My 9 bolt is on it's way out and i would like to replace it with a 4'th gen rear because I can get ahold of one easyer. My question is how much bigger is a 4'th gen rear? How much more will it stick out on each side?

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1989 Iroc-Z Blue T-Tops
Lightly Moded:
Headers, Rebuilt B&M 700R-4 tranny, Airfoil, K&N's

 

Does anyone have pictures of how a 4th gan rear looks on a 3rd gen?

 

Do a search... this question comes up in some form or other every couple of days on the Drivetrain board, with pics of various wheels even. There's names of mfrs. of wheel spacers for interchange, dimensions, etc. etc.

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"So many Mustangs, so little time..."
ICON Motorsports

 

What happened to your BW 9 bolt, they are a fairly strong unit?

 

I bought the car and when I opened up the differential cover surprise surprise 3 teeth were gone from the ring gear. So now I am on a search for a new rear end.

 

The 4th gen rear is 4" wider overall I believe. I have a motorbooks powertech series book that says the only difference is the shocks and springs due to a slightly different floorpan. There is an excellent article on this site's tech board that tells you just what you need to do this swap. I'm getting ready to do this myself and I printed tha article out so I could refer back to it if need be.

 

Using a 4th gen rear end is perfect if you are going to end up using 4th gen style wheels, that way you only need to buy spacers for the front wheels.
Your wheels will stick out 2" more inches on each side after you swap.

I have a 4th gen rear end sitting in front of my driveway which I was thinking about putting in but it has 2.73 open rear end and the gears and posi unit would have cost more than the $170 I paid for my wheel adaptors.


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WS6 Trans Am.

View My Ride @ thirdgen.org

 

I know that precision gear (used to) have a set of 3.73's gears for the 7.75" 9 bolt, borg warner rear end. Before you shell out big bucks on a different rear end and wheels check them out.

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89 Iroc 350 TPI,
Forged pistions
Comp roller Cam .510 lift 230dur
Flowmaster exhaust
Dart Iron Eagle heads 200cc runners 64cc chambers
MINI RAM SOON!!!!!
stock TPI for now 24# inj
87 Trans Am GTA 350 TPI
had engine fire
SHE NOW RUNS!!!! GREAT!!
Flowmaster exhaust
LT1 Injectors