Brake failure !

[Giles Wardle]

I have a live axle Scholarship 7.

Went out for a gentle country blat, pootling in 30mph zone, apply brakes on approach to T junction, NOTHING.. foot goes to the floor without any resistance whatsoever. Pump the brakes a bit and back they come.

 

Does anyone have any idea what the problem is ?

 

Car was recently serviced by Cat. Mid. and new brake fluid fitted and since then I've done no more than a 200 miles and 4 laps of Curborough.

 

The experience is very disconcerting, because this phenomenon was the cause of my crash at Cadwell last year resulting in £5,500 worth of damage and front chassis re-built by Arch. Fortunatley the insurance company paid out and the brake problem was attributed to boiled brake fluid/ingress of water into the fluid.

 

However this cannot be the cause this time as the brake fluid is fresh and hadn't been using the brakes in a manner that would boil the fluid.

 

Surely couldn't be air lock as the brakes wouldn't have come back ? Or would they ? Brake master cyclinder ?

I have contaced Cat. Mid. but no reply. So any suggestions or remedies would be gratefully received.

[Joe 90]

The phrase "pump brakes a bit and they come back" rings bells. This would be consistent with pad knock-back, which is when the disks push the pistons in to the calipers. For that to happen, the disks must be moving sideways, so jack the front wheels up and try to shake the hell out of them. I assume there is no sign of brake fluid where it isn't supposed to be?

 

98,000 miles so far

[Paul Ranson]

Logically, I think, if it's not leaking then it must be the master cylinder. Knock back in the described circumstances seems unlikely, and if it were knocking back the pads sufficiently to get the pedal to the floor then what's holding the wheels on?

 

If the pedal does/did feel right then it's not air in the system. And IMO it would be surprising for trapped air to cause a complete loss of brakes and pedal on the floor.

 

I suggest a consultation with Caterham Midlands and not resting until a cause is found.

 

Paul

[aph]

firstly i'd change the fluid to silicone it doesn't absorb any water and has a high boiling point then check that the disks aren't warping (probably not but worth a check anyway) then check for leaks/air bubbles other that that get it checked asap

[scooby dooby doo]

a change to silicone is a tad excessive and fraught with other problems:

complete flush of system required

new brake fluid required every year

 

for those not racing this makes it impractical.

 

After a few weeks and at low temperature means that this problem cannot be due to the brake fluid being full of water...

 

HOOPY CYCLE WINGS CUCUMBER

[J.R.]

You have a faulty seal in the master cylinder.

 

Try very slowly depressing the pedal with little force (or even down a bit, back a tiny bit then down a bit etc etc) and it will probably go to the floor compared with a sharp hard stab where you will have a firm pedal.

 

If above replace immediately or brake later and harder!!!!!

[Mr Locust]

Try rocking the front wheels

 

If there is excessive play in the front wheel bearings, pad knock off will happen giving no brakes on the first pump 😳

 

Otherwise, if there is no leakage, I'd go for a faulty master cylinder

[Paul Ranson]

Silicone (DOT5) is supposed to last for ever. IMO it's unsuitable for high performance vehicles, unless you can deal with a permanently spongy pedal.

 

Use a good DOT 5.1 and change it annually. Or go with a racing fluid, AP551 or AP600 and change it more often. Dependent on your usage. AP600 is fine if refreshed a the start and middle of the season. YMMV, if in doubt standard DOT5.1 from your local auto-shop.

 

Anyway in the context of this problem the fluid is not the issue. It's the master cylinder or a leak!

 

Paul

 

Edited by - Paul Ranson on 5 Sep 2002 18:12:25

[ashaughnessy]

A warped disk will make itself very obvious as a juddering when you brake gently to a stop. You would probably notice. Also, you can check by jacking the front up and spinning the wheels by hand and looking for binding points.

 

The car has a live axle. The rear brakes can be badly adjusted so there is excessive travel for the shoes to take up to the drum. This would cause a long brake pedal. If this were the case, you would expect pulling the handbrake on would make things feel better, as it would take up the slack. However, you'd notice excessive handbrake lever travel. Easily checked though, and it's always worth re-adjusting the rear brakes.

 

Did the car behave well during the 200 miles and 4 laps of Curborough? If so, has anything else happened in between that might suddenly make the brakes not work?

 

Did you drive the car home after Curborough or trailer it? Hard track work can give you a surprisingly long pedal when everything cools down.

 

Now that you have pumped the brakes, do they work properly or do they still go to the floor on re-application? Is the problem still occurring, and what has to happen for it to re-occur after you have pumped the brakes to fix it?

 

Anthony

[Giles Wardle]

Many thanks for all your suggestions.

 

I, or more correctly Cat. Midlands, replace the brake fluid annually with Dot 5.1

No leaks so probably not fluid related.

 

There is no juddering when braking, so not a warped disc.

I think brake master cylinder may be culprit, thanks J.R. I'll brake late and hard from now on .

 

Wish I had thought up KevSull's sig. ☹️

[allen]

Giles, Braking hard, brake early, and drive slowly, i.e. emergency get you home senario - if you have a faulty seal it is trying to tell you something - stating the obvious - take no chances with brakes, get it properly fixed as soon as possible.

 

Edited by - allen on 6 Sep 2002 11:01:05

[JAG]

If it was a single faulty seal within the master cylinder then you should have had at least half the brakes working - that would have stopped the pedal hitting the floor. You would have had a long, heavy brake pedal but it would have worked. That's part of the legal requirement for every car on the road.

 

Just remebered - what sort of master cylinder is on these cars? do they have two cylinders and a balance bar?

 

My comments above assume a standard 'tandem' type master cylinder.

 

JAG

[Giles Wardle]

I've spoken to Derek Moore. He's as bemused as I am. They do not experience master cyclinder failures at all.

 

Brakes are back to normal now, even when slowly depressing the pedal as J.R sugested. I've tried slow braking, hard braking.. the lot... all works fine.

 

My mind would be at rest but for the history of itermittent failures and my dramatic crash at Cadwell last year.

 

There are two cylinders, so even the front brakes had failed the rears would still have kicked in as per JAG's post. This didn't happen, my foot went all the way to the floor with no resistance AT ALL.

 

Discs are fine, no juddering on braking and also no fluid leaks.

 

*confused* *confused* *confused* *confused* *confused*

 

Might just replace the master cyclinder/s anyway, unless anyone else has any suggestions.

[JAG]

Giles,

 

I've been trying to think of one component that could fail and render the whole system inoperative and all I can think of is the pedal and linkage to the mastercylinder(s). It would be worth checking before spending money.

 

The only other thought is along the same lines as the pad knockback replies. Had you just changed the pads etc... (pushing back the pistons to put in new pads) or tinkered with the brakes at all?

 

Without seeing the car it's a bit bemusing

 

JAG

[Giles Wardle]

Jag,

Thanks for your post. If it was pad knock-back surely the other three brakes would work and the pedal wouldn't go the the floor

 

I looked at the MC and it's a double affair with circuit for rear and a circuit for front. It must be MC failure, albeit intermittent. I think I will take it to Cat. Mid. and get the to replace the MC.

 

Tanks again for you post.

[elie boone]

Castrol SRF ( competition brake fluid ) must be changed every 18 months

[Joe 90]

According to my tame mechanic, it's almost certainly master cylinder failure. Pad knock back does stop the other brake on the same axle from working because you can't build up any pressure until the pad is pushed back. If only your rear brakes are left working, it will feel as if you have no brakes . This also applies to a master cylinder failure, which isn't supposed to leave you with no brakes, i.e. it's supposed to be fail safe.

 

99,000 miles so far