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Girling master cylinder problem.
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52classic



Joined: 02 Oct 2008
Posts: 493
Location: Cardiff.

PostPosted: Thu Aug 06, 2015 9:06 pm    Post subject: Girling master cylinder problem. Reply with quote

I'd appreciate some wisdom from the OCC team about Girling brakes.

MK2 Zodiac restoration progressing nicely. Now fitting up after floor and bay painting. Car came to me with inoperative hydraulics but loads of new parts fitted. New seals in clutch master and a bleed brought that side of things back to life but the brakes are a different story.........

There's a full set of new wheel cylinders, all new flexis, new linings and all.

Master stripped and cleaned, new seals fitted, same method as the clutch one. Bleeding with a Draper Pro vac bleeder which I've used before, lots of times. System appears to fill with fluid OK but the pedal never gains any proper pressure. With nipples open and a conventional bleed you get one spurt of fluid but that's it. As if the chamber is failing to re-fill. No visible leaks - even from the master cylinder bore.

Master is now off the car ready to strip and try again but I'm pretty much in the dark as to what to look for. I did try clamping all flexis except one - to reduce the size of the circuit. Another idea (which I've used in the past) is to switch pipes to cylinders so that the known good clutch one can be tested on the brakes.

All ideas gratefully received!!
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47Jag



Joined: 26 Jun 2008
Posts: 1480
Location: Bothwell, Scotland

PostPosted: Fri Aug 07, 2015 12:45 am    Post subject: Reply with quote

Have the brake shoes been ground to match the diameter of the drums? If not I think that can cause a 'soggy' pedal.

Art
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52classic



Joined: 02 Oct 2008
Posts: 493
Location: Cardiff.

PostPosted: Fri Aug 07, 2015 9:16 am    Post subject: Reply with quote

Thanks Art but this is not a case of soggy brakes but no brakes at all!

I make a practice of adjusting shoes tight to the drums for bleeding, then back them off afterwards.
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PAUL BEAUMONT



Joined: 27 Nov 2007
Posts: 1281
Location: Barnsley S. Yorks

PostPosted: Fri Aug 07, 2015 1:35 pm    Post subject: Reply with quote

There can really be only 3 reasons for absolutely no brake pedal:
1. No Fluid
2. A catastrophic leak
3. something wrong in the master cylinder.
I assume that 1 and 2 can be ruled out so something is wrong with the cylinder: seals fitted the wrong way round, holes blocked etc but the answer must lie there. Try removing all the pipes and blocking the outlet ports. do you then get a pedal?
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Fri Aug 07, 2015 11:10 pm    Post subject: Reply with quote

if you don't get pressure, it can only be air in the system or a leak, the latter should be easy to prove....one can't keep adding fluid without something getting stressed...


Dave
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Farmer John



Joined: 18 Feb 2010
Posts: 181
Location: Manawatu NZ

PostPosted: Fri Aug 07, 2015 11:49 pm    Post subject: Zephyr brake. Reply with quote

It is a Zephyr so you need the wheel cylinder pistons fully retracted. If the cylinders are connected in series and mount vertically it is impossible to remove the air from the upright cylinder if the piston is extended. Clamp the cylinders or shoes. Prime the cylinder with the piston at the top by removing the piston and pouring fluid in if you like.
Always bench bleed a master cylinder before fitting especially if it is overhauled. You need to know that it pumps fluid.
Brake bleeding appliances should never be used by diy car fixers. If the master cylinder cannot bleed the brakes then fix it. It is a test.

John
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goneps



Joined: 18 Jun 2013
Posts: 601
Location: Auckland, New Zealand

PostPosted: Sat Aug 08, 2015 12:02 am    Post subject: Re: Zephyr brake. Reply with quote

Farmer John wrote:
Brake bleeding appliances should never be used by diy car fixers.

Why not? How else do you do it when there's no-one around to pump the pedal?


Last edited by goneps on Thu Aug 13, 2015 1:31 am; edited 1 time in total
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52classic



Joined: 02 Oct 2008
Posts: 493
Location: Cardiff.

PostPosted: Sat Aug 08, 2015 8:45 am    Post subject: Reply with quote

Thanks gents, good ideas all. Common sense really, but sometimes one just needs a reminder of basic principles.

John, I understand what you say about the Zephyr/Zodiac system - The nipples are at the bottom!

Paul's idea of blanking the master cyl outlet port can be tried immediately now that the cyl is off the car - I think a bleed nipple fits it!

Also interested to know what's wrong with single handed bleeders.

Will report back soon.
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52classic



Joined: 02 Oct 2008
Posts: 493
Location: Cardiff.

PostPosted: Wed Aug 12, 2015 5:53 pm    Post subject: Reply with quote

JOB DONE!!

Stripped and cleaned the master. Tested by blocking the port - Thanks PB.
Yes, a bleed nipple does fit!

First go upon reassembly wasn't too promising. Farmer John was right, the 'pro' vac bleeder just didn't work. Thankfully a good old conventional bleed eventually delivered a good measure of air (which I assume to have been trapped in the high spot above the axle).

TBH I wouldn't describe the pedal as 100% even now, but it is very nearly so and serves our given objective to get the car drivable in and out of the garage to get on with the panel work and the interior.
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Farmer John



Joined: 18 Feb 2010
Posts: 181
Location: Manawatu NZ

PostPosted: Wed Aug 12, 2015 8:45 pm    Post subject: Zephyr brake. Reply with quote

Splendid! That is all you need to move it around.

John
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Bitumen Boy



Joined: 26 Jan 2012
Posts: 1733
Location: Above the snow line in old Monmouthshire

PostPosted: Thu Aug 13, 2015 8:02 pm    Post subject: Reply with quote

52classic wrote:

TBH I wouldn't describe the pedal as 100% even now, but it is very nearly so and serves our given objective to get the car drivable in and out of the garage to get on with the panel work and the interior.


A trick that sometimes works in these situations is to pump the pedal until hard - if that's possible, of course - and then wedge it down overnight. Not something I like doing, but it's got me out of a hole on a couple of occasions.
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Farmer John



Joined: 18 Feb 2010
Posts: 181
Location: Manawatu NZ

PostPosted: Thu Aug 13, 2015 9:14 pm    Post subject: Zephyr brakes Reply with quote

DIY and a brake bleeder. However they work and whatever they do the reason for the two being mutually exclusive is that these devices will mask faults in the master cylinder.
For example, you could leave out everything but the piston, the spring, and the primary cup when assembling the mastercylinder and one of those machines will still successfully bleed your brakes. But will the brakes work? No.
Always bleed a master cylinder at the bench or wherever you are working, just not on the vehicle. Wrap it in lots of old rag and hold it in the vice just tight enough to hold it in place. Gently.
Use a Phillips screwdriver if there is no pushrod, if the pushrod is integral slip the screwdriver through the clevis. Add fluid. Leave the filler cap off. Place a finger loosely over the port or ports and pump. The finger is a valve, press too hard and it will not pump easily, adjust the finger-pressure so that you can push the piston in and the finger will close the port on the return stroke. Pump until no air is coming out and then pump the cylinder empty. Most times with the cap off the fill-port into the bore will be visible and as the cylinder gets to be empty you can watch the fluid going into the port like water down a plughole. Keep playing with the master cylinder until you are familiar with it's operation. Do not go fitting a bleeder. If it pumps the cylinder empty and you can see it sucking fluid down it is going to pump when fitted to your vehicle. Once it pumps empty add fluid and bleed it again leaving it ready to fit with fluid in it.
The first movement of the piston will cause a jet of fluid to squirt from the fill-port into your eye. Keep your head away for this initial movement, the rest of the travel will be squirt-free.
Now you, the bench, the master cylinder and anything else within five metres is likely to be drenched in fluid. Cope with it, you are doing the job properly, keep it off your classic though, it might dissolve the paint.
Fit the cylinder to the vehicle.
Using the brake pedal to bleed the brakes confirms the correct operation of the master cylinder as against an accessory bleeder which conceals faults in the master cylinder. That is how it is a test. A double check.

John
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goneps



Joined: 18 Jun 2013
Posts: 601
Location: Auckland, New Zealand

PostPosted: Fri Aug 14, 2015 12:12 am    Post subject: Reply with quote

John,

Fair points, but I still resent the implication that the home mechanic is by definition incompetent. During the fifty years I've spent tinkering with motor vehicles there have been far too many instances of incompetence and shoddy workmanship by professional mechanics, and occasionally dangerous ineptitude. My Morris was 'restored' by a professional mechanic, but after more than thirty years I'm still finding aspects that were botched or overlooked or simply ignored, the whole approach clearly having been one of "that's good enough—can't be bothered to do it properly".

Instead of lumping all home mechanics into the same 'dubious' category, perhaps it would be more appropriate to caution those who may be unsure or inexperienced. When all is said and done, we've all been there and had to learn the hard way.

Richard
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Fri Aug 14, 2015 10:17 am    Post subject: Re: Zephyr brakes Reply with quote

Farmer John wrote:
DIY and a brake bleeder. However they work and whatever they do the reason for the two being mutually exclusive is that these devices will mask faults in the master cylinder.
For example, you could leave out everything but the piston, the spring, and the primary cup when assembling the mastercylinder and one of those machines will still successfully bleed your brakes. But will the brakes work? No. John

John

A brake bleeder is intended to be an aid to get air out of the system, its not a guarantee that the brakes have been properly bled? It doesn't matter if the brakes have been bled with a tool or by solely using the master cylinder, you still have to undertake the same check at the end; ie that the pedal is firm and maintains pressure, what ever method is used?

I have an Eezibleed that has been used successfully for years, like any tool you have to understand what you are doing with it Smile

Dave
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