That's an interesting point. I presume it doesn't make any difference as long as all the wheels carry on turning at the same speed as each other, which they will as long as none of the wheels skid. However there will come a point at which the same braking force (subject to the normal front/back balance) will be enough to stop the undriven wheels, but not to stop the driven ones which the engine will be struggling to keep turning. At that point, all the wheels will be braked intermittently.
I suppose it depends on the algorithm used. I can imagine it being more of a problem if two wheels on the same axle are braked differently, because that would make the car veer to one side. But if both wheels on one axle are braked more than both wheels on the other, that wouldn't necessarily make the car swerve and perhaps ABS is more tolerant of that.
You should also be used to fine movements with the clutch pedal, especially as you live in a hilly area. Using my left foot for both clutch and brake is quite easy.
Yes my Peugeot is like that. When I had the cambelt routinely replaced at
120,000 miles (or whatever) I was advised to have the water pump replaced while they had the engine out, even though it seemed to be fine, just in case it were to fail at some unspecified time in the future and strip the cambelt. For an extra £30, it was probably money well spent, given that the pump was fairly old. The garage said they always recommended replacement, to avoid a second labour cost of getting at the cambelt/water pump area.
A Jagiar XF needs all that and two more belts changed if they are getting on in age or miles.
As the garage said 'by the time you have taken off the whole front of the car plus radiators, A/C condensers and oil coooler, a few belts and a pump wont dent the budget'
Yes. On the basis that hopefully the camshaft and the valve mechanisms will never seize up, causing the timing belt to snap. Put everything that could conceivably seize (water pump, alternator, oil pump) on other drive mechanisms such as belts or direct gear, so that if they seize, they won't wreck the cambelt and cause the dreaded meeting of the valves and pistons.
I presume toothed belts are used in preference to chains for the timing to reduce the noise of a timing chain and the friction of a chain tensioner. I presume gears would be even more noisy.
When I had the timing belt replaced on my previous car, it took the garage 5 days to get the engine running again because a position sensor broke as they were removing the old belt and the replacement wouldn't quite fit due to a change in design. I happened to be cycling past the garage when they were still working on it one evening, and there was the standard noise of a cranking but never firing engine. Suddenly it fired and there was a shout of delight from the workshop (as if England had scored the winning goal in the World Cup final). For some reason that I didn't follow, as soon as the engine had fired once, they know it would work forever after - ie it wasn't a fluke.
Thankfully the garage charged me the standard rate for the job, assuming everything had gone smoothly, rather than all the extra faffing about time.
This was a little local garage in the village. Up until then they had done a perfectly good job of servicing my car and repairing normal consumables like brake pads/discs. This time things didn't go according to plan. I wish I'd not used them again, because the next job they did on my car was to replace the "fan belt" (alternator, PAS and aircon) which had failed - fortunately close enough to home for the RAC to tow me home. The garage seemed to replace the belt OK, but it turned out they hadn't noticed that the flanges of the pulley on the crankshaft were bent (*) so the new belt only lasted a couple of thousand miles. The main dealer where I had the second belt fitted spotted the bent flanges and replaced the pulley as well. The second belt lasted for ages. Sadly the village garage refused to accept that the bent flanges had been there before, so I never got any money back to compensate for the belt that only lasted a few thousand miles. *That* was the trigger for me to stop using the local garage ;-(
(*) Which may have been the cause of the first belt failing.
The wheels are rarely all turning at the same speed, differences in rolling radius and very rarely going in a dead straight line... B-)
ABS doesn't kick in until a wheel has, or is very close to, locking up. You're not likely to be braking (as in rate of slowing vehicle down) that hard. You might be braking hard but that to is counter the torque coming from the engine not from the tyre/road.
Yes but the force needed to stop a wheel that is being rotated by the engine will be greater then the force needed to stop a wheel in normal circumstances - won't it? So won't there be a tendency for both the undriven (eg rear) wheels to lock up while the driven wheels (front) are still able to overcome that braking force. There will be some discrepancy due to the normal difference between the balance of the front and rear brakes.
It has to lock up or at least considerably slow down first, the ABS isn't psychic. I imagine the algorithm simply takes the average of the wheel speeds and then operates on any wheel going much slower or much faster. Of course that has a number of potential issues, eg on snow or ice the ABS has no way of knowing if the car is skidding or parked, if 1 wheel is going much faster than the other 3 is that wheel spinning or are the others skidding etc. I'm sure car manufacturers have written some clever algorithms that remember the speed up until now and cross check against engine rpm and gear but there's only so much it can do.
Very much so. The braking effort needed to 'beat' the engine on full belt will be considerable. And on a FWD very likely to get the rear brakes to the point of locking - especially on a wet surface.
Which goes back to the only sensible way. Switch off the engine but leave the car in gear. You'll still have servo assistance to the brakes while the engine turns. Maybe not power steering if electric, but it will still be possible to steer the car to a halt.
This was discussed in control theory at university. Part of the algorithm is double or triple differentiation of rotation speed. In the days before cheap microprocessors easy to do with phase lock loops.
I guess they have put many more deductions in modern systems. Clever people have been working on it for 40 years and no doubt they have covered any eventuality people on news groups can imagine.
The brakes will win, provided the car is in a high gear. Even in 1st I reckon the brakes will still win, just need a bit more effort.
Which they are designed to do, how much energy do you think they have to take in an emergency stop from 70 mph? 1000 kg car doing 70 mph has around 500,000 J of kinetic energy. Stop it in say 5 seconds(*) that 100,000 J/s or 100 kW. 100 bhp is 75 kW.
(*) A modern car can proably stop a fair bit faster than that with the aid of ABS working overtime.
Yes, "brake fade". Conversely if a brake is binding the disc can glow cherry red and still not lose braking. I've had both.
About 5 mins in a "spirted" 1000' ish foot decent using, the brakes rather more than the gears, down a rather good driving road, B-) Slightly alarming when you start to brake as a corner approaches rather too quickly, just slam it down another gear to make it round. Once faded they'd come back quite quickly but would also fade again quite quickly... It was several minutes of driving with no braking before they came back reliably.
I assumed ABS systems had always been microcontroller controlled, didn't realise there were analogue versions. Interesting to know.
No doubt, but the more complex ian algorithm becomes the more likely it is that there's some nasty undisovered edge cases lurking in there either due to the implementation or the algorithm itself which might cause serious problems. In aviation they do formal proof checking, multiple implementations of the same algorithm by different teams and god knows what else to mitigate this, but I doubt the automotive industry is quite so thorough simply due to cost.
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