Brakes again

[stag36587]

Those with long memories will remember my continuing inability to get a firm brake pedal - first push long then firms up, saggy some time later. Looking at other posts, other owners appear to have similar problems. Just to recap the entire system is new with exception of the snail adjusters. Master cylinder and wheel cylinders are all Lockheed.

Today I've had a bit more time for diagnostics so removed all four drums and tied string round all brake shoes to prevent wheel cylinder pistons popping out too far. All brakes were adjusted up to their limits.

On the front brakes all wheel cylinders moved evenly to same distance except for the offside rear cylinder which didn't move at all. Seized cylinder or air bubble? Bleed nipple attached to this cylinder but no problem bleeding it.

On the rear brakes, neither cylinder appeared to have moved at all. Lever only came up a few clicks when the drums were on and locked rear wheels when both off the ground. But with drums off, handbrake lever is now almost vertical.
Another point is that the top brake shoes are fitted differently on either side - on one side the longer tapered end of the shoe is fitted to the cylinder (see photo ) , on the other side, the shoe is on the other way. Does that make a difference?

Finally, I wasn't entirely convinced that master cylinder pushrod was correctly adjusted so I have lengthened its travel a little which should ensure that the master cylinder piston is completely depressed - which I will also be if I don't solve the brake issues.[frame][/frame]

Please let me have your views on all of these issues? It's really the only thing stopping me getting the car MOT'd and back on the road for first time in 20 years.

Many thanks

[bmcecosse]

What is the picture above - rear offside, but rotated 90 degrees anticlock? For rear brake adjustment - slacken off the cables and only then adjust up the brakes on the snails. The rear cylinder not moving is NOT an air bubble . It's probably being blocked by incorrectly adjusted cable - or it's seized - but you say it's new. Shoes can only go on one way round - with the little slot in the adjuster - so no chance of getting that wrong!

[stag36587]

Thanks Roy, well spotted, photo is indeed Offside Rear photo, it just uploaded this way

Offside Front - rear of the two cylinders is the one that appears to be seized and yes it is brand new.

I think greasing up the handbrake cables again should help the rear brakes.

[bmcecosse]

Block the other cylinder -clamp it shut with something like a G clamp, or even a couple of tie-wraps - and then see if the other cylinder moves...

[stag36587]

Good idea thanks

[les]

The left hand shoe it the photo is on the wrong way round. The leading edge of the shoes should be the end with the most metal showing before the lining starts, and it's a good plan to slightly shamfer that leading edge.

[bmcecosse]

I think it's right enough - but actually - I don't really think it mattersmuch at the rear. It's intended to give a 'leading shoe' effect when reversing, or standing on a hill.

[stag36587]

Ok just back from the garage and thanks to my lovely wife for pressing the brake pedal while I observed.

With the working cylinder (offside front "leading" cylinder) clamped as suggested by Roy, there is still absolutely no discernible movement from the other cylinder. On the front near side, the leading cylinder pushed out by about quarter of an inch the trailing cylinder by about 2mm.

[bmcecosse]

Ahh -to get any pressure you would need to have the other drums on....

[stag36587]

Ahh -to get any pressure you would need to have the other drums on....

Yes maybe though I just thought that having all the shoes tied up would have been sufficient.

[kennatt]

no ,hydraulic brakes work by equalizing the pressure round all brakes,if one drum is off most of the pressure and movement of the cylinders goes to that brake,so nothng much happens in the other brakes.

[stag36587]

Ah thanks Kennat I will replace the other drums and try the clamped cylinder test again

[mike.perry]

With the other brake drums on and the free piston clamped a good shove on the brake pedal should free the stuck piston.

[bmcecosse]

Good idea to assemble them all with a generous dollop of red rubber grease.....

[stag36587]

With the other brake drums on and the free piston clamped a good shove on the brake pedal should free the stuck piston.

Thanks Mike/Roy, piston freed off and red rubber grease will be applied. Still need to solve the non-firm pedal issue.

[kennatt]

do you mean soft spongy pedal or long travel before it goes hard makes a difference as to what reply you get......spongy pedal....air in system..... long travel ......adjustment issue.

[stag36587]

do you mean soft spongy pedal or long travel before it goes hard makes a difference as to what reply you get......spongy pedal....air in system..... long travel ......adjustment issue.

Thanks Kennatt. With all brakes adjusted up tight via the snails and system bled until no air from any of the bleed nipples, I get long travel on first push of pedal then everything firms up on subsequent strokes. Not rock hard, but firm.

Other things I have tried: clamped off each brake hose in turn but no significant difference. Have also tried raising rear of car and leaving overnight with wood on the pedal and checked out the brake light switch too. Also checked master cylinder push rod for travel and seems ok.

Firmest I have got the pedal was when I disconnected front system, replacing union with a blank, so only rear brakes operated.

No sign of leaks anywhere.

[les]

You might need to suspect the master cylinder after all this.

[stag36587]

You might need to suspect the master cylinder after all this.

You might be right Les, although the master cylinder is the second new Lockheed I have tried. I have just taken the previous one apart. No obvious faults except there was a small circular rust stain round the bore about half an inch in which suggests a secondary seal leak to me. What I don't know is if that was always there or has happened since it has been in storage. I will now take out current m/c and see if it has the same fault.

[stag36587]

I have taken the m/c out and carefully dismantled it - it doesn't have any rust in the bore like the previous one. That doesn't guarantee it's fault free of course but as far as I can tell it looks ok -seals look fine etc.

What I did notice though was that I had previously fitted the banjo copper washers differently to how they are shown in various manuals, parts diagrams, etc., ie with large washer up against the master cylinder and small washer between banjo and bolt. (Pic 1). But, to me pic 2 seems more logical - the bolt has a small flange which fits nicely inside the large washer and banjo.

Which is right?[frame][/frame][frame][/frame]