Brown Trouser Event

[Gerry Attrick]

Travelled about fifty miles in the heat yesterday. I was enjoying the drive so wasn't thrashing it, and braking hard. However, for no apparent reason, the brake pedal went to the floor as I was braking for a roundabout. The pedal felt firm when I got it down far enough and it did pull up - eventually. It didn't feel spongy and pumping it didn't help. I stopped for ten minutes to let it cool off (and to wipe the seat), and it seemed fine afterwards. I've just been out today for 30 miles and it also seems OK.

My first thought was overheating the brakes but I'm not sure, as they weren't getting much hard work.

Can anyone offer any ideas / suggestions?

[AM400]

Almost certainly binding brakes boiling the fluid. I had the same thing happen last year as I was exiting the M5 glad the handbrake was ok! once it had stood overnight they were fine the next day on a short test run, recon rear calipers sorted mine out.

Andy

[Gerry Attrick]

That's a good point. On the way home I noticed the brakes were squeeking. There's no sign that the brakes are pulling to one side, and there's no smell of burnt pad material. Will sticky brakes really get the fluid to boil?

[jchase]

I had this happen on a track day in an old Al**. I was told the boiling point of the brake fluid drops dramatically as water is absorbed from the air, so best to replace the fluid frequently, rather than buy expensive stuff. If it boils out the master cyclinder, you get lots of lovely white smoke as it purs over the exhaust manifolds , and the possibility of an engine BBQ - scares the sh*t out of the marshals too...

-Jim

[Rev-erend]

Sounds like a good time to check the breaks are not binding and change to dor 5.1

[AM400]

Gerry Attrick said:

That's a good point. On the way home I noticed the brakes were squeeking. There's no sign that the brakes are pulling to one side, and there's no smell of burnt pad material. Will sticky brakes really get the fluid to boil?

I did have a nice smell coming from mine but I had just come off the motorway, mine was pulling in a straight line too. Worth checking to see if they are binding before looking elsewhere.

Andy

[350zwelgje]

Brake master cilinder with worn/old seals can give same symptoms (my thought is especially based on that you mentioned pumping the pedal didn't give any improvements). If replacing brake fluid, and checking of calipers and pistons doesn't show any obvious improvents: it would be the next thing to look at.

Rob

[nigel_350i]

I'd reccomend 5.1, I put it in my 350i and had no brake issues on a 2hr track day...

[Gerry Attrick]

Many thanks for the comments, guys. I checked the brakes briefly on Wednesday evening, and couldn't find any signs of binding. Pistons were OK to move back and fore. Did a round trip of about 250 miles yesterday (M40/M1) without any problems. However, the brakes now squeel and pull slightly left when I apply them gently.

Seems like a thorough overhaul and new DOT 5.1 is called for. I expect I'll break at least one of the bleed nipples or pipe connectors and have to dig it out of the caliper - there's always one that's corroded in. Getting the rear ones out also looks a b*gg*r as well.

I'll keep you posted.