Swapping out 8-in for 9-in Diff

Faststangfan · Post by **Faststangfan** » Fri Sep 30, 2011 4:46 pm

I am about to swap out the old 8-in 28 spline rear end from a 70 Fastback, and replace it with 9-in 31 spline with 3.25:1 Lsd centre. Housing is from a 67-70 Mustang. Staying with drum brakes and a standard yoke.
Are there any issues that may be involved with this upgrade?

S[_]SPECT · Post by **S[_]SPECT** » Fri Sep 30, 2011 5:00 pm

Whats the ratio in the 8"?
A change on ratio will put your speedo out..
Just a matter of changing the driven gear in the trans though.

Faststangfan · Post by **Faststangfan** » Fri Sep 30, 2011 5:12 pm

Unsure of current ratio. I am going to get the C4 tranny reconditioned at a later date, I assume a change of driven gear can be made then.
Note: What I know about the greasy bits of cars wouldn't cover the bottom of a vegemite jar, hence some of my questions may seem a bit lame.

MUZZY_66 · Post by **MUZZY_66** » Fri Sep 30, 2011 10:41 pm

Pretty sure it requires longer U bolts over the tubes...

A little less clearance,nothing really concerning when mine was done.

donoauto · Post by **donoauto** » Sat Oct 01, 2011 9:04 am

Faststangfan wrote: Are there any issues that may be involved with this upgrade?

Yes, awesome donuts & extreme tyre wear - at least they wear evenly.
See avatar.........

Faststangfan · Post by **Faststangfan** » Sat Oct 01, 2011 9:06 am

Righto, thanks.
I will use the opportunity while the rear end is out to clean up and respray the underbody. No rotisserie will use engine crane to lift rear of body high enough to work under.

Post by **ozbilt** » Sat Oct 01, 2011 2:41 pm

Faststangfan wrote:Righto, thanks.
I will use the opportunity while the rear end is out to clean up and respray the underbody. No rotisserie will use engine crane to lift rear of body high enough to work under.

And adding stands I hope....

Faststangfan · Post by **Faststangfan** » Sat Oct 01, 2011 7:04 pm

Yep, one to hold the beer and one to hold the phone in case the car falls on me and I need to call an ambulance.

shermatt · Post by **shermatt** » Sat Oct 01, 2011 8:37 pm

As Muzzy66 said, the U bolts are a different width and a little longer. Hopefully the donar diff comes with the U bolts other wise you will need a set that suits a 9"

Matt

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shermatt · Post by **shermatt** » Sat Oct 01, 2011 8:39 pm

Faststangfan wrote:Yep, one to hold the beer and one to hold the phone in case the car falls on me and I need to call an ambulance.

Make sure your beer has a stubbie holder incase your pinned under there for longer than 5 minutes

Dont want ya beer to go warm during the wait!!

.

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Swapping out 8-in for 9-in Diff

Swapping out 8-in for 9-in Diff

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Re: Swapping out 8-in for 9-in Diff

Re: Swapping out 8-in for 9-in Diff

Re: Swapping out 8-in for 9-in Diff

Re: Swapping out 8-in for 9-in Diff

Re: Swapping out 8-in for 9-in Diff

Re: Swapping out 8-in for 9-in Diff