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Old 15th March 2016, 14:20   #61
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Default Re: Automotive misconceptions demystified

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Originally Posted by Motard_Blr View Post
To increase the braking capacity of a disc brake, a brake booster boosts the pedal force and increases the braking force at the caliper. The trouble with brake boosters is that they don't work when the engine is shut off.
Vacuum boosters are not only meant for disc brakes. Their general purpose is to reduce driver effort in pressing the brake pedal (by amplifying the driver input at the pedal before it reaches the wheel brakes). They can work on any type of foundation brakes.

And "To increase the braking capacity of a disc brake" may not be the right way to put it. The braking capacity of the foundation brake remains the same, with or without a booster.

Brake boosters don't work when the engine is shut off, or even when the engine is running at idle speed when the vacuum level in the intake manifold is too low to provide any assist.

Quote:
Originally Posted by Motard_Blr View Post
So in cars with all disc brakes, the parking brakes are actually drum brakes on the rear wheel. The drum is hat shaped and combines the drum and disc in one piece.
Not necessarily. There are plenty of vehicles these days which have electric parking brakes with actuators which move the caliper pistons and hold the rear brakes. Drum-in-hat is a pretty old system, though may be commonly used even now.

Last edited by Viju : 15th March 2016 at 14:22.
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Old 15th March 2016, 14:21   #62
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Default Re: Automotive misconceptions demystified

I am sure that auto companies consider all the aspects before they recommend an oil change interval. They should be keeping some buffer and suggesting an oil change much before its actually required to cover instances where people forget a oil change in time.

Big engines, like used in aircraft and ships do not change their oil as often and most actually take a sample of oil and check that in labs to see if the oil has really gone bad. One such lab is http://www.blackstone-labs.com/

I think many of us change oil more frequently than actually required just because we have some kind of fear. Not sure taxi drivers who drive much more than us also do such so often changes and use the highest quality oils available.

Sadly we have started considering just the monetary cost of oil change and not the overall cost of damage to environment which is caused due to spent oils. A large portion of such oils actually goes down the drain and comes back to us in drinking water.

Hope some oil company will come out with a detailed report and article on how to really know if my car really needs an oil change.
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Old 15th March 2016, 14:45   #63
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Default Re: Automotive misconceptions demystified

Quote:
Originally Posted by Viju View Post
...

Brake boosters don't work when the engine is shut off, or even when the engine is running at idle speed when the vacuum level in the intake manifold is too low to provide any assist.
In my experience, vacuum brake boosters do work even at idle speeds. If the brake is applied a few times with the engine shut off, the vacuum reserve is exhausted and the pedal travel reduces. If the engine is started the vacuum generated even at idle speed is enough to pull the brake pedal noticeably and provide adequate braking at slow speeds.

Quote:
Not necessarily. There are plenty of vehicles these days which have electric parking brakes with actuators which move the caliper pistons and hold the rear brakes. Drum-in-hat is a pretty old system, though may be commonly used even now.
Electric parking brakes are a different animal altogether. The human driver's only input is pressing a button to actuate the parking brakes. The force applied by the parking brake depends on the electric motors used.
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Old 15th March 2016, 14:45   #64
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Default Re: Automotive misconceptions demystified

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Originally Posted by sanjeevgpc View Post
I am sure that auto companies consider all the aspects before they recommend an oil change interval. They should be keeping some buffer and suggesting an oil change much before its actually required to cover instances where people forget a oil change in time.

Big engines, like used in aircraft and ships do not change their oil as often and most actually take a sample of oil and check that in labs to see if the oil has really gone bad. One such lab is http://www.blackstone-labs.com/

I think many of us change oil more frequently than actually required just because we have some kind of fear. Not sure taxi drivers who drive much more than us also do such so often changes and use the highest quality oils available.

Sadly we have started considering just the monetary cost of oil change and not the overall cost of damage to environment which is caused due to spent oils. A large portion of such oils actually goes down the drain and comes back to us in drinking water.

Hope some oil company will come out with a detailed report and article on how to really know if my car really needs an oil change.
At least in the West,both Government and the oil companies collect (and at times pay for) used oil. They then recycle the oil, either process it for lubricant use or clean it up for use as a fuel.

Here are some reprocessing facilities in India

http://www.bharatoil.com/
http://www.centuryrefineries.com/
http://arslanenginery.com/used-oil-recycling/
Automotive misconceptions demystified-materialbalancearslanwfeusedoilrecycling1899x1024.jpg
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Old 15th March 2016, 14:55   #65
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Default Re: Automotive misconceptions demystified

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Originally Posted by Jeroen View Post
What do you believe the misconception about Nitrogen and Teflon Coating to be? I have some experience with the first and lots with the second.
Well filling nitrogen is like using premium fuel. You dont get the real world benefits for which you pay for. It costs nothing to fill normal air, maybe max 10rs tip, while it costs around 200rs to fill 5 tyres. But are you even getting twice the benefit for 20 times of what you pay for ? Normally the nitrogen filling stations claim pressure will hold much longer than normal air, also some even say better ride and handling but in real world at least i never felt any difference. Coming to the teflon coating, i believe its one of the dealership money making tactic for charging a huge premium for polishing. I believe we even have a thread to stay away from it. But most of the times customers fall for that trap and end up losing money.

http://www.team-bhp.com/forum/modifi...g-fool-wt.html (Teflon Coating-dupont, Making Fool Or Wt?)
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Old 15th March 2016, 15:16   #66
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Default Re: Automotive misconceptions demystified

Quote:
Originally Posted by sanjeevgpc View Post
Big engines, like used in aircraft and ships do not change their oil as often and most actually take a sample of oil and check that in labs to see if the oil has really gone bad.
Accept. But for Aircraft oil changes are closely monitored by probes and sensors along with extra clean fuel. Ships are monsters who toast spent oils and diesels, majority of that goes into ocean again by controlled effluent discharge.

But, cars have to deal with varying fuel quality, mediocre engine build quality and driving habits. I think passenger vehicles meet more dusty and stressful environment due to which we face oil change interval paradigm.

I am no expert, but oil companies would have taken all these parameters along with profit margins to make sure oil is changed within stipulated timelines to keep sales up.

Quote:
Originally Posted by Aroy
At least in the West,both Government and the oil companies collect (and at times pay for) used oil. They then recycle the oil, either process it for lubricant use or clean it up for use as a fuel.
Happens in India too. A.S.S actually collect all these spent oil in drums. They sell them to following people :
1. Construction companies (for coating girders and templates before cement is poured on them).
2. Powerplants / Energy companies.
3. Ships (major customer which burn them when they are in international waters).
4. Railways and large manufacturing companies that need cheap oils for coating surfaces.
5. Recycle by oil manufacturers themselves and then recirculate as some percentage of base stock.

Got this info from a IOC engineer who happened to be a co-passenger on a vacation flight.
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Old 15th March 2016, 15:31   #67
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Default Re: Automotive misconceptions demystified

Agreed. The problem is that auto companies keep say a margin of 20% so say a oil which should be good for 10 hours is asked to be changed in 8 hours. Now the car owners use an oil which is say 20% better quality than the normal oil used by auto company and than change the oil 25% before time. So many actually use the oil at only 50% of heir life. Possible that many of us are cynical at times and feel that frequent oil changes is making car run smooth and healthy the same way they feel car running smooth after a good wash.

The beneficiary are the oil companies and losers are the auto owners and environment. many times just just because we can afford.

Quote:
Originally Posted by prithm View Post
Accept. But for Aircraft oil changes are closely monitored by probes and sensors along with extra clean fuel. Ships are monsters who toast spent oils and diesels, majority of that goes into ocean again by controlled effluent discharge.

But, cars have to deal with varying fuel quality, mediocre engine build quality and driving habits. I think passenger vehicles meet more dusty and stressful environment due to which we face oil change interval paradigm.

I am no expert, but oil companies would have taken all these parameters along with profit margins to make sure oil is changed within stipulated timelines to keep sales up.





Happens in India too. A.S.S actually collect all these spent oil in drums. They sell them to following people :
1. Construction companies (for coating girders and templates before cement is poured on them).
2. Powerplants / Energy companies.
3. Ships (major customer which burn them when they are in international waters).
4. Railways and large manufacturing companies that need cheap oils for coating surfaces.
5. Recycle by oil manufacturers themselves and then recirculate as some percentage of base stock.

Got this info from a IOC engineer who happened to be a co-passenger on a vacation flight.
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Old 15th March 2016, 15:59   #68
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Default Re: Automotive misconceptions demystified

What about car seat for kids or booster seats? It is legally compulsory in many countries to have car seats fitted for kids, but no regulation or advisory exists in India. Is it because the kids do not have any voting rights that their safety is overlooked by the govt. regulations !?!
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Old 15th March 2016, 16:09   #69
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Default Re: Automotive misconceptions demystified

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Originally Posted by Motard_Blr View Post
Disc brakes have less braking capacity than a drum brake of similar diameter for the same hydraulic pressure. The reason is the self-energising effect that (boeuff has mentioned this above) drum brakes have.
Isn't this sole advantage that drum brakes have also one of it's Achilles heels?

Isn't the limit of frictional coefficient that can be used much lower before it turns too grabby to be functional?

Disc brakes gives you the option to try exotic materials like ceramic and kevlar with higher/better frictional properties.

Cheers
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Old 15th March 2016, 17:17   #70
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Default Re: Automotive misconceptions demystified

Excellent thread SS-Traveller. Rated 5 Stars. Any thing worse than having no knowledge is having incomplete/incorrect knowledge. This thread will help us gain a lot of knowledge. Thanks.


Quote:
Originally Posted by Viju View Post

Brake boosters don't work when the engine is shut off, or even when the engine is running at idle speed when the vacuum level in the intake manifold is too low to provide any assist.
Quote:
Originally Posted by Motard_Blr View Post
In my experience, vacuum brake boosters do work even at idle speeds. If the brake is applied a few times with the engine shut off, the vacuum reserve is exhausted and the pedal travel reduces. If the engine is started the vacuum generated even at idle speed is enough to pull the brake pedal noticeably and provide adequate braking at slow speeds.
May be this is manufacturer specific. In my Duster pumping the brakes on idle reduces the travel as well. Though it is not as much as it would with engine off. This was not the case with my earlier Honda.

Regards,

Pawan
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Old 15th March 2016, 17:55   #71
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Default Re: Automotive misconceptions demystified

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Originally Posted by PapaBravo View Post
May be this is manufacturer specific. In my Duster pumping the brakes on idle reduces the travel as well. Though it is not as much as it would with engine off. This was not the case with my earlier Honda.
Remember the vacuum source is different, petrol engine vehicles use the inlet manifold vacuum while diesels have an engine driven vacuum pump.

In a related note, Hispano Suiza and Rolls Royce had a mechanical servo assistance, the early RR cars had a mechanical servo over mechanical brakes to all 4 wheels and later ones had a mechanical servo over hydraulic. They achieved the assistance by a disc mechanism driven from the transmission.
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Old 15th March 2016, 18:00   #72
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Default Re: Automotive misconceptions demystified

A lot has been said on the disc vs drum topic. I was curious as I thought and believed that discs are better than drums (one of the reasons why I went for the top model i20 CRDi [2010]). I found a really nice answer on Quora which I would like to share (copyright Nathan Kaemingk)
Name:  discdrum.PNG
Views: 560
Size:  57.5 KB
Because cars dive forward due to inertia most of the braking is done by the front discs anyway which is probably why manufacturers feel that front discs and rear drums offer a nice mix of cost and function except a rainy day
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Old 15th March 2016, 20:47   #73
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Default Re: Automotive misconceptions demystified

Quote:
Originally Posted by boeuff View Post
Because drum brakes have a self energising effect, the liner wedges against the drum in the direction of rotation multiplying the braking force. This however is applicable only to the leading shoe and not the trailing shoe, hence twin leading shoe brakes were designed. Unfortunately a downside to this design is the missing servo effect while braking in reverse.
Regards
True.

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Originally Posted by Jeroen View Post
That is an interesting question. I never gave it much thought before. MB brings up some relevant points, but I think the total equation is a bit more complex.
...
Our previous Ford Focus springs to mind (not sure about the current models). Typical set up for a car braking system is to have it balanced towards more braking force generated by the front wheels.
Fairly easy to work out why the leading shoe has a self servo effect. Even easier to visualise, and experiment with a band brake: extremely strong self servo effect in one direction, almost useless in the other.

Quote:
Originally Posted by Motard_Blr View Post
The drum is hat shaped and combines the drum and disc in one piece.
The fact that for a handbrake, it should be one leading shoe, one trailing shoe should be mentioned.
In fact another member had modified his rear drums to twin leading. I told him to mention that this should not be followed by others. (His was a specialised non street use vehicle.)

Quote:
Originally Posted by Viju View Post
Brake boosters don't work when the engine is shut off, or even when the engine is running at idle speed when the vacuum level in the intake manifold is too low to provide any assist.
In a petrol engine, vacuum is pretty good at idling.
Incidentally was hoping to hear from you Re: CBS + ABS + rear mechanical brakes. Still leaves me scratching my head!

Regards
Sutripta
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Old 15th March 2016, 20:51   #74
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Default Re: Automotive misconceptions demystified

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Originally Posted by Sutripta View Post
Incidentally was hoping to hear from you Re: CBS + ABS + rear mechanical brakes. Still leaves me scratching my head!
I am no expert on the subject. Sorry to disappoint!

Regards
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Old 15th March 2016, 20:54   #75
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Default Re: Automotive misconceptions demystified

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Originally Posted by Viju View Post
I am no expert on the subject. Sorry to disappoint!

Regards
We both know that lots of salt needed to digest this statement!

Regards
Sutripta
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