Opinion Please -- Contemplating a rear end swap

Takt · Jan 2, 2006

Thanks for reading. I have an interesting situation. I currently have an 8" rear end and thinking about changing the ratio from a 2.8 to a 3.8 (recently upgraded the motor). Then I ran into a guy.....

This guy that is selling a 9" rearend (correct size for my mustang) that is a posi with disk brakes attached. It is out of an automatic, so I would guess the gear ration is on the lower end. He wants $550 for it.

Here's my question: What will I need to know if I go with the 9"? I might as well upgrade to disk brakes all the way around (right?) -- what does that entail/what will I need?

With the motor I have now, an 8" is enough -- I want some more pep. But in the future (lots of years down the road) I'd like to make some serious horsepower.

How much am I looking at putting into the car to switch to this particular 9"?

Thanks!

Takt · Jan 5, 2006

Anyone have any thoughts?

302 coupe · Jan 5, 2006

if its the right width, and spring perches are in the right location, it should bolt right in. You might have some issues with the spring plates, maybe not, depends on the tube diameter of the 9". U-joint could be an issue if the 9" uses a different yoke, but thats easily overcoem by a trip to the parts store. Should be an easy swap, I'd be tempted to go for it. You wouldn't be able to build a 9" with a 'posi' and discs for that cheap.

krash kendall · Jan 5, 2006

And you are putting this in what? A Fiat? What gears are in the nine inch? Are the spring perches in the right spot? Do you have the cash to uprade to front disks (you will have to do that)?

More info.

LMan · Jan 5, 2006

well, now....a rear disc/front drum setup would be interesting!

12sec67 · Jan 5, 2006

might need to get a shorter driveshaft depending on the stock size driveshaft you have now and how much room you have to the trans.

krash kendall · Jan 5, 2006

12sec67 said:
might need to get a shorter driveshaft depending on the stock size driveshaft you have now and how much room you have to the trans.

Yeah, I know I had to get one built for mine, but I didn't mention it because I don't know if he has an early car or not.

302 coupe · Jan 5, 2006

depends more on which yoke the 9" has rather than just the fact that its a 9". There are short and long yokes which will all interchange.

When all things are considered, the swap can be a real bitch or it can be a direct fit. Just depends on exactly what you've got.

krash kendall · Jan 5, 2006

Mine has the big sheilded daytona pinion.

grego37 · Jan 5, 2006

A 9 inch is the stronger set up.

But it all comes down to what you are asking of your rear end and how much money are you willing to invest in it. If you buy it for 550.00, and the ratio isnt what you want, you'll need to invest a good 150.00 for the correct ratio and labor, It might need a brake job (more $$) and if its not the same exact width it will push your wheels out (or vice versa)

unless your running slicks and launching the thing with allot of HP/TQ, i'd stick with the 8 inch and the rear drums, change your gear ratio, and invest in some front disc brakes .

Takt · Jan 5, 2006

Thanks guys --

Sorry, I thought I posted that I have a 66 mustang, obviously didn't.

The shorter driveshaft is exactly the type of thing I wanted to know. To upgrade to disc fronts -- I'd need the front kit, but also a new MC and a booster, correct?

Thank you for the response. I'm leaning towards just changing the gear ratio for now -- I have other things on my "want-to-do" list.

Thanks!

HistoricMustang · Jan 5, 2006

Takt said:
Thanks for reading. I have an interesting situation. I currently have an 8" rear end and thinking about changing the ratio from a 2.8 to a 3.8 (recently upgraded the motor). Then I ran into a guy.....

This guy that is selling a 9" rearend (correct size for my mustang) that is a posi with disk brakes attached. It is out of an automatic, so I would guess the gear ration is on the lower end. He wants $550 for it.

Here's my question: What will I need to know if I go with the 9"? I might as well upgrade to disk brakes all the way around (right?) -- what does that entail/what will I need?

With the motor I have now, an 8" is enough -- I want some more pep. But in the future (lots of years down the road) I'd like to make some serious horsepower.

How much am I looking at putting into the car to switch to this particular 9"?

Thanks!

At that price buy it..................you can easily sell it for a grand!

HistoricMustang
www.historicmustang.com

65 fastback · Jan 5, 2006

The driveshaft is easy, any good machine shop can cut it down and reballance it - I've had mine cut down twice.

I would, however, check into the condition of the rear and price up the rehab to make it what you want. If it came out of an automatic, it is probably an open differential with 2.73 gears. How good do the rear brakes look?

I had Currie Enterprises make me a custom 9" with 3.55's, a T-lock and disc brakes for under $1,100 (it was 10 years ago, but it's still worth pricing out).

Tim

65up2d8 · Jan 5, 2006

HistoricMustang said:
At that price buy it..................you can easily sell it for a grand!

HistoricMustang
www.historicmustang.com

I agree that for that price you should buy it if its in decent shape. The only way you'll get a better deal is if you get real lucky like I did. I spotted a '77 Lincoln Versailles about 7 years ago and kept my eye on it. I noticed it hadn't moved from the carport after a few fly bys, and I stopped to knock on the door. Noone came to the door, so I went to the neighbor's house and inquired about the person who owned it. Turns out it was an old lady who didn't hear well and was going blind, and she was home but didn't hear me at the door.
Of course, she could no longer drive, and I eventually haggled a deal for $550.00 for the whole car, which had a 351W and only 70,000 miles on the odometer! I had a buddy who wanted the front disks and the 351W (I already had Grenada front disks), and he pulled the rear end out for me and paid me $450.00 for the rest of the car. So, I walked with a 9" rear with disks for $100.00.
If I'd had the extra cash at the time, though, I'd have probably kept the whole car myself. The 351W would have come in handy, and the Lincoln had some neat features I wouldn't have minded to integrate into the Stang.

Opinion Please -- Contemplating a rear end swap

Takt

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65 fastback

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