Isuzu 12 bolt... Worth pursuing?

uncc civilengineer · Feb 27, 2007

OK... Its a 1989 Isuzu 12 bolt:

Specs:
58" WMS to WMS
3" tubes
1.32" splines
26 spline
8.66" Thick Ring Gear (1/2" thicker than 44)
Larger Pinion than 44
Disc Brakes
4.56 factory gears

I know there isnt much support out there for these axles.. However, I found out that there is going to be a Lunchbox locker for them by this summer...

I also know it's short but would have some wheel spacers made to bump it back to around stock or a little larger.

It's 6x5.5 BUT, if I swapped in a Waggy 44 up front they would match.

It also has Discs and ebrake and comes w/ calipers and everything.. just needs to have the perches removed and weld in some new ones.

I am almost positive it has a removable third member.. and from what I have heard they are beefy and there are guys over on pirate supposedly running 40's on them...

Tell me what you think.. I can pick it up for $100.00... Worth pursuing?

TIA,
Chris

EDIT: Ive searched but havent found what im looking for.. Also I plan to run 36's towards the end of the year...

slcpunk74 · Feb 27, 2007

I actually have been driving isuzus for 4 years now both of the ones I have owned have had over 200k on them. My most recent of the two has 32" tires and came stock with I believe 4.56 gear ratio but dont hold me to it. I have heard that these axles are very strong. I run a modded 2.8 with 32s and an open diff so I cannot truely tell you how strong they are but I have not had any problems yet. You can check out independent4x.com they have some stuff for the axle and check some isuzu forums too.

Another note is some of these axles came with factory limited slips I know they are rare but its worth a check
Good luck
Chad

Powerman · Feb 27, 2007

Hey Chris. One thing I am curious is spline count if anyone knows. With Danas, splines are all the same. So 27, 30, 35 we know how big the shaft is. The 12 bolt is 26 spline, but they have to be bigger splines. Surly they are not the same size as Dana's or the 12 bolt shaft would be much smaller. I'm just curious. Does anyone know?

On my Isuzu 44, it has 1.5 inch shafts, but it still necks down to 30 spline. So the 1.5 is as big as a Dana 60, but it will still break at the smallest place, 30 spline. This is why I'm asking, curious how the shafts actually are if it is stronger than a D44.

Powerman · Feb 27, 2007

Also Chris, I forgot to mention. The 58" is going to be tough because of the leaf springs, not because of tire placement. The backing plate will be getting in to the springs. Wheel spacers won't help that.

Others can chime in though. Maybe some of you have used 58" axles. Do they fit? Anyone know the minimum axle width that can go on a XJ???

uncc civilengineer · Feb 27, 2007

It's hard to find much info out there on the 12 bolts.. I do know that the later years had something like 1.5" shafts and the same size ring gear as the D60 but were 23 spline shafts???

Also, aren't 8.8's something like 58" or not?

woodkrawler · Feb 28, 2007

dude don't do it...i think you will be wasting time and money on that thing. not to mention how it easy it is to find parts for dana axles or chrysler 8.25s, put the $100.00 towards spare shafts or alloys. i would start breaking the 8.25 before i went through all that work. ALSO you will need to have your driveshaft resized lengthed, most likely.

woodkrawler · Feb 28, 2007

Also, aren't 8.8's something like 58" or not?

[/QUOTE]

8.8s are 59" xjs are 60" so you are only talking about 1/2" on either size NOT 1" plus 8.8s are 5 on 4.5 not the odd 6 on 5.5. again not worth it.....just my $.02. just wait and get a 44 or 60 or 70 or 14bolt hahaha!!

BlueCuda · Feb 28, 2007

Depending on where the caliper is located the width could really be a problem. I put pads on my 8.8 this last weekend and they are pretty close to the springs. Any narrower I would of had to undo the u-bolts and let the axle seperate from the spring for clearance. Not a big deal but it would have added a few minutes to my 15 minutes pad swap lol.

DirtyMJ · Feb 28, 2007

On early 12Bs:

I run one. I've mentioned it before. Zero failures thus far. I have a GW front too. That's on 37s... Buuuuuuuuuuuuut - only snow wheeling as of yet.

You WILL need to run spacers or really low BS rims. It's the same width as an 8.8. I'm going to say it's 58.5" WMS-WMS as this is what I measured and have heard said before. So, throw a pair of 1" or 1.25" spacers on there and she'll match up cherry to the 61.5" front.

As far as the splines VS dana splines... Well, Dana doesn't use the same pattern on all their splines anyways (I used to think this, until I saw otherwise). Basically it has 26 splines that are larger, but really only by a couple percentage point (okay, 15%~). The shafts have no neck down at all, they actually machined down the area where they are splined. They're about 1.5" for the rest of their length. At least you know where they'll break... DO NOT FEAR THE LOW SPLINE COUNT - it does not make it any weaker than a higher splined shaft of the same size (within what I consider a reasonable limit for the people who get picky).

Oh, there's two gear ratios (stock) for this axle... 4.56 is the common ratio (90%) and 4.77 was optional. 4.77 is bad as there's not much that matches it for a front application, AFAIK. A deeper gear is offered aftermarket (5.29? IIRC).

There's only two lockers avaliable. The ARB and your friend lincoln. Often they came stock with a power-brute LSD - which seems to work alright until you get it too hot. Then it's just a POS and you'll do the one tire fire thing all day.

Be aware that with junkyard axles, unless fresh, 90% of the time the brake calipers will be seized. Also, they use stupid studs to hold the bearing plate on the axle shafts to the housing. If they're good and rusty they will spin and you will have to cut them - then remove the bearings from the axleshaft to replace them. I opted to ream out the holes for them to 1/2" and used Gr8 bolts instead.

You will need the companion flange from a rodeo with a D44 rear to run a spicer 1310 u-joint. I wrote down the spicer P/N but lost it.

Oh, the housing is somewhat weak. If you like air time or slamming tires on rocks - a truss would be a good idea.

On the later 12Bs:

I've personally only ever seen one of these. Unfortunatly it was not in the junkyard. Yes, apparently they have 1.5" 23 or something spline shafts. And a 9.5" ring gear. They share nothing in common with the earlier 12Bs. Also, they're 63" wide - a perfect match for a J-10 D44 front.

Apparently they are absurdly strong for their application. Again, no aftermarket. Just not enough made to justify it.

woodkrawler · Feb 28, 2007

DirtyMJ said:
On early 12Bs:

I run one. I've mentioned it before. Zero failures thus far. I have a GW front too. That's on 37s... Buuuuuuuuuuuuut - only snow wheeling as of yet.

You WILL need to run spacers or really low BS rims. It's the same width as an 8.8. I'm going to say it's 58.5" WMS-WMS as this is what I measured and have heard said before. So, throw a pair of 1" or 1.25" spacers on there and she'll match up cherry to the 61.5" front.

As far as the splines VS dana splines... Well, Dana doesn't use the same pattern on all their splines anyways (I used to think this, until I saw otherwise). Basically it has 26 splines that are larger, but really only by a couple percentage point (okay, 15%~). The shafts have no neck down at all, they actually machined down the area where they are splined. They're about 1.5" for the rest of their length. At least you know where they'll break... DO NOT FEAR THE LOW SPLINE COUNT - it does not make it any weaker than a higher splined shaft of the same size (within what I consider a reasonable limit for the people who get picky).

Oh, there's two gear ratios (stock) for this axle... 4.56 is the common ratio (90%) and 4.77 was optional. 4.77 is bad as there's not much that matches it for a front application, AFAIK. A deeper gear is offered aftermarket (5.29? IIRC).

There's only two lockers avaliable. The ARB and your friend lincoln. Often they came stock with a power-brute LSD - which seems to work alright until you get it too hot. Then it's just a POS and you'll do the one tire fire thing all day.

Be aware that with junkyard axles, unless fresh, 90% of the time the brake calipers will be seized. Also, they use stupid studs to hold the bearing plate on the axle shafts to the housing. If they're good and rusty they will spin and you will have to cut them - then remove the bearings from the axleshaft to replace them. I opted to ream out the holes for them to 1/2" and used Gr8 bolts instead.

You will need the companion flange from a rodeo with a D44 rear to run a spicer 1310 u-joint. I wrote down the spicer P/N but lost it.

Oh, the housing is somewhat weak. If you like air time or slamming tires on rocks - a truss would be a good idea.

On the later 12Bs:

I've personally only ever seen one of these. Unfortunatly it was not in the junkyard. Yes, apparently they have 1.5" 23 or something spline shafts. And a 9.5" ring gear. They share nothing in common with the earlier 12Bs. Also, they're 63" wide - a perfect match for a J-10 D44 front.

Apparently they are absurdly strong for their application. Again, no aftermarket. Just not enough made to justify it.

again,

NOT worth your time and money chris. im not saying that they not a good axle just that you've got a geared and locked 29spline 8.25 that will be plenty strong for your 33s and even 35s or 36s with alloys. add some discs and your done.

you may gain some strength with the 12bolt but the disadvantages far out weigh your current setup. by the time you go to 36s or 37s i think you will be ready for full widths anyway.

DirtyMJ · Feb 28, 2007

Depending what you wheel, fullwidths suck...

In mine I've only got the cost of some reman calipers (durr, shoulda grabbed the other set out of the junkyard), two little peices of brake tube, some steel, the rodeo flange, and the axle itself. Okay, I went as far as to throw new gear oil in it, some paint on it, and a couple flap disks and some welding rod. Oh, can't forget the 8 1/2" Gr8 bolts/nuts.

It came out cheaper than a 4.56 gearset for my 8.8. Which I then sold for more than this setup cost me.

uncc civilengineer · Feb 28, 2007

I passed on the axle purely for the fact that its about the same length as my 8.25.... Here where we wheel full widths really do come in handy for all the off camber situations at Tellico, harlan, etc...

So, if anyone is looking for a super stong 12 bolt let me know and i'll get you the guys contact info.

I think im just going to either:

1. buy some wheel spacers and alloys for my junk (that + new wheels will put me out around 63" or so w/ low BS'ing wheels)

2. buy a HP44 and 9" and and build up..

All depending on if I want to go bigger than 35/36's...

Isuzu 12 bolt... Worth pursuing?

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