Bleedin Brakes

[Andrew Dent]

OK, Ive asked this before, and never really got the hang of it, and after Oulton yesterday, my brakes are totally shot. Went from firmish pedal to lots of travel and not much stopping power, but the car didi spen 4 hours on track. There is plenty left on the pads, so how do I get that lovely hard pedal that others have and I want. THe idiots guide would be helpful. And it has to be done for Saturday morning.

 

Andrew

 

 

[Paul Ranson]

You have probably glazed the pads. This may go away with time, or with the application of emery paper and brake cleaner as appropriate.

 

Changing the fluid is never a bad idea. IME the more 'big' bits you've got the easier this gets, the Sierra rears are particularly problematic, especially as they never seem to be properly adjusted.

 

I think pressure bleeders get the big bubbles out, and put loads of little ones in. I use the tube with a blob on the end things that can be bought for a couple of pounds in Halfords. They do a dual version for calipers with two bleeds.

 

Basically a combination of shallow pumps and full strokes, letting the pedal return under its own spring. Never let the master cylinder run dry. It may be worth detaching the rear calipers, putting a spacer between the pads, and holding them 'vertical'.

 

And finally, the mechanical adjustment between the pedal and the cylinder can be significant, ideally you want the 'centre' of the action to be just after all the slack has been taken up.

 

Paul

[jonhill]

Andrew,

 

What pads are you currently running?

 

Not sure if you are asking for the idiots guide to bleeding brakes, or the long term solution to stopping the pedal going spongy. I'll assume the latter.

 

The short answer is I don't know sad.gif. The reason I'm contributing is that I too get a spongy pedal during every track day, and am also in search of a solution. This is a surprisingly complex subject, in that I've spoken to several professionals about this, including EBC, and also lots of enthusiasts, and to say there are contradictory opinions is an understatement. This is what I've found:

 

The sponginess is due to air in the system. This air comes from the brake fluid boiling. Bleeding the brakes between track days restores the firmness. I always have air at the back, with hardly any in the fronts. This correlates with the toasted state of my rear pads. The fluid boils 'cos the brakes are unable to dissipate the heat generated. It seems that changing the pads will help this, as some pads either dissipate the heat better, or insulate the calliper better (can't determine which, maybe both). Either way they cope with the higher temperatures and therefore won't turn to ash like mine have.

 

I've totalled two sets of rear pads in 2000 miles. These are the pads with blue flashes, fitted as standard to cars with big front brakes. These pads have a higher coefficient of friction than the std rear pads fitted to cars with std front brakes, to balance the increased front braking available. These are clearly not up to the job in my car when it is used on the track. I've also had my rear disks replaced under warranty, and I believe there is still something amiss with the brakes, as they seem to get hotter than anybody else's. However, while I wait for Caterham to suggest why this might be happening, I've just fitted some EBC Green Stuff rear pads. I have already fitted Green Stuff in the front, in an attempt to balance the braking forwards a bit and give the poor rears a brake (ha ha). I will have to see if also putting GS at the back resolves the problem.

 

According to ECB and James Whiting, there's no need to go to Red Stuff pads in a Caterham. Both said they've never seen a problem with Green stuff in Sevens. At Oulton Park two Saturdays ago, I was chatting with a driver who claimed 8 minutes round the 'Ring, and who said he replaced his front disks every year i.e. he is fast and hard on brakes. He was switching back from Red Stuff to Green Stuff, as he said they weren't getting up to temperature. It was a bit damp at the time, but generally seems to back up the previous comments on Red Stuff. However I know there are several people on this forum who seem happy with Red Stuff. He also said he used to toast rear pads in a few laps until he cut some holes in his rear wings and fitted ducting.

 

I don't know if any of this is of any use to you, but I've been trying to ascertain what is a reasonable track day set up for brake pads all summer, and have only become more confused as I talk to more people. There's *got* to be people out there who brake hard and have sorted this out already. Maybe people could post their front and rear pad selections, along with an assessment of how much hammer they get i.e. how fast they drive on the track. This last bit is key, as some people may not have any trouble with a set up that just wouldn't work for someone with a faster car, or who is generally faster and more demanding on the brakes.

 

If you were only asking how to bleed the brakes, that's something I can tell you how to do, as I'm getting a lot of practice at the moment smile.gif Just shout up.

 

Cheers,

 

Jon

[Andrew Dent]

The fronts are Green Stuff and get deglazed after every track day. Not looked at the condition of the rears. Bled the rears last nigh and some air came out, and the pedal felt better, still not perfect. Will replace the rear pads, with green stuff is necessary, but dont like the look of the cost of the rear brake splitter from Demon Theives.

 

Jon we probably need to talk. Can you e mial me your phone number.

 

Andrew

[Mike Bees]

You've boiled the fluid in the rears. Mine does this on some circuits - at Lydden it takes about 10 minutes of running on a cold March day. I'm using AP600 brake fluid already, so I think the only solutions are some hand made ducting to get some air to them and/or replace them with bigger brakes (which would help with the balance too).

 

Mike

[deanteam]

Maybe a totally unrelated question, but whilst we are on the subject of rear brakes...

On those disc brakes which have handbrakes, how does the wear compensation work? Does it rachet in with pedal pressure or with handbrake application or both?

 

Andrew, are you talking about a windback tool? We got a cheaper one from Vehicle Wiring, 0159305454.

[jonhill]

Andrew,

 

I'll mail my home phone, feel free to call any evening/weekend. One thing you will need before tackling the job of changing the rear pads is a calliper wind back tool. This pushes the piston back in to allow the fitment of new (thicker) pads. You cant' simply push the piston in like you can at the front, and with out this tool you'll find it impossible. I got mine from Halfords for £19.99.

 

Paul,

 

Can you expand on the subject of glazing? I initially put my sponginess down to this, and emery paper did seem to help. However I have recently revised my diagnosis (mainly) to air in the system.

 

One thing that I am still unclear about, is the cause of glazing. I thought that this was caused by the pad getting too hot. I have been told that this is not the case, and that in fact it is caused by the pad not getting hot enough. When a pad gets too hot is fragments and cinders, and I've clearly seen this with my rear pads. My fronts do get shiny (this is what I mean by glazing - do we have a terminology issue here?), however I know they are getting to at least 350 degrees as this is when Green Stuff stops being a dust free pad, and starts dusting like mad (information from EBC's technical support dept.). My front wheels are black with dust. Inspection shows they are not showing signs of overheating.

 

How do the upgraded rear brakes help? Is it a case of more pad area to dissipate the heat, or is there a fundamental design improvement over the Sierra item? What's the adjustment issue with the Sierra callipers you mention, and can something be done about it? Which out of the two rear upgrades is the one to go for? I presume since one doesn't have a handbrake, there's more than just cross drilled disks on offer with this upgrade, and the calliper is somehow superior?

 

Thanks,

 

Jon

[sjwb]

Just a few points. You should be using Dot 5 (or greater) fuid. Presumably the vehicles are fitted with braided hoses. Pressure bleeding appliances are fine, just follow the instructions. I can recommend Eezibleed and it is cheap! The best way to evacuate final air residue is, with an assistant, hold the brake under (foot) pressure, crack appropriate bleed nipple and lock before end of pedal travel. This is a motorcycle dodge which is very effective.The sponginess may indeed be due to air in the system however, the hose type is also an influence. The point about air in the system, from causes other than disassembly, is that non silicone fluid is VERY hygroscopic and in our damp climate this is critical. Change the fuid regularly and only use fresh fluid from a sealed container. If you encounter fluid boiling on a track day something else is amiss, "hotter than anyone else's"! There is a clue there perhaps.

I use AP brakes, Pagid RS 14 rear pads and have a pedal that is constantly hard with no excess travel. Just a final thought; using my original (small) brakes, a track day saw off (overheated) the front pads, did not cause any sponginess and only increased pedal travel slightly.

There seemss to be a process issue here. Don't bleed the brakes between track days, renew the fluid and use a pressure bleed system.

[Paul Ranson]

My experience of 'glazing' is that the brakes work fine for a track day, but don't for 'normal' stops on the way home. The problem manifests itself as having to press really hard for not much stopping. Not directly a pedal feel problem.

 

I've presumed it's a consequence of mild pad overheating. I've never used EBC pads on a Caterham, this was with Mintex 1136 on a Vauxhall with standard brakes.

 

Paul

 

 

[Peter Carmichael]

AFAIK, all Caterhams get very hot at the back, whether owners realise it or not. The sensible answer is some ducting.

 

I have had very rapid wear and reduction to dust of Mintex 1144 pads in the back so I now use 1155 which seem to be holding up better. These are metallic pads, so conuct quite a lot of heat to the back of the pad. The caliper design (AP2399 big rear brakes) seem to cope quite well with this heat and I use AP600 fluid.

 

This is all with just a 138bhp Supersport. I am expecting problems on ttack with the more powerful engine and I need to sort out larger tyres and better rear braking (ducting?).

[jonhill]

Mike, Peter,

 

You both say you use AP600 fluid. What's special about this, versus dot5.1 which is what I use?

 

Thanks,

 

Jon

[jonhill]

Mike, Peter,

 

You both say you use AP600 fluid. What's special about this, versus dot5.1 which is what I use? Does it need changing more frequently?

 

The ducting I saw at Oulton was very neat. A round, mesh covered, hole about an inch in diameter in the wing (and wing protector), with a short length of pipe behind to direct the air onto the brakes. Looked very straight forward to implement, and wasn't at all offensive to the eye.

 

Thanks,

 

Jon

[Mike Bees]

AP600 has a higher boiling point (don't have the specs in front of me - you might find them on AP's website. It does need changing more often - twice a year should be OK (ISTR that AP recommend after every race, but then they would wouldn't they?).

 

Mike

[Andrew Dent]

New pads on order, and AP 550 going in. HAd practice getting all the air out, and things are starting to feel better. Am looking at ducting from under the car infront of the diff to the rear brakes. Will also investingate the big brakes. Anyone have an idea of cost.

[ian c]

BRAKE FLUID: THE LIFE BLOOD OF THE BRAKE SYSTEM

 

One of the more interesting topics of discussion around the race tracks the past few years has been the controversy over the choice of brake fluid, specifically silicone or the more conventional polyglycol fluid,(known at the race tracks as DOT 3,4 & 5.) Since the discussion usually ends up being by opinion, and since opinions are worth exactly what you say for

them, I have decided to supply you with some interesting factual data about each to allow you to make up your own mind. (I'll also make it clear as to my preference and why.) A hydraulic brake system will not operate without brake

fluid. To a large degree tthe level at which the brake system does operate is dependant on the choice of fluid. Among other things, the more important elements of brake fluid are high boiling points, consistent viscosity and good lubricating ability. All brake fluids commonly used in automobiles sold

in the United States, are regulated by the department of transportation(DOT). The can will have a number such as DOT 3, which refers to the DOT test designation that the fluid meets. Please note, the number disgnation does not imply a rating for comparison between the fluids. (Refer to table for minimum

boiling points.)

 

 

DOT MINIMUM BOILING POINTS

 

DRY BOILING POINT WET BOILING POINT

DOT 3 401 F 284 F

DOT 4 446 F 311 F

DOT 5 500 F 356 F

 

Both the DOT 3 and DOT 4 fluids are normally polyglycol base fluids.

Polyglycol fluids are hygroscopic, which means they absorb moisture. As the amount of mooisture absorbed increases, the point at which the brake fluid boils, decreases. In a well sealed brake system these fluids will require changing approximately every 1-2 years, depending on the severity of use.

Unfortunately, racers have access to a variety of aftermarket mastercylinders which do not have diaphragms that tightly seal the brake fluid from the air. Use of these types of master cylinders should be avoided, since the moisture in the air will be assimilated by the brake fluid immediately. This

is why you should never buy brake fluid by the gallon, because once you have used the quart you needed to freshen your system the moisture in the air inside the can will ruin the remaining fluid in the can. It is for this same reason you should never reuse fluid removed from your system. Once your system has been filled, re-place the cap immediately to avoid affecting fresh fluid.

 

Never get any fluid in your brake system unless you are absolutely sure as to what it is. Petroleum products, such as oil and transmission fluid can quickly destroy the seals and cause major brake failure. Some import cars do not use fluids compatible with those used in this country. For instance,

Rolls Royce uses aircraft mineral fluid in the brake system that would quickly destroy your brakes, so it is not even safe to assume that if it says brake fluid, its OK. Always look for a DOT number. DOT 3 and 4 can be mixed,but DOT 5 should never be mixed with any other fluid. Both DOT 3 and DOT 4

fluids will attack paint. Since most race car owners pride themselves on the appearance of their cars, this would sound like the "kiss of death" for these brake fluids, but let's not jump to conclusions until we finish exploring all the facts. If brake fluid is spilled onto the paint, flushing with water and quickly wiping up the mess will not result in any damage. This should not be any problem fro a race as a bundle of clean rags is standard equipment.

 

DOT 5 fluid uses silicone as its base. Silicone has none of the problems we have described above because it is not hygroscopic so it does not absorb moisture. Also, it does not attack paint, so spillage is no problem.

Unfortunately, it does have some major drawbacks. First, it is extremely expensive often costing 5-10 times as much as polyglycol fluids.

secondly,and more importantly, the compressiblity of silicone fluid is very unstable throughout the temperature range encountered in normal usage. As the temperature increases, the pedal travel necessary to compress the fluid changes, resulting in unpredictable pedal height.

 

Altitude also affects the compressiblity of the fluid further compunding the problem of pedal travel. This would not be such a problem except for the fact that as we discussed in an earlier article, we must not only be able to develop pressure in a brake system, we must also be able to

remove that pressure. In the case of silicone fluid, the expansiveness can be so severe that when you take your foot off the brake, residual pressure could remain high enough to cause brake drag that would cause further heating of

the fluid and therefore further expansion, therefore more excessive drag that would end up locking the entire brake system, rendering the auto unable to be moved.

It is for this reason race teams that have experimented with silicone fluid long ago found they could not use it.

 

Another characteristic of the fluid is if you experienced excessive sponginess in your pedal after the car is used for a while, then you know the most likely cause. What you may not know if that you may be tremendously shortenin the life of your brake pads due to excessive dragging.

The other factor that has come to light recently is silicone brake fluid affects the seals found in standard brake systems.

 

Ethylene propylene rubber seems to loose its durometer(hardness) when exposed to silicone fluid. This results in a change in the size and an increase in the wear rate of all rubber components in the system.

To further complicate the problem, if your system has the master cylinder mounted under the floorboard and you don't have a two pound residual valve(see last issue) present, you may have trouble identifying the problem due to the absence of this most important valve.

 

Street rodders are avid users of silicone brake fluid,primaril because of the expensive paint jobs they have on their cars.

Unfortunately, since many of their brake systems are composed of components

off of other vehicles, the additional problem of the wrong brake fluid makes

many of these cars very unsafe.

In essence, the point of this entire article is that although both types of fluids have advantages and disadvantages, the bottom line is

that the disadvantages of silicone brake fluid render it unacceptable as a

safe and reliable alternative to polyglycol fluids under all conditions. On

the other hand, although DOT 3 and 4 fluids have problems, these problems are

controllable given reasonable care and maintenance. We all have a tendency to

take the pedal travel of our brake pedal for granted, but I want to assure

you that there is no fear any worse than the fear of stepping on the pedal

and finding nothing there. Consistent even pedal travel is extremely

important to safe stopping distances. It is even more important to giving a

race car a consistent, repeatable feel to the pedal, so the driver knows he

can depend on maximum performance.

 

Whther you own a race car or a street rod, or in fact, any

car, this article offers some critical information for safety's sake. The

next time you see a bottle of brake fluid on sale for $2.90 you may want to

ask yourself is what you are buying truly will handle your intended use. What

may be OK to stop your passenger car at 55mph, probably has no place in a

race car at 125mph.

 

 

Editors Note:

Warren Gilliland, President of "The Brake Man!", has over 27 years in the

design ad development of brake systems for industrial and racing

applications. He feels that the need for technical support on all products

used on race cars is essential and supplies in-depth instruction with all of

the products he supplies. This article was supplied courtesy of "The Brake

Man!" to assist you in your racing activities, and make your vehicle safer

and more reliable.

 

>From TurboTim

Comparison of high performance brake fluids on the market.

 

Dry Boiling

Point

Petrosin 500

Castrol LMA Not sure ? 500

Motul 5.1 509

Motul 300oC 572

Ferodo 554

Girling Dot 5.1 552

Brake Man: 570 H.P. Fluid 570

ATE Super Blue 536

 

[Alex Wong1697456877]

oops - double post

 

Edited by - Alex Wong on 19 Aug 2001 08:24:46

[Alex Wong1697456877]

 

 

What about Castrol SRF synthetic fluid? This is only DOT 4 but look at the wet boiling point. I was having problems with squidgy pedals when warm and they've vanished now with SRF. Flippin expensive stuff though!

 

>>The dry boiling point is at 590°F but what is truly amazing is that it's wet boiling point of 518°F. When other race fluids take on moisture, their boiling point temperatures can drop to less than 300°F. Castrol SRF is also very resistant to moisture absorption for fewer fluid changes, and has extremely low compressibility delivering maximum efficiency and a firmer pedal.

[Graham Perry]

The point that Peter makes re the temperatures of the brakes is I think the key to the whole issue. Because if the brakes are very hot they will boil the fluid regardless of its condition.

 

I have been experimenting with my brakes due to the problems that I have had with my new front Alcons, as the the rears have started locking first. A balance valve has cured this. However, what I thought was perfect brake balance (which I had set by experimentation with the valve position, getting the fronts to lock first rather than the rears) has proved not to be so. When I thought I had finished the job I went round all my brakes with a pyrometer after giving them a thorough shake down, and was amazed that the rear brakes were 100 degrees hotter than the fronts. I had no indication of this under braking as the fronts were locking first, but by implication it was obvious that the fluid in the rears was closer to boiling than the fronts.

 

I have now wound on a bit more front pressure and although I havent yet achieved similar temperatures front and rear (they are now within 20 degrees), I suspect the car is now much less likeley to boil the rears. A quick test of braking distances showed no difference for winding even more pressure to the front.So the story may well be that even though you think the balance is correct it may still need to be biased more to the front than you think, if you are to prevent the rear fluid boiling. I am not a great one for playing with the valve and have now sealed it.

[EFA]

Solve all your problems with AP600. More hydroscopic than any other fluid you should ensure you change it every season, (despite the 3 months quoted on the container which is a "reduction of liability risk" clause)

 

I have run this ever since my squidgy pedal went away. Word of warning however is that you will need to flush the system with meths if you have ever used silicon as AP600 and silicon fluid react nicely.

 

 

 

Fat Arn

See another FAT ARNIE here

See a meaty Vauxhall car here

See the Le Mans Trip Website here

See the Lotus Seven Club North Kent Website here

 

[Mike Bees]

My car always locks it's fronts first, but the rears get *very* much hotter with track use - they get no airflow. AP600 doesn't solve the problem, I can boil it (fresh) in the rears in about 10 minutes of running at Lydden. The 2 problems are (1) with 4-pot APs on the front, the standard rears aren't up to the job, and (2) the rears don't get any airflow to cool them.

 

Mike