Bleedin' brakes!

[NigelH]

What am I missing?

First press of the brake pedal brings on the brakes and slows the car down, but if I release the pedal and press it again staight away the brakes are much more effective and the pedal travel is slightly less.
System bled through....no improvement.
Master cylinder and remote servo rebuilt.
Flexi pipes inspected and appear quite new and stainless steel braided.
All fluid replaced with new DOT 4 and system bled through using Gunson Easibleed.
Symptoms are exactly the same despite several more attempts at bleeding.

Any suggestions gratefully received.

Nigel

[piman]

Hello Nigel,

ensure that the play on the hubs is not excessive, movement pushes the pads back into the calipers so increasing pedal travel. Are all caliper bleed nipples above the brake line ports?

Alec

[NigelH]

Cheers Alec.

Nice try but no cigar....yet.
All inlets are below the bleed points.

Only hub with play in it is rear N/S but the problem returns without a wheel being turned. i.e pedal doesn't go down as far on second push even when sat on the drive.

Still sounds like air in the system doesn't it? but how do I get it out?

Nigel

P.S. Thank goodness it's Friday........curry and beer.....perfect distractions.

[ecosselynx]

Hi Nigel

I assume when you bleed the brakes you started at the furthest away point (NSR), then worked your way forward! If that was the way done, then you could try placing a piece of wood between the pedel and steering wheel, so that the pedel is at least 1/2 to 3/4 way down and leave overnight, remove in the morning and top-up if required.

[NigelH]

Morning John.

Yes, started at NSR etc and even tried opposite way round as it says in Haynes (didn't seem right to me but desperation had kicked in).

Pedal pushed down overnight!! I remember doing that on an old series II land rover years ago. Can't remember wether it worked or not but will be giving it a go.

Thanks for the suggestions,

Nigel

[sweller]

then you could try placing a piece of wood between the pedel and steering wheel, so that the pedel is at least 1/2 to 3/4 way down and leave overnight, remove in the morning and top-up if required.

This is a really effective way of curing similar problems on motorbikes (Except I use a cable tie on the brake lever/handlebar).

I'm not sure why it works, but it does.

[JAGAZ]

I think the idea behind brake pressure overnight on a bike is that any air will make it`s way upwards untill it gets to the master cylinder and when the lever is released the air passes into the reservoir and floats to the top.Used to have to do this when fitting goodridge lines many moons ago as the braided lines had a smaller diameter than the oem rubber ones and the air just seemed to take it`s time getting through when trying to blead at the calipers.
I don`t know if this would work on a car as the lines run horizontal in some places and the air may just sit there.Maybe if the air is in the line running from the rear then it may help to lift the front of the car to help the air on its way.

[piman]

Hello Nigel,

I take it you don't seem to get any air out with the subsequent bleeding? I've found the easy bleed to be very effective generally so why there should be any air left is strange? Does the car pull up straight with heavy braking?

Alec

[NigelH]

Hi All.
Had another fruitless day going round in circles.

There doesn't seem to be air in the system when using the Easybleed.

Prompted by Alecs' thoughts on hub play I wondered if the auto adjusters were doing their job on each piston. So I took out the pads on each wheel one at a time to check if any had more clearance than the others. FNS pads would not budge so I ended up removing the pistons. They were still tight and a struggle to get out due to paint on the caliper (smooth hammerite is my guess). Cleaned the whole area up and the pads slide in and out nicely now.
However on refitting the pistons I must have misaligned the part that pushes on the brake pad which resulted in the pistons not sliding out correctly. One didn't move at all and the other canted over at an angle so only pushed at the top edge.
Stripped both pistons down to see how much damage I had done. Only blemishes were black rings around the bores where the piston seal had been sitting. Cleaned them both up and reassembled them and back on the car.
Bled the air out and both pistons are pushing evenly on the pads. Wheel locks up when spun by hand and pedal pressed.

So...off for a test drive terrifying!!
If I let go of the steering wheel and then brake hard the car vears sharply to the right onto full lock. So I guess that means not a lot of braking force being applied to the near side front.

Also my newly reconditioned servo is now whistling (I kid you not!) when the brakes are applied lightly.

Have now run out of brake fluid as well as paticence and ideas. Also the monsoon season has just hit N. Cheshire.......time for wine methinks.

Thanks for the help and suggestions....much appreciated. Keep them coming.

Nigel

P.S. will go and stick a wedge on the brake pedal over night and start fresh tomorrow

[piman]

Hello Nigel,

it sounds very much like a stuck piston in the L.H. calliper, or a blockage in the link pipe (Not very likely). If that is the case it is a serious problem as it can split the disc. If you don't see any air when you repeated the bleeding it is likely that is not the problem. Paint is not going to cause this, did you remove the pistons from the cylinders or merely remove the cylinders from the frame?

Alec

[NigelH]

Morning Alec.

Yes, pistons out of the cylinders. Gave the bores a very light polish with well worn wet and dry paper to remove any marks before a good clean and reassembly.
The paint was stopping the pads moving freely to and from the disc and I couldn't pull them out of the caliper as you would to change them. I cleaned up the whole area but as you say it wasn't stopping the pistons moving.

I have noticed that the flow of fluid when bleeding is very different at each wheel. FNS is quite slow compared with the gusher from the FOS.

New pistons required?

Cheers for now,
Nigel

[ecosselynx]

Hi Nigel

Are all the bleed screw holes clear, if so then I'd check the pipework for any sign of being nipped or flattened, which is causing a reduction in flow. You could also have someone press the brake pedal for you while you check that all the pistons are moving freely.

[piman]

Hello Nigel,

no, I doubt that you need new pistons, the fact that the flow is poor is very relevant and Nigel is quite right. Possibly a mis routed brake line has been crushed when jacking or some other accident has restricted the fluid flow. (You did say that you have braided flexible lines, the original rubber lines can collapse inside but usually this restricts the flow out rather than in and causes the brake to stick on)

Alec

[NigelH]

Evening All.

After further investigation with another set of eyes and a new bleed pipe it appears that the flow out of each bleed point is fairly even. No signs of damage or kinks to any of the pipes either.

However, after watching each set of pistons move, it appears that one of the pistons I had apart yesterday is moving far more than the others. So, out it came again. The pin that is fixed to the main body is very loose as is the bush in the piston. Conclusion.....the adjuster cannot do it's job hence the extra movement.
Also noticed that the plate that pushes the pad is bent after my misalignment faux pas yesterday. New one on order.

Watch this space. The end MUST be insight now!!

Cheers,
Nigel

[NigelH]

Progress report.

New piston received and fitted etc. etc.

Test drive. Best yet. Not perfect and the initial symptom is still there but much, much better. Car still pulls to the right under hard braking but this could be steering geometry etc.
I have decided to leave well alone for now.
MOT is imminent so that will show up any braking deficiencies.
Servo still whistles when braking lightly.....strange but true.

Heart felt thanks to all of you who have taken the time to help with suggestions and words of wisdom. It is very much appreciated and I owe you all lots of beer.

Cheers,
Nigel