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Old 16th November 2007, 11:49   #1
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Question Stuff regarding new vehicle

I just have a few technical doubts that I had in my mind for a long time.
1. When you buy a new vehicle, why does the manual ask not to apply sudden brakes for the first 300 km?
2. What advantage do you get when you drive in variable speeds for the first 2000 km?
3. When you have stopped your vehicle and you hold the brakes pressed and you switch off and switch on the A/C. You can feel a slight difference on the pedal. What is the exact reason behind this? Same happens when you turn the power steering
4. When you turn the power steering to the extreme corner, you see that there is a small humming noise coming up and the RPM goes up. What is the exact reason for this?
Hope my questions are relevant. Just curious to know all these stuff. Thats it
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Old 16th November 2007, 12:33   #2
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1. Part of the normal running in, of both the brakes and the tires. Drive gently!

2. It allows the engine parts to wear and run in better than constant speed. City driving gives us no choice.

3. AC is drawing power from the engine. So is brake servo assist, so is the power steering pump. At idling speed this sharing may be more noticable.

4. the power-steering mechanism is running, but you are at full lock, so it has to slip.
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Old 16th November 2007, 14:05   #3
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Quote:
Originally Posted by Thad E Ginathom View Post

4. the power-steering mechanism is running, but you are at full lock, so it has to slip.
And that is very bad. Never keep it locked. You'll land up spending some money in repairs. ANd if at all you own a FIAT you'll end up spending extra on auto/taxi/bus charge for the next few weeks!!!!
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Old 16th November 2007, 14:15   #4
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Originally Posted by Thad E Ginathom View Post
4. the power-steering mechanism is running, but you are at full lock, so it has to slip.
Could someone please explain it more. When does it get locked? How does it adversely affect the mechanism? Is it advisable to not to keep it locked only during the run-in period or it should be a general practice?

Regards,
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Old 16th November 2007, 14:20   #5
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When you turn your wheels to the extreme left or right, it gets locked at that position until you turn it the other way.
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Old 16th November 2007, 14:23   #6
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This rule should be followed throughout the life of the vehicle. Never hold the steering wheel at full turn (extreme). It puts high strain on the power steering mechanism.

There is a technical reason but in laymans language, it can be compared to extra load on engine if you drive with handbrake on.
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Old 16th November 2007, 14:44   #7
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It doesn't get 'locked' --- it is, I think a confusion of words in this crazy English language where 'lock' is the thing that keeps people out of your house, and it is also the movement of the steering wheel from one extreme to the other. It's also a small amount of hair cut from the head, but lets not worry about that

Think of non-powered steering; you turn the wheel as far as it can go and ... that's it, it can't move any further, you can only turn it back again.

With power-assisted steering, when you turn the wheel from straight either an electric motor or hydraulic pump starts up, and it's energy is used to move the wheels. When you reach full 'lock', the motor does not stop, but it can not move the wheels further, so it must loose its energy in slippage.

This is the sound you hear.

I'm not certain that it happens with both the electric and the hydraulic systems (I don't even know which my car has!), and I'm probably mixing my mechanical and hydraulic terms badly: I'm no mechanic, but I hope I've given an idea of what's happening.

We may use full lock for a short time, eg doing a sharp U-turn.

One other point: power steering makes it easy to turn the wheels (even with one finger) even with the car stationary. But the same advice applies, that this causes tire wear and is not a good thing.

So, if you are new to power steering, try not to spend too much time being amazed that this is possible!

Last edited by Thad E Ginathom : 16th November 2007 at 14:46. Reason: StationAry... not stationEry!!!
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Old 16th November 2007, 15:24   #8
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@ Thad Thanks for the nice explanation.

I have another one:

Recently while going up an incline from a stationary position i pressed the gas pedal a little more than required, after parking the car i felt there was some kind of burning smell coming from the car (Dont know the exact place where it was coming from) what could be the reason??

Do you recon i should get the car checked at the service station?
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Old 16th November 2007, 15:35   #9
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but isnt the motor assist be in action when the wheel is half turned..and hence the slippage...or is it that "power steering" comes into play only after we have turned the steering wheel more than x degree?
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Old 16th November 2007, 17:14   #10
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Quote:
Originally Posted by amohit View Post
but isnt the motor assist be in action when the wheel is half turned..and hence the slippage...or is it that "power steering" comes into play only after we have turned the steering wheel more than x degree?
In Hydraulic Power Steering (HPS) the assist is available all the way from steering pointing straight to left or right lock. Holding the steering wheel at full lock for long puts unnecessary pressure on the steering rack which might result in blown seals.

In case of EPS the assist is always there, from center to lock, but it would be much easier to detect that the steering is at lock and hence the motor can be switched off.
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Old 16th November 2007, 23:57   #11
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Quote:
Originally Posted by sqwall View Post
@ Thad Thanks for the nice explanation.

I have another one:

Recently while going up an incline from a stationary position i pressed the gas pedal a little more than required, after parking the car i felt there was some kind of burning smell coming from the car (Dont know the exact place where it was coming from) what could be the reason??

Do you recon i should get the car checked at the service station?
Do i smell wheelspin? Were you on a sandy or loose surface?
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Old 17th November 2007, 00:09   #12
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Quote:
Originally Posted by rohan_fonseca View Post
Do i smell wheelspin? Were you on a sandy or loose surface?
Not really , the ground was firm.
Any idea what caused it?
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Old 18th November 2007, 03:22   #13
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Quote:
Originally Posted by joseph5600 View Post
1. When you buy a new vehicle, why does the manual ask not to apply sudden brakes for the first 300 km?
You have probably heard of "brake fade" > where the brakes heat up and it lowers their co-efficirnt of friction, making them fairly useless.

Well, the reason you are told not to brake hard for the first Xkm is for two reasons.
1. So that parts of the braking system (specifically pad + piston mating surface?) have a chance to get to know each other slowly.
2. To prevent GREEN brake fade.

Green fade happens only on new pads.
When brake pads are made, certain resins are used. When these resins are exposed to extreme temperatures right away (i dont know the exact specifics), they release gasses etc which once again affects the braking surface of the pad, causing brake fade.

Quote:
3. When you have stopped your vehicle and you hold the brakes pressed and you switch off and switch on the A/C. You can feel a slight difference on the pedal. What is the exact reason behind this? Same happens when you turn the power steering
The brake booster (assisted braking / "power brake") is run off the vaccum created by the engine. Turning on the A/C or utilizing power steering puts load on the engine, and hence the relation.
Howstuffworks "How Power Brakes Work"

Quote:
4. When you turn the power steering to the extreme corner, you see that there is a small humming noise coming up and the RPM goes up. What is the exact reason for this?
For hydraulic systems, think of it this way :
You turn the steering wheel, which is connected to the steering rack (that physically turns the wheels). This is how it works on a non-PS car, or when the engine is off.
Now, for the hydraulic assistance, the torque that is being applied clockwise / counterclockwise to turn the steering wheel is also activating a valve that lets hydraulic fluid push the rack right / left.

So simply put, if the rack as as far left as it can physically go (full lock) and you are still turning the wheel counter clockwise, its keeping that valve open, which in turn is allowing hydraulic fluid to try and push the rack some more. Obviously this is not good (seals, extra load on PS pump etc).

EDIT : Link > Howstuffworks "How Car Steering Works"

Quote:
Originally Posted by sqwall View Post
Not really , the ground was firm.
Any idea what caused it?
Were you slipping the clutch ?

cya
R

Last edited by Rehaan : 18th November 2007 at 03:23.
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Old 19th November 2007, 12:10   #14
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Quote:
Originally Posted by Rehaan View Post

Were you slipping the clutch ?

cya
R
I guess so.
I seem to have a problem with my timing while releasing the clutch on an incline.I guess this was the cause but would love an explanation from you.

Just to be on the safer side I took the car to the service station and got it checked , all was fine it seems.

Cheers
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Old 19th November 2007, 13:02   #15
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Turning left onto the ECR in heavy traffic; there is quite a steep incline where out side-street meets the main road.

The traffic was heavy, and a cow and calf were taking the left turn in front of me, not to mention the usual two-wheelers buzzing about and the pedestrians getting in the way.

Sometimes, slipping that clutch is inevitable.... can't be helped...
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