The differential in my 66 is a 3.36 non posi. Rather than having it repaired and upgraded to a posi, I was wondering if it would make more sense to just buy a rebuilt differential outright. There are many places that sell rebuilt differentials, but has anyone bought one and had no problems with it... Where would be a good reputable place to buy one from?

 

Possibly Bair’s. And possibly Gary (GTR1999).

 

I would PM Gary (GTR1999) as he may give you advice on which way to go. If he cannot take on the extra work, I am sure he will help you find the right rebuilder or retailer.

 

Bob, is the diff broken or you just want posi? Posi is cool but I have built plenty of 63-69 open vette diff's. For a street car, driven on warm, dry days, it won't make a difference unless you want to lite up the tires.

There a many places selling differentials, my advice is to do your homework well in advance of opening your wallet. I often mention the question I used to get at my seminars in Carlisle or CT. At the end I would have a Q&A time, and someone would always ask me, "who would I use if I retire". They were all expecting me to name a few places, but my answer today is the same as it was 20 years ago, "I wouldn't use any of them. I have repaired the work of many of them, why would use them?"
I am not saying you cannot get a rebuilt, exchange differential, but they are not all the same. When the main driver is profit vs time, it can turn ugly fast. The diff should be built to application, not a one size fits all approach as many offer. There are some honest places out there and there are some slick conmen.
Good luck.

 

So many corvettes and so little people you can trust to buy parts from...Can we clone Gary?

 

Gary's information is perfect again. There is little reason to add a posi on a car driven on the street, it is like adding headers to a street driven car, generally not much bang for the buck. But then again there is braggin' rights' if you are in to them.
Ron

 

Currie sells a Ford 9”…

 

There was the comment 'having it repaired' in the OP's initial post. So, what's wrong with it?

 

It has way to much end play on the side yokes. especially the drivers side. Doesn't make noise or leak.

 

There are a lot of used 4:11 posi's available.

 

Hi Gary, so glad you were available to do our ‘67 rear years ago and car will finally be on the road by Memorial Day weekend. Huge thanks for all you’ve done for both enthusiasts and the hobby.
Chick

 

HI Chick,
That was a while ago, Aug 2014 to be exact. You have a real super 10, not a knock off from a conman. You also have parts in that diff that are no longer available- US Gear and Tom's 10-17 x30 spiders. To build one like that today would be $7k easy. if you want to sell it, it would go fast.
Good luck with the build and hopefully you put the Lucas gear oil in it years ago.
Stay well.

 

Keep in mind that the housing casting is date coded, has a casting number for 66, and stamped date and assy code that matches the car. You get a rebuilt assy, you lose that. Are you going to pull the diff? Just pull it and take it to Auburn Corvette, they can handle it from there.

 

Just giving you an update on my experience. I got a good deal on a rebuilt 3.55 posi differential that had sat for 10 years. After opening it up to look, we put new seals in it and put it in the car. I was told that the Ford friction modifier was the best stuff to use, so 2 4 oz. bottles and then filled with GL5 gear oil. It chattered going slowly around corners, even after turning several circles and figure 8s in a parking lot. After reading several threads about this, I drained the oil and put in 2 4 oz. bottles of G.M. friction modifier and filled with GL5. End of problem! No more noises! So there is a difference in the type of friction modifiers. As fr as the ratio: I went from 3.36 to 3.55. Not very much difference. Just thought I would pass this information on.

 

Little difference between 308 & 336 and 366 & 355. Going from 308 to 370/373 you will feel the difference on launch. Many will say the additives are all the same less the labels, clearly you didn't experience that. I only use the GM additive.

 

Maybe there is a different way at looking at this problem? I use to recommend this approach when it came to carburetors, 7 circuits are in your typical carburetors do you know how many carbs were replaced back in the day just for a choke problem? So you replace your fine running carb (other than your choke issue) with a rebuilt out of the box unit & now it may not have the choke issue (1 of the 7) any more/hopefully, but now it has issues with the other circuits your original carb didn’t have,\., bogging, running rich, run on when turning key off etc etc.

Same issue could develop with the diff “replacement unit” & maybe look at in the same light as replacing a carb?

If you just want to eliminate the issue with the side yokes & I would deal with that problem ASAP before they start digging into the housing & create bigger repair issue's
send the unit out to Gary he will address repair your current issue & go thru it 100% for any other concerns & you will get it back like new with all the “Circuits” gone over.

I had the same end play issue in my 65 (C2 unit), got unit to Gary & we addressed that & other unknown potential issues with differential, Gary will send you pics/updates & when done it will be better than new..
All the best
Chalie