Brake Fluid

[Adrian Williams]

Time for a change of fluid, I’ve had the car for two years without changing it and last time at Brands the pedal seemed to lack a bit of feel.

 

Before I use standard DOT4 is there anything else I should consider? Silicone sounds interesting but Caterham say no, any idea why?

 

Car is used for track days and occasional Sunday morning blasts, has AP 4 pots up front and standard discs at the rear.

 

[Richard Phillips]

I,ve used silicone fluid for the last 3 years

and not had any problems. Its safer if you spill

it near paint and i don,t think it absorbs moisture.

 

[Alex Wong1697456877]

I use the same brake setup Adrian. With standard DOT4 (although probably due a change) on a short track with 2 very heavy braking points, I was getting a soft pedal after about 3 laps. I've now changed to Castrol SRE fluid which is very very very expensive!!! I hope it's better. smile.gif

 

Alex

[EFA]

Adrian,

 

Silicon has a low boiling point like DOT4 relative to racing fluid.

 

If you buy AP RAcing AP600 you will not get the pedal drop, (Although pad material overheat could still give you fade)

AP600 is not cheap, and although AP write on the bottle change every 3 months, this is aimed at those who want to use it forever. I run AP600 for a whole season without issue.

 

It is a good idea to flush your system with meth's before putting AP 600 in also as it can react (It very much does react with silicon fluids!)

 

AP600 will is alos more corrosive than normal fluid, but with a little care this should not be an issue.

 

 

 

 

Arnie Webb

The Fat Bloke blush.gif in a not so Slow Vauxhall wink.gif

 

See the R500 eater here

See the Le Mans Trip Website here

[stevefoster]

I used Lockheed 5.1 last change. (big AP brakes)

Fine on the track, no fade or sponge. After a cool down in between sessions the pedal was a lot softer. This went away on the out lap.

 

The vented disks works when there is air flow! Stop the car and the heat sink takes affect.

 

After that I always do a cool down lap before coming in and haven't had the problem since....

 

This happened on a free pitlane track day where the rest was much shorted than say a L7 one of 40 mins. 40 mins probably gives enough time for the whole lot to cool naturally...

[Adrian Williams]

Thanks guys, I think I'll give the AP600 a try. Presumably 500ml won't be enough but 1ltr will?

[Mike Bees]

AP600 doesn't mix with any other type of fluid, so you need quite a lot of it to give the whole system a good flush through (if you're changing from a different fluid type). It doesn't cure the slop that you get with the std. master cylinder.

 

Mike

[EFA]

Mike,

 

My car has a std master cyl and no slop!

 

Arnie Webb

The Fat Bloke blush.gif in a not so Slow Vauxhall wink.gif

 

See the R500 eater here

See the Le Mans Trip Website here

[EFA]

Mike,

 

My car has a std master cyl and no slop!

 

Arnie Webb

The Fat Bloke blush.gif in a not so Slow Vauxhall wink.gif

 

See the R500 eater here

See the Le Mans Trip Website here

[Mike Bees]

It's not a fluid-related feature though (mine had just as much slop on AP600 as on anything else). Isn't there a mod for the std master cylinder to reduce/remove the slop?

 

Mike

[DonkeyDave]

Anyone know the master cylinder make is it Girling? If so anyone know a cheaper source than Caterhams 160 quid for the uprated master cylinder?

BTW Mike thanks for your help/advice regarding the airbox which is now finished-ish and works.

[murph7355]

There was a thread on master cylinder hunts a bit back. Long and short was that it's a specific part for the 7 and there's nowhere to get one any cheaper than Caterham themselves. You can't buy direct from Girling etc.

 

FWIW I found the pedal much improved with the uprated MBC. I find it much easier to modulate my braking now and feels much more encouraging.

 

Pads might be a cheaper place to start for a brake upgrade. They also make a big difference to feel and stopping power. EBC Greenstuff seem to be the ones to go for (I have Mintex 1144s which I'd avoid!).

 

C7 AJM

[EFA]

Mike,

 

I think there may be more than one bore size on the std master cyl. This is about the only bit on my whole car that I haven't uprated!

 

 

 

Arnie Webb

The Fat Bloke blush.gif in a not so Slow Vauxhall wink.gif

 

See the R500 eater here

See the Le Mans Trip Website here

[elie boone]

Alex,Castrol SRF brake fluid is good but expencive, i raced an Escort MK2 with std front brakes and had no problems.(4 hour races )

 

 

[elie boone]

Rally Design has a Willwood tandem master cyl. for £ 81.90 +VAT The flange is horizontal but you can buy an adaptor so it mounts vertical.

and it is made in aluminium tel.01795 531871

(bore: 1-1/16 or 1-1/32 )

 

 

[Mike Bees]

Arnie - Jeremy @ Hyperion once told me that if he bought an off-the-shelf Caterham the very first thing he would change would be the master cylinder. What a wonderfully diverse world we all live in.

 

Mike

[Asklepios]

Mike,What would the change/upgrade be to ,and to achieve what?

Are we talking bias split etc or power or that more personal concept of "feel"?

[Mike Bees]

Caterham sell a 'racing' master cylinder (it's made by AP) which has a bigger bore. This means less pedal movement, and more pedal pressure. Most of the standard (Girling I think) master cylinders have a half inch of so of pedal movement before anything starts to happen (what I've called 'slop' further up the thread), with the AP cylinder the pedal is rock hard.

 

Mike

[Peter Carmichael]

This does not compute.

 

The master cylinder has two characteristics of any importance. Latency and bore diameter.

 

A bigger bore will give a heavier pedal with shorter throw, altering the hydraulic gearing. If the pedal started off with the right weight (a subjective matter) it will end up too heavy. The gearing will just be masking elasticity elsewhere in the brake system.

 

There are other (more expensive) ways to reduce the pedal travel to better effect and they involve curing the problem rather than addressing the symptom. If there is elasticity or wasted movement in the brake system, remove it. Elasticity can be in the form of tired brake fluid, tired brake hoses. The handbrake mechanism in the Sierra rear calipers is a prime suspect. Single piston brake calipers cause lots of problems because of the flex where the two halves slide. Twin pot calipers fix a lot of the pedal problems.

 

The latency is purely a matter of design in the master cylinder and has to do with how much travel there is before the piston closes off the reservoir hole. I haven't noticed (i.e. it has not been so bad that it has brought itself to my attention) the standard cylinder being particularly bad.

 

IMO, the master cylinder is fine - it has a simple task to perform and it gives a good pedal weight (although that observation is made in regard to the Superlight setup of big front brakes). The elasticity of the brake system is the culprit. The twin pot rear brake setup fixes this for good.

 

On track the rear brakes tend to overheat. The new race big vented rear brake kit is something I am interested in to sort out all problems once and for all.

 

When I have let other Seven owners drive my car they tend to be surprised by the rock solid brake pedal and that is with a standard master cylinder.

[Mike Bees]

I must have a particularly bad standard cylinder... It's now been swapped for an AP one and the result is a slop-free setup. I'm not the only person to have had this experience, but I do remember reading somewhere that there is a mod which can be done to the std. cylinder to take the slop out of it. Just can't remember where though...

 

Mike

[murph7355]

I swapped to the race master cylinder and it made a big difference to "feel".

 

I also think it cost less than uprating the whole braking system would (I've not had a problem stopping to date with the std. brakes and a decent set of pads).

 

But "feel" is I suppose subjective.

 

C7 AJM

[Peter Carmichael]

Some simple questions to try and dig into that subjectivity a bit:

 

How did it improve the feel?

 

1 -> Is it that the weight is better for being heavier? (e.g. some modern servoed car brakes are too light making them difficult to modulate - Fiat Coupe for example)

 

2 -> Is it that the pedal isn't as squashy?

 

3 -> Would it be better still if you had as unsquashy a pedal, but with the original weight?

 

4 -> Is the free travel noticably shorter? (for my hydraulic clutch I got an AP ultra-low latency master cylinder and it makes the bite much more predictable)

 

Obviously uprating the entire brake system is more expensive, but it is attempting to fix more problems.

[Jason Plato]

Peter ,

"The twin pot rear brake setup fixes this for good."

 

Whilst I have no idea what rear brake setup you are running , I can testify that the rear twin pot set up does improve feel to the extent that you are able to brake further to the apex without locking an inside rear wheel , with the correct brake balance obviously !!.

I dont think it has much affect on the initial pedal travel though , as I still have a little "slop" , maybe 10mm , when I press the pedal but it has never concerned me .

No sign of fade what so ever though .

 

Dave

 

[Paul Ranson]

1 -> Is it that the weight is better for being heavier? (e.g. some modern servoed car brakes are too light making them difficult to modulate - Fiat Coupe for example)

 

Yes.

 

2 -> Is it that the pedal isn't as squashy?

 

Yes.

 

3 -> Would it be better still if you had as unsquashy a pedal, but with the original weight?

 

No.

 

4 -> Is the free travel noticably shorter?

 

Yes.

 

Additionally, IME, the AP master cylinder bleeds really easily. I've done a fill from dry with AP600 and only needed a single bottle. I'd bought three.... This with an AP everywhere system, which if you're buying new isn't a very expensive option.

 

It would be interesting to measure it, but I think the standard master cylinder needs more travel than the standard pedal linkage can provide without going out of its comfortable range. I remember lifting the pedal on one of my Caterhams (extend the link from the master cylinder to the pedal) and finding that I no longer had nagging doubts about whether the brakes were bled properly. This was a completely standard everywhere system with the evil Sierra rear calipers.

 

FWIW I've sat in Peter's car and I would put myself in the minority tendency. But I do have a general preference for a short travel firm pedal. Combine this with long legs and the case for AP is irrefutable.

 

I heard that the Caterham AP master cylinder originated as the standard fitting for the XJ220, perhaps one of the R500 owners could take a look around their motorhouse and check this?

 

Paul

 

[StewartG]

Having changed to the racing master cylinder with standard brakes all round and then added the big AP brake kit at the front I can relate to some of the above comments. In my opinion its easier to modulate the pedal pressure with the small m/cylinder, with more travel you get less of a binary, it's either on or it's off, effect. Having said that, with the 4 pot calipers the lengthy pedal travel makes heeling and toeing almost impossible as you can't set the throttle pedal to be at the right height for diifferent amounts of braking when different amounts of braking put the brake pedal at such different heights. I've no experience of the 2 pot AP rear calipers but I understand that with them the hand brake lever is only used to hang your take away carrier from.