Bleeding Brakes!

[Glenn 'Stinky' Stankevicius]

I have just replaced the master cylinder (LC Torana) on the FE and bled the brakes. Before, on an emergency stop brake the car would pull up well and the rears would lock at the last second. Now, after the new master, the brakes aren't as good and no lockup at all.
My question, after replacing a master, how much fluid needs to bleed through to be sure there is no air in the system? I was using one of those cheap kits with a small container, lid, hose and rubber elbow, only a small amount (maybe 1cm in the bottom) of fluid came through before there were no bubbles.

Another question, should the brake pedal hit the floor or is it OK for it to "bottom out"? There is probably a centimetre left between the pedal and floor when fully depressed.

[jimmys57]

Hey Stinky.....im an ex brake mechanic,and it sounds like you still have air in the system.When we did the jobs in the shop,we always had two blokes doing the bleeding.Start at the wheel furthest from the master.Open up the bleed nipple,and get the other person to put their foot on the pedal,push it to the floor,and hold it down.You will get either air, air and fluid,or fluid only.Close the bleed nipple and let the pedal come back up.We sometimes took six or seven attempts at each wheel before it ran fluid only.Make your way around each wheel,working your way to the wheel closest to the master.This is time consuming and sorta messy,but we found it was the best method to make sure no air was in the system.Remember to keep topping up the master,or more air will get sucked back in!
        I hope this helps.......cheers jimmys57

[craiga]

Another question, should the brake pedal hit the floor or is it OK for it to "bottom out"? There is probably a centimetre left between the pedal and floor when fully depressed.

The pedal shouldn't come that close to the floor. There should be a pin that transfers the action of the pedal to the rear of the brake master cylinder. Check that there is minimal play between the pin and the master cylinder, there should be a little bit so that residual pressure is not maintained, but it should be minimal.

The best way I've seen to bleed brakes is with a vacuum fitting. You actually suck the air from the system. You can buy handheld tools that do the same thing (MITYVAC).

You may find you have to bleed the master cylinder as well as it can sometimes be difficult to remove air at this point.

Cheers,

Craig.

[Glenn 'Stinky' Stankevicius]

Thanks Guys, I suspected that I might not have got all the air out.

Craig, I should have also explaind that I have an LC Booster on the firewall too. Minimal free play, as long as I am not causing any damage by "bottoming out" the pedal, I am satisfied that I have full range of the brakes.

[Sheriff]

Sounds like a similar problem I have.  I had a new master cylinder fitted a few months ago and the brakes (all drum) were pretty good.   Lately they need a lot more pressure.   I have a full pedal, but just don't get a good brake.  I have stainless slave cylinders, linings are ok, no leaks.   Will a bleed fix?   Thanks for any ideas.  Mike.

[craiga]

Mike,

What about a collapsed or blocked brake hose? Commonly overlooked.

Cheers,

Craig.

[jimmys57]

Hey Mike....air in the system usually means the pedal has a spongy,soft feel to it.It may well be a blockage,or a siezed up slave or master cylinder.Whatever it is,it dont sound too safe!...........Cheers Jimmy

[Al]

Stinky, I know it's a silly question, but did you ask for a disc brake master cylinder?  on the drum master cyl the back piston has a longer hole in it than the disc brake one which will mean the rod coming out of the booster will only make contact with the piston at the end of the stroke causing a real low pedal. Also did you bleed the master cyl first before putting it on the booster?               Cheers Al                            

[Glenn 'Stinky' Stankevicius]

I did ask for a disc brake master, although, the lid is reversed compared to the one I had before  .

I didn't bleed the master cylinder, not sure how to (or that I had to). What's involved? There is no obvious bleed nipple, only a small bolt underneath.

[Al]

What I would do first is undo master cyl move it back from booster and compare length of the holes in the new master cyl to the old cyl if they are the same then put cyl back on booster and bleed it. If not get correct cyl. Before you bleed cyl put some wet rags under cyl to catch brake fliud because fliud will damage the paint . Have someone put their foot on the brake pedal and genty push down while you loosen the brake pipes about 1/2 turn each on cyl, when the brake pedal is on the floor then tighten the brake pipes, take foot of pedal let pedal come up, put foot back on pedal, push down while you again loosen brake pipes, by now you should get fliud and air comeing out of pipes, repeat this until only fliud comes out of pipes, then rebleed rest of brakes. Hope this helps you         Al

[Glenn 'Stinky' Stankevicius]

Thanks Al, sounds like fun  , I'll have a go this weekend.

[mcl1959]

It is possible to bleed the master cylinder in a vice to save getting fluid everywhere.  All you need to do is fill the reservoir and slowly depress and release the piston in the back of the cylinder with a large screwdriver or such until you get a good flow from the both the outlets.

Ken