Master Cylinder Issues

[Zeke_]

Hi,

I recently bought a moggie, partway through being restored. The previous owner stated that he had done a brake overhaul, but said the brakes needed bleeding and bedding in. During further investigation I found a lack of rear brake bleed nipples and hence installed them. When then bleeding the system, i found it took way longer than expected (3 hours+) and also noticed some bubbles coming up through the master cylinder. When closing up the system and testing the brakes, i found that they shot to the floor until pumped up. Is this normal? and is my master cylinder bad (due to the bubbling).

I have left it a few days and it seems that i now need to pump the brakes before they do anything. Any suggestions as how to fix this as i would rather not go through the hassle of a master cylinder replacement.

Thanks,
Zeke

[oliver90owner]

When closing up the system and testing the brakes, i found that they shot to the floor until pumped up. Is this normal?

Definitely not!

As the system has been interfered with, it’s difficult to tell whether it is operator error or a faulty system.

There are a couple of simple reasons for brakes that require pumping before getting any braking action.

1) The shoes are in dire need of adjustment, or

2) There is air in the system.

Question : Is the pedal hard, once ‘pumped’ or is it still spongy? That would/should indicate where uour problem might be.

[simmitc]

Welcome to the Board and to the world of Minor Ownership, I hope that you enjoy many happy years with your car.

Properly maintained Minor brakes should have a firm pedal and stop the car without any problem, so there is definitely something wrong with yours. It's worrying that the previous owner had omitted the rear bleed nipples - what else had he done wrong?

What year is the car? The front brakes changed size between early and late cars. Are the brakes standard (drums all round) or has it been converted to discs? Is there a remote reservoir under the bonnet, or just the standard master cylinder under the floor?

Do you have a workshop manual, and are you familiar with working on brakes - they are a safety critical item.

In this situation, I recommend checking all the brakes for correct assembly and serviceability of components; then adjust the brakes, and then try bleeding. To adjust the rear brakes, first slacken the handbrake cables, then adjust the shoes, and then adjust the handbrake.

The master cylinder is not that bad a job - contrary to some advice, you do not need to remove the front suspension before removing the M/C.

In my experience, bleeding Minor brakes is definitely quicker and easier with two people rather than any device that claims to allow quick and simple one person bleeding.

[Zeke_]

Thanks for such fast replies,

This is my first time working on brakes however, my grandad, who is well versed with cars and general engineering, is helping me out with fixing the car and i have a workshop manual to help too.

The pedal is hard when pumped, probably a little softer than before bleeding, and there are a few creeks that come from the car when the pedal is firmly held.

The drums for the rear were a little warped so i was unable to get the best adjustment, however i have ordered new rear drums and that should fix that problem.

My hypothesis is that the master cylinder may be letting a bit air into the system, as when bleeding it seemed as though I was getting more air through than the volume of the brake system and there were a few bubbles coming from the master cylinder side of the system. I continued to bleed the system until I saw no air coming out.

I haven't found many major problems with the car other than the nipples so far, only a few minor electrical things which were easy enough to fix.

The car is a 1970 4 door, with stock drums on front and back. The M/C is stock without a remote reservoir

Many Thanks,
Zeke

[don58van]

Hi Zeke

Please let us know how you go. Getting the Minor's brakes working optimally is a subject that most owners take an interest in.

Don

[simmitc]

Sorry, I forgot to ask: Is there a servo fitted? I shall work on the basis of "no" unless you confirm otherwise.

When bleeding the brakes, if the cap is off the M/C then as you depress the pedal, it is quite normal to see a small fountain or geyser of fluid being pushed through the reservoir, and this can sometimes look like air. Also, it is essential to keep the reservoir topped up with fluid as if the level drops then air can be drawn in.

Unless anyone else has any suggestions, my plan would be:
1) Adjust all brakes so that the wheels are locked.
2) Keep the reservoir topped up during bleeding.
3) Raise each corner of the car slightly whilst bleeding that wheel.
4) Fit a tube over the bleed nipple with the other end in a jar of fresh fluid (standard practice).
5) Open the nipple on the cylinder being bled. Assistant in car push slowly on pedal until on floor. Hold pedal down. 6) Close nipple. Gently let pedal return.
7) Repeat5 & 6 numerous times until no air showing in the tube. Ensure that the master cylinder is kept topped up.
Repeat for other wheels.
Bleed in this order: Back left, back right, front left, front right.
If necessary, repeat all steps again.
When finished, adjust brakes correctly.

If, after all that, you still have problems, then I'm afraid that it probably is the master cylinder.

[Zeke_]

Ended up sending the car to a professional to get the m/c replaced.

This fixed the issue of the brakes needing pumping.

Brakes now feel softer with more travel before braking is engaged (I have been told this is normal)

Thank you so much for all the replies, really helped in diagnosing the issue.

Zeke