Are all 8 3/4 Cases the Same? Just the 3rd member is different?

[2Gunz]

I have an 8 3/4 741 rear end.

It has 2.73 gears and no sure-grip.

Im looking to get a set of 3.73 gears and a Sure-grip unit for it.

But at $200 bucks for the gears and $300-500 for a sure-grip.....

Im thinking i will just get a complete 3rd member for it.

Ive found a 489 3rd member with the gears and Sure-grip already.

The 489 is the strongest unit correct?

And will it just bolt in? or will I need a new axle case?

[Nacho-RT74]

supposelly stronger one is between 742 and 489. I have known 742 with 10 spline pinions are the drag racers favourite. I think tappered 489, could be stronger somehow ( that's just an opinion, thinking on how force acts on pinion ), but dunno if they are available on 10 spline setup

Is just bolt in. Axles housing diff is just on perches location and length, but not on bolt pattern

[BROCK]

I was once told by a mechanic that found out the hard way that a big car 3rd member will bottom
out against the rear cover on an A body 8.75 housing   Everything I've ever read says "swap
away - it's all the same"  Naturally, I'm curious to hear other's experiences n this too

[2Gunz]

one more question.....  Will it require a different Drive shaft or is the length the same?

[Ghoste]

Your driveshaft will be the same langth but you may run into an issue with different u-joint sizes.  If you do, you can use one of the conversion u-joints or make the changes to one of your yokes.

[RD]

i do not believe you really have to worry about pinion size and the whole question of "which one is weakest/strongest" if your application only puts out below 500 hp.  the biggest weakpoint on any 8 3/4 is the main bearing caps, not the pinion.  I have seen more 8 3/4's blow up from main cap disintegration than a pinion snapping.  Not saying it doesnt happen, just my experience.

742's have been the choice for racing since there is not a need for a crush sleeve, easier to setup and swap gears than a 489.  but that has changed since the crush sleeve is no longer required with certain aftermarket replacement pieces.

[ACUDANUT]

  I have had nothing but bad experiences when it comes to putting a "posi" in my 8 3/4.  I bought 3 different posi tracks and although they once started out as a posi and seem to work when out, it was a different story once in and under a load.  Bottom line is you never know when dealing with used and abused 3rd members.  I got feed up and bought a new (rebuilt) from Randys ring and pinion. It set me back 1100 bucks, but it works.  Why are 3rd members so damn expensive ??

[Chatt69chgr]

You say that the 489 you found has a suregrip.  What kind?  Is it the cone type or the clutch type.  If clutch, it can be rebuild.  Parts available at dealer.  Cone type----generally no.  The 489 pumpkin will drop right in any 8-3/4 housing.  If clutch type, make sure you have the thrust buttons intalled.  They are also available from the dealer.  Rebuild kits available from

http://www.ratechmfg.com/toc.htm

Gears availble from Strange Engineering.

Bearings and seals from Autozone.