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. 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. You can find information on the spacer I used in by following this link.
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 -Test fit axle -Test fit brake assembly
DIY notes: Members of the Fiero Racing List have done this modification with a rotary file. You only need to remove about 1.25 mm from each side of the bore. The bore dimension does not have to be exact where the bearing fits in, but it does still need to be precise around the axle seal. Tape off the area where the axle seal fits in (or leave it in place) so that you don't grind it, and can still use the stock axle seal. You can slot the holes on the bearing flange using a rotary file as well. You will still need to run an axle spacer. You may be able to adapt an off-the-shelf part such as a precision-ground shim or washer if you can find one that's suitable. Refer to this post for spacer information.
2015-03-20 - Removed drawing for spacer -- needs to be revised; the spacers did not fit correctly on the axles on my car, but they did fit my spare axle.
[This message has been edited by Steven Snyder (edited 03-20-2015).]
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,
After seeing those pictures of flange failures, I can see how that would make for a very bad day! Does the J-body wheel bearing have a thicker wheel flange, compared to the OEM Fiero?
Originally posted by Jims88: Does the J-body wheel bearing have a thicker wheel flange, compared to the OEM Fiero?
Yes, the flange is much thicker. I need to find my OEM Fiero bearing and then I can take some pics to compare.
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Originally posted by nosrac:
Are the stock fiero axles retained?
Yes, this works with the stock Fiero axles. The Fiero outer CV is the same (or very close to the same) as the J-body outer CV, so it doesn't need to be changed.
Steven, sorry if I'm a little slow on the draw here... but this is exactly the same size as the original Fiero hub, and therefore will correctly fit the Fiero wheel's 57.1mm center bore, right?
I suspect it is, but figured I might as well be the one to ask the dumb question just to clarify this for everyone.
[This message has been edited by Patrick (edited 01-24-2015).]
Steven, sorry if I'm a little slow on the draw here... but this is exactly the same size as the original Fiero hub, and therefore will correctly fit the Fiero wheel's 57.1mm center bore, right?
I suspect it is, but figured I might as well be the one to ask the dumb question just to clarify this for everyone.
I certainly appreciate the information in this thread. I autocross my '88, and durability of various car components is something we're all concerned with. I'm actually replacing one of my rear hubs tomorrow (with one from an '87 parts car) as this hub has been "squawking" for awhile now. At some point I imagine I'll be required to do what you're describing here. So thanks again!
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. I'll be able to finalize the spacer dimensions once I receive the axle seals this week.
So this modification allows you to fit the J-body front bearings into the rear of the Fieros, right?
And the advantage that the J-body bearings have over the Fiero bearings is that the J-body bearings are still available from the OE manufacturer while the Fiero bearings are not.
Did I get that right? If so, that's pretty cool. While it lasts!
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.
There are a lot more J body hubs than Fiero hubs available in yards.
[This message has been edited by Gall757 (edited 01-26-2015).]
So this modification allows you to fit the J-body front bearings into the rear of the Fieros, right?
And the advantage that the J-body bearings have over the Fiero bearings is that the J-body bearings are still available from the OE manufacturer while the Fiero bearings are not.
Did I get that right? If so, that's pretty cool. While it lasts!
Correct.
The J-body hubs flanges are thicker (stronger), the bearings have a larger diameter (more load capacity), and the donor cars are much newer so low-mileage used parts and also durable new parts (from GM) are still available at this time. You can probably go to one junkyard today and get enough hubs to last you a decade of racing.
Nice. And while it does require some machining, it's not nearly as extensive as some of the previously presented options of stuffing larger hubs into the Fiero knuckles.
Now if you could just come up with a modification of similar difficulty for the 88 fronts, you'd be a rock star.
Nice. And while it does require some machining, it's not nearly as extensive as some of the previously presented options of stuffing larger hubs into the Fiero knuckles.
Now if you could just come up with a modification of similar difficulty for the 88 fronts, you'd be a rock star.
I'm working on the fronts, but it's not going to be a DIY solution.
You can use same hub w/ same milling etc on older cars too. All Fiero uses same rear hub. Milling and any other issues are very likely same for 84-87.
OE Axle seal might get loose now or over time after hole is bigger... Race only cars might care but driving on street could let allot of road crap get at the back part of hub. Axle seal helps preventing salt etc attacking that area.
I wonder if can ream out the hub section on knuckle and save the small part where axle seal lives. That could use OE seal from TFS etc...
Mill shown could likely do that easy.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
You can use same hub w/ same milling etc on older cars too. All Fiero uses same rear hub. Milling and any other issues are very likely same for 84-87.
OE Axle seal might get loose now or over time after hole is bigger... Race only cars might care but driving on street could let allot of road crap get at the back part of hub. Axle seal helps preventing salt etc attacking that area.
I wonder if can ream out the hub section on knuckle and save the small part where axle seal lives. That could use OE seal from TFS etc...
Mill shown could likely do that easy.
I test-fitted the J-body axle seal, SKF 18765. It fits the machined knuckle and the Fiero axle perfectly (I sized the bore to match the spec from SKF for pressing in the seal). I just need to select the right size spacer for between the CV axle and the hub, since the inner race has a different offset than the Fiero part.
[This message has been edited by Steven Snyder (edited 01-27-2015).]
Yeah, I've mulled a few 88 front solutions, but the project has never bubbled far enough up on my priority list to actually spend real shop time on it and make chips. Someday...
BTW, what you've done to your rears isn't a "DIY solution" for most people either.
Yeah, I've mulled a few 88 front solutions, but the project has never bubbled far enough up on my priority list to actually spend real shop time on it and make chips. Someday...
BTW, what you've done to your rears isn't a "DIY solution" for most people either.
Yeah, please offer it as a service. I would buy if price was reasonable.
Yeah, I've mulled a few 88 front solutions, but the project has never bubbled far enough up on my priority list to actually spend real shop time on it and make chips. Someday...
BTW, what you've done to your rears isn't a "DIY solution" for most people either.
The solution itself is a DIY mod, just not with the tools I used. My future development plans for the rear knuckle necessitate keeping a parallel bore, but that's not relevant to this mod.
The only critical dimension is the bore for the axle seal. If you leave that portion of the bore untouched you can still use the Fiero axle seal, as Ogre suggested. You can grind out the rest of the bore using a die grinder to fit the J-body bearing. You only need to remove 1.25mm of material on each side of the bore and not even over the whole bore. It doesn't take too much time with a die grinder. A dremel will work, it'll just be a little slower. Some members of the Fiero Racing List mentioned doing it this way.
You can slot the J-body bearing flange holes with a grinder or file too.
I added the notes about DIYing it to my original post above.
[This message has been edited by Steven Snyder (edited 01-27-2015).]
UPDATE 2015-03-20: I have temporarily removed the drawing for the spacer. The spacers I made from the drawing fit the spare axle I have, but they did NOT sit flat on the axles on my car, which had a larger fillet radius. You would not be able to easily see that they weren't sitting flat unless you shine a light behind and look for a small gap. If you made spacers based on this drawing, please verify fitment, and grind the chafer larger until the spacers sit flush. The drawing I came up with for the spacer:
The spacer I used is 44.2mm x 29.2mm with a 3mm 45-degree chamfer to clear the fillet on the axle. It needs to be made of steel, and have parallel, flat-ground faces. Aluminum may creep or distort. A non-parallel spacer may not sit right, or may bend the axle. Do this carefully! Also double-check your axle fillet to make sure the spacer actually clears the fillet. If the spacer sits on the fillet you're going to have problems.
The axle end without the spacer is shown below. Note that I had previously removed the dust shield to measure clearances. The assembly will clear with the dust shield in place.
The axle with the spacer installed:
The spacer sitting on the hub bearing to make sure it doesn't hit anything except the inner bearing race.
And finally, the moment we've all been waiting for, the axle installed in the modified knuckle using the J-body bearing, J-body seal, and custom spacer. As you can see, there is plenty of clearance now!
[This message has been edited by Steven Snyder (edited 03-20-2015).]
There are hundreds of potential candidate bearings. I've looked into the Cobalt, J-body, Solstice/Sky, G8, Taurus, CTS, Camaro, GTO, Corvete, Sonic, Spark, Cruise, and more, including import cars.
The J-body is the only bearing assembly that just requires slotting the hub flange and minimal boring of the knuckle, and has the same bolt pattern as the Fiero.
For example, the Cobalt is 5x110, requires a massive 14mm overbore of the knuckle, and doesn't have slottable bolt holes in the flange to make it line up with the Fiero knuckle.
Regarding the 88 front bearings, I believe a couple of mods have already been done for more strength using the Cadillac cartridge and the fiero mounting part of the hub.
Originally posted by IXSLR8: Regarding the 88 front bearings, I believe a couple of mods have already been done for more strength using the Cadillac cartridge and the fiero mounting part of the hub.
Several who have tried to replicate that upgrade have been unable to find the right bearings from Timken with the removable outer races. It would appear that over time the bearing design inside the housing changed, but they kept the same part #. So you have to buy a bunch of bearings and "hope" you get the right ones. Its a great upgrade, but the trial/error in finding the right bearings can be a challenge.
quote
Originally posted by mcguiver3:
Does the Cadillac cartridge have the same wheel stud pattern as the Fiero 5X100? Is the dust cap a stock 88 Fiero piece, I don't think it would fit?
Its 5 x 4 3/4". The wheel pilot will be too large to use stock wheels as well. The aftermarket ones normally have a large (more universal) pilot diameter and use concentric rings to make them application specific - so those would probably work. You bore the fiero hosing out every so slightly, so you can use the caddy dust cap.
Regarding the '88 front bearing upgrades, I would be wary of anything that hasn't been tested either with hundreds of thousands of miles of road use, or a full season on track, with disassembly and inspection afterward.
Rodney Dickman's front tapered roller bearings for the '88 promised to be stronger and I destroyed 3 of them in short order.... they only lasted me a few dozen laps on track each before they had excessive play. The used OE hubs last a whole weekend or more. One reason the OE design is so much stronger and stiffer is because the races are integrated into the housing and shaft. The races have big radii and smooth out the flow of stress through the hub and housing, also making the parts have a longer fatigue life.
The eBearing hubs for the front of the '88 Fiero were the worst -- the flanges would break off after only a few laps on track. Luckily, no-one lost their life to those hub failures. Unfortunately, many of these hubs are still running around on cars. Luckily, they're easy to spot. Inside the brake rotor pilot is a pretty much flat face. There's a large radius there on the OE hubs.
I'm not happy with Timken's hub engineering. They don't select the appropriate hub to shaft radius, or hub shaft thickness. They don't use integrated races, so there are stress concentrations everywhere. Actually this applies to all of the aftermarket hubs, including the Cadillac bearing upgrade shown in the link above. Look at the pictures I linked to at the beginning of this thread to see some failures of Timken hubs and others.
I don't want to lead anyone off track with this thread (rear bearing upgrade), though the fronts were mentioned. Just wanted to point out the Bubba post regarding our quest for better bearing options.
Whoever finds a caddy bearing that works, should document what/where they found it, for those who follow the upgrade...if its still possible.
By the way, I forgot to mention that I read on a racing forum somewhere that a Fiero owner was running an 88 on the track and had reoccurring front bearing failures, particularly the right side. He purged the bearing grease in the cartridges and used Motor Honey instead and the bearings would last. I wish I could find this source again.
[This message has been edited by IXSLR8 (edited 02-06-2015).]
There are hundreds of potential candidate bearings. I've looked into the Cobalt, J-body, Solstice/Sky, G8, Taurus, CTS, Camaro, GTO, Corvete, Sonic, Spark, Cruise, and more, including import cars.
The J-body is the only bearing assembly that just requires slotting the hub flange and minimal boring of the knuckle, and has the same bolt pattern as the Fiero.
For example, the Cobalt is 5x110, requires a massive 14mm overbore of the knuckle, and doesn't have slottable bolt holes in the flange to make it line up with the Fiero knuckle.
I have friends that run a Cavalier in Chump and LeMons. They killed stock bearings. They swapped out knuckles I think, it's been a while since I asked them about it.
There is also a 4x100 Cobalt. 15x7 4x100 wheels are about the most plentiful wheel out there. I thought about adding some plate to the outboard side of the knuckles, the overbore could "live" there. I'd get some free trackwidth too. (Yeah have to figure out halfshafts.) It's a way backburner thing for me though. You have gotten much further than me, and I'm glad you have, does give something to consider doing.
If the J-body stuff wasn't out there, what would you next choice be?
Originally posted by ennored: I have friends that run a Cavalier in Chump and LeMons. They killed stock bearings. They swapped out knuckles I think, it's been a while since I asked them about it.
All of the stories I've read from J-body racers about front wheel bearings include "trips to the parts store every weekend". They don't seem to realize there's a huge difference in the way they aftermarket (parts store) bearings are compared to the ones from the dealer (or what originally came on the car). They probably also don't want to spend $100-$150 per bearing for a car that's built for less than $3000.
Like the OEM Fiero bearings, the J-body bearings won't last forever. They are a little bit stronger than the stock Fiero bearings which last me about 2 seasons. Unlike the Fiero bearings, the original J-body bearings are actually available new. Nothing in the aftermarket counts -- they're all junk as evidenced by the pictures I linked to at the beginning of this thread.
quote
If the J-body stuff wasn't out there, what would you next choice be?
C5/C6 Corvette on custom uprights... also have another idea for using the stock rear uprights but I need to test it first.
[This message has been edited by Steven Snyder (edited 02-11-2015).]
I talked to my buddies with the J-body LeChump car. They DO run stuck front hubs (with custom knuckles and brakes). They can make them last for 24 hours, barely. They run street type tires. But 24 hours is a LONG time in normal road race terms.
I have to run stock knuckles, that's the reason for the question. J-body stuff does seem to be a reasonable option though.
I talked to my buddies with the J-body LeChump car. They DO run stuck front hubs (with custom knuckles and brakes). They can make them last for 24 hours, barely. They run street type tires. But 24 hours is a LONG time in normal road race terms.
I have to run stock knuckles, that's the reason for the question. J-body stuff does seem to be a reasonable option though.
24 hours is 6 weekends for me, or roughly one season. Good to know. Can I get in touch with them? I'm curious about lap times, specific tires used, alignment settings, brake pads, corner weights, etc., as these all have impacts on bearing longevity.
I'd also like to know why they made custom knuckles if they are using the stock hubs.. Usually brakes can just be adapted with add-on brackets.
Thanks again for the info!
[This message has been edited by Steven Snyder (edited 02-13-2015).]
I understand that the Arraut Motorsports (formerly Held) front lowering spindles use rear bearings, if this is true, then this upgrade could probably be utilized for the front of all cars 84-88, as they make drop spindles for all years. Probably slotting the cartridge holes would be all that is needed.
[This message has been edited by Bridgetown (edited 02-14-2015).]
I understand that the Arraut Motorsports (formerly Held) front lowering spindles use rear bearings, if this is true, then this upgrade could probably be utilized for the front of all cars 84-88, as they make drop spindles for all years. Probably slotting the cartridge holes would be all that is needed.
Damn, another reminder why Bloozberry was such an asset to the forum.
Sorry Steven, not trying to hijack your thread. Just wish to show my appreciation to members here such as yourself who have so much to offer the Fiero community.
[This message has been edited by Patrick (edited 03-02-2015).]
I have temporarily removed the drawing for the spacer. The spacers I made from the drawing fit the spare axle I have, but they did NOT sit flat on the axles on my car, which had a larger fillet radius. You would not be able to easily see that they weren't sitting flat unless you shine a light behind and look for a small gap. If you made spacers based on this drawing, please verify fitment, and grind the chafer larger until the spacers sit flush.
Cadillac Rear wheel/hub update to be used on the front of 88's: I decided to look into this. I've been to wrecking yards and the bearings I have found are all aftermarket. I took them apart and the reason you can not use them is that they all have a crush collar compressed around a lip at the end of an unthreaded shaft. You'd have to take a die grinder and cut parts off until the cap can be removed. The collar is on a lip instead of a threaded shaft. Hence the aftermarket unusability as previously stated. However, I did find one new bearing, made in the USA, that had been sitting on a shelf for a long, long time. It has the nut on the end of the shaft with a cotter pin, under the seal cap. The problem is its only ONE and they are all gone.
I eventually did find two US made New Old Stock Green RW402's. These are the specified 513009 bearing hubs made by Green in the USA. They disassemble and have the large castle nut. BUT, they will not work because the spindle is manufactured from the opposite side of the bearing. The spindle is made on the mount to the cadillac side not the hub side. Total bummer.
Additional note: 1984-1985 (non ABS) Corvette front wheel hubs are a direct bolt in for the Cadillac Seville. But I have not taken them apart to see if they have the same bearing dimensions as the rear Cadillac bearing/hubs. They are more readily available but the nonABS ones are hard to find.
Pretty close to a dead end.
[This message has been edited by IXSLR8 (edited 04-12-2015).]
At some point I imagine I'll be required to do what you're describing here. So thanks again!
