Brake failure !

[GORDON STREETER]

Whilst driving sponsors /friends round Bands Hatch yesterday afternoon I had a complete brake failure. I was lucky and got away with a trip across the grass on the bottom straight. It was caused by a fractured fitting on a front caliper. My point on this thread is that I thought (wrongly) that with a tamden system and bias bar that if one half failed you should still have a small amount of braking. I was obviously wrong.

[terence]

Only if you have something like a 50/50 split,I already new that![from experience] Glad you got awy with it though Gordon,well done.

[Peter Mallett]

Hmm,

Will the inside of the car be clean by Spa?

Well done for avoidance. Its something that I tend to think about a lot, but you can't legislate for it just keep cheking those calipers and hoses.

[Al Weyman]

I knew there was a reason why I still run a race version of the tandam cylinder set up in my car, that will work on the circuit that is not effected at least! Glad you got away with it Gordon would have hated to see that car a mess.

[jonners]

Originally Posted by GORDON STREETER

My point on this thread is that I thought (wrongly) that with a tamden system and bias bar that if one half failed you should still have a small amount of braking. I was obviously wrong.

Glad you are ok and got away with it - I've never experienced brake failure and imagine that it could tie up the laundry and valet depts for a day or two

With all the usual disclaimers about being pedestrian on the technical front could I ask someone to explain what happens here?

I've always assumed that a dual circuit means that if one circuit fails the other one still operates so at least some braking remains - albeit not a lot if the front circuit fails and depending on bias adjustment and so forth

Is it the case that the residual braking effort available when one circuit fails is so small that, in effect, the brakes have 'gone' completely?? If so why do manaufacturers bother with dual circuits??

Suspect I've missed the point somewhere - just don't want to get things wrong when I splash out on that bespoke pedal box I've been thinking about for a while now...

[rcarr]

I had a massive brake failure at the beginning of last season, I was heading down into the hairpin at Knockhill, from about 100 mph+, I came up the inside of a guy and out brake him at the last minute to get past him.

Foot on the brake, nothing! Pumping it madly, nothing! Had to use engine braking as best as I could. I didn't realise at the time but my left front had completely locked up whereas the right front was still carrying on at speed. I under steered into the gravel trap, tried to get the car into a position where it would do least damage to me and to the car, I broadsided into the tyre barrier. I knew it was the car's fault because I have done that kind of passing manoever several hundreds of times before, never had any problems before then.

I got out of the car and hit it very hard! I was not happy!

Dad met me as I climbed the tyre barrier to get to a safe distance away, he said it was driver error, I said it was not! I got very annoyed and told him where to go.

I got towed out of the gravel and drove back, when I got out, I noticed the right front tyre was covered in fluid, more on the inside of the tyre as it was on the ramp of the truck, I thought it must be a sheared hose etc. The next weeked I took it to a friend's house that has a car lift, we took the wheel off and saw that the braided brake pipe had been routed the wrong way round the damper. The hose had been rubbing on the inside of the rim and the loads that were put throught the pipe were too great and it squirted brake fluid all over the tyre and I had not brakes!

It was sheer panic trying to get the car slowed down and round the corner!

My Dad had a very similar accident at the meeting before at the same place, he speared the tyre wall in his Mallock with a suspected throttle problem, it was a c.70mph crash straight into the tyre wall!

[MGDavid]

BTDT - wrote off our shared MG at Zandvoort a couple of years ago (single line system and a rear cylinder popped). With a two-cylinder system and a balance bar if one circuit totally fails then it's still possible to run out of movement on the bar and lose braking on the second cyl too. One system that works from a safety aspect is a tandem master cylinder where a single pushrod actuates two pistons in tandem formation with independent circuits. But you lose the balance bar capability, and they can be bu99ers to rebuild. On the MG they usually give a soft pedal too - which doesn't inspire confidence. Bit of a curate's egg really.

[terence]

Because of the fact that really our types of car do not need split system Masters,the problem arrise,s simply because we do not need the amount of braking thats available to the rear,we wind something like 75/80% to the front end,in effect that leaves just about nothing to the rear.Because of the design of these pedal box,es,i.e,the bias bar will always tend to favor the most resistence and there fore you shove the pedal and it just goes staight to the floor,if its the front with a problem,you,d possibly not notice much if it was on the rear.Far better to fit a tandem M /cylinder,the single Push Rod will ensure that no matter what end has failed,you still have the pressure to activate the remaing circuit.This is all I use,Much easier to install/cheaper/less maintenence.

[Peter Mallett]

I remember going through scrutineering at Pembrey with my Metro some years ago and my "team" telling the scrute that the reason the brake pedal went to the floor was that it had been standing for a while. I didn't hear this and nobody thought to tell me. Out to practice and up to the hairpin slowly and I didn't really notice anything, however the next lap was a bit different and after three laps I came in complaining that the brakes were spongy. Turns out I'd got pad knock off (don't know why) but I qualified second.

The race was much of the same but I chewed up a pair of fronts and finished third.

[GORDON STREETER]

Its certainly made me think, and I am fully aware that all road cars made in the last 25+ years have had one tandem bore master cylinders fitted as standard. As I said I assumed that you would still have a ghat's c***k of brake on the type I use. Perhaps some brake scientist could tell me what the difference between a dual circuit(as road) master cylinder with rear line adjustable bias valve fitted, versus twin cylinder bias bar pedal box would make. And before somebody tries to tell me that some of the road cars are piped one front and opposite rear side, I know that. Its just that I wouldn't want this to happen to anyone else EVEN my worst enemy (he may be behind me in a race !! )
Pete difficult to check fittings for fractures best to fit new ones every 2 or 3 years.

[Peter Mallett]

Agreed Gordon.

[Tim Falce]

Originally Posted by rcarr

I had a massive brake failure at the beginning of last season, .............................. I broadsided into the tyre barrier. I knew it was the car's fault because I have done that kind of passing manoever several hundreds of times before, never had any problems before then.

I got out of the car and hit it very hard! I was not happy!

Dad met me as I climbed the tyre barrier to get to a safe distance away, he said it was driver error, I said it was not! I got very annoyed and told him where to go......................
.................The next weeked I took it to a friend's house that has a car lift, we took the wheel off and saw that the braided brake pipe had been routed the wrong way round the damper. The hose had been rubbing on the inside of the rim and the loads that were put throught the pipe were too great and it squirted brake fluid all over the tyre and I had not brakes!

So it was your fault after all then.

[Peter Mallett]

Good job it was only a Fiesta really. Anything faster (can a Fiests get up to 100mph?) and it could have been slightly dangerous.

[Al Weyman]

I have a nice Wilwood competition all aluminium single tandam Master cylinder I installed last year prior to which I was using the standard cylinder then I fitted the huge 6 pot Wilwood Grand Nationals on the front and needed a bigger cylinder because of the fluid movement causing a long pedal, I am glad to report its a real nice piece and does the job admirable with a pressure limiter to the rear I had to import it direct from Wilwood as Rally Design would not stock it but its a good piece for the money, I also have the back up (I hope) of a hydraulic handbrake.

[terence]

Thats a point Al,Gordon ,what size Masters are you using?70 front and 6.25 rear?

[terence]

Originally Posted by Peter Mallett

I remember going through scrutineering at Pembrey with my Metro some years ago and my "team" telling the scrute that the reason the brake pedal went to the floor was that it had been standing for a while. I didn't hear this and nobody thought to tell me. Out to practice and up to the hairpin slowly and I didn't really notice anything, however the next lap was a bit different and after three laps I came in complaining that the brakes were spongy. Turns out I'd got pad knock off (don't know why) but I qualified second.

The race was much of the same but I chewed up a pair of fronts and finished third.

Just goes to show that some people rely on the middle peddal a bit toooo much.

[terence]

Originally Posted by GORDON STREETER

Its certainly made me think, and I am fully aware that all road cars made in the last 25+ years have had one tandem bore master cylinders fitted as standard. As I said I assumed that you would still have a ghat's c***k of brake on the type I use. Perhaps some brake scientist could tell me what the difference between a dual circuit(as road) master cylinder with rear line adjustable bias valve fitted, versus twin cylinder bias bar pedal box would make. And before somebody tries to tell me that some of the road cars are piped one front and opposite rear side, I know that. Its just that I wouldn't want this to happen to anyone else EVEN my worst enemy (he may be behind me in a race !! )
Pete difficult to check fittings for fractures best to fit new ones every 2 or 3 years.

I know what you mean Gordon,like I said,its all down to resistance,when all movement has been used on one Master ,it then transfers to the other,inyour case the rear,if there is too much movement then the peddal just keeps going,Basically,you need pressure from both Masters in order for them both to work.

[terence]

Just another way of putting it,ever tried Bleeding the rears AFTER the fronts.

[Southern Man]

If your pedal box allows one cylinder to fail and the other not to operate correctly then machine uo and fit a stop inside the cylinders so that when the piston reaches the end of the now reduced travel it then transfers all the effort to the other cylinder. You probably need stops that are about 10mm in length but that is very dependant on which / what master cylinders that you are using. The trick is to stop the failed cylinder from using all its travel therby transfering the effort to the cylinder that is operating correctly

[GORDON STREETER]

Southern Man Agreed that should work but you only have to get a long pedal for whatever reason in the race and you would be handicapped thinking about it. I am looking at a long term answer as I and probably quite a few on 10/10ths didn't know this could happen. Terence has pointed this out as he has had experience with this happening, and its only with a forum that it gets to the masses worldwide. Saying all this I shall still disingage my brain next weekend at Snetterton instead of going to the OAPs knitting club, as this is the first time this has happened in 35+years.

[Tim Falce]

Gordon, if you are so worried about it why don't you go for a dual master cylinder with a balance valve on the rear line.
Even with this system how much braking would you have if the front line failed and you have the balance biased toward the front with lttle effort to the rear brakes?

[GORDON STREETER]

Tim I have got a rear balance valve fitted , this was left over from when we were trying to get the best brakes at the time and is left fully open at the moment. My main point now is why twin cylinder pedal boxes were made in the first place, or was it so long ago that the "failsafe" single master cylinder wasn't about. I know that the rally boys all used them for the brake balance change for different stage conditions, but do they still use them in modern hi tech stuff. They are obviously used in classic rallying. As I said maybe somebody could put the pro's n con's on this thread as I am no expert.
I might try winding the bias to the rear on the box and shut the rear bias valve down, although it might need more braking effort because of the leverage angle on the bias bar ?

[Podd37]

Originally Posted by Al Weyman

I have a nice Wilwood competition all aluminium single tandam Master cylinder I installed last year prior to which I was using the standard cylinder then I fitted the huge 6 pot Wilwood Grand Nationals on the front and needed a bigger cylinder because of the fluid movement causing a long pedal, I am glad to report its a real nice piece and does the job admirable with a pressure limiter to the rear I had to import it direct from Wilwood as Rally Design would not stock it but its a good piece for the money, I also have the back up (I hope) of a hydraulic handbrake.

I too use a Wilwood tandem Master cylinder, mainly as I didn't want to use a servo and old cars that are originally lhd seem to my untrained eye to need too much work to fit a dual, adjustable system. It was easy to install, is very neat and the guys from Wilwood were very helpful.

[terence]

I think that really for "our" cars,a Tandam is all thats needed.There are several on the market,are usally much easier to install and maintain.The bonus is that you know that[if it has come from another vehical of similar weight] that it should prove extremely reliable.Most systems do not need a rear bias fitting because of the fact that they were intended for passenger cars that would be used with rear seats / boot loaded ,suspension levels etc.

[Tim Falce]

Just had a thought, when we bleed brakes with a dual master cylinder fitted as on a road car when you open one bleed nipple and pump, the the pedal goes to the floor.
So whilst driving, if we had a total failure of one system then the pedal would go to the floor, would there therefore be any pressure on the other system in this case?