Hey guys I'm new to the forum I have a 79 cutlass with a 260 in it yeah I know but the car only has 49k on it no rust and I'm from Pa so that is not common for a 40 year old car anyway I bought a 77 with a 350 #6 heads and a better transmission and if the rear end fits my question is will the rear end from the 77 fit it also has a Elderbrock 1405 carb sitting on the stock intake I read a few threads on the rear end and with some modifications it can fit not sure and should I ditch the 1405 and go with a Qjet thanks for reading and any advice you can provide

 

Welcome. The 73-77 rear axle is considerably wider than the one in the 78-88 cars.

 

thanks I kinda figured it was guess I will keep looking or build the 1 in it up

 

The 7.5 can be built to accept reasonable HP. The real limiting factor will be how much traction you have. You won't really break the axle if the tires don't hook up.

 

The 7.5 rear will live behind a reasonably stout 350.

If you rebuild the reset end, use a shim kit to set pinion preload, instead of the usual crush sleeve. One of the durability issues with the 7.5 is the pinion bearings loosening up when the crush sleeve continues to crush under heavy loads.

Install a rearend cover that have the cap bolts to stiffen the carrier bearing caps. The factory cap casting is pretty flimsy, the bearing caps move around and causes additional wear.

I wouldn’t put any more money in a 7.5 rear for parts (other than the rebuild/gearset). By the time you spend the money for better axles and carrier, you could have rebuilt a stronger 8.5.

Keep a Q-Jet on the engine. Build a QUALITY rebuild kit from a Q-Jet specialist. A 30 Advance Auto rebuild kit isn’t enough. Get the needed parts to recalibrate the Q-Jet for your application.

I really like the Olds G body cars. I have owned at least one of every year olds cutlass/442 from 68-88. Obviously my favorite Olds is my current 69, but the G body cars are by far more comfortable to drive.

Welcome, and good luck

 

The problem is finding (and paying for) a G-body 8.5. They go for stupid money when you do find one.

 

thanks I was planning on upgrading the axles and doing a Yukon posi 3:23 or 3:42 gears not sure what will be best

 

The difference between 3.23 and 3.42 is negligible - about 6%. You won't feel it one way or the other.

 

Thanks for the information the 8.5 is what I really want. Finding 1 that doesn't cost an arm and leg is the problem lol. I was really hoping the 77 parts cars rear end would fit but I knew it was a wider car. I have a spare 350 I picked up for 150 with the Qjet on it so I will look into rebuilding it. I love oldsmobiles my favorites are the 69 to 70 one day I will own one hopefully lol. Where can I find a Quality rebuild kit for the Qjet?

 

Didn’t someone make upper control arms to fit a A body 8.5 rear into a G body? If I remember correctly, the lower control arm mounts are in the right location, the upper mounts are at a different angle.

 

Found the answer here.

https://www.umiperformance.com/home/...-control-arms/

Looks like the A body tear ends are 3 inches wider than a G body, so it’s probably going to take wheels with different backspacing to fit.

Personally, I’d roll the dice with the 7.5. If/when it breaks, then do the swap. I’m willing to bet the 7.5 will live a long life behind a mild 350.

 

I'll also point out that the 3" applies to the 68-72 A-body axles. The 73-77 axles that the OP was originally asking about are even wider than that.

More to the point, have you priced desirable 68-72 A-body rear axles lately? That's not really a savings as compared to the G-body 8.5, especially once you get past the special UCAs and wheels.

 

The 8.5 68-72 rears are still plentiful around here I’m guessing some places can’t say the same