Dodgy brake pedal

[Noel Mclaughlin]

Driving along yesterday at about 60kph in light traffic fortunately when I braked very lightly on a slight gradient AND SHOCK HORROR the prevoiusly nice firm brake pedal fell almost to the floor with just enough pedal left to apply the rear brakes. After a quick change of undies in a telephone booth handily placed nearby I inspected the near brakeless 7 and found plenty of fluid in the reservoir, no leaks to be seen anywhere. After cautiously driving to my destination and parking for about 2 or 3 hours drove home with what was now a magical self healed braking system.

QUESTION: not being a cheapskate and being totally cowardly about these things I am taking the view that something has gone wrong with the hydraulics, and most certainly in the master cylinder. Can anyone suggest a likely cause of this failure so that when I pull it apart I can be REALLY SURE that I get it right? I was not impressed by the "brake specialist" that I consulted who said that sometimes these things happen, don't worry about it if they feel OK now probably won't happen again!!!!

[Irrelevant]

Are the brakes old - i.e. the car's not a new build?

Have the brakes been working OK for a while and this incident out-of-the-blue?

Had you just been braking very hard and then stopped with the hot disks heating up the fluid? - this can cause the symptoms you explain.

If the brakes normally work OK then I don't see why it should be the master cylinder.

If there's any chance it could be down to old brake fluid, replace it and bleed the system fully. IIRC as a rough guide, brake fluid should be replaced annually and it's often overlooked, so it's a good idea to replace the fluid anyway.

 

J351 TPE . . . battered old X/Flow

[Nov-07]

I have had this happen twice, not in a Caterham but in a former tin-top Stage 2 XR3i. It once happened while driving a colleague from Henley to an urgent meeting in London. When we arrived at our destination I apologised for my lack of conversation en-route and explained that we had no brakes! The second time was on the Missenden (Bucks) bypass with the family in the car. In each case the car had previously been parked facing down a slope. Some failure of the brake master cylinder caused the piston to move forwards and to stay there. Parking the car on the level and leaving it for an hour usually removed the fault symptoms. Replacement of the master cylinder was the immediate and permanent cure.

 

TonyK

[Swiss_Tony]

Double check the rest of the braking system to be certain.

 

It sounds like a master cyl fault. Its quite common for them to behave like this on all sorts of cars.

 

James

Su77on Se7ens

 

[Irrelevant]

Can someone explain how a master cylinder fault can cause this please

 

J351 TPE . . . battered old X/Flow

[Noel Mclaughlin]

Thanks for your input everyone, having now removed the offending master cylinder I can now say with certainty what caused the problem. Firstly old age and some pitting in the bore, secondly some total idiot has had this apart before I aquired the car and reassembled it with ONLY ONE OF THE 2 SPRINGS WITHIN THE CYLINDER. Now according to my brake man the pedal should have been mushy and would not have released properly. The pedal did not behave like this and was obviously being returned by the external spring fitted to the pedal at the pedal box.

Moral of the story ................ If you buy a used car pull it to bits and check every thing safety related, this problem took 3 years to show up in my case.

[Bilbo]

Hi Noel

 

After a quick change of undies

 

I know the feeling I have lost the lot twice on the road with punctured brake lines on tin tops. Well they were a few years ago. To say the least its a trifle upsetting.... rather OH SH*TE...........

 

Both cars had the brake lines on the front of the rear axel....... not fun at the legal limit before a roundabout in one case.

 

'Can you hear me running' ......... OH YES and its music to my ears 😬 😬 😬

1988 200 bhp, 146 ft lbs, 1700cc Cosworth BD? engineered by Roger King, on Weber's with Brooklands and Clamshell wings, Freestyle Motorsport suspension.