Jump to content

Intermittent loss of brake pressure


Recommended Posts

Hi, I hope someone can offer me some suggestions. Recently, driving my Bond Equipe, I suddenly lost all brake pressure, the pedal went straight to the floor without any resistance.  I pulled over and soon afterwards, the pedal was back to normal.  Whilst parked, I removed the master cylinder cap, expecting to find the fluid low, but actually it overflowed.  I also jacked the rear up and the brakes were not binding at all and there were no signs of any leaks anywhere. I drove twenty miles home with no problems.  I don't think the brakes overheated.

However on closer examination, the master cylinder looked old and crusty and may have leaked a little, so I decided to replace the master cylinder.  I have now done this and after bleeding, the pedal felt great. Unfortunately, the next day, the pedal went straight to the floor again with no resistance and then on the second press was perfect again. So I seem to have intermittent loss of brake pressure.  I replaced the rear drums, wheel cylinders and shoes about 18 months ago (less than 1000 miles).  There is no servo on the Bond. The master cylinder I have fitted is actually a clutch master cylinder, but I can't see why this would create an intermittent problem (which I already had before I fitted it)

Any suggestions gratefully received.

Dave.

Link to post
Share on other sites

check the front wheel end float is not excessive and when parked up pushes the pads back

there has been reports of new refurbed calipers doing pad back but you have changed them ??

hand brake holding the rear shoes open can also give a pedal drop , when initial adjustment on fitting new shoes you need to disconnect the cable  lock the adjuster up hard   reconnect and adjust the cable to just fit the clevis pin  then de adjust the locked up shoes 

this makes sure there is no gap btween the shoe and the cylinder which is what happens if the cable is expanding the shoes when they should be fully closed on the cylinder piston 

all worth a look and doesnt cost anything  

Pete

 

Link to post
Share on other sites

Did you have a problem before doing the work on the rear brakes? Poor adjustment mechanism could lead to the shoes being retracted then after some use pushed out, only to return after not braking for a while.

Link to post
Share on other sites

wow you must have had a fright, or two! The first time seems almost certainly to have been a problem with the MC end seal not closing properly so the fluid went back into the reservoir rather than operating the slaves which would explain the high level.

However why it happened with the new MC is more mysterious. If you can get it to repeat (best when not driving) check its reservoir level again. The problem is that on releasing the pedal the MC piston usually returns to its normal position so drawing the excess fluid back and returning the level to normal...

Link to post
Share on other sites

Hi Pete/Matthew/John,

Thank you for your replies; very helpful. Pete; the calipers are not new and look in good shape, but I'll check. Matthew; the problem is very new; the rear brakes have performed well, but I'll check adjustment and ensure shoes return; I guess I assumed that the shoe springs would always keep them firmly against the wheel cylinder piston.

Johnny; yes, it was pretty exciting! My working assumption has been a faulty MC, hence my surprise to repeat the problem with a new MC! I shall try your suggested check.

The next time I will get a chance to work on the Bond will be Thursday/Friday; I'll follow your combined ideas - thank you again for your help. 

In the meantime, any other ideas/thoughts gratefully received!

Dave.

Link to post
Share on other sites

Do you have a load sensing valve on the rear Dave? I had the very same problem on a mk1 Fiesta. Replaced that and all was well. I couldn't even find anything wrong with it........ Someone said fit a new one and it sorted it.

Alf.

Link to post
Share on other sites

Collapsed hose, maybe? 

Allowing the fluid back very slowly, it will allow fluid outwards because of pedal pressure but then won't draw it back as quickly hence the lack of pressure but then the eventual recovery. There must be a lot of movement somewhere in the system to have a complete lack of resistance, though. 
Check the front pads?

Link to post
Share on other sites

Hi Alf, thanks for the idea, but I'm afraid there's nothing that sophisticated on a Bond.

Colin - thanks for your idea; I replaced the front hoses last year and they look good. I will check the rear ones. I'll look at pads also.

Dave.

Link to post
Share on other sites

If i keep going before you know it you will have

3 minutes ago, Dave Bond said:

Hi Matthew,

II haven't checked the wheel bearings for a while. I'll take a look.

Dave

Done a complete service 😅😅😅😅

Link to post
Share on other sites
56 minutes ago, johny said:

Colin, I would expect a collapsed hose to cause a brake to lock on and the pedal to become even firmer as the fluid that doesnt come back is made up for by fresh from the reservoir....

Just thinking out loud... but something is moving very substantially for the brakes to require two pumps of the pedal, and a ballooning hose might be one of the places the fluid's going... 

Link to post
Share on other sites

Hi All!

I spent today working on the Bond. As I suspected, the relatively new drums, shoes, springs and wheel cylinders were all still in good shape; however, I took the opportunity to adjust the brakes (the shoes needed a bit of expanding) and replace the rear brake hoses; the old hoses looked ok, but worth replacing and then bled the brakes.

The pedal feels really good, but of course as the fault has been intermittent, I'm not sure yet if it's fixed and I would be happier if I had actually found a clear fault. 

I'll be giving it some test drives and see what happens!

Dave.

Link to post
Share on other sites

If and i hope it is, sounds like the rear adjustment has done the trick . It would explain the intermittent nature as the rear could have been slowly returning allowing more pedal travel sometimes to push them further out. Fingers crossed for you.

Link to post
Share on other sites
  • 2 weeks later...

Hi, by way of epilogue: I took a closer look at my calipers and found that on the front left, I had one pad that looked almost new and one that was down virtually to metal! So I had one piston a long way out and one (presumably siezed) right back in its bore. I still don't know how this situation would necessarily cause the symptoms I had (intermittent loss of pressure) but it's clearly not good and I have now fitted new discs and calipers and all feels good now! Which of course it should do, as the whole braking system is pretty well new now.

Thanks again for all the help.

Dave

Link to post
Share on other sites
13 minutes ago, dougbgt6 said:

These are good for checking water in Dot3/4. Pete Lewis lines up his members and tests them one by one before they’re allowed in the pub. 😊

https://www.ebay.co.uk/itm/Brake-Fluid-Liquid-Tester-Pen-With-5-LED-Vehicle-Diagnostic-Tool-For-DOT3-DOT4-/114396159192?_trksid=p2349624.m46890.l49286

Doug

I wonder if they can check for water in beer?

Tony.

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...