Odd rear-end combo on my '68 R/T

[Zentelis]

My '68 R/T was originally equipped with an open diff. I'm planning on upgrading to a Sure-Grip this weekend after I pick one up at Carlisle.

So, last night I started tearing apart the rear-end.

Surprise #1: The case is a 489 (as I understand it, they weren't available until '69??)
Surprise #2: The axles are tapered.

I thought tapered axles weren't used after '65?

I haven't pulled the diff out yet, the bolts are soaking in Gibbs, so I'm really curious now to see what kind of odd-balled setup I have.

So, since 489 cases weren't around 'till '69, I'm thinking a previous owner wanted to upgrade to the strong pinion (1 7/8")..ok, but why didn't they upgrade to a sure-grip instead of open diff?? Secondly, whatever open diff is in there, why the devil would the axles be tapered? Unless I mistunderstood when tapered axles went out of style??

Anyone have any possible explanation for all this??

Heck, for all I know, I might pull the diff out and find a sure-grip! (Though I'm certain that won't be the case..every burnout I did was a one-tire liquifier).
Oh, and if it makes a difference, the car has an auto->manual swap.

Also, now that I know I have a 489 case, what sure-grip diff's can I get? And will there be any compatibility issues with the tapered axles?
I don't plan on doing any gear-swapping, I just want to swap the whole center-section. (which I understand to be the case+the internals)

Thanks, folks

[mikepmcs]

 
what he said.

[694spdRT]

You could have a wore out sure grip unit too.  Maybe they found a 489 case to replace a junk 742 or the gears were just better. 

It's hard telling what these cars have had done to them or why through the years.

[69CoronetRT]

The 489 was introduced very late in the 68 model year. What's your car's SPD? What's the casting date on the carrier? Is there a date on the ring gear that matches with the SPD and carrier casting date?

Is there a BS to see what axle assembly it came with?

Can't help with the axles...

As stated above, it's hard to tell what has and hasn't been done over the years.

[Zentelis]

I picked up a 3.55 SG 489 at Carlisle this past weekend.
Looks like I kinda shot myself in the foot with the Cone-type SG (doesn't look like it's very easy to rebuild). I'm worried about the crush-sleeve, and the tapered pinion..I found a replacement solid-sleeve on Ratech (thanks to a thread here), but are the tapered pinions a big cause for worry?

Can someone calm my nerves that the cone-type SG isn't a bad SG? I plan to do some mild engine upgrades (450-500hp?) and don't want the SG to blow out on me, or not perform well.

[Mike DC]

 
From what I know, the cone-type LSD is a strong-ass MoFo as long as it works, and then you have to throw the whole thing away when it finally wears out. 

Officially, Auburn (the manufacturer) says "no rebuilding it."  Unofficially, it's an ongoing disagreement.  Many sources say you can't, a few say you can, and a few more say you can sorta rebuild it but it's not as strong/tight as it should be anymore.

 

[8WHEELER]

You can have a cone SG redone, there is a guy from Montana I know who just machine's the surfice
done, and adds a shim. They work great, I have had a redone unit for 5yrs, locks up perfect.

I have had one cone SG go bad on me over all these years, but that was only on a sharp turn, and if
you hit the gas it would only spin one tire at first. But nail it in a strait line, perfect two tire burn out.

I don't mind the cone units at all, I have found they last longer than the clutch type, but if and when they
wear out, they are no where as easy to repair.

Dan

[mikepmcs]

I picked up a 3.55 SG 489 at Carlisle this past weekend.
Looks like I kinda shot myself in the foot with the Cone-type SG (doesn't look like it's very easy to rebuild). I'm worried about the crush-sleeve, and the tapered pinion..I found a replacement solid-sleeve on Ratech (thanks to a thread here), but are the tapered pinions a big cause for worry?

Can someone calm my nerves that the cone-type SG isn't a bad SG? I plan to do some mild engine upgrades (450-500hp?) and don't want the SG to blow out on me, or not perform well.

here's an article on moparts that backs up Dan's previous post.

http://www.moparts.com/Tech/Archive/axle/13.html

v/r
Mike

[Zentelis]

Thanks a million, guys, I appreciate it

I'm picking up some gear oil and additive today to get this part of the project done   

[deputycrawford]

     Zentelis, I run a cone S/G and a 489 case with a 4.10 and a solid spacer. My car dead hooks at the track with 1.8 60 Ft times. You should have no problems at all with you unit.  Did I just type that?

huh huh huh......he said unit.

     The tapered pinion should not be a problem. Oh, and the tapered axels, as you call them. Are they tapered about 1/3 of the way from the end that plugs into the rear end gear? That is nothing more than a stock axel. I still run those too. I know, I know. I will change them someday. I don't seem to have a problem with them now.

     Anyone know any different on the stock axels? I have multiple sets and they all taper to a smaller size near the pig.