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-   -   what's wrong with the 7.5 malibu rear? (http://www.hotrodders.com/forum/whats-wrong-7-5-malibu-rear-86766.html)

Augusto 04-12-2006 10:25 PM

what's wrong with the 7.5 malibu rear?
 
I have read a lot of bad things about the stock rear of my 81 malibu lately (converted to el camino by myself ) the truth is I didn't pay any attention to it until now, it hasn't braked anything yet ( I hope it won't ) it lives behind a 350 with a 144 B&M supercharger and it's hotter cam, 600 cfm holley, headers, etc. do you think I should worry about it? I have a 1977 malibu rear end sitting in my shop, I'm not sure about the size but it's the one with the squared ears at the bottom of the pumpink, is this a better choice? should I replace it? I don't race the car, it's a street tire fryer only.
Augusto.

curtis73 04-13-2006 01:24 PM

It depends on several things. The 7.5 lives fine in F-bodies behind some respectable torque, but they are very traction limited. The tires go up in smoke long before enough torque gets put to the 7.5.

If you put more than about 350 lb-ft to it and you get any shred of traction, there is a very good chance you'll rip the axle in to pieces. Small bearings, small ring gear, and a small casting. It was designed as a lightweight economy axle. It takes some abuse, but not where traction is involved.

If you feel saucy, go for the 8.5 from a Grand National or 442. They're not as hard to find as you might think, and if you get one from a flat-rate junkyard they're no more expensive than a Chevette axle.

The flat-eared axle you have is probably an 8.2. Its a little better than the 7.5, but if you're putting a 144 blower on things I'd go at least 8.5.

xntrik 04-13-2006 02:02 PM

Run it until you break it. With limited traction, it might run for years.

Augusto 04-13-2006 03:22 PM

thanks for replying, as I begin to understand the problem with this axle is in racing duty, this might explain why it has survived so far, there is the problem that I live ten thousand miles from the nearests junk yard that has american cars and must do with wathever I run into, are the 9 in ford rearends that are so desirable for cars up there the same that are found in the back of mid seventies F-150 pickups? those are plentiful here, lengthwise I don't care I own a machine shop and I'm acustomed to fabricate almost anything, we have to sometimes when parts are imposible to find. should I adapt a new axle or just use until it breaks?

M&M CUSTOM 04-13-2006 05:03 PM

The 77 should have had an 8.5 in it and nothing else.

Guy Hiltz 04-13-2006 05:45 PM

re:whats wrong with the 7.5 malibu rear?
 
I 'm fairly certain that the rear end from the 77 will not be a direct bolt in,the 9 inch from a Ford pickup would be a much better choice.

Augusto 04-13-2006 09:09 PM

a) how good/bad is the 8.5 rear end? ( for my street supercharger )

b) installing lower gears like a 4.10 prolong life expectancy of the rear end?

xntrik 04-13-2006 09:28 PM

Quote:

Originally Posted by Augusto
thanks for replying, as I begin to understand the problem with this axle is in racing duty, this might explain why it has survived so far, there is the problem that I live ten thousand miles from the nearests junk yard that has american cars and must do with wathever I run into, are the 9 in ford rearends that are so desirable for cars up there the same that are found in the back of mid seventies F-150 pickups? those are plentiful here, lengthwise I don't care I own a machine shop and I'm acustomed to fabricate almost anything, we have to sometimes when parts are imposible to find. should I adapt a new axle or just use until it breaks?


If I were you I would find a Ford 9 and begin narrowing it and getting ready to install..... someday. Then when/if the old one dies, you won't be without your fun car for a weeks.

jimfulco 04-14-2006 07:43 PM

The '77 rear end is not a simple bolt-in, but Southside Machine made a set of conversion control arms to make the '73-'77 rear fit the G-body. They're no longer in business, but somebody might have some left-overs or some knock-offs.

Augusto 04-15-2006 12:07 PM

thanks guys, you all are very helpful.
Augusto.


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