AX Brake Problem (Pedal going to Floor)

Jonesy · Post by **Jonesy** » 22 Oct 2003, 16:28

My Ex-wifes '91 AX 11 has a slightly worrying problem with the brake pedal going to the floor on occasions. I recently checked the brakes over and renewed the brake fluid all round (looked original)!
I'm coming to the conclusion that the master cylinder must be faulty but would appreciate any thoughts other than this. It only actually does it maybe once a week or less but its worrying because she's carrying my kids around, otherwise I wouldn't be too concerned (only joking, we get on very well).
Any ideas much appreciated. There may be a slight weep from the offside rear wheel cylinder, but very slight as its recently passed the MOT.

AndersDK · Post by **AndersDK** » 22 Oct 2003, 17:02

I seem to remember from past submissions that the brake valve on the AX has this rather dangerous tendency.
I'd instantly replace the valve for safety measures - given the very precious load your AX has to carry every day.
The low price of a new master valve from GSF calls for an intstant replacement :
N65218 BRAKE MASTER CYLINDER AX 19mm (19 STAMPED ON CYLINDER) 25.50
N65216 BRAKE MASTER CYLINDER AX 20.6 mm (20 STAMPED ON CYLINDER) 27.50

Post by **RichardW** » 22 Oct 2003, 17:21

Worth checking before you go the expense of a new master cylinder that you haven't got a binding brake - these can heat up the fluid to such an extent that you get a gas bubble, which makes the pedal go to the floor - most disconcerting!
Richard

Jonesy · Post by **Jonesy** » 22 Oct 2003, 18:21

Thanks both for your help. I've put new front pads in within the last 2,000 miles so I don't think there is a problem with binding brakes. The calipers were both free and the car has only covered 54,000 miles.

jeremy · Post by **jeremy** » 22 Oct 2003, 19:57

Your AX will have diagonal split brake circuits with drum brakes on the rear. I expect the drums are self adjusting and what has happened is that the self adjusters etc on one side have stuck. As Richard points out if a brake overheats the fluid boils and you loose that circuit. I had this happen to me in my Renault 21 and after pouring the gallon of water I always carried in it over the smoking brake and leaving it for a while all was good enough to enable me to get home. On dismantling I found the handbrake was not adjusting properly and a full strip down and rebuild put things right.
Because of this feature I'm not keen on this design of brake system as clearly if someone accidentally leaves the handbrake on all brakes will fail. This seems excessive punishment for a relatively minor mistake.
jeremy

Jonesy · Post by **Jonesy** » 22 Oct 2003, 21:26

Thanks for the advice, I will have another look at the rear brakes, but I'm very sceptical that it is the rear drums as the pedal is going to the floor when the car has only been driven about a mile or so and the rear brakes are not binding that bad if at all so would not heat up enough in that time.