Major Brake Issue , Servo or ?????

Post by **gregr46uk** » Tue Apr 07, 2009 11:22 am

Hi Guys
Am here on behalf of my father and too scared to now drive her Traveller, mum, problem is lack of brakes. Heres whats happened so far ,

Lack of pedal , ie: goes nearly all way to floor until pumped then a slight improvement .

Garage bleed brakes and it comes back fine and pedal now solid , they have done this twice now.

Serveral days later and petal is back to nearly the floor again but no signs of any fluid leaks.

Rear brakes have been checked and adjusted according to manual , fronts are Marina discs with a servo , pads look ok.

No sign of fluid leaks as the level does not drop in reservoir .

So question is what is allowing the pedal to go to floor after a couple of days of car not being used and why should it come back after bleeding ?

Would appreciate your help on this before mum drives it over a cliff !

Thanks in antcipation of replys
Greg

Ps, my thoughts are the servo is leaking ie: loosing its vacuum , if this might be the case how do we test it.

Post by **Stig** » Tue Apr 07, 2009 11:30 am

I would have though a vacuum leak would mean an inoperative servo and hence a harder pedal, rather than the other way round. I'm no expert on servos though.

Otherwise I'd suspect the master cylinder, when the pedal is firm does it sink slowly if you keep pressing?

Post by **superchargedfool** » Tue Apr 07, 2009 11:47 am

as stig says.

Post by **gregr46uk** » Tue Apr 07, 2009 12:53 pm

am not sure will have to check with dad , so are we thinking that as the piston is pushed down in the Master Cylinder the fluid is passing back past the seal instead of being forced down the line ? .... this would mean they should see a leak of fluid at the pedal end of the MC ? ..yes / no ?

Thanks again , really want this sorted before the summer .

Greg

Tue Apr 07, 2009 7:15 pm

as i understand it if the master cylindar has gone you might not see a leak, the seal is just allowing the brake fluid to pass the piston as opposed to pushing it down the bore. When my master went it failed once and then seemed to work fine for the rest of the day until it failed totally.

Post by **gregr46uk** » Tue Apr 07, 2009 7:32 pm

Guys the plot thickens , APPARENTLY the master cylinder has been replaced BUT with a standard Moggy one , ie: reservoir under the carpets where as the one fitted had a reservoir on the top of the Master Cylinder body which I can only think would have been a Marina one , as its had a Marina disc brake upgrade .

I am now thinking , yes we might still have a leak but also that the moggy MC does not move the same volume of fluid per pedal as the Marina , therefore not taking up the slack on the disc pads then onto the rear shoes .... does this make any sense ?

Cheers
Greg

Post by **d_harris** » Tue Apr 07, 2009 7:39 pm

Not an expert on minor vs Marina M/Cs

but if a totally standard Minor MC has been fitted then thats going to cause the brakes to drag. There is a small "top hat" washer inside the MC that needs to be removed.

Post by **eastona** » Tue Apr 07, 2009 8:12 pm

If when the pedal is rubbish and you bleed them air comes out, then air must be getting in somewhere (I have stunning powers of deduction

)

If so, I'd check all the unions for tightness, and caliper/cylinder rubbers for damage, also bores for corrosion.

I had a V similar issue with an MG midget and it turned out the piston on the front caliper was a little coroded. It didn't spew out or use brake fluid but it did let in air, which made it very difficult to bleed.

It could be that charlie is right and it's a M/Cyl problem. Just because it's relatively new, that doesn't mean it's OK, it's worth checking it as he says for corrosion/seals.

Doubt it's the fact that it's a Minor Master Cylinder as others (e.g. my traveller) use the standard master cylinder with Marina discs, although IIRC shouldn't a remote reservoir be fitted with Marina discs?

A "Wise One" will be along who would know! Why was it changed back to a Minor one?

Andrew

Post by **bmcecosse** » Tue Apr 07, 2009 9:21 pm

Could be a problem with the bearings on the discs - if these have any 'play' they push the pads back from the disc - and you get the long pedal. However - it should be firm - not soft!
If the servo is leaking - the fluid level will go down. You would also see a puff of white smoke from the exhaust each time the servo is used.
If the servo is mounted high up in the engine bay - fluid could possibly be draining down from it when the car stands any time. It shouldn't do this - but it could be happening.
Have YOU checked there are no leaks - or are you taking garage word for this ?
As regulars on here well know - i'm not a fan of these disc brakes on Minors - precisely because of troublesome installations like this. The standard brakes - without a servo - are perfectly adequate if in good condition, and much less trouble.

Post by **Stig** » Wed Apr 08, 2009 7:56 am

gregr46uk wrote:Guys the plot thickens , APPARENTLY the master cylinder has been replaced BUT with a standard Moggy one , ie: reservoir under the carpets where as the one fitted had a reservoir on the top of the Master Cylinder body which I can only think would have been a Marina one , as its had a Marina disc brake upgrade .

I am now thinking , yes we might still have a leak but also that the moggy MC does not move the same volume of fluid per pedal as the Marina , therefore not taking up the slack on the disc pads then onto the rear shoes .... does this make any sense ?

Cheers
Greg

I've got Marina discs and a Minor master cylinder (with top-hat seal removed) and it works just fine. It's quite common to fit an extra fluid reservoir to this set up to avoid having to top up as the front pads wear but it's not essential.

When you said that the level doesn't drop in the reservoir, are you checking the master cylinder itself or is there an external reservoir connected to it?