Brake pedal heading floorwards...

[JimK]

This morning during the 13 miles between home and work the pedal got lower and lower. It's still stopping the car, but only a couple of inches from the floor.

What are the most common causes of this, and are any of them likely to leave me completely without brakes within another 13 miles? I'd appreciate some advice on what to check first.
Somebody has already suggested the master cylinder is giving up - would that be a sudden catastrophic failure? Should I leave the car exactly where it is or can I get home?

I have the tools with me to add fluid to the reservoir so I can do that at lunchtime.

I have discs on the front and standard drums at the back.

[RogerRust]

I would top up the fluid anyway, but the fluid level shouldn't affect the pedal untill it runs our.

I'd worry about a leaky cylinder somewhere.

Perhaps a good hard push on the pedal is called for to see if any thing gives. If it was me I'd drive home steadily - you still have 25% braking with the hand brake!!

[rayofleamington]

if the fluid level is low, then addidng fluid will probably get you home, but there's never a guarantee.
A low fluid level indicated there is a leak. If you see a small bubble rising in the reservoir after pressing the brakes (carefully avoiding the little fountain of brake fluid that comes at start of pedal movement...) then this is a sign that the secondary seal is leaking.
A leaking secondary is nearly always caused by a rusted bore and if so, you will need a new M/C.
It could however be leaking anywhere!

[JimK]

Thanks for the input. The fluid level is very low in the reservoir, and I think I can see a little hole at the bottom which having looked at a cross-section of the M/C leads down to where the cylinder is. I think that means I've run very low and air has got in.

I haven't quite worked out where the M/C is from underneath the car, but there's suspicious amounts of something fluid in a approximately the right place.

Which is the secondary seal? I'm looking at figure M.2 in my Issue 3 copy of the worshop manual, and I can't work out which you mean. If the secondary is dead, does that mean I'm leaking fluid each time I release the pedal? If I top up, then I shouldn't get any more deterioration in the brakes? No warranty on the advice is asked for...

And: Aaargh! I've just read the section on how to remove the M/C! I have to dismantle the suspension to get it out!

[alex_holden]

I haven't quite worked out where the M/C is from underneath the car, but there's suspicious amounts of something fluid in a approximately the right place.

It's inside the chassis rail just ahead of where the brake pipe comes out of the side. If it's leaking you may get fluid dripping out of the nearest drain hole on the bottom of the rail.

And: Aaargh! I've just read the section on how to remove the M/C! I have to dismantle the suspension to get it out!

I think it's possible to lever the torsion bar down a bit to get to the bolts. I took the bar off, but I needed it out of the way so I could do a bit of patching on the crossmember anyway. I found the most difficult and awkward part of the whole job to be attaching the new pedal return spring!

There's a page here that describes how to do it without removing the torsion bar, however I don't agree with the recommendation to put the bolts in the other way around when you reassemble it. The torsion bar is purposely in the way of the bolts so they won't fall out if the nuts come loose.

[JimK]

Right, I've been out and filled the reservoir to the appropriate level. The pedal has recovered a lot of its firmness and I can't push it down nearly as far.

Thanks for the warning about the little fountain of fluid, and I did indeed see a little bubble come up when I pressed the pedal. I didn't see it after a few presses though.

When I pulse the pedal a few times, the first one goes down a little further than any following jabs. Leave it for a few seconds, then the same thing happens: First stroke goes down further than subsequent presses.

What does that sound like? It seems to me like I just let the fluid run too low and I need to bleed the system.

I propose to drive home carefully then bleed the system at the weekend, along with checking for obvious leaks. I'll keep checking the fluid level every day and see how fast it goes down.

[RogerRust]

sounds good to me
The first time you press the pedal the shoes move out. So the next few attempts it will be firmer. If you leave it a while the shoes creep back and the process repeats. If the shoes need adjusting this is more pronounced.
I'd still take the drums off at the weekend and see where the fluid is leaking.
Rog

[JimK]

When I greased the suspension a few weeks ago the front calipers were bone dry, so unless they've started leaking badly in three weeks it's not them. I'll check for leaks in the rest of the system before I go through the hassle of getting the M/C out.

[RogerRust]

It could be an internal leak in the servo if you have one. I've heard of fluid dissapearing that way.

[JimK]

No servo on mine but I'll remember that for future reference as the Trav has one.

[Peetee]

Take advantage of the dry spell and pump the pedal really hard while the car is stationary. Then check for leak patches on the road.

[d_harris]

good plan.

[Packedup]

What does that sound like? It seems to me like I just let the fluid run too low and I need to bleed the system.

The fluid's gone somewhere, and it's highly unlikely that somewhere is inside the brake system!

If the area around the master was damp with fluid (rinse well and repaint, brake fluid eats paint and leads to rot) then the master is probably rather ill.

Remove it and check under the dust seal for signs of fluid. If it's anything other than bone dry rebuild or replace.

[bigginger]

I don't agree with the recommendation to put the bolts in the other way around when you reassemble it. The torsion bar is purposely in the way of the bolts so they won't fall out if the nuts come loose.

And the bolts have a special thin head to stop them wearing on the T bar (OK, to stop the bar wearing ) which the nuts will do - possible breakage.

[rayofleamington]

I think it's possible to lever the torsion bar down a bit to get to the bolts.

yes. I've done this approx 4 times now and although it isn't fun, it gets the job done.
Refitting the bolts the correct way round will avoid having big grooves worn into your torsion bar over the next few years.