Depends if you apply the right solution. I use stack of 1 inch MDF as stand. The max fall for the car is 1-2 inches. Theoretically, I have a 4 post lift at home.
Jacking up using the brake disc
- Thread starter DiyNutJob
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Haven't read beyond the first page but
1) You haven't thought about the forces and moments which apply, static and if the car moves in each dimension. The action of the support must be to return the car to where it was, not let it go further. Your idea does not do that. Think what happens to the bolts . They start with abnormal lateral strain, then if the car moves that strain increases. That's a definition of instability. Very bad.
Compare with supporting under a tyre axis. Forces are not only perpendicular to the ground. Is it reasonable to rely on the handbrake - I would say no, unless you're happy that the handbrake is good enough to stop you getting killed. It has to be stable without the handbrake.
It's clear you can't easily quantify anything. In other words you're guessing.
You might get away with it but is the risk worthwhile?
2) It seems you want to jack up the car, remove a wheel, then use a different jack under the brake disc? Bad idea.
Use one jack, then axle stand(s).
Chock a wheel for added security - they're very cheap.
You can use a small jack to lift the car enough (wheel on) to get a bigger jack under, if it's awkward.
1) You haven't thought about the forces and moments which apply, static and if the car moves in each dimension. The action of the support must be to return the car to where it was, not let it go further. Your idea does not do that. Think what happens to the bolts . They start with abnormal lateral strain, then if the car moves that strain increases. That's a definition of instability. Very bad.
Compare with supporting under a tyre axis. Forces are not only perpendicular to the ground. Is it reasonable to rely on the handbrake - I would say no, unless you're happy that the handbrake is good enough to stop you getting killed. It has to be stable without the handbrake.
It's clear you can't easily quantify anything. In other words you're guessing.
You might get away with it but is the risk worthwhile?
2) It seems you want to jack up the car, remove a wheel, then use a different jack under the brake disc? Bad idea.
Use one jack, then axle stand(s).
Chock a wheel for added security - they're very cheap.
You can use a small jack to lift the car enough (wheel on) to get a bigger jack under, if it's awkward.
This is a fairly typical (and amusing) Nutjob thread, where he asks for everyone's advice and then when they give it, manages to string it out to several pages of telling them that they're wrong...
He's not really looking for advice, he's looking for us all to tell him what a wonderful idea it is and how we all wished we'd thought of it first.
He'll make snide remarks about people lacking in "engineering feel", whereas, if he had the slightest scintilla of it himself, he'd have just bloody gone out, found the appropriate stiff bits of the vehicle structure, and done it, in less time than he's spent typing on here.
As it is, nobody with even an ounce of "engineering feel" would run the same engine oil for 10 years...
that said, My 2p-worth is as follows:
1. He's drawn what looks like a ventilated disc in his fag packet sketch. But mentions the back of the car. Not sure whether they're ventilated or not, but if they are, they're going to be at least 20mm thick and well able to support the weight of the rear corner of the car. Disc edges are usually a bit rusty, and if that's the case, a bit of wood on the jack pad will prevent any serious chipping of the edge of the disc.
2. He's talking about bolting a scrap disc, back-to-back, and jacking up on that, but its mounting face is unlikely to be the same thickness as the wheel, so he might find the wheel bolts bottom-out before they have actually successfully clamped the discs together tightly enough, which means the load will be just trying to bend the bolts.
3. There's no problem with either the hub or the wheel bearing not being able to take the load, because the car will have been designed to cope with cornering at close to 1G, fully-laden, and there will be a safety factor in the original design. However, the vertical loads will be applied through the tyre centre (give or take a bit for wheel offset), and by the time you've got two discs, back-to-back, the offset will be truly ridiculous and whatever prevents camber change, (probably the trailing arm bushes), will be given a really hard time as a result. Jacking on the actual disc edge would prevent this, but he's saying the stone shield is too close. Jacking up on the bell of the disc would probably be an option, though. (At least, in terms of being strong enough).
4. The biggest problem, however, is preventing the disc from rotating, and thus, falling off the jack. Maybe he has enough faith in his handbrake to prevent this, (and as it's not my car anyway, I can't say I particularly care), but that's for him to find out. The minute the force going up through the disc, moves ahead of, or behind a vertical line passing through the centre of the hub, it will try to rotate.
He's not really looking for advice, he's looking for us all to tell him what a wonderful idea it is and how we all wished we'd thought of it first.
He'll make snide remarks about people lacking in "engineering feel", whereas, if he had the slightest scintilla of it himself, he'd have just bloody gone out, found the appropriate stiff bits of the vehicle structure, and done it, in less time than he's spent typing on here.
As it is, nobody with even an ounce of "engineering feel" would run the same engine oil for 10 years...that said, My 2p-worth is as follows:
1. He's drawn what looks like a ventilated disc in his fag packet sketch. But mentions the back of the car. Not sure whether they're ventilated or not, but if they are, they're going to be at least 20mm thick and well able to support the weight of the rear corner of the car. Disc edges are usually a bit rusty, and if that's the case, a bit of wood on the jack pad will prevent any serious chipping of the edge of the disc.
2. He's talking about bolting a scrap disc, back-to-back, and jacking up on that, but its mounting face is unlikely to be the same thickness as the wheel, so he might find the wheel bolts bottom-out before they have actually successfully clamped the discs together tightly enough, which means the load will be just trying to bend the bolts.
3. There's no problem with either the hub or the wheel bearing not being able to take the load, because the car will have been designed to cope with cornering at close to 1G, fully-laden, and there will be a safety factor in the original design. However, the vertical loads will be applied through the tyre centre (give or take a bit for wheel offset), and by the time you've got two discs, back-to-back, the offset will be truly ridiculous and whatever prevents camber change, (probably the trailing arm bushes), will be given a really hard time as a result. Jacking on the actual disc edge would prevent this, but he's saying the stone shield is too close. Jacking up on the bell of the disc would probably be an option, though. (At least, in terms of being strong enough).
4. The biggest problem, however, is preventing the disc from rotating, and thus, falling off the jack. Maybe he has enough faith in his handbrake to prevent this, (and as it's not my car anyway, I can't say I particularly care), but that's for him to find out. The minute the force going up through the disc, moves ahead of, or behind a vertical line passing through the centre of the hub, it will try to rotate.
Exactly, it will be similar to trying to balance a pencil on end, though even less likely to work. The slightest nudge, and over it goes.
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You are projecting. I did not ask for advice. I asked people to share their experience. One did and no disc rotation was reported. I also asked people to speculate, so that I can see if I missed anything. I didn't miss anything.
I see no significant risk of disc rotation with the car locked in place. Nowhere did I suggest using the hand brake alone for that. It has been bricks, logs under the tyre, etc. You could even use plastic. I suggested inserting a wood cradle between the discs and then jack up using the cradle. This would completely eliminate the risk of rotation. I have robust rubber padding on my jack that will act like a mini cradle to resist some rotation. Lifting the car would be gradual and any rotation would be immediately seen. I don't see the need for the cradle in my case. The cradle should be thick enough to fill the entire space between the discs. It could be produced using a pencil and a router.
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Your hub is free to rotate, because it is supported by the single point, which you marked with an arrow and 'Jack here'. Your 'thick wood cradle', would simply tilt to the right, or the left. Even supposing it didn't tilt, what is to stop it slipping away from the hub?
If it tilts then you should wear glasses to pick it up sooner. If it tilts, you stop and reverse. The cradle is pinched between discs and pinched between jack and disc hubs. How does it slip?
There are none so blind, as those who will not see. Best leave it at that and you video how you get on.
Nothing to video. I don't need a cradle. The cradle is for people who are blind.
And, true to form, here you are, telling yet another poster who has offered advice (sorry "speculation"
) that they're wrong...Your piece of wood makes things slightly better, but as Harry has tried to tell you, will not eliminate the risk of rotation because it's lifting...
...a bearing!
A bearing is something whose only job in life, is to rotate.
By saying that you can prevent movement by chocking the other wheels, you completely miss the point that is being communicated to you - which is that this is NOT about the car moving, but the HUB moving. When you start the process, the suspension will be at full rebound. Being a semi trailing arm, as you start jacking, the centre of the hub is going to start moving backwards, until the arm is horizontal, and then it will start moving forwards again. Unless the centre of effort of your jack is EXACTLY under the centre of the stub axle, the hub will try to rotate. You are, in effect, trying to pick a unicycle up by the bottom of its front wheel and expecting the saddle to remain uppermost. The only thing preventing that, is whatever flat area of jack pad, is bearing against whatever flat area of your wooden cradle. As you refuse to be told, you may as well just find out for yourself how hard that is. Fortunately, it's not my car!
Not impossible, but I wouldn't be placing much of a bet on your chances of success... I guessed you'd say that.I'll leave you to find out which has more friction - the little cast iron wheels on a trolley jack, or an actual wheelbearing on a car...
My rubber jack pad overrules both.
I'll leave you to find out which has more friction - the little cast iron wheels on a trolley jack, or an actual wheelbearing on a car...
Perhaps?
He's even trolling his own threads now.
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