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 Posted: Thu Aug 14th, 2008 04:18 am
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KevG
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Mana: 
Is the answer;

"Name a car thats made today that has drums on the front?"

Kev

 

 

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 Posted: Thu Aug 14th, 2008 04:16 am
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KevG
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Well thats cleared that one up then.

Eject    eject   eject

 

Kev

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 Posted: Thu Aug 14th, 2008 03:26 am
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big..E.
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David wrote: Hi Dudsy

you ask for my answer, so here it is;

OK you asked what my answer is; well before I do answer I think a little explanation of some key facts would be beneficial first.

Before we get into the hydraulics, let’s recap on some circle geometry, we do agree the brake pistons will be round don’t we?

Somebody has previously said that the “area” is not counted but the “diameter” is, so let’s start at this point. You can’t calculate brake force from a diameter, so you need the area of the cylinder in question.

There is a relationship between the diameter and circumference of a circle, which is;

The diameter increases proportionally to the circumference, so if C = kd, then C/d = k, which is the constant of proportionality.  Now we now that C/d = , which is usually remembered as C = d or C = 2r.

Now when the service brake pedal is depressed, the force applied to the brake fluid creates a pressure which is constant throughout, undiminished.

Let’s now say that the brake piston diameter is 50mm, to find the force applied we now need to find the area, so we can use the formula C = d or  ï€†d/4;

Find the circumference C = d

C = 3.142•50 = 157  now if you divide 157/4 = 39.3 to 3sf. Or you can use the following formula;

A = d/4        3.142•50/4 = 39.3mm2  which gives the same answer which is the area of the cylinder. Now to find the pressure acting in the brake caliper, you need to find the area of the master cylinder, so let’s say its 400mm2

You now apply your foot to the service brake, and let’s say 100N force as a guide, to find the pressure acting in the master cylinder, you divide;

100/400 = 0.25 N/mm2 multiply this by 10 gives 2.5Bar of pressure, this pressure is undiminished throughout the hydraulic system, so to find the force at the brake caliper;

0.25•39.3 = 9.83N or 98.3 Bar. Let’s say that this brake is the nearside front.

Now we can do the same for the offside front, but this time we will change the diameter, let’s say 05mm less.

A = d/4 = 3.142•34.3/4 = 26.94 4sf.

0.25•26.94 = 6.73N or 67.3 Bar. So as can be seen the offside front brake efficiency is less when the diameter and the area are less, therefore the brakes would pull to the nearside when applied.

Nearside front working pressure = 98.3 Bar

Offside front working pressure    = 67.3 Bar

Hope this clears up any misunderstanding

David:D

 


So....Pass or Fail?????..............;)   lol lol lol lol lol lol lol lol lol ...And for the people who dont understand;););)... JOKING...

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 Posted: Thu Aug 14th, 2008 03:16 am
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David
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Mana: 
Hi Dudsy

you ask for my answer, so here it is;

OK you asked what my answer is; well before I do answer I think a little explanation of some key facts would be beneficial first.

Before we get into the hydraulics, let’s recap on some circle geometry, we do agree the brake pistons will be round don’t we?

Somebody has previously said that the “area” is not counted but the “diameter” is, so let’s start at this point. You can’t calculate brake force from a diameter, so you need the area of the cylinder in question.

There is a relationship between the diameter and circumference of a circle, which is;

The diameter increases proportionally to the circumference, so if C = kd, then C/d = k, which is the constant of proportionality.  Now we now that C/d = , which is usually remembered as C = d or C = 2r.

Now when the service brake pedal is depressed, the force applied to the brake fluid creates a pressure which is constant throughout, undiminished.

Let’s now say that the brake piston diameter is 50mm, to find the force applied we now need to find the area, so we can use the formula C = d or  ï€†d/4;

Find the circumference C = d

C = 3.142•50 = 157  now if you divide 157/4 = 39.3 to 3sf. Or you can use the following formula;

A = d/4        3.142•50/4 = 39.3mm2  which gives the same answer which is the area of the cylinder. Now to find the pressure acting in the brake caliper, you need to find the area of the master cylinder, so let’s say its 400mm2

You now apply your foot to the service brake, and let’s say 100N force as a guide, to find the pressure acting in the master cylinder, you divide;

100/400 = 0.25 N/mm2 multiply this by 10 gives 2.5Bar of pressure, this pressure is undiminished throughout the hydraulic system, so to find the force at the brake caliper;

0.25•39.3 = 9.83N or 98.3 Bar. Let’s say that this brake is the nearside front.

Now we can do the same for the offside front, but this time we will change the diameter, let’s say 05mm less.

A = d/4 = 3.142•34.3/4 = 26.94 4sf.

0.25•26.94 = 6.73N or 67.3 Bar. So as can be seen the offside front brake efficiency is less when the diameter and the area are less, therefore the brakes would pull to the nearside when applied.

Nearside front working pressure = 98.3 Bar

Offside front working pressure    = 67.3 Bar

Hope this clears up any misunderstanding

David:D

 

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 Posted: Thu Aug 14th, 2008 12:36 am
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big..E.
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Mana: 
Hi Kev,

Over the years my previous employer put lots of "mechanics" on the NTTA question paper,in Eight years two of us passed and went on to become Testers..Both of us have done 6+ years now and both hold a clean licence,never even an appeal..;) We both had spanner experience from leaving school,but nothing on paper..

The NTTA way is as good as any...Like i said if Vosa approve it must be good??...

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 Posted: Wed Aug 13th, 2008 10:03 pm
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KevG
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Hi Big E

 

Thats how I did it Too via the NTTA exam.
 
Best way if you ask me, everyone should sit it.

It would keep those out that can Talk about it but can't do it.

Kev


 

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 Posted: Wed Aug 13th, 2008 04:13 am
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big..E.
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DAVID,DAVID big..E.  CALLIN DAVID....The pressure "I" related to was a "MANAGERIAL" one..   IE ... "Sorry Mr PLONKER,but your Forvolksrenault tingywatsit has failed its MOT due to a fault on the POWERSTEERING SYSTEM"...."OOOHHH S**TE THE BED,WE'RE GOING ON OUR JOLLIES TOMORROW...I NEED IT FIXIN NOW!!!!!!"shouted Mr PLONKER........(shouting very loudly actually)

Now as a  "Manager/Tester" (like me)....Its Friday Afternoon,Ican't source a part..SO THE PRESSURE IS REALLY F8CKIN ON...

Get of your high horse...DAVID...I have had enough  awkward customers on the other side of the counter..talkin to ME like im a piece of s**t..I dont need YOU to tell me I need training when YOU cannot read a POSTING in the manner it was MEANT....;););););););)  DO YOU NOT KNOW WHAT A;)MEANS.....?????ffs......


And just to get right up your skirt....I "Got in" via the NTTA exam...Maybe YOU don't like it 0000hhhh But VOSA   DID....:P  

Last edited on Wed Aug 13th, 2008 05:06 am by big..E.

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 Posted: Wed Aug 13th, 2008 03:49 am
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Wesley
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Dubsy wrote: David wrote: Hi Big E

 Whether you like it or not, :Pin the very near distance future the motor trade will be licensed, ;)and if any individual is not up to it, your out:(. Trading Standards are pushing hard for this license system to take effect, :Ptraining is the only option to stay in the game.:D

and with the greatest respect, at this moment in time on this particular thread, everybody sounds like they ALL need training.:D

It is bewildering to me to think that based on this post, none of you would be able to diagnose the true cause of brake imbalance to any accurate degree?

No wonder there are some many unecessary new parts fitted to customers

David:D

 



Everybody/all need training :shock: ????????

Considering in this post we have both answers of two possible answers then some of the replies must be right therefore only some of the people need training, no?

By the way what was your answer? :)

same as mine, never made an actual one.:D

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 Posted: Wed Aug 13th, 2008 03:46 am
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Dubsy
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David wrote: Hi Big E

 Whether you like it or not, :Pin the very near distance future the motor trade will be licensed, ;)and if any individual is not up to it, your out:(. Trading Standards are pushing hard for this license system to take effect, :Ptraining is the only option to stay in the game.:D

and with the greatest respect, at this moment in time on this particular thread, everybody sounds like they ALL need training.:D

It is bewildering to me to think that based on this post, none of you would be able to diagnose the true cause of brake imbalance to any accurate degree?

No wonder there are some many unecessary new parts fitted to customers

David:D

 



Everybody/all need training :shock: ????????

Considering in this post we have both answers of two possible answers then some of the replies must be right therefore only some of the people need training, no?

By the way what was your answer? :)

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 Posted: Wed Aug 13th, 2008 03:40 am
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Wesley
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David wrote: Hi Big E

 Whether you like it or not, :Pin the very near distance future the motor trade will be licensed, ;)and if any individual is not up to it, your out:(. Trading Standards are pushing hard for this license system to take effect, :Ptraining is the only option to stay in the game.

It is bewildering to me to think that based on this post, none of you would be able to diagnose the true cause of brake imbalance to any accurate degree?

No wonder there are some many unecessary new parts fitted to customers

David:D

 



David,

Not even Weetabix?:? or Tim?:?

Wes:D

 

Last edited on Wed Aug 13th, 2008 04:05 am by Wesley

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 Posted: Wed Aug 13th, 2008 01:09 am
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KevG
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David wrote: Hi Big E

Whether you like it or not, :Pin the very near distance future the motor trade will be licensed, ;)and if any individual is not up to it, your out:(. Trading Standards are pushing hard for this license system to take effect, :Ptraining is the only option to stay in the game.:D

and with the greatest respect, at this moment in time on this particular thread, everybody sounds like they ALL need training.:D

It is bewildering to me to think that based on this post, none of you would be able to diagnose the true cause of brake imbalance to any accurate degree?

No wonder there are some many unecessary new parts fitted to customers vehicles,

 

David:D

 



 

MOT testers should not diagnose faults.

If you are a tester you should know that.

That why we dont have "Bad earth" for example, as an RFR.

We have instead "The operation of one light affects another" or similar.

Most garages have experts in different areas, so do not chastise someone who does not know the answer to a question, that is NOT what this forum is for. If you want to do that may I suggest you join a Hydraulics Forum ? For all we know the author is the leading light in the field of Canbus diagnostics and not remotely interested in brakes.

Please think before posting, and continue to enjoy the forum.

 

 



Kev


Last edited on Wed Aug 13th, 2008 01:22 am by KevG

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 Posted: Tue Aug 12th, 2008 11:34 pm
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David
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Hi Big E

 Whether you like it or not, :Pin the very near distance future the motor trade will be licensed, ;)and if any individual is not up to it, your out:(. Trading Standards are pushing hard for this license system to take effect, :Ptraining is the only option to stay in the game.:D

and with the greatest respect, at this moment in time on this particular thread, everybody sounds like they ALL need training.:D

It is bewildering to me to think that based on this post, none of you would be able to diagnose the true cause of brake imbalance to any accurate degree?

No wonder there are some many unecessary new parts fitted to customers

David:D

 

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 Posted: Tue Aug 12th, 2008 10:39 pm
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KevG
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Rebel is right. You should get a score for each section of the NTT.

 

kev

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 Posted: Tue Aug 12th, 2008 06:07 am
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Rebel
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Percentage is given for each section, as wall as overall.

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 Posted: Tue Aug 12th, 2008 05:01 am
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Wesley
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kev1975 wrote: Rebel wrote: Sorry but I have to agree with Dubsy.

The volume of the cylinder makes no difference, It's the cross sectional diameter of the piston which determines the force.

A larger diameter piston will cause greater pedal travel but more force at the piston.

Hence the brakes should pull to the right.

that was my answer when i did my ntt & scored full marks in the brakes section , so it must be right :D


How do You Know in what section You scored? When only an Overall percentage is Given?

Try the "Funnel"! Experiment. lol.

Wes.

Last edited on Tue Aug 12th, 2008 05:14 am by Wesley

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 Posted: Tue Aug 12th, 2008 04:41 am
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Wesley
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KevG wrote: The Volume of the Cylinder is not relavant.

 

Kev

Hi Kev, same as Rebel.;)

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 Posted: Tue Aug 12th, 2008 04:40 am
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Wesley
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Rebel wrote: Sorry but I have to agree with Dubsy.

The volume of the cylinder makes no difference, It's the cross sectional diameter of the piston which determines the force.

A larger diameter piston will cause greater pedal travel but more force at the piston.

Hence the brakes should pull to the right.

Rebel, Lets Have an experiment with a "Funnel"?;)

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 Posted: Tue Aug 12th, 2008 04:36 am
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big..E.
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Wesley wrote: David wrote: Sounds to me like you all need to go on a training course in physics

David:D

David I agree. Guys,

On Another note, Does a pump such as a Power Steering pump Provide Pressure?

Wes.;)
Only on Friday afternoon when the customer "Needs it"..But "you don't want it"..;)

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 Posted: Tue Aug 12th, 2008 03:56 am
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Wesley
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David wrote: Sounds to me like you all need to go on a training course in physics

David:D

David I agree. Guys,

On Another note, Does a pump such as a Power Steering pump Provide Pressure?

Wes.;)

Last edited on Tue Aug 12th, 2008 04:09 am by Wesley

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 Posted: Tue Aug 12th, 2008 03:49 am
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KevG
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The Volume of the Cylinder is not relavant.

 

Kev

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