Destroyed rear end

[jdscofield]

I just got word from my mechanic that my 8.25 rear end is shot.  Evidently it didn't like the 400 bb.  I know they make posi's and lockers for the 8.25, but if I rebuild the rear end with those items, am I still going to blow out the rear end again?  My buddy said to just swap in a ford 9" because it would be cheaper and stronger than the 8.75.  Any thoughts?

[flyinlow]

An 8 3/4 with a sure grip should stand up well to a relatively stock 400.  I subject both of the 8 3/4's in my Chargers to the wrath of  slightly warmed over 440's and they have held up fine. 

Burnouts on rough pavement or in reverse can cause breakage. Higher HP engines with manual transmissions and dead hook slicks will eventually break a stock 8 3/4.

[jdscofield]

I'm currently looking into trying to find a 8.75 rear end.  I'm worried that the shops in my town won't know how to properly swap them.  This is why I'm wondering if a 8.25 rear end can be beefed up to handle a big block.  I don't want to put the money into rebuilding the 8.25 if it's only going to break again 6 months down the road.

[Ghoste]

The "posi" (actually a Sure Grip in Mopar lingo) and the "locker" are just forms of a limited slip differential and have nothing to do with the durability of the differential itself.  If anything, they add more parts to potentially fail.
As to the Ford 9 inch versus the 8.75 Mopar, thats debatable in my opinion.  I will agree that the 9 inch has a superior aftermarket support but I don't know if I would consider MW stuff necessarily cheaper than the Mopar stuff.  The Chrysler 8.75 is a VERY strong rearend that at one time was quite popular with Ford and Chevy guys (especially Chevy) to swap in to their cars.  The Ford might be slightly stronger but the Mopar takes slightly less horsepower to drive and it runs cooler.
Will the 8.75 stand up to your 400?  It was the stock rearend behind the Hemi automatics, you didn't get a Dana unless you special ordered it or you chose a manual transmission.

[John_Kunkel]

I'd be curious as to what components in the 8 1/4" are "shot"...might have nothing to do with the motor installed.

[jdscofield]

I guess the question I should have asked is, "will a 8 1/4 rear end with a suregrip and 3:55's hold up to a mild built 400 making 300hp?"  If i change the heads and cam, i'll probably get an extra 60hp, and if i spray it, I'll only go as high as a 100 shot.  All being said, it will never hit 500hp. I have talked to other people and some are running this set up (big block, 727, 8 1/4 rear) waiting for it to fail, but doesn't.  I would love to swap to a 8 3/4.  However, I'm having trouble finding one, money is tight, need the car back on the road, and the 8 1/4 is already under the car.  As to what it was doing, it was dripping and howling, probably because the motor and trans are fresh and the rear isn't

[RallyeMike]

If money really is tight, keep looking. You can buy a whole used 8-3/4 axle for a fraction of the 8-1/4 rebuild.

A swap from 8-1/4 to 8-3/4 has a zero degree difficulty. You can even take the brakes and drums of the 8-1/4 and bolt them onto the 8-3/4. Worst case scenario, you may have to install a conversion U-joint if the yoke sizes are different.

[flyinlow]

A healthy 8 1/4 with street tires ,automatic and no wheel hop problems should hold up for a while . Maybe a long time if your careful driving it.  However yours dose not sound healthy. Dripping and howling....pinion bearings....crush sleave bad...

Very limited  support for the 8 1/4 compaired to the 8 3/4.

What year Charger? If it's a 73-74 you have the rubber isolators to deal with.

[jdscofield]

It's a 74

[Ghoste]

Your 8.25 probably failed from 40 years of use with a life cycle designed for a quarter of that as much as for any other reason.  That said, with higher power goals in mind and money being tight I also vote for getting the 8.75.  I think you will find its cheaper than building the existing one up or adapting a Ford.  Having trouble finding a suitable 8.75 is matter of patience not wallet.

[RallyeMike]

For a 3rd gen Charger, there are also C-body axles that are within 1/2" of the same width that will directly bolt in.

[John_Kunkel]

3rd Gen Charger spring pad spacing (47.3") is different than the C-body (46.0") so "direct bolt-in" isn't an option.

[ragin sonny]

how about a 9.1/4 out of a cordoba etc.

[RallyeMike]

3rd Gen Charger spring pad spacing (47.3") is different than the C-body (46.0") so "direct bolt-in" isn't an option.

John, experience or source?

I've personally done this swap without modification. To refresh my memory, I looked up the charts ad they indicate 47.3 axle perches for 71-74 B and also early 60's and 70's C. Also, I stated that the axle width was within 1/2" but actually the charts indicate it is a little more than 1/2" wider per side. Trust but verify.