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Bleeding Brakes or new Master Cylinder
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Author:  adios57 [ Mon May 28, 2012 12:11 am ]
Post subject:  Bleeding Brakes or new Master Cylinder
64 Mini 850 with tin tanks and drums. Twin leading shoe fronts have been fitted.
Had to pull engine again and brakes were not great about half pedal.
When reconnected brake line from master bled the brakes but could not get any pressure, pedal on the floor no return.
Put another kit into the master cylinder, put car up on stands and bled from the furthest to the front.
Used same brand of fluid. No leaks seen in the system, nothing done the pedal box.
Front flexible pipes do need replacement, have had trouble undoing them.
Pressure still not good. Was able to pick up to about one third from floor and then lost all pressure.
Sound gurgling from the master. Front slave cylinders look new, rears a bit older but ok.
Clevis pin is a little worn but should not cause this.
What is the opinion, replace master altogether or replace master and all wheel cylinders?
the front pipes will be replaced too.
Is there a possibility of the rear brake valve causing this? I don't think so but would appreciate your views.
Author:  Paddy [ Mon May 28, 2012 7:32 am ]
Post subject: 
Check your adjustment for the brake Pads, I had a problem where everything in the system was good but still no pressure or hardly any pressure, there should be a light drag on the wheels when u jack them up and spin them by hand, if not then u need to adjust them.
Author:  Monaco [ Mon May 28, 2012 8:21 am ]
Post subject: 
Sounds like the master cylinder bore might be scored? Corrosion tends to eat them over the years as the brake fluid obsorbs moisture over time and not many mini owners changed it regularly. Did you have a good look when you put the kits in?
Author:  Irish Yobbo [ Mon May 28, 2012 10:48 am ]
Post subject: 
If you can get a par of vise grips onto each rubber hose, you can then check the pedal to rule out the wheel cylinders and lines. If you get good pressure once you've done this, you know it's either the rubber hoses, the wheel cylinders or adjustment.

Did you bench bleed the master cylinder before installing?
Author:  simon k [ Mon May 28, 2012 11:23 am ]
Post subject: 
Irish Yobbo wrote:
Did you bench bleed the master cylinder before installing?


ditto - put a bleeder in the top of it - eliminates everything else

one of my rear flexible brake lines popped a leak yesterday :roll:
Author:  Giantinamini [ Mon May 28, 2012 8:51 pm ]
Post subject: 
whats bleeding the master cylinder!?
Author:  Fiji [ Mon May 28, 2012 9:00 pm ]
Post subject: 
How are you bleeding them? Having tried 2 person method & those bleed kits from supercheap recommend letting them gravity bleed.

Done this anytime I've needed to bleed after putting in slave, wheel and new master cylinders without bench priming.
Author:  adios57 [ Mon May 28, 2012 11:51 pm ]
Post subject: 
I did not do a bench bleed of the master cylinder.
I don't have any spare bleed screws.
The Master had some pitting at the lowest point of the cylinder just a few mills above the circlip recess.
The old seals did not show the marking of a scored cylinder or any breaks and were still flexible.
I can do the bleed again using vice grips or small g clamps on the front and back flexible pipes. I put the new back ones on when I had the rear subframe out for the new boot floor.
I am doing the 2 man bleed with my brother the owner sitting in while I do all the scrambling and grovelling.
I did buy a bleed kit but found the so called non return valve was crap so I am using clear hose 2 types and a glass jar with all fluid not being re-used.
The gurgling sound of the master under movement makes me think it is the master.
I did adjust the brakes up on all wheels to tight and then 1/8 turn off.
Pedal height should be up not down where Fred Flintsones feet go.
Thanks for the replies they are appreciated.
The car has the sticker The bitch bites on the back and so far it is really biting me.
Author:  simon k [ Mon May 28, 2012 11:54 pm ]
Post subject: 
Giantinamini wrote:
whats bleeding the master cylinder!?


put a bleeder in the outlet from the MC instead of the main brake line, bleed any air out of it as normal (pump a little bit of pressure, crack the bleeder, repeat) and you should get a rock solid brake pedal, if not, the MC is cactus.

I like this method as it's a 100% positive test for a suspicious MC, no guesswork
Author:  Irish Yobbo [ Tue May 29, 2012 6:21 pm ]
Post subject: 
adios57 wrote:
I did not do a bench bleed of the master cylinder.
I don't have any spare bleed screws.
The Master had some pitting at the lowest point of the cylinder just a few mills above the circlip recess.
The old seals did not show the marking of a scored cylinder or any breaks and were still flexible.
I can do the bleed again using vice grips or small g clamps on the front and back flexible pipes. I put the new back ones on when I had the rear subframe out for the new boot floor.
I am doing the 2 man bleed with my brother the owner sitting in while I do all the scrambling and grovelling.
I did buy a bleed kit but found the so called non return valve was crap so I am using clear hose 2 types and a glass jar with all fluid not being re-used.
The gurgling sound of the master under movement makes me think it is the master.
I did adjust the brakes up on all wheels to tight and then 1/8 turn off.
Pedal height should be up not down where Fred Flintsones feet go.
Thanks for the replies they are appreciated.
The car has the sticker The bitch bites on the back and so far it is really biting me.


I'm not suggesting bleeding with the vise grips, I mean putting the vise grips on the hoses, and testing the pedal. This will isolate the master cylinder from the wheel cylinders, and will rule out anything near the wheels.

I would recommend bench bleeding the mc before putting it in the car, because the pedal may not push the plunger all the way along the bore. If the mc hasn't been bled, there may still be air in there, which would explain the gurgling.

I bought a 1 man bleed kit too, and I figured that most cars have more fluid moving than a mini, because I didn't have much luck with mine either. I think I'll buy some kind of a power bleeder, I hear the gunson's ezybleed is pretty good.
Author:  Giantinamini [ Tue May 29, 2012 7:03 pm ]
Post subject: 
simon k wrote:
Giantinamini wrote:
whats bleeding the master cylinder!?


put a bleeder in the outlet from the MC instead of the main brake line, bleed any air out of it as normal (pump a little bit of pressure, crack the bleeder, repeat) and you should get a rock solid brake pedal, if not, the MC is cactus.

I like this method as it's a 100% positive test for a suspicious MC, no guesswork


Do u need to bleed it if it's new? or is this just a diagnostic method?
Author:  drmini in aust [ Tue May 29, 2012 7:06 pm ]
Post subject: 
Always bench bleed a new MC before fitting, it gets most of the air out so bleeding everything on the car is much easier.
Author:  Timbo [ Tue May 29, 2012 8:05 pm ]
Post subject: 
I bleed mine on the car, before fitting the brake line to them. I have an old bit of flexible brake hose that I screw into the top to divert the fluid into a bottle. Then I can screw in the brake line and bleed the rest, without delays.

Tim
Author:  1071 S [ Tue May 29, 2012 8:11 pm ]
Post subject: 
Don't forget that bleeding TLS drums can be a major PITA even if there's nothing wrong with any of the parts. Have spent many frustrating hours bleeding the system from every joint that can be opened.

The only (minor) good idea I can suggest is to make sure the drums are as "un-adjusted" as possible when pumping the fluid (this allows the maximum amount of slave piston travel which seems to help shift the air).

Cheers, Ian
Author:  michaelb [ Tue May 29, 2012 10:06 pm ]
Post subject: 
Having worked on drum brake minis for many years I would advise that all components MUST be in good condition. I have given up on any attempt to replace rubbers in wheel cylinders as they only cost about $10 each, BUT will only last about 18 months or 2 years before they start to weep. The master cylinders will last a little longer as I always have them fitted with a stainless sleeve if they don't already. I find the rubber hoses are usually OK for 20 years so if you are sure all of your components have been renewed within those time frames then it is now a process of elimination. As most have said, try an eliminate the master cylinder first, and by the sound of your I would suggest it is not healthy and probably needs a professional brake shop to look at it for you. Even if the master cylinder is found to be OK it will at least give you the comfort of not being an issue and you can then move on to isolate each wheel cylinder and hose.
And please if in doubt have it checked by a brake shop, it may be cheaper than running into a Lamborgini when your brakes fail :shock:
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