RazMan
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| posted on 21/1/07 at 10:00 AM |
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Scary Brakes - wrong pads?
Following on from another thread I am trying to get my brakes working better and it has occurred to me that my pads might be wrong for the car.
My setup is:
Front: 4 pot Wilwood Midilites with 260mm ventilated discs. Greenstuff Pads
Rear: Std Sierra 2 pots with solid discs. Greenstuff Pads.
The pedal is really firm but I need to exert LOADS of pedal pressure to make the car stop - I can't seem to lock anything up no matter what I
do!
Are the Greenstuff pads the source of the problem? What other pads would be suitable for a 800Kg car?
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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Wadders
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| posted on 21/1/07 at 10:11 AM |
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Do the brakes improve when they're warm? greenstuff pads take a bit of warming up.
what m/c's are you using?
Also how many miles have you done, new brakes take some time to bed in properly, and i'm only guessing but a lighter car might take longer to do
this. IIRC mine got better after a few miles (also use wilwoods and greenstuff)
Al.
Originally posted by RazMan
Following on from another thread I am trying to get my brakes working better and it has occurred to me that my pads might be wrong for the car.
My setup is:
Front: 4 pot Wilwood Midilites with 260mm ventilated discs. Greenstuff Pads
Rear: Std Sierra 2 pots with solid discs. Greenstuff Pads.
The pedal is really firm but I need to exert LOADS of pedal pressure to make the car stop - I can't seem to lock anything up no matter what I
do!
Are the Greenstuff pads the source of the problem? What other pads would be suitable for a 800Kg car?
[Edited on 21/1/07 by Wadders]
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Doug68
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| posted on 21/1/07 at 10:27 AM |
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Sounds to me like you've not got enough leverage on the master cylinders, or perhaps too large a diameter cylinder.
How much pedal travel would it take to use the full master cylinder travel?
I have no idea what the correct ratio would be though as I've not go to that stage yet.
Can anyone inform on this?
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RazMan
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| posted on 21/1/07 at 11:00 AM |
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The brakes do improve a little when they are warm but this is no good for normal road use (for me anyway) as they soon cool off and after a few miles
of dual carriageway they are cold again. Maybe a softer compound would be the answer? I suppose the standard Sierra pads would be a good starting
point.
I've done about 100 miles of shakedown tests so far and still no sign of much improvement - the swept area on the discs are now clean and the
surface rust has gone so I think they are bedded in now.
Not sure what m/c bores I have but they were supplied by Aeon (same as the pedals) so I have to assume they are suited to the car. The lever feels
about right for the m/c movement - just rock hard.
Is there a softer compund than Greenstuff?
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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Johnmor
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| posted on 21/1/07 at 11:01 AM |
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Master cylinder volume
I was thinking along similar lines to Doug.
If volume in the calipers is to large the ration of movement in the master cylinder is too small their may be problem.
I know its not really a help but i could lock my front wheels with new pads, but the pedal is probably using 75% of its availiable travel.
How far can you depress the pedal?
If its stiff from the very start then the ratio is too much and you wont provide enough force.
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Wadders
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| posted on 21/1/07 at 11:03 AM |
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have heard good things about mintex pads, but can't remember the number, sure someone will tho.
I know its obvious but are the M/cyls piped the right way round (smaller front, larger rear) ?
Originally posted by RazMan
The brakes do improve a little when they are warm but this is no good for normal road use (for me anyway) as they soon cool off and after a few miles
of dual carriageway they are cold again. Maybe a softer compound would be the answer? I suppose the standard Sierra pads would be a good starting
point.
I've done about 100 miles of shakedown tests so far and still no sign of much improvement - the swept area on the discs are now clean and the
surface rust has gone so I think they are bedded in now.
Not sure what m/c bores I have but they were supplied by Aeon (same as the pedals) so I have to assume they are suited to the car. The lever feels
about right for the m/c movement - just rock hard.
Is there a softer compund than Greenstuff?
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britishtrident
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| posted on 21/1/07 at 11:23 AM |
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All to do with pedal leverage and master cylinder bore --- Note nothing to do with the volumes of mastercylinder or calipers.
To reduce the pedal effort you will need either to reduce the bore of the master cylinder or increase the pedal leverage.
First step is to obtain the bore of the mastercylinder(s) and measure the pedal leverage ratio.
[Edited on 21/1/07 by britishtrident]
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TimC
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| posted on 21/1/07 at 11:31 AM |
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I'd agree, you're barking up the wrong bush with the pads. Greenstuff are about as mild and user friendly as 'performance'
pads get. I've used them in flyweight Peugeot Gtis, MX-5 etc. Mate also ran them on an Elise which weighed about the same as your machine.
Must be somthing else i.e M cyl or leverage.
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Johnmor
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| posted on 21/1/07 at 11:39 AM |
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quote:
All to do with pedal leverage and master cylinder bore --- Note nothing to do with the volumes of mastercylinder or calipers.
I may of misread but if you "reduce the bore of the master cylinder, you reduce the volume of fluid within and therefore the volume of
fluid moved in relation to pedal travel
Just being pedantic, 
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britishtrident
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| posted on 21/1/07 at 11:45 AM |
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quote:
Originally posted by Johnmor
quote:
All to do with pedal leverage and master cylinder bore --- Note nothing to do with the volumes of mastercylinder or calipers.
I may of misread but if you "reduce the bore of the master cylinder, you reduce the volume of fluid within and therefore the volume of
fluid moved in relation to pedal travel
Just being pedantic,
Forget volume it just dosen't come into it --- this is just very basic (static) hydraulics all to do with the ratio of piston cross
section areas.
[Edited on 21/1/07 by britishtrident]
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britishtrident
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| posted on 21/1/07 at 11:55 AM |
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To save a lot of explanation
http://auto.howstuffworks.com/brake.htm
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chockymonster
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| posted on 21/1/07 at 12:20 PM |
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personally I find greenstuff pads 'kin scary. I've never had a good experience with them. Try some mintex 1144s
PLEASE NOTE - Responses on Forum Threads may contain Sarcasm and may not be suitable for the hard of Thinking.
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C10CoryM
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| posted on 21/1/07 at 05:14 PM |
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If the pedal is hard and has very little pedal travel before it gets hard, your m/c bore is probably too large. Larger the m/c bore, the faster the
brakes apply but the more pedal effort it takes. Figure out what size your m/c is, and what size your calipers are and someone should be able to help
you figure out your options. Pedal leverage may also play into it as well as has been mentioned so let us know what pedal, or measure it. If it were
the pads you should still be able to feel some spongyness of the hoses/seals flexing. Sounds like you do not have enough mechanical, or hydraulic
leverage.
Bore and volume are directly related but volume affects how fast things operate, not how hard. In this case, how high/low the pedal is.
Cheers.
"Our watchword evermore shall be: The Maple Leaf Forever!"
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procomp
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| posted on 21/1/07 at 05:21 PM |
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Hi it is a bit hard to compare pad type with so many differences between the various cars and pedal/mc setups as some are using original sierra/escort
m/c and some are using twin m/c bias setup.
Green stuff - ferodo DS2500 - mintex 1144 are all perfectly useable but different people will always prefer one to an other . And they do have
slightly differing caracteristics butt all work really well with well setup braking systems/pedal boxes wich is ussually where the problems are to be
found.
cheers matt
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JB
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| posted on 21/1/07 at 05:48 PM |
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Brake Part Sizes
I did pages of calculations to arrive at my MC sizes using Fred Puhns Brake Handbook, you can borrow it from any libarary.
The basic variables are:
Brake disc diameter.
Total bore area of the calipers.
Bore area of the master cylinder.
Leverage ratio of the brake pedal.
If you want to start speccing sizes for front and rear, you need tyre coeffiecent of friction and C of G. The coeffiecient of friction gets
interesting when you calculate for wet and dry conditions, which alters weight transfer so the balance required..............
When I calculated my front system, total travel on the master cylinder would move each "pot" of the front calipers 0.008" !! I
actually spoke to AP to check this and they said thats fine. Also in use my brakes are very good.
It is a compromise between a solid pedal with little movement and being able to shift enough fluid and being able to press hard enough against lower
pedal effort with more movement.
A solid pedal is important as it is easier to modulate pressure than movement and its easier to toe and heel.
In your case I would guess you have a MC bore / caliper bore mismatch. Also bear in mind that if you are used to modern servo brakes then your un
servoed brakes may just need pushing harder, however you should be able to lock everything up at 70mph.
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RazMan
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| posted on 22/1/07 at 10:49 AM |
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Thanks for all the input guys 
Ok, after a little bit of investigation I have discovered the following:
M/C bore = 3/4" (19mm)
Caliper piston size = 35mm x 4
Disc size = 260mm
As I see it there are three ways to improve braking for the same pedal pressure (ignoring the leverage ratio for now)
1. Decrease M/C bore to 5/8" (15.9mm)
2. Change calipers to larger piston size (44mm x 4)
3. Fit bigger discs and move existing calipers outwards from axle
Any preferences?
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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Fred W B
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| posted on 22/1/07 at 11:13 AM |
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Hay Raz - Have sent you mail with Mike polan's (from here) brake spread sheet .
Cheers
Fred W B
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britishtrident
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| posted on 22/1/07 at 11:13 AM |
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Is the mastercylinder setup a single dual tandem cylinder (as on most modern road cars) or twin cylindrs with a balance bar ?
With a balance bar setup it is normal to use 0.7" or 0.625" cylinders, 0.75 cylinders are too big.
With a single master cylinder 0.75" is the norm for production cars with discs brakes but no servo, however master cylindrs down to 0.7"
were used on some Triumph models.
[Edited on 22/1/07 by britishtrident]
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ned
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| posted on 22/1/07 at 11:21 AM |
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Stupid question, have you asked Aeon?
There are other cars on the road and track no doubt and I'm assuming you're using standard/aeon spec'd parts?
Ned.
beware, I've got yellow skin
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RazMan
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| posted on 22/1/07 at 11:37 AM |
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Fred - Many thanks for the spreadsheet I have done some 'quick & dirty' calculations using it and it looks as though my M/C needs
to come down a size (as britishtrident also pointed out)
Aeon said that they normally use a 0.75" M/C but it depends on the individual setup. (twin m/c with bias bar btw) My Wilwood Dynalites appear to
have the smallest piston size (35mm) which doesn't help matters either.
Looks like I will need to swap the M/C for a 0.625" jobbie then - bugger of a job in my case 
[Edited on 22-1-07 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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andyd
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| posted on 22/1/07 at 12:03 PM |
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quote:
Originally posted by Fred W B
Hay Raz - Have sent you mail with Mike polan's (from here) brake spread sheet .
Cheers
Fred W B
Fred, any chance of making that available to all? Attach to this post perhaps?
Andy
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britishtrident
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| posted on 22/1/07 at 01:17 PM |
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quote:
Originally posted by ned
Stupid question, have you asked Aeon?
There are other cars on the road and track no doubt and I'm assuming you're using standard/aeon spec'd parts?
Ned.
Interestingly if you do a Google for Aeon it comes up with a road test that mentions the very high brake pedal force required..
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Fred W B
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| posted on 22/1/07 at 01:20 PM |
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Hi andy - I give it a try
Cheers
Fred W B
FM, it works........
[Edited on 22/1/07 by Fred W B]
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Fred W B
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| posted on 22/1/07 at 02:28 PM |
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So, at least 8 of you are going to be sitting across the passage outside the bathroom tonight, trying to press the wife's weighing scale through
the wall with one foot?
Cheers
Fred W B
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RazMan
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| posted on 22/1/07 at 03:52 PM |
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Already done that - I was thinking about doing some weight training to bring my right leg muscles up to spec
Just had a word with Rally Design - their brake guy (Andy) is very helpful. He basically confirmed what the spreadsheet calculated and what people on
here have suggested. As a result I have ordered a pair of Wilwood M/Cs. Front = 0.625" & rear = 0.70" which should improve my brakes
immensely. Just in time for the snow that we are about to get in the next few days - god I hate working outside in winter
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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