brake calipers. loss of brake power

[VN-88]

hey guys, i got the new rotors and brake pads of my commy wreck and put them on mine, i did the right first and had to rush to town and they worked fine, the day after i did the left one and put it back on after bleeding it but once i started the car the brake peddal lost all power and hit hte floor. i tried again on both sides over and over. ive noticed since then that around the left caliper it was loosing oil, so ive replaced it with a spair and now it has no more leaks.

problem is it still losses power, i can brake but i have to push my foot right down before it does anything.. what could it be, ive kept the oil up in the canister and it doesnt seem to leak anymore. is it possible that the rear ones got air in them aswell?? cause i didnt touch them.

any other ideas?

[samuels]

hey guys, i got the new rotors and brake pads of my commy wreck and put them on mine, i did the right first and had to rush to town and they worked fine, the day after i did the left one and put it back on after bleeding it but once i started the car the brake peddal lost all power and hit hte floor. i tried again on both sides over and over. ive noticed since then that around the left caliper it was loosing oil, so ive replaced it with a spair and now it has no more leaks.

problem is it still losses power, i can brake but i have to push my foot right down before it does anything.. what could it be, ive kept the oil up in the canister and it doesnt seem to leak anymore. is it possible that the rear ones got air in them aswell?? cause i didnt touch them.

any other ideas?

try bleeding the whole system....when you pushed caliper pistons in did the fluid decide to come out of the brake fluid reservoir?...not that,that matters,but usually indicates no air in system,but since you had to change calipers,obviously air will get in,try bleeding the whole system and see how you go

[BrianH]

Try bleeding the whole system but if that does not work it is possible you have some major problems inside the master cylinder. It is normal for dirt and corosion to build up over time in front of the seals in the cylinder but in normal use the seals do not slide over this area. When you bleed the brakes the pedal goes down to the floor and the seals are pushed over whatever has built up in front of them and can easily be damaged.

I worked in the motor industry for years back in the sixties and seventies and saw this happen a few times. A simple job of changing the brake fluid during routine servicing can suddenly end up in a master cylinder overhaul or a cylinder replacement as well as a customer who thinks you are conning them.

Brian

[samuels]

Try bleeding the whole system but if that does not work it is possible you have some major problems inside the master cylinder. It is normal for dirt and corosion to build up over time in front of the seals in the cylinder but in normal use the seals do not slide over this area. When you bleed the brakes the pedal goes down to the floor and the seals are pushed over whatever has built up in front of them and can easily be damaged.

I worked in the motor industry for years back in the sixties and seventies and saw this happen a few times. A simple job of changing the brake fluid during routine servicing can suddenly end up in a master cylinder overhaul or a cylinder replacement as well as a customer who thinks you are conning them.

Brian

being in the industry myself for many,many years,the piston has only so much travel,so this cannot happen,however it can happen if there is build up within the piston travel,but this problem would of occured before replacing caliper,it is also possible that the caliper you put back on is sticking,giving you the "feeling of no power" to brakes
when you bleed the hydraulic brake system,it is normal practise to bleed the whole system,which i dare say you will have to do by the sounds of it

[VN-88]

ok then, looks like i will have to do that. fun fun, i wouldnt say the brake systems is ****ed cause its just hppened wen i change the brake pads

[samuels]

ok then, looks like i will have to do that. fun fun, i wouldnt say the brake systems is ****ed cause its just hppened wen i change the brake pads

agreed
as a rule of thumb,you should always bleed the furtherst caliper from master cylinder..hence the rear left wheel,then rear right,then left front then finally right front...

[VN-88]

ok well i did my rears aswell cause there was no pads on them, well almost, and the left rear had white crap come out after the 10th bleed, so i kept going and now its heaps better

[samuels]

ok well i did my rears aswell cause there was no pads on them, well almost, and the left rear had white crap come out after the 10th bleed, so i kept going and now its heaps better

so it's all fixed then ?

[BrianH]

the piston has only so much travel,so this cannot happen,

I can't agree with that comment. The first time I saw it I was the apprentice pumping the pedal. Everything was going fine when suddenly the pedal became noticeably softer and would sink to the floor in about two seconds if I kept my foot on it. The mechanic I was working with knew immediately what had happened as he had seen it before.

I remember it happening four or five times over about fifteen years so it is not common. The last time I was the service adviser and that was when I found some customers find it hard to believe when you try and explain it to them.

The pistons only move a few millimetres when you apply the brakes but a lot more than that when the pedal goes to the floor. I checked the full travel of a VP master cylinder a few mouths ago because I was using it in another application and had to make and mount a new pedal and it was about 32 mm. The front piston does not travel that far but the rear one does. Both of them move well out of their normal operating range while bleeding the brakes.

Brian

[samuels]

I can't agree with that comment. The first time I saw it I was the apprentice pumping the pedal. Everything was going fine when suddenly the pedal became noticeably softer and would sink to the floor in about two seconds if I kept my foot on it. The mechanic I was working with knew immediately what had happened as he had seen it before.

I remember it happening four or five times over about fifteen years so it is not common. The last time I was the service adviser and that was when I found some customers find it hard to believe when you try and explain it to them.

The pistons only move a few millimetres when you apply the brakes but a lot more than that when the pedal goes to the floor. I checked the full travel of a VP master cylinder a few mouths ago because I was using it in another application and had to make and mount a new pedal and it was about 32 mm. The front piston does not travel that far but the rear one does. Both of them move well out of their normal operating range while bleeding the brakes.

Brian

sorry i can't agree with you,we are at a stalemate...i have never seen this happen,sure i have seen pedals go to the floor,but not due to yor comments,but anything is possible in the automobile.
technically...the gunk build up below the piston,is caused from lack of service of or contaminated fluid,as the pad wears down the piston does have to travel further,when it's metal to metal the piston can't travel any further,you will bugger your rotors before your calipers,now take the pads out....then you will obviously get full travel into the gunky area,as there is nothing to stop the piston.....well until it hits the rotor anyways,if you have caliper right off naturally it is going to pop right on out.
i have seen brake damage from gunkYES,but it's because it's where the fluid has dislodged it from the unused area of the bore and moves with the piston causing seal and bore damage
also i think you will find that the front move more than the back,technically they are suppose to be 50-50 but in actual fact they aren't,you will find that front pads will need replacing more often than rear pads or shoes
hence the nose dive under sudden braking..

[Blown V6 Hatch]

I believe brianH was talking about the piston in the master cylinder not the pistons in the calipers! I have seen what he is talking about happen before. When you bleed the brakes the piston in the master cylinder moves further when it goes to the floor and when the piston moves past its normal operating range the seals can run over muck build up the seals can get damaged and cause the master to leak from the rear. But having said i dont think this is the problem in vn 88 case, i think the system just needed a good blead.

[Blown V6 Hatch]

Oh, and by the way braking is done 60/40 not 50/50.

[BrianH]

I believe brianH was talking about the piston in the master cylinder not the pistons in the calipers!

That is exactly what I am talking about. When you bleed brakes by pushing the pedal you push the piston seals over whatever has built up in front of them and if it is rough enough it can damage the seals.

I suppose the ideal thing is to use a pressure bleeder and not move the pedal. The first company I worked for had one but it didn't work and looked old enough to have been built before the T model. Other companies had a squillion dollars worth of equipment but never a pressure bleeder.

Brian

[VN-88]

after i re-did my backs it made it some what better, alot harder, but still once the car is running there is a gap. now maybe i shuld take all 4 tyres of and do it properly. but like i said its better but still some gap even and my "diagrams" below the first one is what its like now and the second is what it was like wen it was bad, but it still aint perfect.
legend- (-) distance from pushing pedal from the start till wen it gets harder , (/) pedal (]) floor

--/ ]
----/ ]

[BrianH]

VN 88

How are you bleeding them? Are you on your own or is someone helping you? If you have assistance then one pumps the pedal a couple of times then holds it down. The other opens the bleeding nipple. Fluid should spurt out and the pedal should go suddenly to the floor. The nipple must be closed before you let the pedal come back up again. Keep doing this until no more air comes out of the nipple. Start with the caliper that is the furthest from the master cylinder and work through to the closest.

If you are on your own get a bottle half full of old fluid and place it on the ground close to the caliper. Run a piece of clear plastic tube from the nipple to the fluid in the bottle. Make sure the tube fits the nipple tightly and remains submerged in the fluid at all times. Open the nipple a little bit and slowly pump the pedal. Look at the tube after a few pumps and if there is clear fluid in it with no sign of air, close the nipple. Do the same at each wheel.

This method can waste a lot of fluid but it works.

If that does not work and there are no leaks at the calipers then you will have to start looking at the master cylinder.

One quick check you can try is remove the vacuum line and check valve from the booster. Get a piece of very thin rope or a length of insulated automotive wire and push it in through the hole in the booster making sure it reaches down to the bottom of the vauuum chamber. If it has brake fluid on it when you pull it out then you are loosing fluid out of the back of the master cylinder and you will have to overhaul it.

No sign of fluid still does not guarantee the cylinder is ok but more often than not a leaking cylinder will leak back into the booster.

Brian

[VN-88]

i normally have some one helping me, i should really do as u say start from the furtherest to the closest, see i change my fron right and noticed afterwards that it was leaking from in between the caliper and were the pipe attaches cause some how i doubled up washers, and after i put just one on it was still leaking so i replaced the whole thing and it was good, but still cant get full pressure in the brake, its good untill i start the car then i loose alot of pressure, well about half

[BrianH]

VN 88

It is normal for the pedal to go down a little when you start the engine. That is the booster operating. To check the pedal and booster start with the engine off then pump the pedal a few times to remove any vacuum in the booster. Hold the pedal down for about thirty seconds. It should feel very hard and should not sink down slowly under your foot. If it does you have a leak somewhere and if it is not visible at the wheels or lines then it is in the master cylinder.

Keep your foot down on the pedal and start the engine. The booster will now start working and the pedal should immediately sink down about 20 to 30 mm. This is normal. Keep your foot on the pedal, switch the engine off and keep the pressure on the pedal for another thirty seconds or so. See if the pedal is trying to push your foot back up. If it does then the little vacuum check valve in the vacuum line from the engine to the booster is leaking. This valve is supposed to prevent air entering the booster, should the engine stop while driving, so there is sufficient vacuum left to apply the brakes a couple of times.

Go through these checks and if the pedal feels the same as it did prior to working on the calipers then everything is ok. If not then you are going to have to go further.

Brian

[samuels]

Oh, and by the way braking is done 60/40 not 50/50.

50/50...equalising valve

[samuels]

That is exactly what I am talking about. When you bleed brakes by pushing the pedal you push the piston seals over whatever has built up in front of them and if it is rough enough it can damage the seals.

I suppose the ideal thing is to use a pressure bleeder and not move the pedal. The first company I worked for had one but it didn't work and looked old enough to have been built before the T model. Other companies had a squillion dollars worth of equipment but never a pressure bleeder.

Brian

my apoligies,however you didn't state "master cylinder",we were discussing calipers...i had already explained to vn 88 as you probably saw in one of my posts on how to bleed the brakes

[BrianH]

I mentioned the master cylinder in the first line of my first post but never mind it is easy to miss things. I should have realised we were not thinking of the same thing. It looks like I have done the same with your description of brake bleeding because I did not see it. All that matters in the end though is VN-88 gets his car fixed and I hope we have given him enough information.

Brian

[VN-88]

yeah this has been a great help, i guess my brakes will have a full test on the way to sale, over an hour away from here, if they hold up fine i guess there not leaking some were, just guess they have air some were and ill have to find out were, ill do a full bleed next time some one is round to help, is it normal for the brake floid to be a little gunky, just a little

[samuels]

I mentioned the master cylinder in the first line of my first post but never mind it is easy to miss things. I should have realised we were not thinking of the same thing. It looks like I have done the same with your description of brake bleeding because I did not see it. All that matters in the end though is VN-88 gets his car fixed and I hope we have given him enough information.

Brian

glad we have that sorted out,my apoligies once again,i looked back at your post...as you stated all that matters is that we can all be of assistance to each other on the forum.

[VN-88]

well ill wait till dad gets home then ill re bleed all my brakes the right way this time, then ill test for any leaks by doing what use told me, then ill see how i go, if its all good i tell use, other wise, im gonna be anrgy, have to use the spare master of my wreck

[vt1538]

50/50...equalising valve

From my understanding the equalising valve only affects the pressure in the 2 circuits not the volume. Since the front & rear calipers have different sized piston diameters that will give a bias to the front brakes.

[samuels]

From my understanding the equalising valve only affects the pressure in the 2 circuits not the volume. Since the front & rear calipers have different sized piston diameters that will give a bias to the front brakes.

well yes kinda but it is also suppose to equate the braking evenly, i know i said 50/50....but we all know that thats not entirely true....like i also said,hence the nose dive on a quick stop..