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Hey folks. My team is building an amateur race series C4, we have a stock 1986 C4 with 4+3/L98. We would like to use the robust fbody wheel hubs in the front however they include an integrated speed sensor that sticks out the back, which won't fit through our '86 steering knuckle (has a cast over back wall). Looks like the 88+ steering knuckle will work, however from the reading I've done it sounds like upper/lower/steering knuckle parts all changed between the early and late C4's. I have also read that some people mix and match the upper/lower arms to attain greater camber.
Can I buy a later steering knuckle and use it with the early upper/lower arms without effecting the front geometry too much? Sounds like it might change scrub radius which I should be able to account for with wheel and tire package.
Does anyone know the definitive difference between the early and late control arms or have part numbers? Does the whole front geometry need to be swapped as a package?
Another thought I had was taking a hole saw to the back of my stock knuckle to open it up for the hub's ABS sensor (just like the later knuckles) - Similar to what's shown in this post https://www.corvetteforum.com/forums...post1593074267
Yeah, there are really big differences in the geometry between early and late C4s. The kingpin inclination angle (KPI) was around 7-8 deg in the early cars but jumps to something like 12-13 deg in the later ones. The spindle on the knuckle is obviously set at a different angle to accommodate that. I don't know how you'd make up for all that. And even if you do, the increased KPI is not good for front grip at high steering angles because you lose camber when you most need it. And you can't make it up by adding static camber, because that just increases KPI by the same amount as you added camber. You need to run serious caster to make up for that KPI, but you can't use different front and rear shims on the upper control arms (UCAs) to do that because you: 1) run out of space to adjust it enough, and 2) introduce bump steer that you can't correct. You end up needing to make a custom UCA that sets the ball joint back an inch or more. While you're at it, you can make it shorter so you can get the -3.0 deg or more camber that you want.
If all that is sounding insane, I agree. The early front end you have is generally considered the better one from a racing standpoint. If you want to keep the ABS operable, you may just have to treat the front bearings as wear items and replace them frequently (not sure how long the races are that you are planning, but they fronts are super easy to replace). The hole saw idea is interesting. I suppose the question is whether the reluctor wheels on the early and later versions have the same number of teeth and if the sensor sends the same signal. Hopefully you could rig up the connector for the newer sensor pigtail (maybe they're the same?). I'd make the hole as small as possible to minimize any structural weakening. If you don't need/want ABS, then there may be another option that is discussed here. Pay attention to Kubs' post #6, which speaks to your issue.
Also, regarding your quest for more front camber: VBP used to sell offset lower control arm bushings in urethane. The hole was offset from center by 1/8". You can get at least -3.0 camber with them. But VBP is out of business. If you know someone with a lathe you could buy some LCA bushings and use them as a pattern to turn your own out of delrin (supposed to be easier to machine than urethane), and you could make the center hole offset. Hell, if you make more than one set you could probably sell them here and they'd be free or better.
Yeah, there are really big differences in the geometry between early and late C4s. The kingpin inclination angle (KPI) was around 7-8 deg in the early cars but jumps to something like 12-13 deg in the later ones. The spindle on the knuckle is obviously set at a different angle to accommodate that. I don't know how you'd make up for all that. And even if you do, the increased KPI is not good for front grip at high steering angles because you lose camber when you most need it. And you can't make it up by adding static camber, because that just increases KPI by the same amount as you added camber. You need to run serious caster to make up for that KPI, but you can't use different front and rear shims on the upper control arms (UCAs) to do that because you: 1) run out of space to adjust it enough, and 2) introduce bump steer that you can't correct. You end up needing to make a custom UCA that sets the ball joint back an inch or more. While you're at it, you can make it shorter so you can get the -3.0 deg or more camber that you want.
If all that is sounding insane, I agree. The early front end you have is generally considered the better one from a racing standpoint. If you want to keep the ABS operable, you may just have to treat the front bearings as wear items and replace them frequently (not sure how long the races are that you are planning, but they fronts are super easy to replace). The hole saw idea is interesting. I suppose the question is whether the reluctor wheels on the early and later versions have the same number of teeth and if the sensor sends the same signal. Hopefully you could rig up the connector for the newer sensor pigtail (maybe they're the same?). I'd make the hole as small as possible to minimize any structural weakening. If you don't need/want ABS, then there may be another option that is discussed here. Pay attention to Kubs' post #6, which speaks to your issue.
Also, regarding your quest for more front camber: VBP used to sell offset lower control arm bushings in urethane. The hole was offset from center by 1/8". You can get at least -3.0 camber with them. But VBP is out of business. If you know someone with a lathe you could buy some LCA bushings and use them as a pattern to turn your own out of delrin (supposed to be easier to machine than urethane), and you could make the center hole offset. Hell, if you make more than one set you could probably sell them here and they'd be free or better.
Thank you for the detail Matt! I agree, there would be too many changes to suspension geometry to justify mixing/matching parts. For our series (ChampCar Endurance) we'll go ahead and stick with the factory '86 upper/lower arms and factory steering knuckle, then make incremental adjustments to camber/scrub/ride height etc. Due to the rules we're penalized for using certain non-stock components. I want to document some of the differences between the wheel hubs for future readers, so below I've posted what we've discovered along with potential paths forward:
Here is the '86 knuckle with newer Fbody hub shown. The sensor connector section is all that interferes with the knuckle pocket. One idea is to holesaw the knuckle for clearance. As you mention we could potentially rig up a circuit to change the pulses for wheel speed to the ECM if needed. Or we could just leave it disconnected and run without ABS for the time being:
Here is the newer Fbody hub shown with the black plastic removed. The ballbearings are exposed and have been packed with grease. Another user mentioned that he removed this cover and ran the knuckle pocket with gear oil to bathe the now-exposed bearings. I'm unsure how the grease would move if we left it open, and we may look into producing a shorter aluminum or 3D printed plastic cover to clear the stock knuckle. More to come:
The backside of the plastic cover with reluctor mating piece and contacts:
Last edited by 85'irocz; Apr 13, 2020 at 08:08 PM.
We would like to use the robust fbody wheel hubs in the front
What are the difference compared to stock C4? ( except for sensor )
What are the difference compared to newer C4 with similar sensor on hub?
What year fbody?
Just bore an APPROPRIATE BORE in the back-side of the knuckle for the 'sealed' later F-body to protrude through. I'm assuming you've defeated ABS so there's no issues.
Using a caliper - what is the diameter of the F-body at the same dimension depth of the knuckle pocket? Oil bath is a poor choice for an attempt!!!!!
I'd like to throw out there too, that the later LCA is quite a bit longer than then early arm. This is meant to work in conjunction with the newer knuckle. So, if you put an '88^ knuckle on '87 and earlier arms, I think you'd have radical positive camber that is unresolvable no matter what upper arm you use.
What are the difference compared to newer C4 with similar sensor on hub?
Literally the only difference between a 89-96 C4 front hub and a 4th-gen F-body hub is that the four bolt holes used to attach the hub to the knuckle are threaded on the F-body version, so that the bolts thread directly into them from the back side of the knuckle. On the C4, those holes are smooth-bore and you use through-bolts with nuts on the back side of the knuckle. Otherwise they are interchangeable, and I've run both on my C4.
What year fbody?
I think it's all 4th-gens, but I'm not 100% sure of that.
Ok, so f-body hubs are 'the same', not more robust.
To really get a 'better' wheel bearing the SKF X-tracker hub with adapter is the way to go.
I have not had any problems with front bearing hubs. I know that one was replaced before I bought the 1984 over 20 years ago. One front bearing hub has a reluctor ring and not the other that probably still is original.
For traction control I need front wheel speed and I have a temporary solution with a sensor on the disc brake now.
Using 1991-1996 wheel bearing hubs with intergrated ABS sensor seems like the simple solution. I only need to open up the knuckle to get access to the connector.
The other option I have been inverigating is using 1986-1987 knuckels that used ABS sensors and the same geometry as my 1984. But then I need to get knuckels, ABS sensors and at least one new wheel bearing.
Ok, so f-body hubs are 'the same', not more robust.
I'm also curious as to if/how the internals of the Fbody front SKF bearings are different than Delco or other OE-replacement front bearings. In my research on this forum and feedback from others it sounds like they've had longer life with the Fbody units vs parts store bearings as well as Delco replacement. Perhaps Matt or others can add their thoughts and experience. I wonder if most bearings are fine for occasional track duty, while endurance racing really shakes out the longest lasting parts.
Last edited by 85'irocz; Apr 14, 2020 at 10:36 PM.
I have run both "Vette" front hubs and "Camaro" hubs (what I have now). The casing of the Camaro hub is a bit more robust; the flange is thicker, the case is a bit more substantial looking. A bit.
My opinion is that the beefier casting would support the bearing better, and deflect less. Would that help the bearing's life? I don't know.
I'm also curious as to if/how the internals of the Fbody front SKF bearings are different than Delco or other OE-replacement front bearings. In my research on this forum and feedback from others it sounds like they've had longer life with the Fbody units vs parts store bearings as well as Delco replacement. Perhaps Matt or others can add their thoughts and experience. I wonder if most bearings are fine for occasional track duty, while endurance racing really shakes out the longest lasting parts.
I have not swapped to the F-body hubs yet on my 96, but when I was looking at doing it last year the SKF's were supposedly still "made in America" where everything else, including Timken was "made in China" and of dubious quality. AND you can not get the Corvette specific SKF's anymore, only the F-body's. Rear "corvette" SKF's are available though. So are the SKF's visually any different? My guess is no. Are the parts "better" because they are USA made? maybe... QC better? Probably.
I would love to do the swap to the C5 X-tracker hubs, but last I checked the conversion was 1000... I dont race my car so thats a lot of money to spend.
I'm also curious as to if/how the internals of the Fbody front SKF bearings are different than Delco or other OE-replacement front bearings. In my research on this forum and feedback from others it sounds like they've had longer life with the Fbody units vs parts store bearings as well as Delco replacement. Perhaps Matt or others can add their thoughts and experience. I wonder if most bearings are fine for occasional track duty, while endurance racing really shakes out the longest lasting parts.
As far as regular replacement bearings, I went through one Corvette part and one Camaro part doing nothing but street driving and autocross competition. The Camaro casting may be a bit beefier in places, but my experience and reading tells me the problem isn't the casing strength. The problem is that these are ball-bearing designs that don't have an adequate thrust surface and retention designs to handle the side loads imposed by hard cornering. In the old days of needle bearings on conical seats, the taper of the seats took the lateral loads. The X-tracker design addresses those issues with an asymmetric ball bearing setup and by improving the strength of the bearing retention design, and it also has a beefier flange:
I would tend to think that even with greasing... a lack of support is hard to make up for. It may extend the inevitable but a design deficiency will still ultimately fail I'd think. Right Tom?
Front Suspension Inquiries
