Bleedin' Brakes!

[Maccer 0]

I am having troubles with bleeding my brakes! Front flexis and calipers needed replaced and the steel lines weren't looking that great so I decided I would do the whole lot in one go and put solid copper lines on as well. When bleeding up the first time I did as the book of lies sayeth and went osr, nsr, nsf, osf. Bled it up on the pedal method and all seemed fine, clear fluid coming out of all wheels, nice firm pedal. Started the thing up and the top 1/3 of travel on the pedal went spongey. Tried bleeding it up again - no more air out and still a spongey bit at the top of the travel. It needed the MOT that weekend so I took it out for a drive and made sure it pulled up square then took it for the MOT. It passed, but front brake imbalance was 19%, 25% is a fail so only just passed. The tester reckons he always bleeds from the shortest section first then goes to the longest - the reverse of the official method. My dad also said I'd probably need to do the master cylinder as I'd done all the lines. So I tried doing the master with a friend, got a little bubble out of the rear circuit, and pedal firmed up a little, then took it out for a hard drive and the pedal got softer again!

I then bought one of those eezibleed pressure kits last weekend and gave that a go, seemed to get a couple of bubbles out of the osr, but no air coming out of the others.

Now I still have the situation where I have a soft pedal at the top, which firms up if you give it 2/3 pumps with the engine off, soft again at the top as soon as you start the engine. I have read that the rear compensator/bias valve can create an airlock. Curiously the pedal seems to be a lot firmer when braking from significant speed - would this fit with air in the rear circuit? Also, as I now have the eezibleed thingamy should I need to bleed from the master and round or just from the wheels, and in which order? Basically can anyone please give me a step by step idiots guide to getting the air out of the system!!? Any help would be most appreciated!

 

Cheers, Mike

[welshpug 1,655]

is it a 1.6 or a 1.9?

 

was is just the front imbalance or was there some rear as well?

 

unless the fluid level has become low/non-existent I just bleed whichever brake I've been working on, otherwise I follow the Haynes process, not failed me yet! (well it has, but only because I had a seized load compensator on a 405!)

 

if there really is no air in the system I can only think its a brake pressure limiting valve issue, or a brake flexi hose on its way out.

[dch1950 37 1 Cars]

Hi,

I've also been having brake fun over the past few days.

The book of lies actually says NSR,OSR,NSF,OSF which seems counter intuitive as the long pipe run is to OSR which you would think would be first.

When bleeding the NSR do a normal up/down bleed cycle then close and re-open the bleed nipple, and do 4 or 5 fast pumps of the pedal to bleed the compensator (not full strokes - if you'll pardon the expression!)

regards

Dave

[Maccer 0]

She's a 89 1.6, there was some rear imbalance too but I put that down to variance on the self adjusters in the drums as the handbrake was out by the same amount. The flexis on the front are braided steels now and the back ones are good so I don't think it’s a problem with them either.. Trouble is as I've replaced all the solid lines, air has been able to get into everything.

Not heard about the quick pumping round the back! Hehe, I'm sure it didn't say anything about that in the Haynes.. Perhaps I will give that a go then, do the master again first then go round again. Just getting bleedin' frustrating! I'm on my 3rd litre of fluid now! Can you bleed the brake valve by loosening the union, like you would with the m/c or does it need to be pumped to get it working!?

[jackherer 543]

Sounds like the seals have gone in the master cylinder. I've had this loads with 205s where the MC works fine until you bleed the brakes which moves it further than it normally would go and finishes off the seals. Fit a new MC and it will be fine I reckon.

[Maccer 0]

I think the m/c is only a couple of years old, the previous owner said it had been done very recently and I've only had the car 18months. It still looks nice and new with bright silver paint on it! Can it really be shot already? Anything I will be able to do to make sure this is the case?

[welshpug 1,655]

bright silver paint? alarm bells!!!!!!

 

its only £30 odd for such a critical part of the braking system, i'd fit one due to the faults Jackherer pointed out that is pretty common on older vehicles.

[jackherer 543]

Press the brake pedal down hard and hold it, if the MC is dead it might very slowly sink down. Its not conclusive though, like I say I've had this a lot with 205s, I think the pedal can push the MC a long way while bleeding the brakes which is what causes the seals to fail.

[Maccer 0]

Hehe there is a receipt for it too! I don't think someones given it a DIY spruce up!

If the seals are shot presumably it should be using fluid and I should see fluid weeping out at the bottom of the cylinder?

 

Edit - just seen your reply Jack, thanks. I'll try this

Edited October 20, 2009 by Maccer

[welshpug 1,655]

depends which bit has gone, more often than not no fluid leaks from them.

[jackherer 543]

If the seals are shot presumably it should be using fluid and I should see fluid weeping out at the bottom of the cylinder?

 

No, to be clear I'm talking about internal leaks across the piston seals so fluid that should be being pushed down the brake lines is going back into the reservoir.

[Maccer 0]

I tried holding the pedal down last night, and it almost felt like it was moving down slowly, but I couldn't say whether it was the symptom of the m/c as you described, or flex in the pedal-servo mounting as there is definitely a little there - you can see the end of the m/c move up and down when you press the pedal. I think I'll have to wait til the weekend when I can have a proper go at it in the daylight.

[jackherer 543]

The bulkhead itself flexes quite a lot too believe it or not! But once all the flex is taken up it shouldn't move any further, the potential moving down slowly you describe sounds like a dead MC to me. You don't really need daylight to test it, just sit in the drivers seat and press the pedal as hard as you can.

[GG205rob 0]

Master cylinders can also be killed by pumping them when not full of fluid. If you have changed lots of the system as you have then you should open all 4 bleed nipples and let the fluid drip through for 10 mins before starting to bleed anything.

[davev 1]

this might sound like im taking the mick here, but am i the only one here who thinks that the opening post sounds like a standard servo action?

 

hard pedal, start car and top part goes soft, then once its turned off 2 or 3 pumps and its back hard.

 

its just a thought but i had to mention it.