Re: Rearend strength vs size question...

From: Gary Shook (gary.shook@wcom.com)
Date: Tue Sep 21 1999 - 19:11:55 EDT


>
> Does the size of a rearend directly correspond to its
> strength? I've noticed that it seems like the bigger it
> gets, the stronger it gets, (i.e. 9 1/4 is an upgrade from
> the 8 1/4 on the Dak, dump trucks have 12" rearends, etc.)
> but is size the only determining factor?
in general, yes... it has to do with leverage... the larger ring gear
provides better leverage, and more surface area to push against

>
> The reason I'm wondering is, for a high horsepower
> (drag racing) application, which would be better, the
> tried and true 8 3/4", or the 9 1/4" from the R/Ts, Rams,
> and late model Daks? Is the 9 1/4" stronger? I'm just
> wondering because I see a lot of quick cars using the 8 3/4,
> but I never hear of anyone using the 9 1/4. Is this a
> price issue? A weight issue? A strenth issue? An
> availablility issue?
Probably price & availablity, as well as serviceability... the Chrysler 8.75
rear is a quick-change design... pull the rear wheels & drums, turn a few
bolts, slide each axle out 6-8", remove the driveshaft from the yoke, then
remove the bolts holding the pumpkin on, and all the gears are out... if you
have 2 pumpkins (one with street gears, one with ultra low drag gears) and
you get good at it, you can change the rear pumpkins in about 20-30
minutes... The 9.25 rear is very stout... I don't think a normally
aspirated small block can break either rear end... the Dana 60 was used
behind Hemi's and 4-speed 440s (Stick shifts are MUCH harder on rear ends..
because of torque reversal and the proverbial "clutch drop")

> Also, are rearends "rated" for a particular HP or torque?
> If so, where can I find these ratings?
Some guides I've seen rate rearends on what size tire you're running... if
it doesn't hook up, it pretty hard to break one... I think 8.75's were
recommended for 9-10" (wide) slicks, but don't hold me to that number (it's
pretty fuzzy)

>
> Since I've torn the 8 1/4 out of my Dak once already, and
> Eric has done so several times, obviously this thing isn't up to
> serious drag strip duty. So, I definitely will be putting
> in a stronger rearend in the future, but I'm undecided as
> to what to use. Obviously, cost is a big factor, but I want
> strength too. I'd like to get something that'll be able
> to handle a thousand horsepower or so, rather than get
> something intermediate just to have to upgrade again later.
> Obviously I don't have anywhere near that much power now, but
> who knows what the future holds?
If you want the ultimate, you want the Dana 60 (9.75 ring gear if memory
serves), it was known to hold together behind blown hemi's, but the 9.25
should be more than adequate for a small block, even if it is blown.



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