'88 wheel bearing and hub upgrades

[Series8217]

70mm is the size of the bore in the Fiero knuckle. A little will need to be removed from the 70mm bore to make it fit whatever I would machine the 73.5 mm bearing carrier down to.

Taking 7mm out of the bore of the Fiero knuckle is not possible. There's less than 5mm before the threaded holes are siamesed with the bore!

[draven]

70mm is the size of the bore in the Fiero knuckle. A little will need to be removed from the 70mm bore to make it fit whatever I would machine the 73.5 mm bearing carrier down to.

Taking 7mm out of the bore of the Fiero knuckle is not possible. There's less than 5mm before the threaded holes are siamesed with the bore!

sorry, realized what you were referring to an hour after I posted... makes perfect sense.. ironic, I'm having a set of 88 rear knuckle pilot holes bored to accommodate two ACDelco Achieva/Jbody hubs before I start measuring and "templating" for C5 ebrake and calipers. I'll get some pics over in my thread and post here if you think it's prudent.

[Series8217]

70mm is the size of the bore in the Fiero knuckle. A little will need to be removed from the 70mm bore to make it fit whatever I would machine the 73.5 mm bearing carrier down to.

Taking 7mm out of the bore of the Fiero knuckle is not possible. There's less than 5mm before the threaded holes are siamesed with the bore!

sorry, realized what you were referring to an hour after I posted... makes perfect sense.. ironic, I'm having a set of 88 rear knuckle pilot holes bored to accommodate two ACDelco Achieva/Jbody hubs before I start measuring and "templating" for C5 ebrake and calipers. I'll get some pics over in my thread and post here if you think it's prudent.

Great! I'm working on that project (the rear hub upgrade) too. I'll probably start boring out parts this weekend.

[draven]

you going with the 20-25k delco bearings for the rear or something else up your sleeve?

[Series8217]

you going with the 20-25k delco bearings for the rear or something else up your sleeve?

Yes I plan to use use the J-body parts (AC Delco 20-25K) for now. I have a set of OE ones from a junkyard. The J-body bearings require the smallest overbore, so I can always go to other bearings later if needed.

[draven]

you going with the 20-25k delco bearings for the rear or something else up your sleeve?

Yes I plan to use use the J-body parts (AC Delco 20-25K) for now. I have a set of OE ones from a junkyard. The J-body bearings require the smallest overbore, so I can always go to other bearings later if needed.

Are you milling the face of the hub down or going with a .25" spacer between the base of the axle spline and hub?

[Series8217]

you going with the 20-25k delco bearings for the rear or something else up your sleeve?

Yes I plan to use use the J-body parts (AC Delco 20-25K) for now. I have a set of OE ones from a junkyard. The J-body bearings require the smallest overbore, so I can always go to other bearings later if needed.

Are you milling the face of the hub down or going with a .25" spacer between the base of the axle spline and hub?

Haven't decided yet. I'm going to bore it first and see how the thread length and spline engagement looks.

[FieroWanaBe1]

I don't have any pictures,
But the first generation caravan had bolt in stub axles in the rear that accepts tapered bearings (and a 5x100 bolt pattern hub)
Here is a thread showing some of this type of assemblies:
http://www.turbo-mopar.com/forums/knowl ... ke-Options

as well as the rear of some FWD VW and Audi cars:
http://www.nextdayauto.com/1997-volkswa ... 02011.html

I don't know if this is something that could be adopted to the front of any 88 but could be worth investigating, if they can be attached at the rear of the spindle. Its a common conversion for dirt trackers to convert the rear of their J-body cars to the caravan parts prevent catastrophic rear bearing failures and subsequent rollover crashes.
Autocrossers of J-body cars will attest that front bearing replacements are regular for them as well.

http://www.j-body.org/forums/read.php?f ... =26802&p=1
A thread detailing some issues cavalier racers have.

[draven]

[quote="FieroWanaBe1"]
as well as the rear of some FWD VW and Audi cars:
http://www.nextdayauto.com/1997-volkswa ... 02011.html
quote]

these look interesting

[Series8217]

I've read the J body bearings thread. The consensus from the Fiero racers on the Yahoo Fiero racing list is that the J body bearings are the solution for the 88 Fiero rear, but you HAVE to use OEM; the aftermarket bearings snap off at the flange or have other nasty failures. The people in the J body forum thread seem to be using aftermarket bearings since they all talk about going to the parts store to buy them...

The VW stub axles look neat but they are $260 each for new OEM parts (not a part to trust the aftermarket with) and even the OEM rear end assembly isn't going to be designed to hold up to heavy front end use on a track car. The rear end of a little front-engine front wheel drive VW is pretty light.

[The Dark Side of Will]

If you can find out who the OE supplier to VAG for those parts is, you can likely get the same part MUCH cheaper when it hasn't gone through the VAG parts system. That holds true for everything I've had to get for my girlfriend's '99 Passat and '02 A6... The OE parts are typically available through the aftermarket for 1/2 - 1/3 of VAG's prices for EXACTLY THE SAME ITEM. Behr radiator for $150 vice $450, for example.

[Series8217]

If you can find out who the OE supplier to VAG for those parts is, you can likely get the same part MUCH cheaper when it hasn't gone through the VAG parts system. That holds true for everything I've had to get for my girlfriend's '99 Passat and '02 A6... The OE parts are typically available through the aftermarket for 1/2 - 1/3 of VAG's prices for EXACTLY THE SAME ITEM. Behr radiator for $150 vice $450, for example.

That may be true for common wear items like radiators and bearings, but hub flanges and stub axles are either junk Chinese at junk prices or OE at genuine OE prices. For example the available parts for the VW GTI Mk III hub are VW ($201), rein ($49.95) and Vaico ($62.36). You can see in the product photos that the heat treat or material is different on the OE parts than the cheap aftermarket parts. rein and Vaico do are not OE suppliers for anyone.

[The Dark Side of Will]

I was wondering about that. The supply chains for worked metal are frequently more complex. Foundries like to melt, pour and forge metal... they don't like to cut metal.
I compare to the Northstar cam blanks I was researching a while back... CWC foundry made the blanks, but just shipped them to GM who did the machine work. Even though the flat tappet cams were out of production, CWC by contract couldn't sell parts made from the GM patterns to anyone but GM.

[FieroWanaBe1]

http://www.fiero.com/forum/Forum2/HTML/1 ... .html#p236

Not sure if this was mentioned. Passat/A4 bearing and hubs on the rear of an 88.

[Series8217]

http://www.fiero.com/forum/Forum2/HTML/1 ... .html#p236

Not sure if this was mentioned. Passat/A4 bearing and hubs on the rear of an 88.

Thanks for the link! I had seen that before but didn't post it here. The bolt-in housing approach doesn't work for the front knuckles since it doesn't minimize the material. There seems to be a lot of room in the back for that kind of solution though.

A similar approach to what I designed for the front using the GTI bearings has been used on the rear. Old Europe member Peabody pressed apart an aftermarket Pontiac 6000 hub/bearing assembly and installed it into a modified knuckle with a bolt-on bearing retainer. The photos are here:
http://www.fiero.com/forum/Archives/Arch ... 65.html#p6

Being that those aren't OEM parts, I wouldn't use the same parts as Peabody did. It's still a useful reference though.

[Series8217]

I took a break from the front bearings project to work on the rears.

Racers on the Fiero Racing List documented numerous scary failures of aftermarket hubs (including higher-end brands like Timken). These failures included the hub flanges breaking off completely and the wheel assembly separating from the vehicle. The original GM parts are no longer available, and with the age of these cars, junkyard parts are pretty high up there in miles. You can see pics of some of these failures here (pics courtesy of Alan Hamilton):
* Broken flange
* Completely separated flange (on left)
* Three broken flanges (one far left, two middle left).

Since most of my Fiero's miles are now spent on a track this is a problem I needed to solve in order to improve my chances of long-term survival. I took the common path used by Fiero racers as documented on the Yahoo Fiero Racing List (https://groups.yahoo.com/neo/groups/Fie ... gList/info). I believe this mod was pioneered by Alan Hamilton.

J-body front bearings (GM p/n 07470014 or AC Delco 20-25K) were used in J-body and N-body cars, including the Chevy Cavalier and Oldsmobile Achieva. Cavaliers were produced up until 2005, so GM bearings (and the practically identical AC Delco version) are still available for prices ranging from $100 to $120. According to discussions on the Fiero Racing List, the aftermarket J-body bearings are not suitable -- they break like the aftermarket Fiero parts.

I've been making some trips to the local Pick Your Parts over the past year or two and have amassed quite a collection of hubs and spare knuckles, so I figured it was time to put them to use.

The 84-88 Fiero rear bearing (the same bearing was used for all years) has a 71mm hub pilot diameter (minimum bore size in the knuckle) and a 102mm bolt circle on the mounting flange. On the other hand, the J-body bearing has a 73.5mm hub pilot diameter, and a 98mm bolt circle. Adapting the J-body bearing to the '88 Fiero rear knuckle requires boring out the knuckle to 73.74mm (this is the diameter that accepts the press-in axle seal used on the J-body) and slotting the bearing mounting flange holes by 2mm.

The flange offset on the J-body bearing is 44.43 mm, compared to the Fiero rear bearing's 42.2mm offset. If this matters, 2.2mm can be removed from the face of the knuckle so that the stock offset is retained.

One member of the Fiero Racing List said that an ~0.25 inch spacer is required to prevent the outer CV from binding up with the knuckle, due to the shallower height of the J-body bearing cartridge. I measured the difference in axle offset and it's ~5mm. With the J-body bearing the axle is pulled 5mm further into the knuckle. With the stock bearing there's about 5.5mm of clearance before the dust guard hits the knuckle... so a small spacer will be needed. Alternatively, a few millimeters can be milled off the front of the knuckle to get back to the stock offset and get some clearance back. The disadvantage of using a spacer is that the spline engagement decreases by the thickness of the spacer.

On to the machining:

Knuckle installed face down on the mill table:


I zeroed the mill by touching off to three points inside the bore then calculating the center of the circle from those three points.

Checking zero by spinning the boring head around to scrape the bore:


G-code for each cutting cycle: (NOTE: ignore the feed rate and spindle speed here -- this was some template code that I later modified)


Making a pass:


A depth of cut of ~0.17 mm ended up working pretty well, but I tried as much as 0.25 mm. The slot at the bottom of the bore was banging up the boring bar pretty bad when I tried to make deep cuts.

Close enough for my purposes:


Decent surface finish when the cut depth was kept under 0.15mm:


Slotted hole on the bearing cartridge mounting flange (sorry, no in progress pics; I didn't like my fixture):


Showing the slotted hole, how it lines up with the knuckle:


Final assembly:



Next steps:
-Install axle seal
-Fabricate axle spacer
-Test fit axle
-Test fit brake assembly

[draven]

ya kill'n me steven!

haha! wow.. you saved me some post time in my build thread

I just got my rear knuckles back from the machinist, as I couldn't do the pilot bore with my tools on hand. I even had the same measurements and yahoo racing list post referenced too!

I did bore and tap the brake dust plate holes out to 6mm as I'll be using those to support a 7075 T6 backing plate for the C5 ebrake setup and not pushing the hub out further than it is already over the stock hub.

Let me know what you find out on the .25" spacer as I'm sure you'll beat me to the punch..

[Series8217]

I measured the difference in axle offset and it's ~5mm. With the J-body bearing the axle is pulled 5mm further into the knuckle than with the stock Fiero rear bearing. With the stock bearing there's about 5.5mm of clearance before the dust guard hits the knuckle... so a small spacer will be needed to get adequate clearance. Alternatively, a few millimeters can be milled off the front of the knuckle to get back to the stock offset and get some clearance back. The disadvantage of using a spacer is that the spline engagement decreases by the thickness of the spacer.

[draven]

yep.. while looking at how much I'm going to have to slot the hub flange holes with my makeshift drill press "trying to pull off a mill press" I verified what you stated above with the axles from the 86GT I stripped. But funny enough while digging out the axles, dust plate, etc.. for assembling to the knuckle , the PO, procarnut, had a set of aluminum spacers on the axles that mic out to exactly 5.5mm thick with and OD of 47mm and ID of 37 mm, apparently due to his C5 rear caliper/ebrake plates being bolted between the hub and knuckle offsetting the stock hub the same amount as the 20-25K hub.. ha!

I'll throw some pics up in my build thread when I get my butt in gear and update it...

[Series8217]

Nice! I'm not sure if aluminum is the appropriate material to use here, being that it's a relatively small spacer that's under extreme compression.. it might creep. I have no desire to loose axle nut torque! I'll be making mine out of steel.