why 8.8, why not 9"?

[skout4lyf]

ok this is probably a gay question, but seeings how I'm a cheap ass I am curious. Ok, I see everybody swapping the 8.8 for the rear, but my question is why not a 9"? I got an 81 bronco with the 9" that I'd llike to use in the back of my zj and I'm just trying to figure out why I never really see a whole lot of 9" swaps....or maybe I'm just completely off and there is tons of em out there.....hmmmmm. Oh well, so overall, my question is this, what are the pros/cons of swapping an 8.8 instead of a 9".

[mtnzj]

the 8.8 is a popular swap to the ZJ because it has the same stock bolt pattern, is nearly the same width as stock(little narrow), and can come stock with disk brakes.
The 9" is a good axle too, but have to deal with changing bolt pattern and front track width, among other things.

[Troy]

the 8.8 is a popular swap to the ZJ because it has the same stock bolt pattern, is nearly the same width as stock(little narrow), and can come stock with disk brakes.
The 9" is a good axle too, but have to deal with changing bolt pattern and front track width, among other things.

Yep, if you're going full size with 5X5.5 bolt pattern (like when it's coupled with a front D44) then it makes sense. I run that combo.

[Jim311]

Too wide, wrong bolt pattern.

[grnd93]

If you wanted to spend the money you could have the 9" narrowed and the axles drilled to the correct bolt pattern. There's also a ton of disc brake kits for them out there. Keep in mind that the pumpkin for the 9" is considerably larger. you'll lose ground clearance unless you shave it.

[jeepnzj1]

ive got a 9'' that is the exact width i need the exact bolt pattern i need 5on4.5. it cost me 200.00 for disc conversion that sucked but its way stronger than a 8.8 and no c-clips thats worth it right there, so dont say you will have to change every thing there are options for us with the 9'' and you dont have to be rich to build, mines cost me about 1000.00 for everything over time. 60 3/4'' wide ford 9'' 31splinewdetroit currie axles i just need to weld brackets and install. unless your going fullwidth??

[ATL ZJ]

The 9" is perfect for a zj.. If you wheel in the east, you'll want the added trackwidth (of course that depends on personal preference too). You can swap complete third members in 9", which makes it a lot easier to get gears setup or swap between ratios or lockers. Another advantage over the 8.8 is that it's not c-clipped. It also is very easily paired with a hp44, wheras the 8.8 is not. The aftermarket for the 9" is great- 40 spline shafts, a wide variety of lockers, and high pinion thirds like the TrueHi9 are out there. The 9" blows an 8.8 out of the water in my opinion, and that's coming from someone who runs an 8.8.

[jeepnzj1]

that truehi9 link is sweet tons of info

[CurtP]

Why not just run C-clip eliminators with the 8.8? How many people are blowing up 8.8's?

[ATL ZJ]

Why not just run C-clip eliminators with the 8.8? How many people are blowing up 8.8's?

Not many are blowing them up, because most people swap them in with hp30s... guess which one of those will break first? Also, if you're looking at running 37s or larger, you're likely starting to look at d60s. Most people run 8.8s with 33s or 35s, so you won't see much breakage with that size rubber.

[Jim311]

Someone post that strength chart that was floating around. In terms of breaking strength the 8.8 fairs pretty well even up against the 9.

[Jim311]

Here's an article I found about breaking strength on the 8.8

http://www.jeepsonly.com/project1/axle_rear.html

Axle strength for a 31 spline Ford 8.8 is reported to be 5,707 pounds-ft yield torque. Yield strength is the point at which the metal deforms, before breaking, which makes it a more relevant figure for determining axles strength. The axle size is 1.29 inches and the material is usually 1040 carbon steel in stock format. 1050 carbon steel is 10% stronger, 1540 carbon steel is 15-20% stronger and 1341H, 1541H and 4340 carbon steel are 20%, 20% and 40% stronger than 1040, respectively. Comparitively speaking, the 27-spline Dana 30 and Dana 35 have a yield torque of only 3,640 lbs-ft., partially due to their smaller 1.11 inch size. (Summary: Ford 8.8 - 5,707 lbs-ft and Dana 30 and 35 - 3,640 lbs-ft) Source: Off-Road Adventures, June 2003

[nate]

Because having C Clips isn't really an issue.

Why not just run C-clip eliminators with the 8.8? How many people are blowing up 8.8's?

[Jim311]

We could also do some quick math here to determine what kind of torque your ZJ is capable of putting out. For ease of math, lets say your ZJ puts out 300 LB/FT of torque. We can multiply that by (roughly) 3 because the transfercase has a 2.72 ratio unless you're running something more beefy than a 231, 242, or 249. Then factor in the multiplication by your transmission. First gear in my ZJ with a 44RE is a 2.74 ratio, so we can multiply our number again by roughly three just for easy math.

300 x 3 x 3 = 2700 LB/FT of torque by the time it reaches the rear pinion. Depending on your gear ratio from there, it could be anywhere from like 4-5 or maybe a little less. Let's assume you're running a 4:1 gear ratio again for easy math.

2700 LB/FT x 4 = 10800 LB/FT of torque delivered to that axle shaft! It will probably be a little less than that, considering we rounded up for easy math. So what kind of axle is capable of handling 10800 LB/FT of torque? In order to reach this huge number you'd have to be wide open most likely, and you'd have to bind that tire up against something so it wouldn't move. That's also assuming nothing else in your drivetrain would blow up.

[JeepinHank]

FYI - C-clip eliminators are around $300 for a set. Every set I've ever seen leak, and most are only recommended for drag strip use bacause they don't handle side loads well. That kind of rules them out for our application.

[OverkillZJ]

2700 LB/FT x 4 = 10800 LB/FT of torque delivered to that axle shaft! It will probably be a little less than that, considering we rounded up for easy math.

I wouldn't say it'd be less by any means, don't forgot about giving it gas while you're trying to bounce your rig up an obsticle: that ads a massive amount of shock load!

[JohnBoulderCO]

If you are just swapping one axle, it is cheaper to do a 8.8 over a 9".

The 9" will most likely be too wide (front spacers needed), wrong bolt pattern (new wheels or re-drill) and no disk brakes (disk brake conversion). Factor that in and it will cost more.

If you swapping both front and rear axles at the same time, then you have more options and could get a matched pair of axles. With just new wheels, it would be cheaper then building your front and swapping the rear.

If I could roll the clock back 5 years, I would have swapped both the front and the rear axles at the same time, instead of building both of them up and then swapping the rear axle.

But back then, I swore a 2" BB was as big as I would go.

[CurtP]

FYI - C-clip eliminators are around $300 for a set. Every set I've ever seen leak, and most are only recommended for drag strip use bacause they don't handle side loads well. That kind of rules them out for our application.

They're all over Summit Racing and Jegs for $150 or less a set. I don't know if they leak or not - I've never heard anyone complain but I've never run a set myself. I know a couple people who auto-X on a 8.8 with C-clip eliminators and they've never said anything. There are a couple of different styles though - the ball bearing ones don't like side loads and are listed for drag race only. The roller bearing versions should be fine (they're listed for oval track).

If/when the times comes to build a rear for my ZJ, I'll probably use the big Ford 9" bearing housings like what's on my Moser 12-bolt that's under my Formula. It's never leaked or given me any other problems.

[grnd93]

the c-clip elim's are very popular for the guys drg racing the 8.8's. If i ever build one for my grand I would definitely add that to the parts list.

[TrojanMan]

We could also do some quick math here to determine what kind of torque your ZJ is capable of putting out. For ease of math, lets say your ZJ puts out 300 LB/FT of torque. We can multiply that by (roughly) 3 because the transfercase has a 2.72 ratio unless you're running something more beefy than a 231, 242, or 249. Then factor in the multiplication by your transmission. First gear in my ZJ with a 44RE is a 2.74 ratio, so we can multiply our number again by roughly three just for easy math.

300 x 3 x 3 = 2700 LB/FT of torque by the time it reaches the rear pinion. Depending on your gear ratio from there, it could be anywhere from like 4-5 or maybe a little less. Let's assume you're running a 4:1 gear ratio again for easy math.

2700 LB/FT x 4 = 10800 LB/FT of torque delivered to that axle shaft! It will probably be a little less than that, considering we rounded up for easy math. So what kind of axle is capable of handling 10800 LB/FT of torque? In order to reach this huge number you'd have to be wide open most likely, and you'd have to bind that tire up against something so it wouldn't move. That's also assuming nothing else in your drivetrain would blow up.

9173.65152 for me.

What are the shock load numbers on the 8.8 vs 9"? I know that's an important number to compare. When you blip the throttle to work up over something you're sending all of that torque in the form of a shock rather than a slow build-up.

[JeepinHank]

They're all over Summit Racing and Jegs for $150 or less a set. I don't know if they leak or not - I've never heard anyone complain but I've never run a set myself. I know a couple people who auto-X on a 8.8 with C-clip eliminators and they've never said anything. There are a couple of different styles though - the ball bearing ones don't like side loads and are listed for drag race only. The roller bearing versions should be fine (they're listed for oval track).

If/when the times comes to build a rear for my ZJ, I'll probably use the big Ford 9" bearing housings like what's on my Moser 12-bolt that's under my Formula. It's never leaked or given me any other problems.

From my experiences, the $150 ones are for drag strip only. You start looking for ones for street use, and they're more like $350 and up. Hell, I only had $250 in my axle.

I did a lot of looking for them when I was building my 8.8 because I really wanted to be able to run a full spool. After a ton of research I found it just wasn't worth it IMO. I ended up going with a mini spool, and I've been very happy with it.

Another option is to use 9" ends and retaining plates, but that seemed like a lot of fabrication to put into an 8.8. Search PBB if you really want to do some more reading on it.