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big..E.
Trade Member
| Joined: | Wed Jan 30th, 2008 |
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Posted: Thu Dec 18th, 2008 09:56 pm |
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sam87 wrote: hi am gona sit in ntt exam, can u plz advise me wat book to study?
What you shouting for Sam???....Calm down a little,when you are in the correct frame of mind read Hilliers,Fundamentals of the motor vehicle...available from wh smiths..and online...Also learn to spel cuz ya neid 2 let ya kustomazzzz no wat ur on abaaaaaattt!!!! LOL.... E..
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sam87
Member
| Joined: | Thu Dec 18th, 2008 |
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Posted: Thu Dec 18th, 2008 09:17 pm |
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| hi mate am gona sit in ntt exam, can u plz advise me wat book to study?
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David
Banned
| Joined: | Mon May 26th, 2008 |
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Posted: Fri Nov 14th, 2008 06:00 pm |
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Weetabix wrote: But why ?
If the performance test on the RBT was satisfactory and the decelerometer test showed a braking braking efficiency that was deemed a pass, then is an Advisory Notice (VT32) really necessary ?
Hi Weekabix,
Not sure if your post here is in relation to what I have said, if it is, then the reason why a VT32 is issued is because the brake efficiency test performed on the rolling road would not be considered to have been met, unless more than half the wheels locked out, therefore without a brake test weight a tester cannot know if the minimum criteria had been met, therefore a decelerometer test shows the efficiency result, a VT32 explains the reason for your actions.
David
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craig79
Member
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Posted: Fri Nov 14th, 2008 01:53 am |
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my name is craig can u help me been for exam in september ntta can u contact me
please can u help 07826242861
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craig79
Member
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Posted: Fri Nov 14th, 2008 01:48 am |
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hi kev its my name is craig been for exam in september please can u help me email
craigsmith250@hotmail.com contact phone number 07826242861
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Weetabix
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Posted: Tue Oct 14th, 2008 10:59 pm |
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But why ?
If the performance test on the RBT was satisfactory and the decelerometer test showed a braking braking efficiency that was deemed a pass, then is an Advisory Notice (VT32) really necessary ?
Last edited on Tue Oct 14th, 2008 11:00 pm by
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David
Banned
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Posted: Mon Oct 13th, 2008 06:56 pm |
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RFR wrote: RFR wrote: RFR wrote: David wrote: Hi Kev
No Brake test data is not a refusal you do a decelerometer test and issue VT32
David
Hi David,
just a quicky , why do a decelerometer test and what would I say on the vt32 if I did?
rfr
Hi David,
good to have you back,could you get back to me on the above.
rfr
Hi David,
it was about what you posted to Kev, with reference to no brake weight data and what to do, as above. my question was why do a decel, and what would I advise? with reference to your comment.
rfr
Hi RFR,
If a vehicle tested on the rollers does not produce more than 50% wheel lock out, then a calculation using the BTW would be required. When no such test weight is available the right course of action is to perform a decelerometer efficiency test. When producing the VT32, a record should be provided saying that no brake test weight was available and a decelerometer test has been performed. When entering brake test data on computerisation, I would use the combination facility for entering the results, therefore a record of brake results for each wheel is recorded on the VT40,and a combined set of readings via computerisation.
Thanks
David
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RFR
Member
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Posted: Sun Oct 12th, 2008 11:48 pm |
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Hi Weetabix,
thats my question really, as per manual I would put through rbt, if more than half locking thats it. If not decel. I do not issue vt32 either????
rfr
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Weetabix
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Posted: Sun Oct 12th, 2008 10:54 pm |
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I've never issued a VT32 specifically for vehicles that I have not had a brake weight.
As per inspection manual, a performance test is done on the RBT, then, if necessary, an efficiency test is done using the decelerometer.
Is there something I have missed with regards to the VT32 ?
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RFR
Member
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Posted: Sun Oct 12th, 2008 02:43 pm |
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RFR wrote: RFR wrote: David wrote: Hi Kev
No Brake test data is not a refusal you do a decelerometer test and issue VT32
David
Hi David,
just a quicky, why do a decelerometer test and what would I say on the vt32 if I did?
rfr
Hi David,
good to have you back,could you get back to me on the above.
rfr
Hi David,
it was about what you posted to Kev, with reference to no brake weight data and what to do, as above. my question was why do a decel, and what would I advise? with reference to your comment.
rfr
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David
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Posted: Sat Oct 11th, 2008 09:58 pm |
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RFR wrote: Hi David,
now we've got that nailed , how we looking on the brake data and vt32 issue as previous post.
rfr
Hi RFR
please refresh my memory as to what we were discussing with regards your post.
thanks
David
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RFR
Member
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Posted: Sat Oct 11th, 2008 09:10 pm |
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Hi David,
now we've got that nailed, how we looking on the brake data and vt32 issue as previous post.
rfr
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David
Banned
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Posted: Sat Oct 11th, 2008 08:32 pm |
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knowlep wrote: Final Extract from Davids formula says :-
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
Therefore if the off side diameter is 0.5mm LESS that's-- LESS-- or SMALLER and the final applied pressure is LESS or 67.3Bar compared to 98.3 on the nearside (which has a LARGER piston) car will pull towards the greater force or GREATER DIAMETER PISTON.
No insults from me BTW - too professional.
That`will`do ok, fundamentals also ok, lots of different ways to explain fundamental workings of systems, pressure,forces, kinetic energy, sometimes can get a bit confusing, but in essence, small diameter master cylinder piston + large caliper piston = greater energy force at the brake. When different size pistons/calipers fitted across axle then larger diameter will give greater force.
David
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RFR
Member
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Posted: Sat Oct 11th, 2008 06:18 pm |
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Hi David,
please do not forget my previous post, taa.
While you have blinded me with science, I have been sat here thinking that all this is being based on reaction times etc and it did not make sense in reality. I did start a post to totally disagree with all the statements that fall in favour of going for the smaller diameter. Then I found my old Hillier book, fundementals of motor vehicle technology 3rd edition from which we are told all the questions are based.
Quote "The layout of the system ( 4 wheels / shoes) shows the foot brake acting on a master cylinder, which supplies fluid to the various wheel cylinders. The system is fully compensated: no one brake can apply until all clearances have been taken up. Depression of the pedal displaces fluid to move each shoe to the drum, and at this point the pedal feels solid. Extra pedal thrust will now cause the fliud in the system to be pressurized, and so the force felt at each shoe will be govened by piston area; the larger the piston area the greater the thrust".
From this the vehicle will pull to the larger diameter, because until all clearances are taken up, which gets rid of the reaction theory nothing is going to happen. If the above is wrong, then in reality everthing I or any Tech has been taught at college is wrong and we need our money back.
Hope this puts an end to it "not"
rfr
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RFR
Member
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Posted: Sat Oct 11th, 2008 05:44 pm |
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RFR wrote: David wrote: Hi Kev
No Brake test data is not a refusal you do a decelerometer test and issue VT32
David
Hi David,
just a quicky, why do a decelerometer test and what would I say on the vt32 if I did?
rfr
Hi David,
good to have you back,could you get back to me on the above.
rfr
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knowlep
Member
| Joined: | Sun May 25th, 2008 |
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Posted: Sat Oct 11th, 2008 04:10 pm |
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David wrote: I don't wish to continue the debate with the`brakes for too long guys, but there is`still some misunderstanding of hydraulics which is a very compl perex subject when you get into it. However, eneregy transfer must also be considered as well as fluid pressure, this is `why some brake pipes are a larger diameter than others, take a look at ABS modulators, compare the pipes you will see what I mean.
If you look at Air braking systems you will notice the pipes have a larger diameter,they operate at a much lower pressure than hydraulics, but are considered much safer because of that fact.
Back to our hydraulics, larger diameters produce lower pressure, fluid in a braking system ideally should not move,its the energy transfer we want to work the brakes, not fluid movement.
When two brake calipers or cylinders across an axle have a different diameter to each other, then fluid ideally does not move, the pressure created generates energy to do work, the smaller diameter will do work faster because there is less area to do work in, the larger area will generate less energy per unit time so the reaction will be slower,hence smaller diameter smaller area increased working pressure,faster reaction.
Sorry for delay in response, my computer failed, have had to borrow one until new one arrives.
David
HMMMMMMMMM!!!! Interesting and I fully agree.
So------what do you reckon the ACTUAL answer is to the "EXAM" question now.
BTW thats why I like air brakes - the compressor will always make more air if required. Not so in hydraulic systems.
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David
Banned
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Posted: Sat Oct 11th, 2008 03:42 pm |
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I don't wish to continue the debate with the`brakes for too long guys, but there is`still some misunderstanding of hydraulics which is a very compl perex subject when you get into it. However, eneregy transfer must also be considered as well as fluid pressure, this is `why some brake pipes are a larger diameter than others, take a look at ABS modulators, compare the pipes you will see what I mean.
If you look at Air braking systems you will notice the pipes have a larger diameter,they operate at a much lower pressure than hydraulics, but are considered much safer because of that fact.
Back to our hydraulics, larger diameters produce lower pressure, fluid in a braking system ideally should not move,its the energy transfer we want to work the brakes, not fluid movement.
When two brake calipers or cylinders across an axle have a different diameter to each other, then fluid ideally does not move, the pressure created generates energy to do work, the smaller diameter will do work faster because there is less area to do work in, the larger area will generate less energy per unit time so the reaction will be slower,hence smaller diameter smaller area increased working pressure,faster reaction.
Sorry for delay in response, my computer failed, have had to borrow one until new one arrives.
David
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big..E.
Trade Member
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Posted: Wed Oct 8th, 2008 09:36 pm |
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| . Last edited on Wed Oct 8th, 2008 09:37 pm by big..E.
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kev1975
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Posted: Wed Oct 8th, 2008 08:47 pm |
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mjk wrote: The answer, as I see it, is the same reason why Transits have bigger wheel cylinders than Ka's. Martin
couldn't have put it better myself , you should have posted this about 4 pages ago 
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mjk
Trade Member
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Posted: Wed Oct 8th, 2008 08:36 pm |
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| The answer, as I see it, is the same reason why Transits have bigger wheel cylinders than Ka's. Martin
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