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PSA: Performante hubcaps come off on track


The Lamba Genie
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My apologies if this has been covered before with other cars and it's old news!

 

My car came with the centerlock wheels, with a small plastic hubcap.

post-228218-1511293660_thumb.jpg

 

 

On my first day on track, one fell off. I suspect thermal expansion of the wheel itself, or the heat affects the O-ring that holds the cap in place. I contacted the dealer to get another, and they'll take care of it under warranty, but also sent me pix from the Thermal event that showed other cars with the same issue.

 

No big deal, I'll just take them off before each track day. The notch above the A is where you insert a tool to pry off the hubcap, you can see I left a small scrape even though I was very careful and wrapped the screwdriver blade in blue tape.post-228218-1511293667_thumb.jpg

 

 

That's with a flash, this is without:post-228218-1511293674_thumb.jpg

 

I'm not very worried about the mark, it's tiny and a black Sharpie will take care of it.

 

Here's a shot of the 3 remaining caps:post-228218-1511293681_thumb.jpg

 

You can see the cap was also scratched, and one cap is missing the black O-ring that holds it in place. I was very careful, but apparently it is easy to lose when you pry the cap from the wheel.

 

For now I'm just going to leave them off, I don't think the gloss plastic goes well with the satin wheels, and I rather like the numbers/letters and the hex nut.

 

If I were to choose to leave them on and perform an on/off ritual, I'd definitely invest in a plastic tool to avoid any scratches.

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Use a suction cap to get them out.

 

Had the same thing when using the sv hard on Italian tour, wheel expanded and bye, bye centre cap, gone when I got to the top of the moutain, Lambo replaced under warranty.

 

Just put a dab of silicone on one edge of o ring then you won’t lose them again and easy to get off.

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I'm guessing the O-Ring groove in the cap doesn't properly align with the receiver groove in the wheel, and they never fully seat. Heat related expansion has absolutely nothing to do with them coming off.

 

1. The wheels don't get that hot around the hub, or at all.

2. Thermal Expansion is wildly over used and completely misunderstood. If you increased the wheel hub temperature to say, 400F (from a 70F ambient) the change in ID is about equivalent to the thickness of 1 sheet of standard paper. And that's assuming none of the temperature transferred to the cap, heating and expanding it as well.

 

Sounds like either the caps weren't fully seated from the start, or something is misaligned and not hitting the retaining grove. Put a little lube (non-petrolum base) on the o-ring before installing them to ensure they seat fully, I bet it's not an issue going forward. Also consider measuring the factory o-ring and getting one a slight bit larger in diameter.

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This had occurred with the Aventador SV's Dianthus wheel. The centre cap pops off at high speed. Most people think it's thermal related but after reading emanon's post, I won't be countering his professional expertise on the subject at all. Lamborghini is aware of this and they are supposedly working on a fix but no solution has been offered yet. Some say drilling a tiny hole onto the cap is the solution but if that is the case, then it sounds like it is thermal related which does not make sense. Anyway, there are enough dealerships that had already filed warranty claims to get Lamborghini's attention so a solution would come sooner or later.

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Same happened to my SV ones, Lambo replaced them and it never happened again, not exactly sure what they’ve done, talk to your dealer.

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Some say drilling a tiny hole onto the cap is the solution but if that is the case, then it sounds like it is thermal related which does not make sense. Anyway, there are enough dealerships that had already filed warranty claims to get Lamborghini's attention so a solution would come sooner or later.

 

Well that's an interesting thought. If the whole thing is sealed tight enough, if it it got sufficiently warm the air pressure temp change could result in positive pressure behind the cap. With such a very small air volume i'm shocked it would be enough to dislodge the cap, but it's something to consider.

 

:eusa_think:

 

Has anyone confirmed that drilling a hole in the cap solves the problem?

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I'm guessing the O-Ring groove in the cap doesn't properly align with the receiver groove in the wheel, and they never fully seat. Heat related expansion has absolutely nothing to do with them coming off.

 

1. The wheels don't get that hot around the hub, or at all.

2. Thermal Expansion is wildly over used and completely misunderstood. If you increased the wheel hub temperature to say, 400F (from a 70F ambient) the change in ID is about equivalent to the thickness of 1 sheet of standard paper. And that's assuming none of the temperature transferred to the cap, heating and expanding it as well.

 

Sounds like either the caps weren't fully seated from the start, or something is misaligned and not hitting the retaining grove. Put a little lube (non-petrolum base) on the o-ring before installing them to ensure they seat fully, I bet it's not an issue going forward. Also consider measuring the factory o-ring and getting one a slight bit larger in diameter.

This is entirely possible, it was just a working theory!

However, I do take exception to 1., that the wheels don't get hot. IME on a track, they get boiling hot and are untouchable, I assume from heat transfer of braking-generated heat to the hub to the wheel. Is it not possible that this intense heat affects the O-ring material?

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This is entirely possible, it was just a working theory!

However, I do take exception to 1., that the wheels don't get hot. IME on a track, they get boiling hot and are untouchable, I assume from heat transfer of braking-generated heat to the hub to the wheel. Is it not possible that this intense heat affects the O-ring material?

 

It could, but is highly suspect. Also consider 'too hot to touch' doesn't translate to "super hot" in the materials world. 200F will feel too hot to touch but most materials are essentially unaffected. EPDM is good to ~300F and Viton to ~400F. I would be absolutely shocked if your wheel hubs are anywhere in this ballpark. It's possible they used a completely shit o-ring that fails well under 200F, but again, that would be surprising.

 

I'm pretty curious to see what the fix is. Anyone want to spend $4 on some viton o-rings and swap them out to test?

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It could, but is highly suspect. Also consider 'too hot to touch' doesn't translate to "super hot" in the materials world. 200F will feel too hot to touch but most materials are essentially unaffected. EPDM is good to ~300F and Viton to ~400F. I would be absolutely shocked if your wheel hubs are anywhere in this ballpark. It's possible they used a completely shit o-ring that fails well under 200F, but again, that would be surprising.

 

I'm pretty curious to see what the fix is. Anyone want to spend $4 on some viton o-rings and swap them out to test?

 

I would love to. Link to purchase? I need O-rings for other purposes and have been looking for a source.

And absolutely I can see how "too hot to touch" could be meaningless to the materials involved. This is obvious in that wheel itself does not melt... :)

 

(and to add to your seating theory, when re-installing the caps, there is a sense of uncertainty, as if they are not fully pushed in and "clicking". To counter that however, they are difficult to remove once installed, it takes a fair amount of force as is evidenced by the scrape marks I left. What I'm feeling as I pry seems to be the O-ring unseating, there is some sense of compression and rolling involved)

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I would love to. Link to purchase? I need O-rings for other purposes and have been looking for a source.

And absolutely I can see how "too hot to touch" could be meaningless to the materials involved. This is obvious in that wheel itself does not melt... :)

 

(and to add to your seating theory, when re-installing the caps, there is a sense of uncertainty, as if they are not fully pushed in and "clicking". To counter that however, they are difficult to remove once installed, it takes a fair amount of force as is evidenced by the scrape marks I left. What I'm feeling as I pry seems to be the O-ring unseating, there is some sense of compression and rolling involved)

 

mcmaster-carr, your one stop shop for literally fcuking everything odd/random/mechanical.

 

https://www.mcmaster.com/#viton-fluoroelast...-rings/=1acv8b8

 

Just need to know the width and ID.

 

The required force to pry it off could be a vacuum seal. A dial caliper could pretty easily tell you if the o-ring is seating into the receiver groove in the wheel or not. It should give you a pretty reassuring feeling when it gets into place.

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mcmaster-carr, your one stop shop for literally fcuking everything odd/random/mechanical.

 

https://www.mcmaster.com/#viton-fluoroelast...-rings/=1acv8b8

 

Just need to know the width and ID.

 

The required force to pry it off could be a vacuum seal. A dial caliper could pretty easily tell you if the o-ring is seating into the receiver groove in the wheel or not. It should give you a pretty reassuring feeling when it gets into place.

Thanks. I assume these can be used as drive belts as well? They also sell O-ring drive belts made from neoprene, this is for a small motor / pulley / turning plastic gears application rotating minimal weight, say 600g max. The other belts are cheaper, but we're not talking a lot of money here.

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Mine has never popped off (fingers crossed) but I do know the wheels get hot. And reports tend to say the caps popped off after "spirited" driving. The first time I heard this was actually from the staffs of my local Lambo dealership. They went on a track event. When the car pulled into the pit and stopped, after a few minutes, the caps popped out as if they were jettisoned. Could that be heat building up from a parked car after it was driven hard? Possible I guess. A few weeks later, the same Lambo staffs also said one veteran colleague of theirs in Europe figured out a quick & easy way to solve the problem --- drilling a tiny hole into the cap. If that is indeed true, I too am a bit perplexed by such a small volume of air would build up sufficient pressure to pop the caps. But coming from the Lambo staffs themselves, I suppose it has some merits.

 

emanon, coming from me it really isn't a surprise, but I think some of those O-rings you posted are also used in some esoteric tube hi-fi gears. They fit onto tubes like 12AX7, ECC83 and ECC801S etc... to damp microphonics feedback which results in eliminating the "ringing" in the playback.

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I can confirm what VCR is saying, after a spirited drive two caps popped off so when I got home they were completely missing, when I parked the car at home after few minutes a cap popped and hammered the glass wall of the garage/office, it just about gave me a heartattack LOL so there is certainly pressure built up behind the caps to make them pop that way.

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Mine has never popped off (fingers crossed) but I do know the wheels get hot. And reports tend to say the caps popped off after "spirited" driving. The first time I heard this was actually from the staffs of my local Lambo dealership. They went on a track event. When the car pulled into the pit and stopped, after a few minutes, the caps popped out as if they were jettisoned. Could that be heat building up from a parked car after it was driven hard? Possible I guess. A few weeks later, the same Lambo staffs also said one veteran colleague of theirs in Europe figured out a quick & easy way to solve the problem --- drilling a tiny hole into the cap. If that is indeed true, I too am a bit perplexed by such a small volume of air would build up sufficient pressure to pop the caps. But coming from the Lambo staffs themselves, I suppose it has some merits.

 

emanon, coming from me it really isn't a surprise, but I think some of those O-rings you posted are also used in some esoteric tube hi-fi gears. They fit onto tubes like 12AX7, ECC83 and ECC801S etc... to damp microphonics feedback which results in eliminating the "ringing" in the playback.

 

Well think about it this way (say like a piston in an engine), when the caps are installed, you're already creating positive pressure as soon as the O-Ring contacts the wheel nut, and you push it into place (piston compressing air essentially). Typically this small bit of pressure would dissipate over time, but these parts are machined to tight enough tolerances they must be pretty much air tight. With a 2" diameter cap you have 3.14 square inches of surface space, so it wouldn't take much pressure to apply some real force there. 3 PSI (pretty easily achievable if you get 150F temp swing) would have about 10psi behind the cap when fully seated.

 

I asked about the cap being plastic because it looks like there is a metal cover tabbed over the top. It wouldn't be hard to drill a small hole in the plastic without piercing the metal face plate, but this would still be enough to let the air pressure equalize. It wouldn't take much more than a pinhole to get the job done.

 

It wouldn't surprise me if they use off the shelf o-rings as tube dampeners. Now you know where to buy your own :D They are absolutely used as drive belts on small assemblies and work very well so long as the drive isn't position sensitive requiring a cog belt. It's pretty amusing we can all geek out on O-Rings :icon_mrgreen:

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I asked about the cap being plastic because it looks like there is a metal cover tabbed over the top. It wouldn't be hard to drill a small hole in the plastic without piercing the metal face plate, but this would still be enough to let the air pressure equalize. It wouldn't take much more than a pinhole to get the job done.

 

(snip)

 

It's pretty amusing we can all geek out on O-Rings :icon_mrgreen:

 

post-228218-1511376231_thumb.jpg

This should be clear. The logo face is a metal stamping held over the plastic cap by 3 bendable tabs and probably an adhesive. I cannot easily separate the pieces nor will I try any further. If the cap were drilled horizontally, pressure should be allowed to escape from the area behind the O-ring with no drilling thru the face. The flat plastic flange is filler, and does not seem to be part of any seal.

 

And yes, this is much more interesting and amusing than XXX vs YYY threads.

And it's probably a good thing I sold my tube amps a few years ago... :icon_mrgreen:

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Hubcap_fix_.jpg

This should be clear. The logo face is a metal stamping held over the plastic cap by 3 bendable tabs and probably an adhesive. I cannot easily separate the pieces nor will I try any further. If the cap were drilled horizontally, pressure should be allowed to escape from the area behind the O-ring with no drilling thru the face. The flat plastic flange is filler, and does not seem to be part of any seal.

 

And yes, this is much more interesting and amusing than XXX vs YYY threads.

And it's probably a good thing I sold my tube amps a few years ago... :icon_mrgreen:

 

Yeah, that looks like a solid option. Hit that with a 1/16" bit and you'll be good to go.

 

Then go drive the shit out of it and see if they remain in place :icon_super:

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^^^

The popping behavior suggests that the factory O-ring and its sealing efficacy are good enough. I need a replacement ring anyway, so I'll order a high quality tube dampening one, drill the caps, and report back if anything happens.

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Well think about it this way (say like a piston in an engine), when the caps are installed, you're already creating positive pressure as soon as the O-Ring contacts the wheel nut, and you push it into place (piston compressing air essentially). Typically this small bit of pressure would dissipate over time, but these parts are machined to tight enough tolerances they must be pretty much air tight. With a 2" diameter cap you have 3.14 square inches of surface space, so it wouldn't take much pressure to apply some real force there. 3 PSI (pretty easily achievable if you get 150F temp swing) would have about 10psi behind the cap when fully seated.

 

I asked about the cap being plastic because it looks like there is a metal cover tabbed over the top. It wouldn't be hard to drill a small hole in the plastic without piercing the metal face plate, but this would still be enough to let the air pressure equalize. It wouldn't take much more than a pinhole to get the job done.

 

It wouldn't surprise me if they use off the shelf o-rings as tube dampeners. Now you know where to buy your own :D They are absolutely used as drive belts on small assemblies and work very well so long as the drive isn't position sensitive requiring a cog belt. It's pretty amusing we can all geek out on O-Rings :icon_mrgreen:

 

I would never doubt your expertise and recommendations on anything that's engineering-related.

 

And yes, thank you on the O-rings link! :eusa_dance: I can now experiment and have a borderline-lunacy report on "what type of O-rings yield the best sound"! :aiwebs_017: :lol2:

 

And yes, this is much more interesting and amusing than XXX vs YYY threads.

And it's probably a good thing I sold my tube amps a few years ago... :icon_mrgreen:

 

Fully agreed and :lol2:

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Fascinating discussion. Can’t wait to hear if the tiny drilled hole solves the problem.

 

Back in the late ‘70’s I took hubby’s (then boyfriend’s) 1978 silver anniversary C0rv3tt3 for a “spirited” solo drive. It had the L82, close ratio 4 speed. Not a great performance car but back in the day it was fun.

 

A minute after I parked in the driveway -as he walked up to the car - all four center caps popped off as though they were exhausted and could no longer hold on.

 

He just smiled.

 

Now I”m wondering if it was related to the discussion above, or just poor GM design and quality....

 

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