Atilla the Fun

I had every intention of doing a Ford 9", but I have been given a free, complete 8.5" GM rear axle assembly. Just this morning, actually.
This axle swap keeps getting discussed here from time to time, and I used to chime in.
The first thing you want is pics. Well, not today.
Second, when? I'll be starting this project in 3 weeks. Maybe I shoulda waited to start this thread.
Third, why?
Well, it's not easy to make a good case for this swap. Not yet any good solution for mounting the torque arm, or deleting it. Only 28-spline axles in most versions. Big and heavy like a 12-bolt, but without those last 2 bolts.
Now, the upsides:
33 spline axles aren't common, but have been done enough that it's not custom, either.
The 7.5's weakest link was the ring and pinion, so that got upsized to 7.625". After that, we learned that the next weakest link was the 26 spline axles, so those got up-sized to 28 spline. After that, we learned that the next weakest link was the ring and pinion, but there's no more room in there to go past 7.625"
There's been 3300# (race weight, with driver) early '70s F-cars running in the high 9s (quarter mile) , (power-adder big blocks and slicks) , with 33 spline 8.5s.
All the '73-'81 F-cars got the 8.5, as did all the '73-up 1/2 ton 2WD pickup trucks. That means there are plenty of them still available for cheap. The remaining supply is far better than for the Ford 9", let alone the old 12-bolts.
'92-'98 had 30 spline. '99 was revised to 8.625", but same basic thing. The freebie was under an '05 Silverado 1500 WT, so it's 3.23:1, open diff, 30 spline, and 8.625". But my '83 C-10 has a real 8.5, so I can make sure whatever bracketry I design will fit both versions. And my landlord has an '81 Firebird that I work on for him, so I can check my work on that 8.5, also.
And being so similar to the 12-bolt, it can fit.
I'm planning to try making a new bracket for a stock torque arm, and making it a no-welding-required design.
I'll post pics as I go.
Also, this 8.6 I got has big drum brakes and 6-lug. Overall width is 3" more than the '93-'02 F-car axles. And I got a pair if the 17x7.5" wheels that came with this axle. They have a 5" backspacing, so they'll still stick out past the fenders. I'm thinking of getting them widened 5", to a total of 12.5", then fitting 335/35 tires. Otherwise, I'll just try some 225/50s for the sake of getting some pics, then get the housing narrowed.

big gear head

Sounds like a plan. Are you going to make a bracket that bolts to the rear of the housing where the cover bolts on?

Just an FYI, the Camaro and Firebird got the 8.5 in '71 and the 1/2 ton trucks didn't get it until '82. The trucks used the truck 12 bolt up to then. The Nova didn't get the 8.5 until '72 and the full size car got it in '71. The A body got a 8.5 in '71, but it was slightly different from the others. It had bolt in axles with no c clips, but it also got c clips in in the mid '70s. All internal parts for this early A body rear end would interchange with the other 8.5 except the axles. The Chevelle still got the old 8.2 10 bolt until '73. All of the car and truck 8.5 rear ends got 30 spline axles in '90. The upgrade to 8.6 also included larger differential bearings, the same size as the 12 bolt.

92droptopws6

iTrader: (10)

This is whats goin on around on other sites aswell. Why spend 2200 when you can do it for much less. I have used a few rears 8.5( Fbody74-81),12bolt,9",dana60 etc.

http://www.ls1tech.com/forums/gears-...8-8-build.html


Now, seeing a few people use stang8.8s,grand marq.,I have chosen the Explorer rear 97up simply due being thicker 3.25 tubes to availability and they all come with good gears and most come with lockers and 30-spline already.
Gears are
3.55--------tag says 3 55 or 3 L 55 L denoting LOCKER
3.73--------" " 3 73 or 3 L 73 " "
4.10--------" " 4 10 or 4 L 10 " "

Moser axles measure yourself and order $340.00
Exper. welder fabricator to weld if you are unable $80.00
TA rear end girdle $180.00
This is expensive however,will work with some X-member mods and fabrication since it was designed for a Stang
http://www.mustangdepot.com/OnLineCa.../mm-tq-arm.htm
Fab. TQ arm mount or do mini upper bars seen in pic following link.

You can use the factory ford disc brakes that come with rear just fab your own e-brake cables.

Atilla the Fun

Thank you for clarifying.

Atilla the Fun

Maybe for the trucks. All the Mustangs had 3.27:1 or 3.08:1 or 2.73:1 gears. Cougar XR7s had 2.73:1.
The stock Traction-Lok diffs aren't worth the $105 rebuild kit, and if you do that, you're still 28 spline. And by now, all the gears are too worn for any power level that requires stepping up from a 7.625".
My 8.6 has 51,000 miles on it, but since there are no conversion-style lockers for it, such as the PowerTrax / Lock Right, I'm not much better off.

junkcltr

iTrader: (1)

Are you going to install c-clip eliminators for safety? That is the only thing I don't like about the 8.5 rears. The nice part is that limited slip units aren't that hard to find. The stock limited slip (not locker) take some abuse. I tune mine with the NS and non-NS additive from Redline and they are pretty tight.

Atilla the Fun

Big Gear Head may need to clarify again, but as I understand it, if you're going to 33 spline axles, then you'll need to cut off the stock housing ends and weld on some 9" Ford style housing ends. Strange offers a bunch of choices, one of which is sure to work.
This is always superior to c-clip eliminators. Which leak, and can't take much cornering.
Right now, I'm just wanting to start selling swap parts. I'm not making enough power to need to worry about breaking an axle, even if I do use drag radials.
Besides, my axles are 30-spline, and my truck housing uses larger outer wheel bearings than the '71-'81 Camaro 8.5
The tubes on the Camaro version visibly taper there at the brake backing plate mounting brackets, the late truck axles don't. It's still too dark out to look at my '83 C-10, to see if it tapers or not.

big gear head

That is correct. I don't recommend the Strange housing ends because they don't allow for the use of stock Ford axle seals. They rely completely on the sealed ball bearings and the O ring on the outside of the bearing. The Moser housing ends allow the use of the stock Ford axle seal, which holds the oil in much better than teh other method. There are other housing ends that also allow you to use the stock seal, but I don't know exactly who has them. Moser also has these housing ends now that allow you to use the larger truck brakes.

Atilla the Fun

I had no idea about the seals, but it's good to know. Again my thanks.

Atilla the Fun

Atilla the Fun

Atilla the Fun

sorry, no progress yet.

Atilla the Fun

today's progress wasn't pic-worthy.

86blackiroc

iTrader: (12)

If you're going to go to the trouble of using a truck axle, why not use the '88-'98 2wd 14 bolt semi-floater with 6 lugs? (454 SS trucks used it in 5 lug, but good luck finding one, and the 4x4 axle is a little wider) It would be the same amount of work and you will never break it.

Atilla the Fun

I'll let you do that swap / kit.

86blackiroc

iTrader: (12)

Lol, I've thought about it. The strength would be similar to a dana 60 I think.

I'll watch you do yours first

Atilla the Fun

So tomorrow I'll start removing the truck bracketry from the tubes.

jmd

iTrader: (4)

It's good to see someone fabbing and not just bowing down to the "easier to order a 12 bolt / 9 inch" thinking. I still need to see if a Caprice 8.5" has the same UCA mounts as a G-body. Ooops, non-F-body content.

Atilla the Fun

It seems like these might be the best housing ends for this axle:
http://www.moserengineering.com/othe...lip-axles.html

Atilla the Fun

I spent 2 hours grinding, but forgot to take my camera.

Guest

Any updates?

Atilla the Fun

One more week from tomorrow, I'll be back home. Then I can get back on this.

brandoz28

iTrader: (1)

been there checked that, not the same

bowtie88

i am about to swap an 8.5 from a 81 formula 400 firebird with disc brakes and limited slip and i am trying to figure out a solution to the the torque arm issue as well?? there must be one??

sofakingdom

iTrader: (1)

And that would be because of ..... ???

As has been posted COUNTLESS times on here whenever ANY foreign rear swap is proposed for these cars, you MUST do somehting about the torque arm, OR completely re-design the rear suspension (basically, back-half the car). Go out there and LOOK AT your existing rear, and then LOOK AT the 2nd gen rear, and then come back and tell us what makes you think there "must be" a way to do this.

That's in addition to the 2nd gen rear being too short.

jmd

iTrader: (4)

They did it with a cast rear cover on the 87 Buick GNX.

sofakingdom

iTrader: (1)

Did what?

The GNX is a G-body. Has a 4-link setup. Doesn't use a torque arm.

jmd

iTrader: (4)

I'm sorry for posting correct information.
Google is your friend. Try it sometime.

bowtie88

i hate when people are smart asses for no reason anyways your wrong about everything you said they both measure the same maybe off by fractions of an inch. and there is a way if you look at the link posted earlier you will see the it was done on a fourth gen totally eliminated the torque arm all he did was fab up two short ladder bars, connecting the lower control arms to a bracket on the axel tube... EASY it's a good thing i am training to be a welder/ fabricator...

Primetime91

iTrader: (15)

That's not exactly ideal

sofakingdom

iTrader: (1)

"2 short ladder bars" is about the crappiest thing that can be done, especially for the street.

Problem is, that doesn't allow the 2 sides of the rear, to deflect differently. That's one reason ladder bars work great on a drag car, specifically why they make the car launch level: it's essentially IMPOSSIBLE for the car to tilt from side to side, because of that. If the car tries to tilt, it has to (a) bend the "frame", (b) bend the bars, (c) twist the rear end, or (d) break the brackets off the rear.

That's why people WHO ACTUALLY KNOW WHAT THEY'RE DOING, back-half cars, instead of half-assing them like you're talking about.

Yet another classic example of how just because a thing "looks like" it "can be done", or even "has been done see says so right here on the interwebz", doesn't automatically mean it's A GOOD IDEA.

And of course, your 2nd gen rear doesn't have control arm brackets anyway, so you'll be fabbing that, as well.

jmd:

Educate me. What am I supposed to Google? Every GNX I've ever seen was a G-body, with the same rear suspension style as a Monte Carlo, Cutlass, El Camino, etc. 4-link, long straight lowers and short angled uppers.

bowtie88

ignorant people like yourself also said that we could not go to the moon, well we did... oh and smartass i am building a drift car SO i don't want deflection in my rear i WANT it to be more solid. if you don't have anything good to say then shut the f*** up...

Primetime91

iTrader: (15)

He's trying to reason with you bud

What he's stated is factual, sorry you don't like it. We're actually trying to help you here

bowtie88

sure it is but he was a dick when he said it and i have no time for that kind of attitude.

86blackiroc

iTrader: (12)

Please educate me too. What do you mean by "they did it"?


I also will say that it can be done. It would take a lot of welding, a lot of individual small parts (that would be welded), and a lot of trial fitting. I also believe my method may not be strong enough to last for the long haul. With that said, just because it can be done, does not always mean it should be done. There may also be a method that is better than what I came up with, but I have yet to see it.

Also, what EXACTLY is the 8.5's pumpkin cast out of? Certain types can be safely welded to, and by the average guy (or gal) with some welding experience.

86blackiroc

iTrader: (12)

What can you expect from someone with a name like that Are you really that surprised?

Johnny Blaze

iTrader: (15)

The GNX had a torque arm.

"The GNX had a ladder bar that ran from the mid-section of the car to the rear axle, so as to increase traction. This is also the reason why a GNX will actually lift the rear end up when the car is about to launch heavily."

http://image.gmhightechperformance.c...on+rearend.jpg

86blackiroc

iTrader: (12)

^ That's really cool! I'm guessing nobody makes that nice aluminum cover now?

jmd

iTrader: (4)

Of course not, because the GNX was just like every other G-body and nothing can be done unless it was already done in which case it can be done, or dom in this case.

bowtie88

you are a voice of reason, and yes they are cast steel so you can weld on to them fairly easy

big gear head

The center casting for the 8.5 rear end is cast iron, just plain old gray cast iron. It can not be easily or safely welded without some prep work, the correct welding material and a lot of welding skill. Nickel is the only material that I know of that will weld cast iron, and I wouldn't trust it to hold the suspension under a high performance car.

bowtie88

thanks for the info , it's the tube thats steel well it's a good thing i did not attempt that

naf

iTrader: (7)

Wow. This is the WORST case of thread jacking I've seen in quite some time. And to an Atilla thread? Wow.


Just for the fun of it (I've seen a few up close but thought perhaps 'internet' GNX's were different in some way) I DID Google it (actually Buick GNX rear end) and guess what was on top......a four link GNX rear end. JFYI the GNX did use a ladder bar/torque arm but only as a traction enhancer.

http://www.turbobuick.com/forums/par...io-1200-a.html

And again, Wow. There's so much mis-information and mis-understanding here that I'm uncertain a frame of reference exists for a common understanding of even basic concepts.

jmd

iTrader: (4)

I'm sorry for posting correct information.
Google and attention to detail are your friends. Try them sometime.

You found a Grand National differential picture. And no, you have not seen a few GNXs in person.

The GNX was a limited 500 some production version of the Grand National in 87 only. It had a torque arm. It did not have upper control arms bolted to the top bushings.

Use of a rear cover with mounting points is one way to get a torque arm on an 8.5" and the cover fits a huge number of 8.5" and possibly the newer 8.6" diffs. I was a bit surprised that hadn't been mentioned in this thread by the time I did so.

sofakingdom

iTrader: (1)

You're right, I went and looked it up, I apologize.

Doesn't look like that will go into our cars as-is, since our TA is on the DS, not the PS like that setup has it. So, not a practical solution, at the "bolt-in" level. Although in principle, something that worked similarly but put the TA in the right place (where the floor pan and exhaust can accomodate it), might be possible, if a suitable TA was also fabbed up.

naf

iTrader: (7)

Dammit, you got me. The GNX was a special breed and not to be confused with the GN, like I just did.

jmd

iTrader: (4)

It's really not a good comparison but ...

Since aluminum tailhousings in torque-arm F-bodies tend to crack far more than in non-torque-arm applications, I'd look into fabbing a diff-cover (like the GNX kinda sorta) mount from steel w/ welded on attachment points instead of alum. anyway.

Set it up for whatever side you wanted while you're at it. Making it out of steel plate, use extra long bolts, two gaskets and a stock cover would be one way to do it.

naf - you're not alone.

bowtie88

^thats not a bad idea it would not be that diffacult to fab up a new torque arm with bushings that go from that cover to the stock torque arm mount on the trans... i would try it

86blackiroc

iTrader: (12)

I think the stock cover is likely too thin. However, there should be a couple off-road type supply companies that offer a heavy gauge welded cover, since the 8.5 was used in half ton pickups.

92-Z28

So what happened to this swap ?!