Brake disc screws: what do they do?
Discussion
I've encountered the amusing socket-headed screws that go through the brake disc to the hub. It seems extremely common online for these to be reluctant to undo and the first video I saw was on a Porsche, so it's not just Renault who make them out of cheese.
Notwithstanding the carp design, what do they actually do? The disc is firmly located by the hub central flange and the wheel studs pass through the disc so that takes care of rotation. I'm just ordering some more and reflecting on the mysteries of life.
Notwithstanding the carp design, what do they actually do? The disc is firmly located by the hub central flange and the wheel studs pass through the disc so that takes care of rotation. I'm just ordering some more and reflecting on the mysteries of life.
They are to get stuck fast precisely 3 days after the car is built and thus become part of the disk and hub forever more and need drilling out.
They do seem superfluous as one small screw when as you say, there are four or five massive bolts holding the whole shebang together, I suspect they are for those first three days, so if in that time you have occasion to remove a wheel it stops the disk parting company with the hub, beyond that point regardless of the screw we all know a lump hammer, colourful language and the strength of ten men will be required to budge a disk from the warm embrace of the hub.
They do seem superfluous as one small screw when as you say, there are four or five massive bolts holding the whole shebang together, I suspect they are for those first three days, so if in that time you have occasion to remove a wheel it stops the disk parting company with the hub, beyond that point regardless of the screw we all know a lump hammer, colourful language and the strength of ten men will be required to budge a disk from the warm embrace of the hub.
Talking of studs. In tbe olden days the studs came off the hub and it was easy to hang the wheel on them. Now you have to try and persuade the wheel to stay in place whilst you rotate the damn thing to get the first stud in before it falls off.
Being charitable here, I'm assuming there is some sort of engineering progress?
Being charitable here, I'm assuming there is some sort of engineering progress?
RazerSauber said:
I must admit, these are super helpful when you have wheel bolts as opposed to studs and nuts. I find that the disk spins very easily and lining the hub, disk wheel up perfectly is quite fiddly. They're about as much use as a chimney on your dog for hubs with studs built in though.
I was about the add the same thing. My old Audi coupe has floating discs that don't have a locating screw in them. The ur-quattro came with a thing in the tool kit that has a wheel bolt thread in one end and a long thin body, the main use of that was to screw through one of the wheel bolt holes when replacing a wheel, to keep things lined up. I had all sorts of trouble with mine, until I made a similar thing.UserError said:
Talking of studs. In tbe olden days the studs came off the hub and it was easy to hang the wheel on them. Now you have to try and persuade the wheel to stay in place whilst you rotate the damn thing to get the first stud in before it falls off.
Being charitable here, I'm assuming there is some sort of engineering progress?
Because a snapped bolt can be replaced by another bolt. A snapped or damaged stud would mean replacing the entire hub as they are fixed items in the assembly. Being charitable here, I'm assuming there is some sort of engineering progress?
The wookie. Did that. And gave it some heat. The problem was that the heads were in a poor state already. I got one out, but the other wasn't having it and I threw all the tricks I know at it. Tomorrow I'll try drilling a 4 or 5mm hole in what's left and sacrificing a torx bit and hammering it in. I might see if I can get a blob or two of weld on it.
Stev-rsv4 That would be a reason. I also think I have recollection of the knurling failing once and the stud just rotated.
Stev-rsv4 That would be a reason. I also think I have recollection of the knurling failing once and the stud just rotated.
InitialDave said:
An old school impact driver and a hammer is very effective with most recalcitrant brake disc retaining screws.
Exactly this. A dash of penetrating oil and a mug of tea while you wait for it to help; then apply cheap hammer-driven device from machinemart, £20-25, the best-fitting bit in the slots, and hit once, very hard and square with a big hammer - job done.*The impact driver thing works well for door hinge fixings etc.
- if job not done - drill the head out and don't worry about it, IME.
Cylon2007 said:
They hold the disk in place while the wheel is off and the wheel bolts are removed. obviously if you have studs in the hub they are redundant.
Even on a hub with studs the screws are handy to stop the brake disc dropping onto the floor (or your feet) when you're trying to pry the caliper off, and to reduce the need for an extra arm when trying to get the caliper back on.Edited by anonymous-user on Saturday 16th November 13:08
STe_rsv4 said:
Because a snapped bolt can be replaced by another bolt. A snapped or damaged stud would mean replacing the entire hub as they are fixed items in the assembly.
Damage to threads is probably more likely than breakage. Generally speaking male threads are more likely to be damaged than female, so using bolts means that the component more susceptible to damage is the that's more easily replaced. Sound engineering practice or an unintended consequence of cost reduction?Gassing Station | Suspension, Brakes & Tyres | Top of Page | What's New | My Stuff