Brake Failure

Post by **Chris** » Sat May 15, 2004 12:47 pm

Had a very scary moment yesterday; The footbrake failed while going down an 18% hill onto a main road!

Unfortunately I couldn't stop her before the road (to use the handbrake never occured to me), and I'm just counting how lucky we were (as I had some mates with me) that there was a lull in the traffic.

Shes now at a local garage (thanks to the AA) but I'm just wondering what could have caused this so I can maybe go and buy some new parts, for monday so that they can be fitted.

The symptons are these:

There is still fluid in the system
The pedal still feels fairly normal
The brakes do work but only incredibly lightly (not even enough to make a difference while going uphill!, but enough to stop a jacked up freely spinning wheel)
The handbrake still works
They failed very suddenly

Cheers for any advice,
Chris

Post by **Kevin** » Sat May 15, 2004 2:15 pm

When was the last time the brake fluid was changed as it absorbs moiture over a period of time, plus being fully loaded on a steep hill may have caused the fluid to overheat/boil, what happens if you press on the brake pedal for a time, does it start to go down a sure sigh of air in the system, and when were the brakes last adjusted.

Post by **Chris** » Sat May 15, 2004 2:30 pm

I'm not too hot on brakes, but on the last MOT (in November) a leaking wheel cylinder was found, this had to be replaced so I presume that the fluid had to be bled and changed in the process, as well as the brakes being adjusted.

I can't really comment much more on the pedal as the car is under lock and key at a garage until monday, but the pedal didn't creep down before.

Cheers,
Chris

Post by **Chris Morley** » Sat May 15, 2004 5:56 pm

Sounds very hairy, lets be thankful it worked out o.k for you...

There's a lot of possible causes, but I would guess that the brakes suffered from severe fade (not surprising with such a steep hill). Glazed material on the brake shoe pads would account for the lesser braking ability even after they had cooled down. Any car with drum brakes can suffer from this and boiling hot brake fluid certainly won't help the situation. The idea is to use engine braking descending a steep hill, additionally using the brakes sparingly for short applications (then releasing to allow an element of cooling).

Questions:
Did you pump the brakes ? - this can help in certain situations...
Was there are strong smell from the brakes?
Were the front wheels radiating heat?
How new are the front brake shoes?
What gear were you in?

I would select 2nd for descending such a steep hill and I know my brakes are well adjusted (if I was in any way unsure I would have used 1st). Then if the brakes failed I would crash the gears into 1st, pull the handbrake hard and try to weave from side to side. If it was properly adjusted the handbrake would just about stop you on a 1 in 6 gradient unless the brake material was already very hot.

Chances are you will need new brake shoes and new brake fluid (the garage will probably have only partly replaced it). The condition of your drums will need to examined very carefully, especially if they are old & worn. In this case new drums on the front would increase stopping power and help to some extent with fade.

The garage should have adjusted the brakes on both front wheels (at a minimum) but 7 months of subsequent braking will probably mean they needed further adjustment. I do mine every 3/4 months (i.e 1000-1300 miles) to be sure. And there aren't any steep hills around here either....

Post by **Chris** » Sat May 15, 2004 9:18 pm

Cheers Chris

Did you pump the brakes

- Yes I managed that, I held the brakes for a short period, and then released for a short period before applying again.

Was there are strong smell from the brakes?

- No there was no smell

Were the front wheels radiating heat?

- The wheels were warm to the touch and were hotter than the rears, but I don't think they were hotter than usual.

How new are the front brake shoes?

- I've no idea on this - I've never had them changed and I don't have much of a service history with the car.

What gear were you in?

- I was in second gear for that, but never managed to down to first

And cheers for your advice I will try and adjsut these myself more often now.

Think I may well enquire about an advanced driving course soon!

Cheers,
Chris

Post by **Peetee** » Sun May 16, 2004 9:47 pm

Glad to hear nothing nasty came of it. I had a moment in one of my Mogs once where the pedal just went to the floor. Two seconds later it was fine but my nerves wern't!

I have often wondered if killing the ignition whilst the car was in gear would act as an emergency brake? In the case of a moggy, being rear wheel drive they wouldn't be as effective as, say a Mini or Morris 1100. Anyone have any comments?

Post by **rayofleamington** » Sun May 16, 2004 10:08 pm

As long as u dont have a steering lock it is ok to turn the ignition off in an emergency, however engine braking is not particularly improved by that until you get to low speed.
You can get down to 2nd for best braking - to get down the gears easily you may have to rev the engine up, then let the gas off after you got into the low gear.

Post by **brixtonmorris** » Mon May 17, 2004 4:19 pm

failed master clyinder, or the plundger on the master came out.
do the brakes work after 2 or 3 pumps, could just need adjusting.

Post by **Chris** » Mon May 17, 2004 7:35 pm

Hi all, the garage aren't exactly sure what could have caused it. Although the adjusters were at the end of adjustment, the brake linings are really hard, and the master cylinder seals may be really stiff.

So I'm going to get all the linings or shoes replaced, and the seals on the master cylinder (or maybe a new master cylinder altogether).

Cheers for your help,
Chris

Post by **Chris Morley** » Mon May 17, 2004 8:41 pm

Hi all, the garage aren't exactly sure what could have caused it. Although the adjusters were at the end of adjustment, the brake linings are really hard, and the master cylinder seals may be really stiff.

It's worrying that they can't pinpoint the cause. The snail cam adjusters shouldn't get to the last notch even if the brake shoe lining was fully worn -I think this is a big clue if this is what you mean by 'at the end of adjustment'. This might point to the drums also being badly worn? This is something you would certainly notice was wrong if the brakes were regularly adjusted by yourself as the snail cam clicks over after the last notch and suddenly feels loose.

In your first post you mentioned a replacement wheel cylinder - which wheel was affected? If it was a cylinder on one wheel then it doesn't follow that the garage would take all the wheels off and adjust the brakes for you. They should do this during a service however.

Do you know how thick the remaining brake material was? - it's supposed to be replaced when it gets down to 4mm thick. As for the hard surface of the lining - it may be that at some point in the past they overheated and glazed over and when you really needed them to work they were too glazed to work properly. If you get the modern lining material (without asbestos) it gives off a really bad smell when very hot - however I'm not sure what happens with the older material.

It may be of course also be that there was a leak or seal failure in the master cylinder which allowed the pressure in the brake circuit to reduce after the initial push on the pedal. In that situation rapid pumping might have helped the brakes to bite for a short while.

To be sure you'll have to go down the same hill (but in 1st this time) once the new brake linings are worn in. Make sure all the brakes are properly adjusted (backed off one notch) before you do this.

Post by **brixtonmorris** » Mon May 17, 2004 8:51 pm

chris Morley, do you think that if funds are avalible the master clyinder should be replaced along with shoes. then over the next year Chris can see how the clyinders hold up?

Post by **Chris Morley** » Mon May 17, 2004 9:04 pm

Ideally yes, I would replace the master cylinder unless you could be 100% certain it wasn't at fault. The chances are it's well past it's prime. The same goes for the front drums as well. I guess this might cost £200 including fitting but this is an area where cutting corners isn't wise.

It depends on Chris how far he wants to go - after such a frightening experience I wouldn't want to leave anything to chance.

Post by **Chris** » Mon May 17, 2004 9:33 pm

Hi Chris, it was the front right which had a new cylinder fitted, and I think both fronts were adjusted afterwards.

If the drums themselves are in bad shape (as you've said could well be the case) then I will try and get them replaced (maybe the rears aswell) along with the master cylinder and shoes. Unfortunetly it's likely to be far more than I can afford, but thats what parents are for

Oh and it looks like more frequent adjustment for the brakes - I think it's well justified!

I don't think I'll test by going down the same hill again as it's a fair few miles away (although there was a nice pub at the bottom - probably one of the best places to breakdown), but devon isn't short of hills! Thinking about it I could well have overheated them in north devon a couple of months ago, where there were two or three 25% gradients.

Cheers,
Chris

Post by **Matt** » Mon May 17, 2004 9:37 pm

Its not hard to adjust the brakes.... I normally do it at around 1500 mile intervals, takes about 5 minutes per wheel

Post by **Chris** » Mon May 17, 2004 9:39 pm

Brill!

Post by **Matt** » Mon May 17, 2004 10:48 pm

I'm assuming you know how to do it?

Post by **Willie** » Mon May 17, 2004 11:24 pm

I must say, having read your previous posts that it appears
that, as Chris Morley suggested, that you have suffered the classic
drum brake failure due to chronic overheating. You cannot drive
downhill,as all modern disc braked cars do, with your foot on the
brake pedal to control your speed because the drums/linings will
overheat and lose all their stopping power. This stopping power will
restore when everything has cooled down again. Even pumping the
brake pedal when you are in this situation will not help much because
you merely raise the temperature even more! Use the engine to
slow you down by engaging 3rd or 2nd gear then you will have no
need of that pub at the bottom of the hill!
PEETEE..I cannot see what difference being front or rear wheel
drive makes to engine braking? Turning off the ignition,provided
that the car is still in low gear should be marginally more efficient
than having the engine on 'tickover'(i.e. foot off of the throttle)
Or is your theory based on the fact that the front wheels do most
of the braking effort normally?

Post by **andreaj** » Fri May 21, 2004 4:44 pm

I have just had a similar experience. Last summer one of the brake pipes split and dumped fluid down the road - not much use when coming up to a roundabout! Still engine braking and handbrake did the job, with wobbly legs and a hot flush the only negative results.

The brakes were fixed by my usual garage and everything was hunky dory. In December, pushed for time, I took Betty off for her MOT to a garage closer to home. I collected the car, with fresh MOT only to find the brakes, that had been working before the test were now not working - fine if pumped but no good under load.

Off she went, back to the garage and brakes were duly bled. Braking did improve but then on testing an emergency stop, they still weren't as solid as they should be. This time, I tried bleeding the brakes myself. Again an improvement but still wouldn't hold the car on a steep hill without pumping.

Betty has just come back from a brake examination at my usual (trusty and reliable garage). The brakes are now back to normal and working perfectly (or as perfectly as Moggy brakes ever do). Although it was suspected that a new master cyclinder might be required, this was not necessary. The garage had replaced the brake fluid and used a high pressure brake bleeding instrument, and the problem is fixed. Replacement of the fluid was only necessary because I originally had silicon and the garage only had the bleeding instrument for use with Dot 4 fluid.

Moral of the story - when you find a good garage, stick with them even if they are miles from home.

I also thank my lucky stars that driving a classic encourages the use of engine braking as standard driving practice - by the time I realised the brakes had failed, I was only travelling at 5mph. In a new car, I think the consequences could had been more serious.