My brakes, my brakes, why doth my brakes not work...

[handi_andi]

I think I might be going mad but I am pretty certain that I am not getting proper brake pressure. The brake pedal is firm until half way down and I can push it almost to the floor. If I pump it, it does not get harder, which I think it should do, however, I am doubting myself about it. As I have just fitted a new master cylinder, have bleed the system twice with a pressure bleeder and have run through fluid for like 20seconds after sight of the last bubbles etc so there shouldn't be any air in there. I checked all the flexible houses whislt i was bleeding the system just now and they all look ok with no obvious bulges.

So I am completely at a loss to understand what the problem is, if there is one. Any one got any pointers?

Thanks

Andy

[Robbie693]

You may have air trapped in the master cylinder. It's a good idea to bench bleed it before fitting, but you can get air out by slackening the outlet slightly and bleeding it there - pedal down tighten, pedal up, slacken, pedal down etc - the usual routine.

You could also try wedging the pedal down overnight - sometimes works.

Otherwise, you may have a leak somewhere.

[twincamman]

thith withdom doth maketh a truth --yea varily----ed

[ppnelan]

Do you have a servo

Matthew

[handi_andi]

Yes I do, it looks like a replacement unit as it is far too shiny and the body looks anodised.

Have had the brake pedal depressed overnight, but only a slight difference, haven't had time yet to release the pipe into the master cylinder as have been busy fitting a new frame in the nose cone to hold the foam air filter, relays for the main and dipped headlights which are now halogen, fog lights and lotus elise bug type driving lights that are also fitted to the frame.

Thanks

Andy

[handi_andi]

The brakes would appear to be worketh now with a good firm pedal, having released the union on the master cylinder with the pedal held down to be greeted by a slight hiss followed by bubbly fluid followed by clear fluid. So thanks for the sugestion and I'll remember enxt time to bleed the master cylinder first before fitting.

Now just need to sort out:
i) Why only 3 cylinders are firing, although I suspect a bad spark plug
ii) Why I can't flash the headlights although all the rest of the front lights are working
iii) Why I have no instruement lights or fan

So time to hit the wiring diagram

Cheers one and all

Andy

[worzel]

Hi

Glad you appear to have solved it- but- if it recurs- try what I did. Unplug the brake line at the master cylinder and replace with a bleed nipple. Have a helper handy and depress the pedal, when air stops being released out of the nipple and keeping the pedal in exactly the same position screw up the nipple. top up if necessary and try the pedal. should be absolutely minimal movement if the cylinder is ok.

John

[handi_andi]

Hiya
It's bleeding the master cylinder time in an attempt to get the brakes as firm as they should be as they appear to have gone spongy again and so have decided to embark on a top down method to try and get to the root of the problem as the brakes have been pressure bleed twice now and the master cylinder once the easy way. Hence can someone please tell me what size of brake nipple I need to purchase in order to bleed the master cylinder?

Also any other suggestions as to why the brakes have gone spongy when the car hasn't moved but the engine has been run several times and the brake pedal depressed would be gratefully received. For reference without the ending running I have about an inch of sponginess then hard pedal but with engine running the pedal goes firm after about two inches but then can slowly but firmly be depressed to almost the floor.

Thanks

Andy

[AussieJohn]

If you have a servo fitted then bridge it out, the brakes will be bl**dy heavy but if the pedal is ok then the servo is the culprit, good luck and keep us posted, John.

[oldokie]

I'm begining to suspect your 'new' master cylinder, if by-passing the servo doesn't firmup the pedal return the master cylinder and start over. I had a Cortina GT with the same problem years ago!

[robertverhey]

Don't forgrt the mechanical side of things. I spent days trying to chase the cause of a spongy pedal, bench bleeding, the works, only to find that one of the pads was sticking on the locating pin, and not making solid contact with the disc.

Robert

[handi_andi]

Robert
That makes a lot of sense as well given I haven't driven her since last year and she has to live outside. I am thinking of getting the new tyres on her and giving her some braking tests before I go any further to make sure everything is shaken down and then start fault tracing all over again.
Thanks
Andy

[handi_andi]

OK, I have bleed the master cylinder and have re-bleed all the brakes and have just pulled a front and rear set of pads only to discover that my back pads are more worn than I thought, which would also explain long pedal travel.

Can someone please tell me the cheapest place to get rear pads and what other cars they were fitted to please?

Also does anyone know what the new thickness of the front pads is meant to be and what is the recommended minimum thickness to help me to decide whether to replace the fronts as well as they look relatively new.

Thanks


Andy

[types26/36]

to discover that my back pads are more worn than I thought, which would also explain long pedal travel.

what is the recommended minimum thickness to help me to decide whether to replace the fronts as well as they look relatively new.

Not really, as the pad wears it moves forward and and brake fluid takes its place, the pad is still the same distence from the disc so it should not increase the travel (unlike drum brakes unless they have an auto adjuster)...this is the reason why brake fluid goes down as it replaces the worn pad.

This was cast into the disc's I removed from my sprint.
MIN DISC THICKNESS .325 INS WITH .230 INS MIN THICKNESS OF PAD & BACKPLATE ASSY

[handi_andi]

Thanks. I know the theory is the fluid replaces the pad wear but have noticed even in my audi that the medal travel does appear to get a little longer with pad wear or perhaps that's just my imagination.