I have an axle dilemma and I need your input

TurboMinivan

Still plays with cars
Location
Lehi, UT
(This is not 4x4 related, so that's why I put this thread here.)

As most of you know, I recently picked up this 1980 Grand Prix:

12006195_800815816683730_6688391393194752976_n.jpg


Not long after, I then bought this 1999 Chevy Express 3500 cargo van:

12043076_803356913096287_2312746554083573999_n.jpg


My plan is to remove the 454 and 4L80-E from the van and drop them into the Grand Prix. Muscle car nirvana awaits me.

Of course, there is no way the Pontiac's wimpy 7.5 axle will withstand that kind of torque. I'd probably frag it just dropping the trans into Drive. Clearly, an upgrade is in order... and I've been researching exactly that.

The best option from the factory (read: that totally, completely bolts right in) was the GM 8.5. This axle was used in very few G-body cars (typically only the Grand Nationals and some 442s). As such, they have always been somewhat rare... and nowadays they are practically extinct. Doesn't sound very promising. Even if I did find one, odds are I'd have to lay out a significant sum to acquire it.

Are there any other options? You bet. There is a nice little cottage industry for adapting a Ford 9" axle into a G-body. I can look around the web and find housings which have been modified and are ready to install. Sounds easy enough, right? By the time I have a complete package--the housing made to proper width and ready to install, with axles, a center section, and everything--I'd be spending at least $1500, maybe more. Hmm.

As I've kept digging, I made an interesting discovery. For a G-body axle on a budget, it turns out the Fox-body Mustang's 8.8 is nearly perfect. It is the right width (only 1.0" wider than my 7.5 axle), its outer control arm mounts interface perfectly with the G-body, the inner/upper control arm mounts also do not need modification thanks to an aftermarket adapter kit that attaches new mounts to the body of the car, allowing the kit's adjustable control arms to them make the axle bolt into place. Weld on some coil spring perches and I should be on the road for under a grand, even including the cost of the axle itself. This sounds like the best all-around plan, and it's what I had decided I would do. (You can read more info about this swap here.)

But then my co-worker (who is dropping a very similar 454 into his '64 El Camino) stopped me. Since I need to find and buy an 8.8 axle, why not just use what I have? Namely, the axle in the van. "Be like the native Americans," he says, "and use every part of the buffalo." :rofl:

So the other day I drove down to Orem to crawl under the van and see what is there. Here is what looked back at me:

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It's a GM 10.5" 14-bolt. On the plus side, it's a one-ton axle that can certainly stand up to whatever amount of torque I throw at it. As another bonus, I already own the thing. And one more benefit is I already own the driveshaft that attaches both to it and the transmission I will use; I'll just have to have it shortened. From a parts cost standpoint, it sounds like a fabulous idea.

But then there is the not insignificant matter of making it fit under the Grand Prix. All the OEM spring and shock mounts will need to be removed, then I'll have to graft in the appropriate equivalents for the car. Oh, and I'll most definitely need to have the housing narrowed to the correct width and have new ends precision welded as required. Then there will be the new custom-length axle shafts, and who knows what else.


Now I know there are many RME members who can do (and have done) this sort of thing in their 4x4 rigs. Converting to a stronger axle is a decades-old experience in our hobby. But here is my question to you who have done such a conversion: is this a better overall move for me? Would it be worth all the added work and effort to convert what I already have on hand? Or does it make more sense to go out, buy a different used axle, and then take the path of easier fabrication? Do any of you think the GM 14-bolt route would actually end up saving money compared to using a Ford 8.8? (Keep in mind that I do not have the tools or knowledge to do this sort of fabrication, so I'd be paying someone to do it... maybe even somebody on this forum.)

I welcome all thoughts, comments, questions, snide remarks, etc.
 
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I Lean

Mbryson's hairdresser
Vendor
Location
Utah
What bolt pattern is the Mustang axle? If it matches your wheels, then go that route. The 8-lug 14b is not going to be easy to make 5 lug...basically it would mean making it a semi-float axle (new bearing ends and new axleshafts, plus new side gears or carrier to go 35 spline) At that point you'd likely be money ahead to just buy the axle that will fit.
 

I Lean

Mbryson's hairdresser
Vendor
Location
Utah
Then you can sell your 14b, and that $100 will offset what your Mustang axle will cost. :)
 

Toad

Well-Known Member
Location
Millville(logan)
I have a co worker building a LS s10. He decided on a 8.8 explorer rear end. Bought a explorer for 300 bucks that gave him 3.73 limited slip and disk brakes. Hauled the explorer to the scrap yard for 200 bucks. Any idea the width difference between the mustang and explorer 8.8?
 

TurboMinivan

Still plays with cars
Location
Lehi, UT
Any idea the width difference between the mustang and explorer 8.8?

Yes. The G-body uses a 57.25" width axle. Fox-body Mustang and Ford Ranger are both 58.75" width, which is fine since the factory tucked the rear wheels far into the fenders on the car. By comparison, the Explorer axle is 59.75" width.

Also, from the article I linked above:

Unless you plan to cut and narrow the rear, the Fox-body rear is by far the best choice of the bunch, since it is the closest to the factory G-body width (57.25-inches). Though the Ranger rearend is the same width and comes with 5-lug axles, as well as 3.73:1 or 4.11:1 gears, you will want to steer clear. The differential is offset in the Ranger, making driveshaft alignment impossible with a 200-4R, TH350, T56, or other GM trans of your choosing. In addition, most have an open differential, which is no good for a performance application.
 

blznnp

Well-Known Member
Location
Herriman
I personally would shy away from doing the 14 bolt and keep an eye out for a 8.5", mustang axle, or a 12 bolt (although they aren't going for cheap) Not sure what your looking to spend but have a buddy that has a 9" under his nova that he should be selling soon. I have a 8.5" under my camaro, 426hp to the wheels, I get on it a lot and have no issue with it. yukon axles and a posi unit and gears. Mine isn't a normal dimension one so you have to make sure you take good measurements on the axles if you ever order some.
 

Hickey

Burn-barrel enthusiast
Supporting Member
The 14 bolt would be my last choice. I'd go for the 8.8. You ought to be able to find a limited slip to swap in pretty easy.
 

lhracing

Well-Known Member
Location
Layton, UT
Is there any chance of finding a 8.5 10 bolt that was the standard rear in the Buick Grand National , turbo T-types, '84 Hurst Olds, and the 442's of the 80's. If not, I would save up some money and get one of the 9" kits available, which in the long run may not be a lot more after you buy a used axle. adapt it into the car and rebuild it.
 
I'm currently building a 5 lug 14 bolt and could use some spares... I'll give ya $100 for yours!
Also, I could probably scrounge up a 9" if you're interested, I'd have to double check width though
 

kmboren

Recovering XJ owner anonymous
Location
Southern Utah
On the ford 8.8 you could cut the long side to be even with the short side this centers it and then you just use two short side shafts. Get a bracket kit for your car and you will be done.
 

StevenS10

New Member
Location
North Salt Lake
Your car came with the same 26-spline 7.5" 10-bolt that Camaros got for '82. By '98 the Camaros were combining 305 RWHP with a 28-spline 7.625" version of that axle, running 12.90s at 109 MPH through a T56 on 245/50R16 Goodyears.
That Vortec 454 is only 290 HP at the crankshaft, the 4L80E has a lamer first gear than the T56, and while the torque converter can multiply engine torque, it still tends to reduce the shock-loading to the rear axle that breaks the ring / pinion.
There are LS1 '98-'02s putting down 500 RWHP through drag slicks, at a street weight over 3500#, with non-upgraded 7.625s, not even a girdle.
So even if you do a cam and headers, you're not likely to break it once you do gears, shafts, and a girdle.
 

Gravy

Ant Anstead of Dirtbikes
Supporting Member
We're all offroaders. We've seen full size truck 10 bolts break when you look at them wrong. Maybe in the drag world people are different, but I wouldn't trust a rear 7.5" 10 bolt with any job other than a boat anchor.
 

blznnp

Well-Known Member
Location
Herriman
my friend has gone through a couple 7.5" rear ends with his LT1 and a top end build. He might be putting down 350rwhp. maybe some make it work, but im sure a lot can't
 

Greg

Make RME Rockcrawling Again!
Admin
I beat on the 10 bolt in my '71 Camaro relentlessly w/ a 400 HP SBC and it was the most reliable piece of my drivetrain! Went thru a few transmissions, but as far as the axle I put fresh oil in it and never gave the rear axle a 2nd thought... all stock parts right down to the 3.08 gears. It all depends on the tire size and how much those tires hook up.
 

blznnp

Well-Known Member
Location
Herriman
very true, the hook is the big deal, just like a guy in washington that ran a stock D44 with 44" swampers and a built big block on nitrous, but he only ran in mud, so not a lot of traction. My buddy has ran some good tires and 315 width, so not some cookie cutters. but he also broke them with ease.
 

Greg

Make RME Rockcrawling Again!
Admin
I was running smaller BFG Radials... spun them on command. Had I been running something bigger with a softer compound, I'd imagine I could have had problems. Other factors include the transmission, what RPM the converter hooks up at, etc.
 

TurboMinivan

Still plays with cars
Location
Lehi, UT
I think a 9" is likely the best solution here? 8.8 would be fine but I think the 14 bolt will be a LOT of work to use and you'll be into hubs and such as much as you would be by just buying a bolt-in 9"?

Yeah, I've decided my co-worker is loopy for suggesting the 14-bolt. :D

The above is $1000 from Summit. That seems like the way to go for the work/reward deal?

But that Summit axle still needs work before installation--there are no spring perches on it, for example. I think I'll stick with my plan and use a Fox 8.8 axle.

By '98 the Camaros were combining 305 RWHP with a 28-spline 7.625" version of that axle, running 12.90s at 109 MPH through a T56 on 245/50R16 Goodyears.
That Vortec 454 is only 290 HP at the crankshaft, the 4L80E has a lamer first gear than the T56, and while the torque converter can multiply engine torque, it still tends to reduce the shock-loading to the rear axle that breaks the ring / pinion.
There are LS1 '98-'02s putting down 500 RWHP through drag slicks, at a street weight over 3500#, with non-upgraded 7.625s, not even a girdle.

Two thoughts:

#1: horsepower isn't my cause for concern; torque is. High-winding horsepower poses relatively little threat to an axle, but gobs of torque that can shock load the axle is a much more pressing issue. I'm not so worried about the ring and pinion as the axle shafts themselves.

#1: I spent six years bracket racing at RMR. I competed in the Heavy class, meaning I ran side-by-side with Camaros and Firebirds (along with all the other domestic RWD V8 cars). I watched a number of LT1/LS1 F-bodies frag their axles at take-off, even cars which weren't running any faster than my minivan. So, no thanks, I'll pass on "upgrading" to the 7.625 axle.

We're all offroaders. We've seen full size truck 10 bolts break when you look at them wrong. Maybe in the drag world people are different, but I wouldn't trust a rear 7.5" 10 bolt with any job other than a boat anchor.

^^ That.

my friend has gone through a couple 7.5" rear ends with his LT1 and a top end build. He might be putting down 350rwhp. maybe some make it work, but im sure a lot can't

^^ And that.
 
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