll need to drive the car long enough to warm up the fluid so it will come out easier.

Hrm... Thanks Dave.

Yeah makes a lot of sense just to leave it. Should I change the half shafts, or the side yokes at least? I remember reading somewhere on here that the half shafts were part of the rear alignmnet. ANd if I change the haft shafts, I have to change the yokes. Is this true?

For now, since you're on a budget, your T arms are done. I'd put all new U-joints on and run the beast! See how it all behaves. You could very well be in good shape. Then enjoy the car while you're saving some cash for your other upgrades.

When I built mine I was also on a budget. I would at least check the end play of the yokes, if it's less then .050" you should be in good shape for a while. More play then that is asking for serious problems in the near future when the retaining rings wear off and have their way with everything inside.