Brake warning light flickers on

R

Rovertron

Member
Just as I was readying the car for its MOT as well.....

On the dash, the brake light warning keeps flicking on for a while and then off. It seems random, the brakes not being applied, sometimes being applied and sometimes when I'm just encountering some rough road or an incline, decline or even a bit of more eager cornering :)

This a '69 V8 and has such as a very simple brake warning circuit.

There's a reservoir sensor, pressure sensor and handbrake switch and that's it. As far as I know, the pads have no wire in them on a '69.

Originally, I just topped up the pot. There's more resistance on the pedal and the light goes off. Then down the road a few miles, light on, off, flicker, on, flicker, flicker, off again, flicker, off.... Check fluid level to find it exactly where it was, a little fluid seems to have wept out from the top of the lid, nothing in the engine bay.

With only two sensors, drove around with each one disconnected in turn, it was the reservoir pot sensor. Judicious use of a medium spanner on the lid had no effect as the sensors have been known to stick.

I cleaned up the sensor contacts, unwound that part of the loom to check it and cut about 2'' of wire back to shiny copper as it was a little green, new connectors scrimped on.

Sure enough not even 800 yards down the road.

Grrr.. Light still taunting me!

Park the car, start it, pump the pedal and pressure good can even hear servo piston atmosphere in operation. Not a drop of fluid on the road or from any of the numerous junctions under the bonnet, nothing weeping then.

I fitted a replacement reservoir lid and not a dicky bird from it for over 30 miles.

Then brake warning light on again! Conclude that something must be wrong with the braking system. Drive gingerly, find a quiet stretch, apply brakes fairly hard and brakes are still good. I know the pads and discs still have 50% servicable life in them. There's plenty of resistance at the pedal, little fade and not spongy at all.

The fluid itself looks a little manky, I'm wondering if air has got into the system, bubbling in the reservoir pot and then tripping that sensor... I'm clutching at straws a bit. I would have thought though that the pressure sensor would go off. I'm going to bleed the system and refill it anyway prior to the MOT.

Any ideas what could be causing this flickering light?
 
On our 2200 it was the handbrake switch which I just screwed out a bit to cure the flickering. We also have flicker on our V8 which I'm hoping is the same thing as she has pad sensors all round so it could be any of them as well as the reservoir. I'll try the handbrake first though & I suggest you try it too as it's easy enough to do though the centre console can be a bit of a pain to remove sometimes. Maybe you cured the reservoir but the handbrake switch is intermittently playing up.
 
i had the same problem, changed the cap no difference but i have just bled the system and the problem seems to have gone so it could well be air in the system.How this would cause the light to flicker is anybodys guess.
 
Thanks for some more tips here, as luck would have it, there was a job lot of bits on E-bay last week for the princely sum of £11, included was the reservoir lid and a new-ish handbrake switch too not to mention two BW65 speedo angle drives which I can sell to get my £11 back. :)

An adjustment to the handbrake switch would be first, I did check the brake is always fully down, a bit of wiggling so far yielded nothing.

One good thing has come out of it, cleaning up some contacts fixed something else, the oil pressure sender unit contacts were filthy, a bit of emery cloth and suddenly that light has sprung to life when it should at startup or in worse circumstances....

I feel in the warmer weather, replacing all the crimp contacts with new and a clean up of all the spade connectors would be a worthwhile investment.
 
The car had its MOT yesterday and sailed through prior to a service (nothing more than change of fluids and new plugs). My mechanic is brilliant, the owner an ex-P6 test driver.

Nothing wrong with the brakes, the fluid was manky so it was fully flushed, no weeping calipers, master cylinder and servo are more or less new, brake pads and disc still fine, handbrake switch is properly set too, basically two clicks on the ratchet and then light on.

The flicking brake light is a sticky float, despite changing the reservoir lid, basically the floats aren't much cop at the best of times (can't lubricate it, swimming in brake fluid all the time). He recommended getting the old one which I kept and taking it to bits which can be done apparently and giving it a good clean up.

Thought I'd let you all know.
 
When /if you go to replace the crimps can I suggest you obtain the un-insulated type that have a plastic/rubber cover. This will allow you to solder the crimp to each wire, it takes a bit longer but makes a much better job of it, especially on slightly older cables as you have to get them clean to make the solder flow, try a little fine wire wool.
 
scauto,

I did consider this as I got a nice gas soldiering tool for Chrimbo as yet unused. Basically, I am of the school of 'if it ain't broke.....' All the electrical contacts I've gone at with a bit of emery cloth have been fine..... so far :)

So I set to the brake pot with a joinery hammer and actually managed to park at home with the light still on (no handbrake)

'Smack', light off, 'Smack', light on, 'Smack, Smack, Smack' light off, 'Smack, Smack, Smack, Smack, Smack', light still off

It's better than it was, it flickers over rough surfaces at speed now :)

The other pot lid I have has drained nicely, a friend recommended an electrical contact cleaner which is apparenly very good at cleaning up and dissolving gunk dries without residue as it's solvent based. Judicious use of this inside the float mechanism might work. I haven't tried this yet though.... will let keep you posted.
 
A few issues ago in the p6 news I had describe this problem and how I resolved it.

If you take the cap off the reservoir and pull off the chrome tube bit that sits in the fluid. this revels the cork that is the float for the switch. It is a bit like a cocktail sausage on a stick.

I found that the outer layer of the cork was swollen and was easily scraped off with a finger nail. I trimmed the cork down and put everything back together.

I haven't had any trouble since.

Colin
 
Hi,

had just this problem yesterday (May 30, 2010), brake warning light flickering occasionally & randomly, but all fluid levels fine. Took off the LH (dual line system) cap to see whether the warning light came on (it should, as the float then sets to lowest position). Warning light actually didn't light up, so I guess the swollen cork is sticking in my reservoir cap as well. I will try the scraping-off job on the cork float next weekend.

Thanks yet again for maintaining this brilliant forum!

All the best,
Klaus
 
Re:

arthuy said:
A few issues ago in the p6 news I had describe this problem and how I resolved it.

If you take the cap off the reservoir and pull off the chrome tube bit that sits in the fluid. this revels the cork that is the float for the switch. It is a bit like a cocktail sausage on a stick.

I found that the outer layer of the cork was swollen and was easily scraped off with a finger nail. I trimmed the cork down and put everything back together.

I haven't had any trouble since.

Colin
Click to expand...

I tried this on my car Colin but unfortunately there was very little cork left after :shock: so I've simply cut the old cork off and replaced it with a nice new one I had lying around. No more flickering brake light now. I also took the opportunity to clean all the contacts while it was apart.

Dave
 
You must log in or register to reply here.
Back
Top