AdrianH
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| posted on 7/10/09 at 09:02 PM |
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Help please with brake balance on front & rear axles
One of my fail points on IVA was the brake balance between the two axles
Here is the results sheet from the brake test
Image deleted by owner
Now am trying to understand this, but can not really get it.
I was told I need to loose effort from the rear axle. So I am considering reducing the rear brake cylinder bores.
I have 22.22 mm fitted at present, possibly standard Sierra and can go down to either 20.65 or 19.05 mm bores.
If I go down to 19.05 I make it to be a reduction of 27% of braking force on the back axle, would this be too much.
If I dropped it to 20.65 it would be a reduction of 14%.
This assumes my maths is correct based on the area or CSA of the cylinders all else remaining the same.
19.05 CSA is 285 mm^2
20.65 CSA is 333 mm^2
22.22 CSA is 385 mm^2
I would appreciate you comments especially of you know and can explain the results in the sheet above.
Cheers
Adrian
[Edited on 7-10-09 by AdrianH]
Why do I have to make the tools to finish the job? More time then money.
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Mark Allanson
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| posted on 7/10/09 at 09:08 PM |
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Fiat uno bias valve, £10 - job done
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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mookaloid
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| posted on 7/10/09 at 09:12 PM |
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just fit a balance valve in the brake line to the rear.
something like this
"That thing you're thinking - it wont be that."
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Humbug
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| posted on 7/10/09 at 09:20 PM |
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quote:
Originally posted by mookaloid
just fit a balance valve in the brake line to the rear.
something like this
I think for IVA it needs to be non-adjustable... certainly if you have a balance on the brake pedal it has to be locked
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matt_claydon
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| posted on 7/10/09 at 09:22 PM |
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Balance valves are completely banned for IVA, even if locked.
You can use fixed pressure reducers as found screwed into the M/C of some fords. Someone will know which cars had them. Late 90's fiesta
maybe?
I will explain brake distribution calcs for you in the morning if no one else has by then.
[Edited on 7/10/09 by matt_claydon]
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RickRick
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| posted on 7/10/09 at 09:25 PM |
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would the tester be able to see a bias valve hidden errr mounted inside the tunnel?
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AdrianH
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| posted on 7/10/09 at 09:34 PM |
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I could fit a regulator, but not an adjustable one, even if locked up when set as they are not permitted as I was told by the tester for IVA.
Note 4: Hydraulic valves that only operate automatically and react to
vehicle loading or braking forces are permitted (Load Sensing and
Gravity valves) Manually adjusted valves (other than to permit presetting
the automatic function of a valve) are not permitted to be fitted even if
they are rendered un-adjustable.
When speaking with a tech guy from Brakes International, I was told that the regulators only work after a certain pressure is reached and as I seemed
to have failed at low pressures it could potentially still fail.
The regulator was my first thought.
Crap, way to slow in responding!
Adrian
p.s. I also had to remove the top of the trans tunnel for inspection of the seat belt mounts so could be asked to do again if they suspect such!
I would appreciate it Matt, if as you say not answered before.
[Edited on 7-10-09 by AdrianH]
Why do I have to make the tools to finish the job? More time then money.
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mccsp
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| posted on 7/10/09 at 09:45 PM |
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Using a twin master cylinder set-up I have a 0.7" girling front master cylinder and a 0.625" rear master cylinder. Passed no probs once
they were the correct way round.
Read accidenrtally fitted the wrong way round originally and just couldn't lock the fronts before the backs
Why do it the easy way, when I can do things my way!
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AdrianH
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| posted on 7/10/09 at 10:23 PM |
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I have been staring at the sheet and worked out the Brake distribution ratio as just being the total axle2 forces divided by the total axle 1 forces
so for P1:
37+44 = 1.05 etc
43+34
Still trying to discover where the weight distribution comes from as it varies?
mccsp
I would have assumed you would need small cylinder for the front and larger to the rear to put more effort on the fronts callipers.
Unfortunately to far gone down single cylinder route at present.
Adrian
[Edited on 7-10-09 by AdrianH]
Why do I have to make the tools to finish the job? More time then money.
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britishtrident
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| posted on 8/10/09 at 07:18 AM |
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You already know a very simple solution that will work ie smaller rear wheel cylinders.
Part of the problem is that drum brakes have a very different friction characteristic from disc brakes --- drum brakes self-servo to an extent at low
pressures.
You need at least a 12% reduction in pressure to the rear brakes so go for the 19mm (ie 3/4" wheel cylinders.
[Edited on 8/10/09 by britishtrident]
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matt_claydon
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| posted on 8/10/09 at 07:54 AM |
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When a vehicle brakes, weight gets shifted to the front axles, that's why your weight distrubutions change with pedal effort. The calculation is
based on COG height.
These numbers are fixed so there is nothing you can do about it - what you need to do is alter the rear brake efforts so that the ratios becomes less
than the weight ratios for all 5 pedal efforts.
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AdrianH
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| posted on 8/10/09 at 10:24 PM |
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Finally solved the problem using this web page
http://autopedia.com/stuttgart-west/Physics/StuttPhysics01.html
From information on there have managed to do a spreadsheet that gives me a prediction of brake distribution and weight distribution based on the
original results. With no change to the rear cylinders, it all works out as per IVA figures.
So happy'ish that I can now start to understand effects of changes.
Cheers
Adrian
[Edited on 8-10-09 by AdrianH]
Why do I have to make the tools to finish the job? More time then money.
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gdp66
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| posted on 11/2/10 at 11:03 AM |
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any update on a solution.
As I have exactly the same issue with failing IVA test on brake distribution.
If I want 19mm rear slave cylinders where can I get these from, ie what car to I tell the motor factor.
Any help much appreciated
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hughpinder
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| posted on 11/2/10 at 04:05 PM |
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An alternative would be to fit higher friction shoes if you can get them. For instance standard pads have a coefficient of friction about 0.4, EBC
'blackstuff' is about 0.45 and 'greenstuff' about 0.5 (about 10% and 20% more braking force respectively). I dont know whats
available for your particular set up though
Just a thought
Hugh
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MikeRJ
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| posted on 11/2/10 at 05:32 PM |
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quote:
Originally posted by hughpinder
An alternative would be to fit higher friction shoes if you can get them.
Lower friction shoes to reduce braking effort!
I don't think this will be a very reliable solution though, unless the OP knows the coefficient of friction of his current brake shoes which I
suspect is unlikely. Smaller slave cylinders seem like the best solution overall.
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britishtrident
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| posted on 11/2/10 at 08:16 PM |
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quote:
Originally posted by gdp66
any update on a solution.
As I have exactly the same issue with failing IVA test on brake distribution.
If I want 19mm rear slave cylinders where can I get these from, ie what car to I tell the motor factor.
Any help much appreciated
If it is Girling style cylinders Escort Mk3 --- compare the Sierra and Escort 3 cylinders on the brakes international online shop
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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britishtrident
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| posted on 11/2/10 at 08:17 PM |
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quote:
Originally posted by hughpinder
An alternative would be to fit higher friction shoes if you can get them. For instance standard pads have a coefficient of friction about 0.4, EBC
'blackstuff' is about 0.45 and 'greenstuff' about 0.5 (about 10% and 20% more braking force respectively). I dont know whats
available for your particular set up though
Just a thought
Hugh
Only opens a can of worms --- friction coefficients change with temperature.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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RK
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| posted on 12/2/10 at 01:20 PM |
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Silghtly related, not wanting to thread-jack:
My Tilton system doesn't seem to work: the rear piston never moves, no matter what the adjustment. It appears the balance bar thing is stuck
inside the pedal. Can one get rid of it all and have a system that is rigid, as your IVA requires anyways? How would that work?
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