306 MOT Service Brake Efficiency

[Xsarahdi]

I had my 306 (1999 1.9TD with drum rear brakes & ABS) MOT'd today (at the local Citroen garage for only £27.50) and it failed on a couple of things, which I could do with your thoughts on. The 1st thing was "Nearside rear brake pipe excessively corroded". I haven't had a chance to look at it yet as was wet and miserable this evening. If it doesn't look too bad, is it acceptable to clean up the corrosion and not replace the pipe?

The other thing was the "service brake efficiency below requirements". The guy said it was only a few percent off and implied that some weight in the back of the car would increase the brake pressure to the rear (by putting more load on a compensator valve) and it would make a difference. He also said it may be a build up of rubbish in the mechanisms in the drum and taking apart and cleaning would also make a difference.

On the print out of the brake test it gives the figure of the service brake at 45% which is not far off 50%. Do you think the weight in the back trick would get this figure up? It appears there is an imbalance of 17% as well. The strange thing I thought is that the parking brake locked the wheels and on the right side especially gave a greater weight reading. I did tighten the handbrake cable a couple of weeks back if that makes a difference but still thought the foot brake would be stronger.

So do you think it is just a case of needing a clean up, or could the imbalance suggest a leaking cylinder? I'm not very hard on the brakes with my driving so would a bit of more heavy usage help to free things and improve the drums performance?

Sorry to ramble on and ask so many questions! Any help and advice is much appreciated.

Thanks
Mark

[citronut]

i would back off the cable adjustment so you can easily remove the drum/s then blow the brake dust out,
then remove/grind any lip from the inside outer edge of the drum, and manually adjust the mechanism up till you can just get the drum over the shoe without it being to tight a fit,

be carefull when adjusting the mechanism not to disturb/loose the tinny stainless steel blade that locks the adjuster from unwinding, if it hasn't disapeard already as this is very common,

you should never adjust cables first as all that does is reduce the hand brake lever travel, and does not put any more load onto the shoes/brakes,

regards malcolm

[JohnD]

My Saxo got an advisory last year for the hand brake being just at the minimum requirement. It's fairly low mileage so I didn't expect the linings to be worn, but the drums haven't been off in 14 years. Prior to this years MOT I took off the drums and found them to be full of dust. I washed them down with brake cleaner, inspected the pistons for any signs of leakage, then refitted the drums. It went through the test without problem.

[addo]

Could there be air in the brakes?

Not sure about drum rear axles, but disc rears can be right mongrels to bleed. Many people find using a vac bleeder is the only way to eliminate sufficient air in the system.

Compensator valves can be hardwired to "full flow" with a bit of baling wire.

[Xsarahdi]

Thanks everyone for your replies!

I have slackened the handbrake off & taken both drums off. One had quite a bit of dust, but may have been dragging a little as the wheel was harder to turn than the other one. Cleaned both up, removed dust and put back together. I tried to click the adjuster up a few clicks once the drum was back on (very hard to turn with a screwdriver through the hole!!), I did it so you can hear the shoes slightly rubbing if that's correct.

I did notice the pistons in the brake cylinder are quite hard to move and are slow to return but is this normal?

With the rear wheels in the air, with the engine on, I tried to spin the rear wheels whilst having someone apply the brakes and they are still turn-able by hand even with the pedal quite hard down - further down than "normal" braking in my opinion. Is this right?

Now I've got an abs light on the dash which hasn't gone away after a few engine starts!!!!! Although I haven't taken it for a drive. The light itself will be another reason to fail it!

Lastly I noticed the compensator lever is not in contact with the spring even when the car is down, so the rod/spring bit rattles around. When pushing the lever up it seems to make no difference to the binding of the wheels at the same pressure on the brake pedal if that makes sense. Will having weight in the back make any difference if this is the case.

I've got the MOT again this Fri but who knows if I've make a difference to it.

[Xsarahdi]

The ABS light has gone out after taking it for a drive but don't think it felt any different

How exactly are the rears meant to be set up? Should they rub much when you spin the wheel?

[addo]

I normally set up drums so they lightly drag (more of a heavy brushing) when stone cold.

The load compensating valve needs wiring tightly shut for full bleeds or it may displace under fluid pressure. Seriously,there is no substitute for a vac bleed although a reverse pressure bleed will come close on some cars.

[Xsarahdi]

Thanks, I may need to tighten the drums slightly more, although if the self adjusters are working (which I saw it move on one side whilst someone pressed the brake pedal) shouldn't they move the shoes towards the drum a little.

I haven't tried bleeding yet, do you think that could be the main problem? The pedal doesn't feel spongy though, but the rears only work with the pedal pushed hard - with no servo when engine off you can barely see movement at the rear with the pedal pushed hard.

With the compensator, how is is meant to work. I can't see mine doing anything as the lever part seems to always be fully sprung back, even with weight, and moving the lever up whist feeling the resistance on a drum whist pushing the brake pedal seemed to do nothing.

This is getting frustrating now

[citronut]

if your cylinder pistons are not moving in and out relatively easily they probably need replacing,

i hold two large screw drivers near the top's of both shoes with the tips inside the back plate lip, this way you can stop the cylinders coming out to far then have someone press on the pedal,

did you try to spin the wheels with the compensator valve pulled hard on, if not this could stop you getting full pressure to the cylinders,

i always clean/grind the lip from the drum then adjust the the adjusters up before refitting them so the drum just goes on without being to tight,

were are you located,

regards malcolm

ps,
also try the rear brakes with wheels off the ground and engine running,

you have to put quite a bit of weight on the back of the car to get the compensator to come into play,

[Xsarahdi]

Thanks Malcolm, that's very helpful information. With the cars history of reciepts I can't see record of any work to the rear brakes. The cylinder pistons are not moving that easily. When you try to push them in with a screwdriver they are very stiff and don't move back very quickly (if at all) - but maybe I should do as you say and watch them with someone pressing the brake. Yes I've tried to spin the wheels with the engine running and get someone to operate the pedal, I think it takes quite a hard press of the pedal for them to move as the rears only work when pushing the brake pedal hard.

With the compensator, its lever is fully down towards the back of the car normally. I've tried pushing it up and forwards a couple of inches and couldn't notice much difference when spinning the drums by hand and getting someone to press the pedal. I'll try putting lots of weight in and taking it for a drive.

I can't remeber if there was too much of a lip, but I had freed the shoes off before removing the drum so it wasn't too hard to get off. I'll take them apart again and clean if there is a lip and adjust with the drum off as it seems very had to do through the bolt holes. Also I'll try and free the adjuster to hope it will do its job automatically.

I'm located in Norwich

Regards Mark

[citronut]

the reason i say to grind the lip from the drums is then you can adjust the shoes out manual before re/fitting the drums,

without the lip you can adjust the shoes that much more and still get the drums back on,

it is very usual for self adjusters not to work in normal use as they are ment to,

i invariably have to remove drums and manually adjust the shoes on my customers car's when failed on an MOT,

i certainly would replace the rear cylinders,


regards malcolm

[Xsarahdi]

Ok that makes sense, I'll definitely give that a go. I had heard that the self adjusters rarely work, just being hopeful

I've bought replacement cylinders this evening from ECP so I'll try and fit them tomorrow. The pistons are MUCH easier to move on these, but could that be because of the lack of brake fluid behind them? They move in and out with ease compared to the old ones on the car. When changing them, is it best to clamp the flexi hoses? Is bleeding them a nightmare if there are 2 people?

Thanks
Mark

[JohnD]

When changing them, is it best to clamp the flexi hoses? Is bleeding them a nightmare if there are 2 people?

I usually remove the reservior cap, lay a piece of plastic over it and screw back the cap. Very little fluid leaks from the union. For bleeding I use an Eezybleed tube then I can do the job single-handed.

Do use the correct union spanner otherwise an ordinary open-ended one will round off the corners. I also find putting a square ended drift on the union and giving it a few smacks with a hammer helps loosen them.

[citronut]

i clamp the flexi and leave it clamped till the last second's before ready to bleed, then just give it three or four press's of the pedal with nipple open and clear pipe running into a container, then shut off the nipple this usually works, as long as you do it straight away after removing the pipe clamp,

it is also best to wire the compensator full open before bleeding,

regards malcolm

[Xsarahdi]

I changed the wheel cylinders today. Brake pipe bolt was very tight and the tread quite rusty for some of the way down. I went for the plastic tightened under the cap and hardly any fluid came out the pipe. The cylinders came out quite easily and got the new ones in ok.

On refitting the brake pipe I tightened it until it was tight but couldn't remember if the thread goes all the way in or not? The top end is very rusty and hard to turn anymore but does it have to be fully in? I bled only the rears but forgot to wire the compensator fully open. Pedal seemed fairly normal so took it for a test drive.

The brakes now feel spongy!!!! They still work but not as well as before and can no longer lock (the fronts used to before ABS kicks in). The brakes don't work from the top of the pedal like they did. Have to push harder than before. Also noticed the pedal sinks a tiny bit if you push and hold the pedal whist still.

Do you think they just need bleeding again? I take it I just need to do the rears? When bleeding, between each depression of the pedal, do you need to pump the pedal (with the nipple closed)?

Thanks
Mark