Brake performance
Discussion
I have a Sierra based kit car and I’m a bit under whelmed by the braking performance 
, probably because I’m used to servo assisted brakes. I would like to get more power and more initial bite. I was looking at Hi Spec or Wilwood kits but I would like a more cost effective solution. I have looked at the Sierra 4 pot callipers but I don’t know if they are compatible with the standard uprights. Suggestions please.
I’m also getting some rust on the chassis, what rust treatment would you recommend?
Thank
, probably because I’m used to servo assisted brakes. I would like to get more power and more initial bite. I was looking at Hi Spec or Wilwood kits but I would like a more cost effective solution. I have looked at the Sierra 4 pot callipers but I don’t know if they are compatible with the standard uprights. Suggestions please.I’m also getting some rust on the chassis, what rust treatment would you recommend?
Thank
If you are used to the feel of servo brakes, you might want to consider changing the master cylinder size and pads as a first step.
I've just removed the servo from my Elan (you can't get original Girling servos any more and the Lockheed replacements have a nasty habit of sticking on). I changed the .7" bore m/cylinder for a smaller 5/8" bore item and changed the pads to a softer compound, and it now stops better, with less pedal effort and more feel, than it did with the servo.
Changing the master cylinder for a smaller one increases pedal travel and decreases pedal effort, which is exactly what your servo is doing anyway...
I've just removed the servo from my Elan (you can't get original Girling servos any more and the Lockheed replacements have a nasty habit of sticking on). I changed the .7" bore m/cylinder for a smaller 5/8" bore item and changed the pads to a softer compound, and it now stops better, with less pedal effort and more feel, than it did with the servo.
Changing the master cylinder for a smaller one increases pedal travel and decreases pedal effort, which is exactly what your servo is doing anyway...
A couple of questions before you change anything:
1) How many miles have the discs and pads done? If you are on your first 10 miles then don't change anything. New discs AND pads will take quite a bit of bedding. Brakes don't work until pads have transferred their friction material to the disc. The pads don't start to transfer their friction material to the disc until they get hot, and a kit car takes such a small amount of braking to slow down due to their weight that it's very hard to build up heat - this is why they take quite a bit of bedding!
If they are very new, go out to a fast and quiet road, and do a few stops from 60mph down to 30mph, gradually increasing braking force. Then drive for a half a mile to give the brakes a rest, then repeat the above. Do this a few times, then let the brakes cool. Do they feel any better?
2) Did you attach the master cylinder push-rod to the pedal yourself? If so, how near to the pivot point is it? You might want to move the master cylinder attachment location nearer to the pivot point. This will multiply the force behind your foot even more, meaning you do not need to press the pedal as hard to stop the car.
3) Is the pedal firm or does it squish a little? If it does not feel very firm then you need to re-bleed the callipers and get the air out. Any air in the system will affect the braking force.
There are plenty of kit cars out there that stop extremely well with the most basic callipers. This is why it's worth going through some things first before upgrading.
1) How many miles have the discs and pads done? If you are on your first 10 miles then don't change anything. New discs AND pads will take quite a bit of bedding. Brakes don't work until pads have transferred their friction material to the disc. The pads don't start to transfer their friction material to the disc until they get hot, and a kit car takes such a small amount of braking to slow down due to their weight that it's very hard to build up heat - this is why they take quite a bit of bedding!
If they are very new, go out to a fast and quiet road, and do a few stops from 60mph down to 30mph, gradually increasing braking force. Then drive for a half a mile to give the brakes a rest, then repeat the above. Do this a few times, then let the brakes cool. Do they feel any better?
2) Did you attach the master cylinder push-rod to the pedal yourself? If so, how near to the pivot point is it? You might want to move the master cylinder attachment location nearer to the pivot point. This will multiply the force behind your foot even more, meaning you do not need to press the pedal as hard to stop the car.
3) Is the pedal firm or does it squish a little? If it does not feel very firm then you need to re-bleed the callipers and get the air out. Any air in the system will affect the braking force.
There are plenty of kit cars out there that stop extremely well with the most basic callipers. This is why it's worth going through some things first before upgrading.
Also...As the car is probably lighter than the one the brakes came from, don't be in a hurry to go for hard pads. It may well be that a soft pad will give you better feel and retardation.
If the car is only used on the road, it is unlikely that you will need bigger disks, racy pads etc.
If the car is only used on the road, it is unlikely that you will need bigger disks, racy pads etc.
Thanks for all those comments. I think I will try bleeding the brakes first and if that doesn’t do anything I will try some softer pads, after that I will look at new master cylinders. The pads that are on the car have done around 2000 miles so they should be bedded in and the pivot point is about 30mm from the push rod. I’m hoping to take the car hill climbing next year so I will need my brakes to work to be competitive.
If you're hillclimbing, you definitely need softer pads, 'cos they'll get no chance to warm up before you need them.
Do you know what pads are fitted at present?
Quite often, people fit 'competition' pad compounds, in the mistaken belief they'll give then better braking. If they're for the brakes of a saloon model, one of the main aims of such compounds is often to prevent pad fade on a heavy car being flogged round a circuit at high speed. In road or hillclimb use on a light car, you'll simply never get enought heat into them to make them work, in which case the pedal effort needed will be enormous.
Do you know what pads are fitted at present?
Quite often, people fit 'competition' pad compounds, in the mistaken belief they'll give then better braking. If they're for the brakes of a saloon model, one of the main aims of such compounds is often to prevent pad fade on a heavy car being flogged round a circuit at high speed. In road or hillclimb use on a light car, you'll simply never get enought heat into them to make them work, in which case the pedal effort needed will be enormous.
It is not an exact science, but i quite often use standard cheap pads like Ferodo's for £20'ish. If your kit is only 500kgs or so then normally pads designed for a 1300kg car will suffice. I rememer particularly on my Libra which had monster AP Racing brakes, i found the standsrd road pads designed for the 1100kg MGF were more than enough for my 780kg Libra. Absolutely NO fade on track ever, and superb feel. I had EBC greenstuff on my Furyblade, but took them off and put cheap standard pads back on and they were much better, especially when cold. the EBC's were downright nasty in the rain. They just grabbed with no feel whatsoever.
Furyblade_Lee said:
It is not an exact science...
Actually, it is, but as with tyres the problem is getting hold of the information you need. 
If you do a bit of ringing round, and manage to get through to the right guys in the technical departments of the brake pad manufacturers, you'll often find that they have superb knowledge of their own range of pad compounds and can recommend something that will meet your needs exactly.
Ferodo's technical guys used to be particularly good, as did Mintex... I used to use their testing facility at Sherburn in Elmet occasionally when I was up in Yorkshire and knew a few of the guys quite well, but I'm not sure if they're even still there, these days.
And another also...
On some kits, the actual pedal box isn't that well mounted. What can feel like dull brakes has sometimes turned out to be a flexing pedal box/mounting. get someone else to simulate emergency braking pressure whilst you examine the system for movement or flex.
So; make sure the pedals are firmly mounted, fit proper braided lines (They have less flex than rubber) and bleed the sytem to flush out any old water contaminated fluid.
Hill climbing is pretty demanding since both the car and the driver have to be working spot on right from the start.
I would find a level dry road (preferably quiet and out the way, but with a consistent surface). Take the car up to about 40 or 50 and slam the brakes on HARD. You have to make them lock up, but don't keep everything locked, ease off the regain control. Do this a few times and note which end locks up first, is it consistent, or does the feel or performance change as the brakes heat up?
If all OK, do some more serious stopping; take it up to 70ish and brake as hard as you can without locking the wheels, see if you can modulate the pedal so that you can hear the tyres yelping without locking as you bring the car to a complete stop, immediately accelerate and repeat.
Now you will be getting the brakes really hot and you can see how the feel/balance changes as they increase in temp. You may cook them doing this a few times, does the pedal stay hard and the car not stop (pads too hot), or the pedal go soft and the car not stop (fluid too hot)? NOTE after this sort of treatment - drive around gently for a mile or so to cool the system, and when you do stop, don't park it with the handbrake, just leave it in gear. Oh and by the way it's possible for heat soak after stopping to boil the fluid.
You should now know if you need to alter the balance of the brakes, change the overall pedal pressure to make it easier to push or easier to modulate, change compound to cope with the type of braking you need. As an example, Mintex 1144 and Greenstuff are sort of similar in hot performance, but greenstuff has significantly better coefficient of friction when cold.
On some kits, the actual pedal box isn't that well mounted. What can feel like dull brakes has sometimes turned out to be a flexing pedal box/mounting. get someone else to simulate emergency braking pressure whilst you examine the system for movement or flex.
So; make sure the pedals are firmly mounted, fit proper braided lines (They have less flex than rubber) and bleed the sytem to flush out any old water contaminated fluid.
Hill climbing is pretty demanding since both the car and the driver have to be working spot on right from the start.
I would find a level dry road (preferably quiet and out the way, but with a consistent surface). Take the car up to about 40 or 50 and slam the brakes on HARD. You have to make them lock up, but don't keep everything locked, ease off the regain control. Do this a few times and note which end locks up first, is it consistent, or does the feel or performance change as the brakes heat up?
If all OK, do some more serious stopping; take it up to 70ish and brake as hard as you can without locking the wheels, see if you can modulate the pedal so that you can hear the tyres yelping without locking as you bring the car to a complete stop, immediately accelerate and repeat.
Now you will be getting the brakes really hot and you can see how the feel/balance changes as they increase in temp. You may cook them doing this a few times, does the pedal stay hard and the car not stop (pads too hot), or the pedal go soft and the car not stop (fluid too hot)? NOTE after this sort of treatment - drive around gently for a mile or so to cool the system, and when you do stop, don't park it with the handbrake, just leave it in gear. Oh and by the way it's possible for heat soak after stopping to boil the fluid.
You should now know if you need to alter the balance of the brakes, change the overall pedal pressure to make it easier to push or easier to modulate, change compound to cope with the type of braking you need. As an example, Mintex 1144 and Greenstuff are sort of similar in hot performance, but greenstuff has significantly better coefficient of friction when cold.
I have driven many Fury's and the like and on a well set up system even "donor" brakes should NEVER leave you feeling "underwhelmed". Remember, the brakes are designed for cars twice+ the weight so even on standard pads, with the right master cylinder to compensate for the lack of servo they should stop the car on a sixpence. I remember my first Fury came with mastercylinders which were wrong, i had a rock hard pedal with no feel and had to literally be brutal to get the car to stop. A change in cylinder cured it (£35) and it was lovely. I then put greenstuff in and took them back out. Then i got monster Hi-specs but in all honesty i do not think they made the car stop any quicker, but they looked bloody cool.
Lots of good stuff, thanks. My pedal box does look a bit flimsy as it’s just a few bits of angle but it is compact, I have thought about getting a decent pedal box but it will take up valuable space in the foot-well. I think my first job is to bleed the system, if that doesn’t help think I’ll do the pads, after that I’ll investigate the M/C and improving the pedal box.
Thanks for all the comments. They have been most helpful.
Thanks for all the comments. They have been most helpful.
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