Brake Master Cylinder Question

[Bob and Carol]

Would anyone know what make and type of master cylinder this is please?

The car is a 420R, 11 months old built by Caterham and I have never been happy with the brakes from day one.

My thinking is, if I was to have a smaller bore then this would increase the pedal stroke and give me more force onto the pads. I have not been able to lock the front wheels, my van has better brakes than this car!

I did not want to change the pads to a type that need to be warm before they work, I would sooner have consistency from the brakes. I plan to use the car mainly on track.

Any ideas would be great please.

[Wrightpayne]

That looks like the AP race master cylinder. I've fitted one of these and you're right they do need a good shove over the standard cylinder, however, I've never had an issue stopping (on a sixpence).

You've also got to factor in any 'normal' vehicle has servo assistance on the brakes whereas the seven doesn't.

I'd perhaps see if you can try a seven with the normal cylinder and/or look at pad material / glazing etc. they may work better with a different pad material. (I have mintex 1144s I think)

[aerobod - near CYYC]

Hi Bob, I think the 420R with the AP 4-pot front brakes is likely to have the 13/16" relatively high ratio master cylinder as standard. My R400D has a high ratio master cylinder and a firm pedal, requiring about 30mm or so of pedal travel and I would estimate 700N / 160lbs of force to lock the wheels. It certainly has enough braking power to flat spot fully warmed slicks at over 170km/h. I would say it needs more than two times the pedal effort than most vacuum assisted braking systems on modern BMWs or Porsches and three times that on most other cars.

If the pedal feels spongy, then the classic rear brake bleed issue may be the problem, as it is hard to bleed the rear calipers in a horizontal position.

Caterham commonly also use 5/8" master cylinders that would require 60% of the effort but with a 70% increase in pedal stroke length for the same force at the brake pedal and give pedal forces similar to that of normal sporty cars.

[Bob and Carol]

‘they need a good shove’ I had wondered if the problem was with me, as I unconsciously know when the ABS is about to come in on my other cars and know not to brake any harder. I seem to be unable to undo this automatic reaction with the Caterham. Thanks Wrightpayne.

[Bob and Carol]

Hi James, I ordered the car with 4-pot front brakes. The pedal is firm so no air. The pads and discs look fine to the eye.

It would help if I could get the car’s brakes to feel like my other cars.

Another thought was to move the top hole in the brake pedal nearer the fulcrum and angle the M/C down to keep the piston in line but think this option feels a little reckless?

The 5/8” sounds the one to try as I feel the problem is me, although one person told me they had a faulty M/C and it transformed the brakes when it was replaced.

[aerobod - near CYYC]

Bob, if you want the pedal effort and travel to be like most other cars, you would need the small bore master cylinder. The large bore one requires about the same effort as body weight for maximum braking and is best with an almost straight leg, but does give a very progressive braking effort under high deceleration braking without being too touchy.

[paul richards]

I think you will have the uprated master cylinder. The standard master cylinder has a smaller bore but I wouldn't change it as I suspect you will have far too much pedal travel. Caterham do need a good push on the brakes but could it be that your pads are glazed? I would look to change to a better pad especially if you are using on track.

[Gridgway]

Here's a mad thought.  Back in the day there were two brake pedal "leverages" the long and the short.  The long one had lots of travel and the short was a higher leverage.  I had a standard MC plus the long brake pedal, horrible, lots of travel, nasty.  I changed for the high ratio pedal which firmed up the brakes perfectly.  Now bear with, I'll get to the point sometime soon.

The race MC is renowned for being very low travel and needing lots of shove.  If the two ratio pedals still existed in the current metric Caterham world, then maybe the long ratio pedal with the race MC might be a good combo?

[Gridgway]

And completely OT, but who would do that daft cable routing along the brake pipe run?

[paul richards]

"And completely OT, but who would do that daft cable routing along the brake pipe run?"

Not sure I understand what you mean.

[ScottR400D]

#8 There are still two brake pedals, the standard one and the high effort. The latter cuts down the pedal movement but increases the foot force needed. 

Bob currently has the standard pedal and the big cylinder. Fitting the HE pedal would make his issue worse. 

Fitting the standard cylinder would require him to move the pedal further but would cut down the pedal force needed. 

[Gridgway]

#11 then the solution is probably standard MC with high effort pedal.  As I descibed I found the standard MC with the stndard pedal to be horrible,.  YMMV

#10 sorry probably too forcibly put.  If it was me I would have routed the cable in straighter route and not tried to follow the zig-zag of the brake pipe.  Just aesthetics.  Didn't mean to be insulting!

[paul richards]

Not insulting. Just seen the picture and realised what you meant and I fully agree with you. 

[ScottR400D]

#12 Having spoken to Bob I think he's looking for increased braking with a lower force from his foot and isn't too concerned about having to move his foot further. Both the race MC and high effort pedal increase the force needed from your foot with the advantage of less pedal movement. 

The high effort pedal with standard MC might be a compromise that works but theoretically the standard pedal and standard cylinder would solve Bob's issue best. So the way forward is perhaps to fit the standard MC and see how things are. If then the pedal travel is too much for Bob he could fit the HE pedal

What I think is certain is that fitting the HE pedal with his current MC would make it worse for him. 

 

[Bob and Carol]

#11 and #14 I agree, a standard M/C with my pedal and it would make it more like I am use to as James said in #6

[Bob and Carol]

#12 As I have the standard pedal I will try that first and if I find, as you say “it’s horrible “then I change the pedal also.

Either way something has to change, just I hope it’s not me.

[paul richards]

I have a standard master cylinder if you want to try it.

[Bob and Carol]

Thanks very much, PM sent.

[22daz]

Bob and Carol,

With you having the 4 pot brakes and assuming you have a firm pedal, I don't think the issue you have is with the master cylinder. I had exactly the same problem with my new 420R and it was down to the material of the AP-DS25HP standard pads Caterham supply the 4 pot kit with.

When I removed them after 4000 miles and a couple of track days they had only lost 0.1mm in wear and my front wheels never got dusty. In fact I was pressing the brake so hard, I wore the rear pads away first! I could never lock the front up. 

I believe the AP calliper is from a Lotus which requires harder compound pads, however the Caterham isn't heavy enough to get them to work. Swap them for Ferodo DS2500 for around £90 and see how you go. You will often see brand new DS25HP for sale, there's a reason for that. 

22daz

[Bob and Carol]

#19, thanks 22daz.

Same with myself, I have little pad wear and nearly all my miles have been done on track.

I have done the odd track in another car I have and got brake fade in just a few laps. I was recommended to change the pads to DS2500, this I did and it gave better braking, I was told to change the rears also to DS2500 to keep the car braking in balance. With the car being so light, would you know if this could be the same for a Caterham?

[aerobod - near CYYC]

For track use the DS2500 are good on the rear of the Caterham, they are more aggressive once hot than the standard 507CC pads. The DS2500s when cold provide less braking than the standard pads, so will require more pressure for emergency use on the road if cold. With the standard AP pads, as mentioned previously I have no problem locking the front wheels at any speed on track, in fact on cold tyres they can lock the wheels a bit too easily.

I have also had little front pad wear, but 507CC pads only give about 5 track days on the rear and DS2500 about 7 days (about 1,800km / 1,100 miles) before being worn down to 2mm.

[22daz]

When I changed my front pads to DS2500, the difference in performance was much improved. After a 20 mile drive there was finally some brake dust on the front wheels, I could lock the wheels easily, which I never could. However I still didn't have the firm pedal I desired.

I realised that the rear pads had been overcompensating the lacklustre fronts and wearing excessively. Surprisingly they were almost down to to backing plate. I quickly changed them for similar pads which restored the pedal feel (I needed them quickly for a track day).

I have replaced the rears now for DS2500 which I have all round now. If your front pads are AP DS25HP, which is likely, then I would recommend trying this route before reverting to an inferior (standard) master cylinder. 

22daz

[Beagler]

Ferodo DS2500 Competition Brake Pads offer low and high speed braking efficiency, reduced stopping distances and a consistent brake pedal feel from the start.

Low noise / low dusting

Long pad life

Kind on discs

Race pedal feel

This new generation of friction material is very low in compressibility ensuring a firm pedal, whilst still providing low wear rates for discs and pads. Combined with low wheel dusting and good noise characteristics, this compound is the brake pad for the driver who demands the ultimate in track day braking performance.

DS2500 pads offer a consistent coefficient of friction (0.42) at all temperatures

Ferodo DS2500 brake pads are designed for competition / off-road use, and as such are not approved for use on the road.

[John Vine]

#23:  Well, that's (verbatim) what Demon Tweeks say here.  Do you have personal experience of these pads?

JV

[Bob and Carol]

Thanks everyone for all the suggestions, reading all that has been said has been very interesting.

So for now, I am staying with the master cylinder and pedal the car came with and changing the front and rear pads to Ferodo DS2500 and then learn to push harder on the stop pedal.

I had to take the front caliper off because the top caliper pin hits the mug guard stay, I wonder why Caterham has not put a small kink in the stay, have they not been making these cars for a few years now?

No worries, I will just unbolt the calipers then.

Ha-ha that was a laugh, using a Torx bolt would be ok if not for the red (I am not letting go) compound that has been used on them. Four new cap heads and the use of a tap, sorted.

Next stop, Castle Combe 9^th May.

An interesting car to work on and so much easier with the help from this site and you guys, thanks very much for all your input.