Sure Grip help

[Samuelson1022]

Alright well time to upgrade my axle.  I have an 8 3/4 rear end with the non sure grip 3.23 3rd member in it.  Not sure exactly what 3rd member it is but I'm planning on buying a whole new 3rd member with a sure grip in it and 4.10 gears.

First off, can i just unbolt the old pumpkin and bolt in the new one?

If so where can i find the 3rd member for fairly cheap?

How do you tell if it's still good?

I found one on ebay last night, let me know what you think.

http://cgi.ebay.com/ebaymotors/411-SURE-GRIP-8-3-4-FITS-A-E-B-BODYS-FROM-68-71_W0QQcmdZViewItemQQhashZitem260172399307QQitemZ260172399307

Besides all the questions,  I love getting into arguments over whether to call it sure grip or posi as my shop teacher is a chevy guy.  He was going as far to say my axle was a ford 9 inch design  but I dont have much pull since im the student.  When your young (17) people assume you don't know what your talking about.  Oh well I guess i'll just stick to my guns, even though my friend insists on calling it a posi-grip so he can stay neutral.

[Aussie Challenger]

  Looking at the Nos. on the case it is 742 which is the weakest of the rear ends. It appears to have a small uni joint flange, you would be better off buying a 489 case with the larger flange. That will take a lot more punishment than a 742 of unknown history.
  You will kick yourself if it doesn't last toooo long, consider buying a new unit (489) and it should last awhile.

[tactransman]

742 is the highly desired (rebuildable clutch type) sure grip. 741 is the smallest pinion (weakest)  489 is the cone type(not rebuildable) 

 I personally would not buy anything like that off e-bay.   I would want to see it first.

[Samuelson1022]

Well I have no idea what I would need to look for in person.  What are my options on where to buy one?

[Chryco Psycho]

Dr Diff can sell you a new unit
 the 742 is by far the best center section for strength , get a clutch type sure grip
 I also agree I would never buy a used one from Ebay , I went to buy 5 in person here & asked the seller if I could disassemble them to inspect them & told him I would buy all 5 if they were in good condition , I ended up purchasing none they were all worn out

[Ross]

...I went to buy 5 in person here & asked the seller if I could disassemble them to inspect them & told him I would buy all 5 if they were in good condition , I ended up purchasing none they were all worn out

If the clutch type is rebuild able, why not buy a worn out one and rebuild it?

What are the telltale signs that it is worn out?

[cowboy]

If the clutch type is rebuild able, why not buy a worn out one and rebuild it?

What are the telltale signs that it is worn out?

_ The ring and pinion could be worn out to, - like mine,   - terribly noicy...

[Chryco Psycho]

the axle & spider gears can be worn or damaged in a clutch type , look for wear or scarring on the teeth

[duodec]

Chryco,
     is there a writeup online somewhere for examining a used assembly, or the differential unit itself, both for making a purchase decision and also just to see what work needs to be done?

     I've got two used pigs I bought 14+ years ago (cheap!); ones a 742 with clutch type, the other is a 489 open.  The 742 looks perfect, the 489 is a usable core (though the gears look fine).

[73_Cuda_4_Me]

I have a 73 340 auto with 489 rear running 3.23 open, and just couldn't take having a 'muscle car' that lit up one tire only. After comparing prices, I ended up buying the 'Power-Trax' locker from summit for 380, instead of forking over 650 for new sure-grip... installation was pretty easy, but even with shop manual WARNING the ring gear bolts are left hand thread, I ended up breaking 5 of the 12 bolts due to someone red-loctiting them. Managed to get them out by wire-welding nuts over the broken shank of the bolts this past week. Yesterday the new diff install kit from summit arrived, with 12 brand new ones, plus gasket, shims, and bearings. The rest of the install was a breeze, and I just got everything buttoned up last night. Took her out today, and boy - WHAT A DIFFERENCE!!!  8  )

Here are some pix - old vs new....

   <---my 73 is Lemon Twist with black stripes... LOL

[moper]

If the seller can take a good picture of the checking pattern, it might be an ok sell. Personally, I buy alxes as cores. Nothing else, unless I've seen the car it came from before. It's very difficult to "see" a bad bearing on the pinion without takig them apart. And if you take it apart, the "might as well go thru it" takes over. A pattern tells a lot, but assume the worst, be ready for it, and you'll never be in trouble.

An example: A swap I sold at Sunday in CT.. I have a used, worn cone type 'grip I was selling. It was in a Ford Motorsport box, clearly written "Blown, needs rebuilding" on it. I dont do that, but I know guys that do, so I figured if I could get $20-30 I'd be happy knowing I recycled...lol. Well, a guy read the box, looked right past it, and was grilling me on "Why so cheap?" I had to be fairly abrupt in telling him "It's BLOWN. IT SLIPS. It is a CORE.." before he got it. That's why so many guys get bit by Ebag...