Kapos79kutlass

Hello fello olds family . Ok long question shorten . I have a 79 cutlass with stock 7.5 2.29 gears rear end . I just did a stock overhaul on a 73 455 out of a delta 88 . The plan is a cruiser and an occasional tire burner when an old head asks for it . Im on a 2 kid (2yold and 6yold) budget . What can i do to accomplish this ? . Can i hit my local pull a part and get what is need ?

joe_padavano

A 455 will frag that 7.5" axle if you actually get on it (assuming you have enough tire - if the tires spin that's the "fuse"). There are no readily available swaps. Only the 1984 H/O, 1985-87 442, and 1984-87 Buick Turbo Regals and GNs came with the stronger 8.5" axle. These were rare when the cars were new and nonexistent in wrecking yards today. I suggest saving your pennies.

66_Jetstar

A Ford 9" from quick performance is pretty affordable. You can buy the bare housing and axles for about a grand. Then go find a 9" donor from an f-150 with 3.50 gears. Grab the center section and the brakes. It's pretty cost effective. You'll be all in for less than 1500 if you do it right.

matt69olds

I have had several 455 powered G body cars with the 7.5 rear, the quickest went 12.90s. Surprisingly, the only 7.5 rear I have ever shattered was a peg leg, I tore it up rocking the car out of my parent snowy driveway.

I certainly wouldn’t put any money into a 7.5 other than routine maintenance. The money spent on upgrades would be better used for a stouter rearend.

I friend had a low 11s Camaro, he was constantly tearing up the 7.5. He tried the performance aluminum diff covers, he used solid pinion spacers instead of the crush sleeve, still tore up ring gears. The biggest durability improvement for was removing the 6 speed manual trans for a 400. He never tore up the rearend again.

Battenrunner

Best idea!

https://www.quickperformance.com/QP-...kage_p_63.html


You can easily change gears and diff later to best fit what you want to do at any time with a 9”.


We had an ‘82 Regal that I found an 8.5 out of an ‘84 GN. That was 22 years ago, and those rear Diffs were hard to find then. I think we paid $300….

Those days are gone.


We installed a 12 bolt in our ‘67, but in hindsight, a 9” would have been stronger and cheaper and easier to mod later, if needed.

joe_padavano

I'm guessing that the OP's "2 kid budget" doesn't allow for an expensive aftermarket rear.

JohnnyBs68S

As was mentioned, the best way to make a 7.5" rear survive behind 455 torque while having the ability to give a smoke-show is to run skinny tires that won't hook up in 1st gear. The 7.5" rear in my '98 T/A gave up the ghost (broke a pinion tooth off) behind a stock LS1 / T56 at ~20K miles (stock 275-width tires). I didn't think twice about repairing it and swapped in a Strange S60 from Midwest Performance. Best upgrade I've done to that car so far.

olds 307 and 403

Having broke my 7.5" twice behind a slow Olds 403, this info will help. The first thing to change is the stock spider gears. They are very soft, when I exploded mine, it took out the pinion. Yukon makes hardened spider gears. The later 7 5/8" case and the Monte SS had larger, more evenly sized spider gears. The smaller 7.5" Yukon spider gears held up on slicks doing a 9.4 in the 1/8 mile with a 2.1 60 ft. I broke the Power Trax No Slip which are also questionable behind any torque in the 7.5". For cheap gears, the S10 or in my case for my 3.42 gears were the Astro van are places to look. The 26 spline models were actually mostly 3.23 gears, according to the wrecker. The best used posi, which will also requires a 28 spline axle upgrade is the Zexel Torsen worn gear posi. The 4th gen Camaro/Firebird they come out of seem to have again, either 3.23 or 3.42 gears for the most part. Install the gears with either the Zexel posi or hardened spiders with the solid pinion spacer, get the girdle cover and Moser axles, it should live forever, without slicks. I did it with a 3 kid budget.

66_Jetstar

Well a moser 12 bolt is 3k, this is a much cheaper option that will provide a stout rear diff for half the money. I'm guessing he'll be waiting a long time to find a $500 dollar 8.5 rear..