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Unread 04-03-2013   #1 (permalink)
69coupegrande is offline Apprentice

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Default how to beef up the 8 inch differential?

I finally got my 69 mustang to hook, but then after 1 pass I grenade'd my rear end when I launched. Does anyone have any tips for strengthening the 8 inch? Or will I need to upgrade to a 9? This car is my daily driver but it will see a bit of track time.
The car is the factory weight, .040 over 302 never dyno'd but I'm guessing around 350 horse, it's a 4 speed car, 26x10 street tires, traction bars, and a mini spool with 3.55 gears. It runs 8.20's in the 1/8th.
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1969 ford mustang coupe grande. was 302 auto, now 308 4 speed daily driver. still needs paint

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Unread 04-03-2013   #2 (permalink)
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Quote:
Originally Posted by 69coupegrande View Post
I finally got my 69 mustang to hook, but then after 1 pass I grenade'd my rear end when I launched. Does anyone have any tips for strengthening the 8 inch? Or will I need to upgrade to a 9? This car is my daily driver but it will see a bit of track time.
The car is the factory weight, .040 over 302 never dyno'd but I'm guessing around 350 horse, it's a 4 speed car, 26x10 street tires, traction bars, and a mini spool with 3.55 gears. It runs 8.20's in the 1/8th.
I seriously wouldn't bother with the 8".. an 8.8 would even be a huge upgrade and can be bought super cheap. You can pretty much drive the car off a cliff and a big axle 9" would hold up though.
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Unread 04-03-2013   #3 (permalink)
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Stout fellow ! I sure never blew a pinion out the front complete with its bearing. My 8.8s both broke axles and (2nd one) spider gears first.

There used to be options for 8 inch, but I haven't seen any for a while. Since the Mustang 9" rear end width should work with the smaller engine, you may want to save up the $2 grand for a 9-inch complete.
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Unread 04-03-2013   #4 (permalink)
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I have heard of doing the 8.8 swap using an Explorer as the donor. If I remember correctly it is the right width and is made for leaf springs, rear disc would be a nice upgrade also with the 8.8.

2 grand is way out of my budget for a rear end, I only have about 3 in the whole car including what I paid for the car initially lol.

I found a factory 9 inch housing out of a 69 mustang for $200, I'm seriously considering picking it up tomorrow.
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1969 ford mustang coupe grande. was 302 auto, now 308 4 speed daily driver. still needs paint

1964 ford f-250 flat bed. 223 inline six 4 speed
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Unread 04-03-2013   #5 (permalink)
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that is very odd! did it wheel hop?
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Unread 04-04-2013   #6 (permalink)
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Quote:
Originally Posted by cindys_sn95 View Post
that is very odd! did it wheel hop?
It used to wheel hop until I put the traction bars on. I didn't even launch it that hard, I left at like 2k rpm.
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Unread 04-04-2013   #7 (permalink)
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i bet it was already somewhat damaged and the bars were more than it could handle.
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Unread 04-05-2013   #8 (permalink)
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man i didnt see it happen but i was 2 cars behind you when it did


when we left about 10-1030 ish

i told my wife i feel bad for you cause it was cold as heck and you were laid out on the motorcycle side still working on it


i would put an 8.8 under it in a heart beat and never look back
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Unread 05-12-2013   #9 (permalink)
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I've been working on building a 9 inch for the car, I decided against the 8.8 for 2 reasons. 1 is it is alot easier to do gear swaps not under the vehicle, with a 9 i can pull the chunk and swap the gears on my bench. and 2 with an 8.8 if I break an axle there is nothing to keep said axle and wheel on the car, with a 9 i will still be rolling on all fours and with the spool i will still be able to drive the car home.

My housing came out of a 78 thunderbird I got at a swap meet for 5 bucks, the guy had already cut all of the brackets off with a torch and burned two holes through it while doing so. So the first thing I did was weld up the holes and grind the hole thing down smooth. I found a 9 inch chunk at the junk yard that had a 3.50 gear in it out of a 65 f100. I ordered some new axle housing ends off of Ebay for my 28 spline axles and also ordered new bearings/seals/spring pearches/etc for the 9.

I cut the housing down and welded my new ends on it, and re-built the chunk and installed my spool. I put it under the car and had an issue with the U bolts. My housing is 3 1/4 inches in diameter and the only U bolts I could find were 3 1/8, and I went to 17 different places to try and find the right ones. But I ended up grinding a little off of the housing where the U bolts go so that they would fit.

That is where I'm at right now, hopefully I'll be able to finish the swap tomorrow because I have to drive it to work on monday
Attached Thumbnails
how to beef up the 8 inch differential?-img00218.jpg  how to beef up the 8 inch differential?-img00219.jpg  how to beef up the 8 inch differential?-img00220.jpg  how to beef up the 8 inch differential?-img00221.jpg  how to beef up the 8 inch differential?-img00222.jpg  

how to beef up the 8 inch differential?-img00226.jpg  how to beef up the 8 inch differential?-img00227.jpg  how to beef up the 8 inch differential?-img00228.jpg  how to beef up the 8 inch differential?-img00233.jpg  how to beef up the 8 inch differential?-img00235.jpg  

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1969 ford mustang coupe grande. was 302 auto, now 308 4 speed daily driver. still needs paint

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Unread 05-12-2013   #10 (permalink)
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Quote:
Originally Posted by Deer Assassin View Post
man i didnt see it happen but i was 2 cars behind you when it did


when we left about 10-1030 ish

i told my wife i feel bad for you cause it was cold as heck and you were laid out on the motorcycle side still working on it


i would put an 8.8 under it in a heart beat and never look back
Thanks for your concern, I remember seeing your car there. Luckily my girlfriend was nice enough to bring me my original chunk out of the car and some gear oil and tools, or i would have been stuck there lol
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1964 ford f-250 flat bed. 223 inline six 4 speed
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