Spongy Brake Pedal Woes

[ec524]

Hi All

First off just like to say thanks for all your support so far - this forum has been tremendously useful to us with friendly happy people tripping over themselves to help, knowledgeable and experienced! Thanks! ( bmcecosse and philthehill you know who you are )

Spread across a few other threads you may have seen me and my wife are giving our 1957 Morris 1000 a bit of TLC.

At the moment we're struggling with a spongy brake pedal. The symptoms are you can press the pedal once and it goes to the floor, twice and it comes up to 75%, three times 50% and four times - good solid pedal that doesn't creep. Leave it 30seconds to a minute and you're back to the floor again (repeat!). Doesn't matter whether engine is running or not, and it's had a remote reservoir conversion, front disc conversion, remote servo conversion and a lot of new components (new copper pipes all round, new flexis etc.). The original "problem" was that the front calipers were seizing on, albeit due to a lack of regular use.

First off, freed off the front calipers and put new pads in, they now work, but the pedal is still spongy.
So I bled the brakes, no improvement.
Adjusted the rear shoes up and the handbrake no improvement
Then I spent last weekend replacing the seals in the master cylinder (what a pain of a job that is), blew through all of the brake lines with compressed air and replaced/re-bled with brand new fluid - no improvement.

No fluid is leaking at all, the calipers/pads and rear shoes/cylinders are in decent order, just a terribly spongy pedal.

So now, feasibly, the only thing I can see left is this remote vacuum servo. Are there any seals inside this unit? Can they be replaced or serviced? Or is a replacement the only option?

Last thing I'm thinking of trying this weekend is to bypass the servo by making up a short length of brake pipe with two female ends on and bleeding up the pedal to see if this removes the spongy-ness. Then it should be clear... I hope? Is there something else I'm missing?

am I right in thinking the only components in the braking system are
(Fluid Reservoir) > pedal > master cylinder > pipes to servo > servo > pipes to four corners incl. flexi > either a caliper or a drum with a cylinder > pad/disk or shoe/drum.

Anything else!?!?

Oh at least we had the opportunity to re-paint the floorpan with the entire interior gone!!





Thanks in advance for your suggestions.

Cheers
Steve & Emma

[bmcecosse]

Are the calipers on right way up -with the bleed nipples at the top? Is the servo mounted correctly - with the nose above the horizontal? If all that is ok - then yes -can only suggest you try the by-pass pipe. I assume when you fitted new seals (often not worth doing - better with a new cylinder) did you leave out the top hat seal as required for disc brake use ?

[stag36587]

I would suggest bleeding brakes and check rear cylinders are primed - check technical tips section for more detail

[Trickydicky]

I have a servo on my car and found that after replacing the Master Cylinder bleeding the brakes from the front n/s then o/s first was the best way. Bleeding the conventional way, I struggled to get all the air out. Once the fronts were done the rear was a doddle.

[bmcecosse]

I have never ever had to 'prime' a rear cylinder.......

[ec524]

Thanks for the suggestions.

Not sure about a top hat seal... Every seal that came out was matched up perfectly, by type and direction with a new one (where given in the kit, and matched up to the drawing in the haynes manual) and put back exactly how it was before. I checked it on the bench with hydraulic fluid, and one stroke of the piston gives a lovely high-pressure jet of brake fluid out of the outlet.

The servo is fitted correctly, like I said it worked fine for two years (or at least I thought!) the only thing that's changed is the pedal spongyness.

This weekend I'll try the bypass pipe and go from there. Not sure how we'll get on without a servo and disc brakes, but worth a try. My kit car doesn't have a servo, weighs about the same as a moggy (740kg?) and the brakes on that will detach your retinas from 130mph on the track lol.

Thanks again

[bmcecosse]

With disc brakes there must be no 'top hat' seal in the master cylinder - or the discs will drag horribly. However - that's not what's causing your sponginess. To set the rear brakes correctly you need to slacken back the handbrake cables - then adjust up the drums - and only then - readjust the cables to put the handle where you want it.

[ec524]

eek! That sounds scarily like the what we had before The front discs were dragging indeed. I put that down to the calipers seizing (they were seized). D'oh...

So it may happen again. Drat. That's a lot of work to re-do. I might leave it for a bit and see if it crops up again, because with the previous setup it worked fine for over a year and only started dragging when we left it parked up for a period.

Hopefully I've solved the spongy pedal saga - in bypassing the servo I seem to have a decent brake pedal. Now just remains to finish putting it back together and see if we can live without a brake servo.

It's fighting me all the way though - have to re-do the suspension again because the front driver's side corner is now 2" lower than the rest of the car. *sigh* why didn't I mark up BOTH ends of the torsion bar and not just one...

Oh well, all part of the fun I spose!

[bmcecosse]

That's easy - it's only a 15 minute 'side of the road' job to lift the low suspension. Don't even need to take the wheel off!

[ec524]

Yeah hope so! And then we both desperately want to get it her out of her workshop prison for the last 6 weeks and get out on the open road!

Which end of the torsion bar would you recommend sliding off and rotating around a few splines? I gather either would give the same end result, but looking at it i assume the rear one (e.g. under the driver's seat) would be easier?

Thanks...

[bmcecosse]

No! The front end...

[ec524]

Just like to say thanks to everyone for their help

All back up and running and the wife has used it every day for 2 weeks. She's happy, the car is running sweet and I can get back to my projects as well Everyone happy here.

Without a servo it's "ok", but in the fullness of time we'll probably put one back in. For the moment, just going to enjoy pottering around in it.

Thanks again, great forum for help this.

Cheers
Steve