Brake cylinder questions

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the_weaver
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Brake cylinder questions

Post by the_weaver »

I'm considering replacing the rear wheel cylinders in the drum brakes on my ZX. Last time I tried it I ended up having to take it to a garage as I rounded off the union nut on the cylinder.

I've heard that you can buy the brake pipes/unions that fit into the cylinder and run along the suspension arm to the rubber hoses, from the main dealer. Are these brake pipes already bent to shape or do they come as straight pipes which you have to bend yourself? If so, how do you bend them? Do you need a special tool?

If I damage the original pipe I will need to make a new connection to the rubber hose. Is this connection likely to give problems on an old car? Is there any point on the brake pipe run where it's easy to connect/disconnect?

Is it wise to clamp the rubber hoses on a ZX or will they be damaged? I've got a brake pipe clamp from years ago. The two bars that clamp the hose don't quite meet. Is this correct?

How free should the pistons be in the rear wheel cylinders? Should they be easy to move with your fingers or is a bit of leverage from a screwdriver in the gaiter slot needed?

Paul
citronut
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Post by citronut »

yes Paul if the pipes are still available from citroen they will be pre/shaped/formed,

but i prefer to make them up in copper knickle they are just standerd flaires not the citroen type that use pipe seals,

it is very common for ZX pipe nuts to be seized solid,

i usualy try to free them with vice grips, once you have cracked them of it is posible to then undo the cylinder retaining bolts pull the cylinder clear of the back plate, hold the pipe nut in the grips and unwind the cylinder from the nut,

with the flexi's it depends what age/condition there in, but yes use the clamp and yes it should have a gap between the rods/bars as its not ment to crush the hose,

i usualy peel the dust cover away enough to check how cleal it is inside, if its clean they are usualy ok, but also before reomeing the shoes put a srew driver in between the top of each shoe and the back plate edge to lever to and frow, doing this you should be able to tell how free the pistons are

regards malcolm
HDI
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Post by HDI »

I would also advise replacing the rigid brake pipes in cupro nickle , they will never be an MOT issue again :wink:

You will need a brake pipe flaring tool to make them yourself.

There is a company that sells ready made cupro nickel pipes , they just need bending to shape. Thats pretty easy with CN pipes though , they are very soft compared to steel. Just use a broom handle or similar as a bending mandrel. You can buy a tube bender , they aren't too expensive for the simpler types but if your only going to use it occasionally it may not be worth it to you.
Now using '00 Xantia LX HDI, pov spec :(
My past Citroens :-
'00 Xantia SX HDI, now dead due to accident :(
'99 Xantia HDI 110 Exclusive, RIP :(
'97 Xantia TD SX
'96 Xantia TD LX
'96 ZX TD
'89 BX TD
'88 AX GT
'79 CX2400 Pallas (scrapped :( )
& a couple of Peugeots !
the_weaver
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Post by the_weaver »

Thanks for the replies.

Is a small amount of leakage from the wheel cylinder pistons normal? When I first checked I found some liquid/grease under the rubber dust cover. I wasn't sure if it was brake fluid or oil/grease/copper grease. It may have been brake fluid and brake dust mixed together. I cleaned it up and now after a few days there's a small amount of brake fluid in the dust cover. It's not a major leak and I can't see any fluid running down the backplate but I suppose it could be the first sign of trouble. Do you think I should replace the cylinders because of this? Would a small leak allow air to get into the system and cause a spongy brake pedal?

When the cylinders are new I think they come with a bit of oil or brake fluid under the dust covers. I suppose this is to stop rust and provide some lubrication until they are fitted. Should this be cleaned out after fitting or left in? Should I put anything under the rubber dust covers on my existing cylinders to keep them corrosion free? If so, should it be brake fluid, grease or oil?

Is the rubber cap that's fitted to the bleed nipples meant to be left on after fitting the cylinder, or is there some MOT rule that says that bleed nipples have to be uncovered? In the past, whenever I've had garages fit new cylinders, they have always left the rubber cap off. I'm thinking of keeping the rubber caps in future and fitting them myself after the garage has fitted the cylinder. Would the car fail an MOT because the rubber caps were missing?

If I fitted two new rear cylinders I would probably want to bleed the brakes until the brake fluid is clean, so that the brake fluid was new. Could I do this without touching the bleed nipples on the front calipers? I think there are two circuits on the ZX with the left rear being coupled to the front right and the same on the other side. Does this mean that the brake fluid in the left rear is mixing with the brake fluid in the right front? So if I bleed the brakes from the rear only then I will end up with a mixture of old and new fluid.

Paul
HDI
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Post by HDI »

Leaks on any part of the braking system are not normal or acceptable. Any leaks on the wheel cylinders mean replacement. Fluid leaking out means air can leak in.
Greasing the pistons under the dust covers may stop corrosion , but the grease needs to be a special type compatible with brake seals. Normal grease will attack the seals.
Thing about brake fluid is that it is hygroscopic , it absorbs moisture from the air. This is why brake systems corrode internally if the fluid in the entire system is not replaced at least every 2 years. If your replacing the wheel cylinders you really should replace the fluid in the whole system.
Nipple caps are good and bad. If they are not totally air tight they will allow water in and the nipple will corrode. I blob silicone sealer on them , it then sets molded to the nipple and is easily pulled off at service time.
Now using '00 Xantia LX HDI, pov spec :(
My past Citroens :-
'00 Xantia SX HDI, now dead due to accident :(
'99 Xantia HDI 110 Exclusive, RIP :(
'97 Xantia TD SX
'96 Xantia TD LX
'96 ZX TD
'89 BX TD
'88 AX GT
'79 CX2400 Pallas (scrapped :( )
& a couple of Peugeots !
the_weaver
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Post by the_weaver »

I've bought two new brake cylinders and I'll get them done by a garage, followed by the MOT.

How much brake fluid will I need for a complete fluid change?

If air has got into the system what symptoms would I see? Is it just a spongy brake pedal? Any other symptoms?

Is it possible to use a brake hose clamp as an aid to diagnosing problems? For example, if I want to pinpoint a problem to one of the rear wheel cylinders, then I clamp it and the problem that it's causing might go away while it's clamped. I'm wondering if the leaking cylinder will cause a loss of pressure and a weakened braking system.

Paul
the_weaver
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Post by the_weaver »

Is the master cylinder reservoir cap meant to be airtight? When I was pumping the brake pedal to get the self-adjusters to adjust there was brake fluid leaking out from the reservoir cap. It looks like I've got too much fluid. I wonder if the air leak into the system has increased the total volume of fluid and air. Or it could just be the fact that the rear of the car is up on axle stands causing the fluid to move to the front. It only leaks when I pump the pedal. I suppose the cap seal might have gone or maybe the seal is airtight normally but can't cope with excess pressure that it's under when I pump the pedal.

Paul
citronut
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Post by citronut »

buy your self an easy bleed one man presureised bleeding kit, they dont cost a lot thev one i have you fill the container two thirds with new fluid, attatch the apropriate one of the various sized caps to your fluid reservoir, now conect the air pipe to a tyre with no more than 20psi, then with a clear bleed tube on one of the kniples open it and wait for clean fluid with no air bubbles to show in the tube, shut that one off and go to the next one,

YOU MUST NOT TOUCH THE BRAKE PEDEL WITH A PRESURE BLEEDER CONECTED AS YOU RISK INVERTTING THE MASTER CYLINDER SEALS

usual practice is work from the futhest from the reservoir in turn to the nearest,

your reservoir cap has a vent hole and if you have over filled the reservoir it will leak fluid, because there is to and frow movement in the fluid every time you press and let go of the pedel,

ps.
here is the type i own very good

http://www.carparts-direct.co.uk/Brake_Bleed_Kit.cfm

regards malcolm
the_weaver
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Post by the_weaver »

Malcolm

I've got an Eezibleed and also one called a Vizibleed which is a one-way valve with a container to catch the expelled fluid. I bought them years ago but I hate undoing bleed nipples because of the danger of shearing them off. As I'm replacing the cylinders anyway I suppose I've got nothing to lose this time.

Am I right in thinking that if you shear off a bleed nipple then the threaded bit will still be left sealing the system so the car will be ok to drive but impossible to bleed ever again?

Do the ZX bleed nipples use a ball bearing with a brass tube pressing on it.

Any tips for undoing the bleed nipples?

Are you allowed to extract a sheared bleed nipple and replace just the nipple, or is not a good idea?

Paul
citronut
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Post by citronut »

i find the easybleed is best as it push's the fluid through and you are not going to risk knackering you master cylinder, because when bleed the conventional way UP DOWN UP DOWN UP DOWN UP DOWN UP DOWN UP DOWN UP DOWN,

your master cylender seals/pistons will be entering un/used cylender bore, this can cause damage to the seals,

the bleed kniples are just cone ends which fit snug into the seat in the cylinder/calliper, if they undo in the slightest before shearing off it is possible they might leak,


obviously the new cylinders will be fine, i dont offten have knipples shear off

regards malcolm
the_weaver
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Post by the_weaver »

Malcolm

Is pumping the brake pedal always a bad thing, or only bad when you're bleeding the brakes? I've been doing a lot of pedal pumping recently to get those self-adjusters to work. I hope I haven't ruined my master cylinder. At least they're cheap from gsfcarparts anyway.

On the Eezibleed did you have to buy a special cap for the ZX or did you use one of the ones in the box?

Following my pedal pumping for the self-adjusters I've had brake fluid leaking from both rear cylinders. Luckily it hasn't got onto the friction material of the shoes as it goes down the middle and out of the bottom of the backplate. However I will need to drive a short distance to the garage so it might get on the shoes by the time I get there. It only leaks when you use the brakes so I will drive slowly and use the handbrake if possible. Is it possible to drive with the rear hoses clamped to stop leaks? Will the front brakes function normally? Is it possible to clean brake fluid off shoes if it does get on there?

Paul
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Post by uncle buck »

When you are bleeding brakes & you push the brake pedal right down to the floor you stand a good chance of damaging the master cylinder seals as they will be traveling into a part of the master cylinder bore that they never normally go to under normal everyday use. Due to lack of use this part of the cylinder bore could be slightly rusty & this will damage the seals.
You can help avoid this by only pressing the peddle down a little when bleeding the brakes however doing this will make bleeding a long slow process....hence the recommendation of a pressure bleeder by citronut.

If you clamped the rear hoses the front brakes would still work normally...however this isn't necessary in your case by the sounds of it.
If brake fluid gets on the shoes you will be able to clean it off with brake cleaner spray....if the shoes have been covered in fluid for a while & it has soaked in to them new shoes should be used.


Cheers.
2006 C4 1.6 HDi 16V (92) non FAP
2001 Xsara II 1.4 LX
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citronut
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Post by citronut »

not usualy its just when you have the bleed kniple open this alows the master cylinder pistons to travel the full length of the bore/cylinder,

i usualy grind any lip/s of the inside edge of the drums then it is possible to manualy adjust the shoes out more or less as fare as they need to be before re/fitting the drums,

one of the caps in the kit fit the ZX,

if fluid is leaking even donw the inside of the back plate it will get onto the shoes, because when it runs down the back plate it will get on the working surface of the drum then onto the shoes,

why are you taking it to the garage cylinders are usualy easy to fit,

regards malcolm
the_weaver
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Post by the_weaver »

Looking at the age of the brake pipes, unions and bleed nipples I think that the simple job of replacing the cylinders is likely to end up with me replacing brake pipes etc. I think that job is best left to a garage. They've quoted me a price of 66 pounds labour plus vat and I think they're going to give me a free tow in. The MOT is due anyway so I may as well get both done at the same time.

I don't think any brake fluid has got on the shoes yet. I started off with a small leak on one side which was contained in the rubber boot. The pistons were very heavy and I pushed them in and out to try to free them up. I think that's caused the leak on the other side but the car has been on axle stands all the time so the drums haven't been spinning. There's a cutout/drain at the bottom on the backplate and any brake fluid runs out of there. I think it's behind the edge of the drum so in theory I should be ok. I've cleaned the backplate with brake cleaner. Now it all depends on what the garage say. As they're doing the MOT I can't really argue with them if they say there's fluid on the shoes. I'll suggest that they clean it off with brake cleaner if it's a small amount and we'll see what happens.

Paul
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