The cheapest way to upgrade the brakes.

[DeanG]

Thanks. I wish I had this information when I went through the agony of having my master cylinder rebuilt. I may have to get one of these as a spare.

[inkitin]

I'm also interested in this "upgrade". I'm not unhappy with my standard OEM brake set up but a small improvement would, I think, be beneficial.

I have just one question and it's about a situation which may well be very unlikely but I'm still going to ask it.

What would an insurance company's attitude be to this modification if it was undeclared and found following a claim? I do think I'd be unhappy to carry out this modification without declaring it!

[epipete]

Interesting question, I think that they might try to wriggle but if you have had an MoT done between the mod and the claim then the car was deemed road worthy and so should be covered, but there might be some legal wrangling.

On the other hand why would they look?

[dapinky]

On the other hand why would they look?

And if they did look, they'd see a master cylinder which looks the same as the OE one (it's only the internals which differ) - unless they took it apart and measured it, and I can't see that happening.

Put it this way, with all of the Vehicle Examinations I performed whilst working, I never once dismantled a master cylinder.... calipers, yes - but not the master. As long as it was free and displacing enough fluid to lock the brakes (tested static, not driving the car!) with 15% reserve travel, it was all that is/was required.

[Rusty Wishbone]

As long as it was free and displacing enough fluid to lock the brakes (tested static, not driving the car!) with 15% reserve travel, it was all that is/was required.

I would be interested to know if you are happy that there is at least 15% reserve travel when you install it.

[dapinky]

Well, if the weather is a bit improved tomorrow, I'll measure the movement of the pedal/pushrod/cylinder as fitted at the moment and do some more maths!

[Rusty Wishbone]

I see that Euro Car Parts stock Pagid master cylinders (132720748) at £86.40, which seems expensive compared with the prices mentioned earlier in this thread.

[johanvanboven]

It's back in stock now at mister-auto.co.uk for £48,58.

[epipete]

Would this change have any impact on the (currently non existant) dual system or am I barking up the wrong tree? Having lost all brakes a couple of years ago when a hose gave out I am very minded on the safety issues, the previous comments have assured me somewhat on standard usage but what would be the impact of sudden brake line failure if this was installed would it restore the system to allow some two wheel braking?

[Rusty Wishbone]

I have to say that I thought the main benefit of a dual circuit braking system was that failure in one circuit would not affect the other. So far as I understand it, the Elan already has a dual circuits, but it didn't prevent epipete from losing brakes. His question about whether this GM master cylinder improves safety is a very good one.

[dapinky]

Pete,

I believe the term 'dual-circuit' brakes (certainly on the elan - and probably everything else on the market, with the exception of the exotics) is often missunderstood.

In a 'true' sence, the only way to have a 'dual' system is to have 2 master cylinders - side-by-side - and the pistons are activated together with an adjustable linkage from the brake pedal.....

....by careful selection of the cylinder bore, and the pivot points on the linkage, you can regulate the flow from the cylinders so that one works much 'better' than the other - as such, one does the front wheels, one does the rear - giving an almost infinate percentage split front/rear (in the same sort of way that the elan has a rear presure-limiting system). As the 2 hydraulic systems are totally seperate, and failure of the pipework means that the other system should still work, to some extent. This is the system as used in Competition Cars, and other high-end stuff.


What we actually have is a 'duel-reservoir' tandem master cylinder - a clever bit of design to fit in a smaller (comparatively) space.

The inside chamber is split in 2 - so you have one piston working one circuit, and the other feeding the oposite corners....

static-schematic.gif

The link between the 2 pistons relies on some pressure in the system 'pushing' against a spring which is sending it the other way - only when the fluid pressure overcomes the spring pressure will the second 'cylinder' generate any force into the system. If the 2 pistons were simply joined mechanically, then you would still get one half working when one half fails - but it isn't the case (although most people think it is!).

One option is to replace the 'dual' system with a single piston M/C of larger bore (as the current system sends twice the volume of fluid into the calipers than a single piston would) - but this would be illegal on a 'modern' car!!!

What you will actually have (if one circuit fails) is a chamber full of air, which when you press the brake pedal, compresses - so no fluid goes down the pipes. There is insufficient pressure to overcome the spring tension sufficiently to operate any brakes.....

.....if you pump the pedal, you *may* get enough pressure to do something, but in reality, it doesn't usually work like that.

The whole thing is meant to stop a 'slow' fluid leak from emptying the reservoir totally, meaning that when the warning light comes on, you realise that you have a problem (which needs rectifying!) before the fluid all dissapears onto the floor - and into the environment (bloody 'green' policy gives everyone the impression they have 'dual brake circuits'!).

In reality, the biggest issue is the maintenance of the brake cylinder seals - it is often (read 'always') overlooked as it isn't on any maintenance schedule anywhere in the world - it's a fit-and-forget component which no-one ever looks at - until it fails

If the brake fluid is changed every 2 years (in accordance with the maintenance schedule), and complies with the relevant design specs (DOT4 in our case), then all WILL be okay - the seals will self-lubricate and remain intact.

If the fluid isn't changed (or has been in use for longer than that at ANY time in the past), then the seals *MAY* be beyond their best, and liable to fail at some point.....

....as we know, brake fluid is hygroscopic (it absorbs water), lowering it's boiling point over time - leading to a possibility of water vapour in the system under extreme pressure (normal working!) and temperature - vapour compresses, and brakes feel 'spongy' - time to change the fluid, and all is well.....

....except it isn't.....

....the rubber seals in the M/C will have been affected by this vapour, and will be liable to degenerate.....

...the vapour causes corrosion inside the system, which can cause abrassion to the seals....

NONE OF THIS GETS SEEN - AND IS OFTEN IGNORED, until it's too late.

As such, the only remedy is to remove the M/C and replace all seals (and clean the bores!) before a catastrophic failure of the M/C. (and then stick to proper fluid change regime).

Whilst this is a bit of a 'scare story' scenario, and M/C failure is far rarer than a flexi-hose failure (which in turn - as long as they're fitted properly and checked regularly - is rarer than a caliper seal failure), it is a real danger as any 'leak' of the seals doesn't always get seen - it leaks inside from one chamber to the other, and no fluid actually escapes - but if it does, it tends to go into the servo anyway, so gets sucked away into the engine and burnt off - unseen.


Bottom line (to answer the actual question posed!) - this change will NOT give a true 'dual' system, as there is still only one cylinder - but at least you'll have new seals which will last forever (as long as you regularly change the fluid).

(PS - best value DOT4 brake fluid at the moment is at Halfords - £18 for 5 litres!)

[epipete]

Again, Dave, I bow before your encyclopaedic knowledge; seriously I am keeping a folder for all this interesting data that you and John provide to me (really, these articles should be in the wiki under a new category "Mechanical Information for ignorant former Civil Servants' would make a good heading).

Thanks

Pete

[dapinky]

Again, Dave, I bow before your encyclopaedic knowledge; seriously I am keeping a folder for all this interesting data that you and John provide to me (really, these articles should be in the wiki under a new category "Mechanical Information for ignorant former Civil Servants' would make a good heading).

Thanks

Pete

Pete, it's just a combination of a reasonable memory, interest in the 'what-if?' questions of life, and a desire to understand how/why things do or don't work..... (some would just say I'm a 'nerd' - but quite handy to have on a pub-quiz team )

[Simon_P]

A good find Johan - Can you give us an update on your experiences now that you have had a few months trial?

Ray's sage observations all those years ago hold good today. Having re read loads of the stuff that has been written I reminded myself of the somewhat logical ratio between the diameter of the master cylinder and the calliper pistons. It seems that it is popular (and expensive) to go up in size on the callipers, rather than down in size on the M/c. The pedal travel being a function of that ratio.

£50 for a 20.6mm Master cylinder buys you 16%
£500 for bigger brakes buys you how much? 13 - 30%? so 5 times more expensive.

But there is more to it than that
- Bigger callipers move the brake bias forward
- When the Brake limiters cut-in the bias is moved further forward still
So with bigger front callipers the rear brakes do less and less.

Whereas the smaller diameter M/C will maintain the same bias but reduce the pedal effort.

That's where my thought process runs out at the moment - Does anyone know which is better?
Has anyone tried the smaller master cylinder?

[dapinky]

Has anyone tried the smaller master cylinder?

Sort of.......

.....i fitted one in February, then broke my leg a bit so havent driven the car since!

(in fact, I only bled the brakes through 2 days ago, so can't comment on how it feels!)

[Simon_P]

Please let us know how you get on Dave. I've great hopes that this is the right way forward (as well as the best value)

I've been doing some research on other master cylinders - so far today I have an Obsolete, an on order , and an out of stock not getting any more.

The issues seem to be the same as for the standard M/C - The outlets are different sizes.

Assuming you have the UK M/C and it all fitted ok - Does yours have the bleed screw in the middle of the M/C ?

[rip]

Please let us know how you get on Dave. I've great hopes that this is the right way forward (as well as the best value)

Value - no contest.
Improvement - yes.
The 'right way forward' - a matter of opinion.

The biggest problem with the stock setup is that the front disks & calipers don't dissipate heat very well. They are so bad that disks are warped well before the pads have worn out.
So if you are happy to change your discs every year (& I know at least 1 owner on here is ) then fine.

[johanvanboven]

Hi, as I told before, it is a nice improvement for normal use.
Now you can slow down and stop in any situation, but do not slow down from 100 mph untill zero for a few times, the original brakes cannot handle this.
If bleeding was done well, you won't even notice the slightly longer pedal feel.
As it still uses the original discs setup, in rain the rear wheels can be locked, the system stays well balanced.
FYI, the plug and play master cylinder is still available: http://www.mister-auto.co.uk/en/search_ ... MF172.html
At the front, I fitted Brembo Max discs and braided steel hoses, but don't feel a lot of difference. The discs clean-up faster, this is better.
BR. Johan

[HJ2]

Bedankt Johan!

Any thoughts on this swap combined with, dare i say, Bob's Hi Spec's on 16" ? (or PNM for all that matters

[RayD]

The biggest problem with the stock setup is that the front disks & calipers don't dissipate heat very well. They are so bad that disks are warped well before the pads have worn out. So if you are happy to change your discs every year

You sound like Bob Iain,

The biggest problem with the stock set up has nothing to do with their capacity for dissipating heat.

If it were possible to install equipment to keep them at whatever temperature you deem suitable, you wouldn't notice any difference.

My front discs were last changed on 10th April 2003.

Ray