Classic cars forum & vehicle restoration.

[JC T ONE]

Hi all,

have a problem with the brakes on a 1968 Minor Super.

I cant get a decent pedal on her If I pump it once its OK, and with good pressure / solid = not spungy at all.

I have rebuilt most of the wheel cylenders, or fitted new ones.

All 4 front ones have the spring & plastic cup under their pistons.

It has new & correct brake shoes/linings = can only adjust them 1 or 2 click, before they lock the drum.

We have bled the system 3 times, and also pumped the pedal, and then opened the bleed screw, and closed it again, when the pedal hit the floor.

Only clean bubble free fluid came out of the bleed screws.

I also tried to adjust the arm under the floor, that goes from master cylender to pedal = no difference

Any ideas ????????????????


Jens Christian
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[ka]

Sounds like you have covered most of the options, only thing I cannot see, is if your bleed the wheel cylinders before you started.
A couple of ways, but concentrating on the easy option. De-adjust the brakes to allow the piston in the wheel cylinders to be fully retracted, use the bleeding pipe and an open bleed nipple to see if any bubbles are present. Bleed the brakes as normal again, before adjusting the brakes back to operating requirements.
If this does't help you may have disturbed the master cylinder.
_________________
KA

Better three than four.

[Rick]

Are the flexi pipes ok?

RJ
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[Dipster]

You mention repaired wheel cylinders.

Over the years I have had similar problems. I gave up using repair kits many years ago as I occasionally found that the cylinder was worn or damaged enough to cause similar problems. As you are finding tracing the fault is time consuming and, especially if you are in business, lost time is never welcome.

It is rare that a new, quality, component are very expensive. They are not big enough to be a problem if carried as spares. And replacements are available for so many vehicles of all ages.

Brakes are obviously a very serious matter, working clutch hydraulics make life so much easier. So it is new components for me.

[ukdave2002]

On the assumption that you are not getting any fluid loss, and that when you pump the pedal it holds the pressure (if it doesnt check the MC) you must still have air in the system. It is possible to get a pocket of air at a high point in the hydraulics that resists being flushed out.

Using a power bleeder like Ezibleed or a vacuum bleader may be the solution. Other times leaving the system for a couple of days and then bleeding in the normal way works.

Dave

[Bitumen Boy]

Another trick which can sometimes help in difficult cases is to pump the pedal until hard, then wedge it down to the floor overnight with a piece of wood or similar.

One possibility with symptoms like this is that the valve seal in the master cylinder is defective, and this would also bear checking. If this isn't working properly - and when they go they tend to go intermittently, at least in my experience - then the piston will simply push the fluid in the bore back into the reservoir rather than pressurising the hydraulic system.

[47Jag]

Jens,

Did you get the brake shoes ground to the radius of the drums? If the shoes are not making 100% contact with the drum you will be able to 'apparently' adjust so that they lock but the contact will be minimized.

Art

[ka]

Fitting shoes to a drum is a good point. There are professional ways to do this, but I did mine at home, the high spots on the shoes were noticeably higher and took some sanding down.
How did I do it, fine grit wet and dry cut into strips, fitted to the inside of the drum held at the ends and the shoes rubbed around the drum on the paper. Tedious but effective.
_________________
KA

Better three than four.

[ukdave2002]

I have an old Ferodo brake lining catalogue, they list shims for brake shoes, to be fitted when the drum is skimmed in order that the lining and drum are the same diameter.

I will still bet that the problem in this case is air in the system.

Dave

[MVPeters]

& always start with the longest brake line first.

I've tried the spring-loaded EZ-bleeds (rusted solid in less than a year) & various rubber tubes with valves in them.

I always return to the milk bottle with an inch of fluid in it & a tight fitting rubber tube on the bleed nipple. A few long, steady stokes of the brake pedal flushes the entire line. If you still have bubbles, try again, but you may be sucking air in from somewhere. Don't forget to top up the M/C between each wheel or you'll have to start all over again.

If this doesn't work, I have a feeling your M/C needs attention.
_________________
Mike - MVPeters at comcast.net
2002 MINI Cooper 'S'

[Farmer John]

Hello Jens, we need to have a little think about what is happening to Morrie.
Your first application results in some travel because either the master cylinder is not pushing fluid from the first pedal movement or because the m/cyl is pushing fluid which is pushing one or more w/cyl pistons before being stopped by the piston pushing the shoe into contact with the drum.
You say it is not spongy, that means there is no air in the system so no need to bleed.
To find out which of the the two possibilities we are dealing with we must isolate the master cylinder. As there is no tap on the end of the m/cyl the simple way is to clamp the brake hoses closed. I hate doing it, but in a case such as this, it is the only way. Use pieces of wood, steel, or hard plastic to clamp the hoses, just make sure that the edges are rounded, curved, to minimise damage to the delicate inner tube.
There are proper clamps for this purpose, worth buying.
If the pedal is still higher on it's second application the master cylinder is faulty. Fit a new one unless you have a really good knowledge of brake systems, bleed it on the bench before fitting.
If the pedal is good on it's first pump then the problem is at a wheel. Or two. Or three or four. Releasing one clamp at a time then trying the pedal might lead you to the end of the car needing attention.
One other thing. Before adjusting the rear brakes the handbrake adjustment must be completely off. Disconnect it, remove the clevis pins, you must be absolutely sure. Might be worth doing this first if you have been adjusting the rear brakes without doing this. Could be your answer.
Let us see if any of this helps, before we proceed through the next steps.
Good luck!

John

[ukdave2002]