Real Fiero Tech

Hi!

I'm looking to switch to the 5 on 4.75" lug pattern because cheap wide OEM wheels are available, I get a bigger rear wheel bearing, stronger outboard CV, and other reasons. I've found some info about this swap but it is pretty scattered and I see occasional comments about problems or foreseen problems. In this thread I'd like to pull everything together and maybe avoid some pitfalls in the process. Thanks to all of the pioneers that figured this out originally!

The plan: I have the knuckles (pictured below) and should get the outer CVs and bearings in the next week. Deadline to have everything installed and race ready is October.

Needed:
1 Pair (Left & Right) Heavy Duty (HD) GM A Body knuckles
2 4WD S10 Front wheel bearings
6 M12 by 55mm long 12.9 bolts to hold bearings in
2 outer CV Tripods from the HD A Body (works with manual trans Fiero axles) *EDIT The S10 outer CV is bigger and will NOT work with Fiero manual axles
Machine time and tooling

Basic Operations:
Open up the knuckle bore from 3.55" to 3.62"
Mill new triangle bolt pattern on 4.75" circle with 1/2" mill (0.085" outward from old pattern) *EDIT Move them out 0.100" to for extra clearance
Face back side of knuckle where bolts go through
Break edges (stress risers) created on last operation
Assemble bearing to knuckle with M12 bolts
Prepare outer CV for Fiero axle center shaft

Things I don't want to cover because I think they're outside what this thread should be:
What to do with your brakes - what I do won't apply to most people, but the brake caliper mounting pattern is the same as the Fiero knuckle (but for 10.5" rotors)
Assembling the new axle - I will show the 27 spline come apart, that's enough
The van knuckles - They're similar to the HD A Body knuckles but heavier and require a van ball joint swap... according to the internet

So far I have the HD A Body knuckles. I pulled these from a 93 Cutlass Ciera. I verified that they were the HD version by measuring non-adjacent lugs center to lug center, ~4.25" is right, ~3.75" is light duty (no go). I cleaned them up a little and cut off the bits that will interfere with bigger brakes. In the picture you can see the aluminum scrap I made a mounting fixture from.

Comments and additions welcome! Thanks!

Sam

Cool. Good luck with it!

u body minivan uprights would work too, but you have to hone out the bore to direct fit the S10 bearing. you still have to spot face the back where the bolt heads will fit as well.

I said I didn't want to talk a lot about axles and I don't. However, I came across an annoying fact that is worth mentioning. The Autozone "new" axles are crap, which is not terribly surprising but why they are crap is pertinent. The retaining clip is in a different spot and is cut in such a way that it is not removable without destroying something. Even after all of that the axle is a smaller diameter and the spline count is not the same. So to round it all up do not buy these axles, even if you aren't planning this conversion because they are definitely weaker. I'm hoping that the "reman" axles follow the OEM specs. *EDIT This information is not correct see below for explanation of how I messed up

Picture: with S10 stub axle next to the Autozone "new" axle.

I figured this was all but common knowledge by now. All parts stores carry garbage axles at this point. I don't think you'll find any better result with "re-manufactured" axles, it's all the same shaft metallurgy. Even if they fit and the clip were machined in the correct place, the shaft's themselves are weak. Albeit the diameter of the shaft's you are using are larger, the metal will fatigue and snap much easier in anything you can buy on the shelf that isn't from GM.

I had figured they wouldn't be OEM quality but I was a little surprised at what was different. I also don't need shafts capable of 400hp. I didn't see any shafts from GM or AC Delco from my usual part sources. Where is everyone buying these now?

Here is what I found:
Driveshaft shop 400hp axles - overkill (for me) and reflected in price
Cardone re-manufactured from Summit - ~$70 but not necessarily better, also not necessarily correct dimensions
Autozone "new" or re-manufactured - ~ $70 but questionable quality
raxles.com - read some good reviews but unknown price & might need core
Used - ~$50 JY

I'm leaning toward used but that has it's own pitfalls. I guess I also shouldn't be replacing these things every time we bend a control arm. I had 2 low mileage OEM spares last year...

Aren't you building a LeMons car? Shouldn't junk yard axles be your default choice for that application?

Also, 200k mile junkyard axles with intact boots are probably better quality parts in better shape than anything we can get from a parts house these days

Also, have you checked the housing dimensions of the U-body mini-van hub vs. those of the S10 hub? It might require less machine work to start with a U-body knuckle vice an A-body knuckle.

Aren't you building a LeMons car? Shouldn't junk yard axles be your default choice for that application?

Short answer is yes, the real answer is time to get to a JY when they're open is scarce. I can also send any team member to a parts store with a part number. If some one goes to the junkyard half way through a race on Saturday it has to be one of the better wrench turners and they need to be... turning wrenches. Nevertheless I'll make time and hopefully we won't need to mess with it until I can get a spare.

My recollection is that the U-Body knuckles require the same machining but are heavier. The machining isn't hard or terribly time consuming, I just have to prioritize it. I really wasn't expecting this axle pitfall.

I managed to get all the mill work done yesterday. I need to smooth out some edges with a burr and build the axles and then I'll be ready for assembly. I managed to find a pair of axles on the shelf at the local JY and I own them now.

Notes:
I made two patterns on my fixture but only used the smaller one
I chamfered the fixture holes so I could use a flat head, this was unnecessary
I used a measured stack of two washers to space the part off the fixture
Initially the part was held to the fixture with the M12 threads in the knuckle
As the holes are cut for bearing bolts they must be replaced with through bolts and nuts
If you're using a 1/2" end mill, this is a very close fit on an M12 bolt, I moved the holes out 0.100" instead of 0.085" because 0.085" wasn't enough

SO! I screwed up by assuming that the S10 CV center shaft was the same diameter as the Fiero manual CV center shaft. This means that I need to get new outer CV joints from an HD A-Body or other car with the right spline for the Fiero shaft and S10 bearing. I guess the S10 outer CV would be a good option if you wanted to build a super axle for either the S10 bearing or HD A-Body bearing. I have a pair I'd sell cheap

Also the Autozone "new" axles are the same size and spline as the stock Fiero but it is still lacking in overall fit/finish and most importantly has the retaining ring in a truly awful place. I will however clean it up, cut a new groove and make it into an emergency spare.

Above posts will be edited to reflect the new information. Hopefully this won't result in too much confusion!

neophile_17 wrote:SO! I screwed up by assuming that the S10 CV center shaft was the same diameter as the Fiero manual CV center shaft. This means that I need to get new outer CV joints from an HD A-Body or other car with the right spline for the Fiero shaft and S10 bearing. I guess the S10 outer CV would be a good option if you wanted to build a super axle for either the S10 bearing or HD A-Body bearing. I have a pair I'd sell cheap

Also the Autozone "new" axles are the same size and spline as the stock Fiero but it is still lacking in overall fit/finish and most importantly has the retaining ring in a truly awful place. I will however clean it up, cut a new groove and make it into an emergency spare.

Above posts will be edited to reflect the new information. Hopefully this won't result in too much confusion!

IIRC, the Fiero races, go in the S10 outer joints and you use the stock fiero axle shaft.

IIRC, the Fiero races, go in the S10 outer joints and you use the stock fiero axle shaft.

Unfortunately I tried this. The CV spider, cage, and ball bearings are all larger on the S10. I only got so far as to put the Fiero cage in the S10 outer shaft but it rattled around. I measured the Fiero ball bearings and they were smaller. Setting the cage and spiders on top of each other, the Fiero stuff was obviously smaller.

So the shaft spline into the outer CV is larger on the S10?

So the shaft spline into the outer CV is larger on the S10?

That's correct. I measured the snap ring groove which is close or identical to the spline root.

Fiero 0.970"
S10 1.020"

I race a Fiero in Chump and I use the P6000 HD spindles and hubs, bolt pattern is 5 x 114.5 which is a common tuner size. I usually can pick up a set of 17 x 8s and 9s for less than $300. All bolt-in parts, cheap and easy to find. Have about 80 hrs on one set of wheel bearings with no signs of issues. Also, the HD axle stubs slide onto the Fiero inner axle shafts. I redrilled the front hubs to match when I machined the rotors off for the bigger slide-on rotors.

I race a Fiero in Chump and I use the P6000 HD spindles and hubs, bolt pattern is 5 x 114.5 which is a common tuner size. I usually can pick up a set of 17 x 8s and 9s for less than $300. All bolt-in parts, cheap and easy to find. Have about 80 hrs on one set of wheel bearings with no signs of issues. Also, the HD axle stubs slide onto the Fiero inner axle shafts. I redrilled the front hubs to match when I machined the rotors off for the bigger slide-on rotors.

I'm using the same knuckles, but I want the 4.75" bolt pattern. I was guessing that the S10 axles had the same outside CV as the A Body HD stuff since they have the same wheel bearing spline but no luck. I'll need to get a couple A Body HD outer CVs but that shouldn't be too hard as soon as I can get to the JY.

mender wrote:I race a Fiero in Chump and I use the P6000 HD spindles and hubs, bolt pattern is 5 x 114.5 which is a common tuner size. I usually can pick up a set of 17 x 8s and 9s for less than $300. All bolt-in parts, cheap and easy to find. Have about 80 hrs on one set of wheel bearings with no signs of issues. Also, the HD axle stubs slide onto the Fiero inner axle shafts. I redrilled the front hubs to match when I machined the rotors off for the bigger slide-on rotors.

Everything I've seen says the pattern is 5x115mm... which is a smidge different than 114.3. Did you measure it? I actually never have.
I have this setup on my Northstar car, but haven't been tracking or racing it.

neophile_17 wrote:

I race a Fiero in Chump and I use the P6000 HD spindles and hubs, bolt pattern is 5 x 114.5 which is a common tuner size. I usually can pick up a set of 17 x 8s and 9s for less than $300. All bolt-in parts, cheap and easy to find. Have about 80 hrs on one set of wheel bearings with no signs of issues. Also, the HD axle stubs slide onto the Fiero inner axle shafts. I redrilled the front hubs to match when I machined the rotors off for the bigger slide-on rotors.

I'm using the same knuckles, but I want the 4.75" bolt pattern. I was guessing that the S10 axles had the same outside CV as the A Body HD stuff since they have the same wheel bearing spline but no luck. I'll need to get a couple A Body HD outer CVs but that shouldn't be too hard as soon as I can get to the JY.

Are you referring to the interface where the male spline on the CV joint housing slides into the hub cartridge?
The S10 spline is bigger? Have you looked at Dustbuster minivan (U-body) outer CV's for compatibility?

Yes, 115 mm, thought about that after but didn't edit. Good catch, 4.50" is 114.3; 0.013" difference on the radius so not much if using Ford wheels.

Are you referring to the interface where the male spline on the CV joint housing slides into the hub cartridge?
The S10 spline is bigger? Have you looked at Dustbuster minivan (U-body) outer CV's for compatibility?

The fit problem is where the axle shaft from the disassembled Fiero axle assembly would slide into the outer CV. The spline that passes through the hub/bearing assembly is the same between the S10 and the HD A-Body. I haven't looked at any Dustbuster stuff- maybe if I don't find an HD A-Body, but they seem to be plentiful in the yards near me.