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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1810
Registered: 5-2012
Posted on Saturday, 07 October, 2017 - 03:44 am:   Edit PostDelete PostView Post/Check IP

I've just reconditioned my brake calipers and brake hoses. I am having trouble bleeding the low pressure brake circuit. The car is a master cylinder model, 1974, SRX18501.

After bleeding the brakes (all circuits) I road tested the car and the high pressure circuits work fine with good braking force. However the brake pedal was going too far to the floor so in an effort to improve this I bled the system in the conventional way. My thinking was that by pumping fluid through the circuit rather than "sucking" it using a vacuum pump, I would be able to dislodge any air locks in the system. The result after this second attempt at bleeding the low pressure circuit is a "floppy" pedal.

I pumped a good 100 ml through each circuit and the receiving container and polythene tubing were completely free of any air bubbles. With the bleed screws tight - nothing. No pressure at all. I've checked the calipers for leaks and there are none, so the fluid is not leaking past the caliper seals.

I guess this has to be a master cylinder fault, but before removing it, I wanted to see if I've missed anything. I'm at a loss on this. I know it is difficult to bleed the low pressure circuits, but I thought once I had a good flow of air-free fluid coming out of the bleed screws then everything would be ok.

I'm also wondering, if the master cylinder is faulty, why is it pumping fluid so well when I bleed the system.

Geoff
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David Gore
Moderator
Username: david_gore

Post Number: 2682
Registered: 4-2003
Posted on Saturday, 07 October, 2017 - 06:00 am:   Edit PostDelete PostView Post/Check IP

Geoff,

The problem is most likely associated with the pressure limiting valve attached to the rear of the master cylinder - the rolling ball in the valve can jam against the discharge port when pedal pressure is applied to bleed the circuit and not return to the non-blocking position or if the car is elevated from the front to allow crawl space under the car, gravity will move the ball back and again block the discharge port stopping fluid flow.

The valve cylinder is inclined upwards when the car is level so gravity ensures the ball does not interfere with the fluid flow in normal braking but will act when high pressure is applied in emergency braking to control rear wheel lock up.

If the ball has "locked up" against the discharge port, just open the bleed screw on top of the valve body and tap the side of the cylinder to free the ball. Of course, the car has to be level for the ramp of the cylinder to be present for the ball to roll back under its own weight.

Another possibility for the bleeding failure is an air lock in the brake line loop at the rear of the cylinder compressing when the brake pedal is being depressed to bleed the line and the fluid flow involved is sufficient to move the ball to the closed position. For this reason, the initial bleeding should involve very slow pedal movements to move the brake fluid without triggering the anti-lock valve and then allowing gravity to bleed the low-pressure brake lines.

Hope this helps...................
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h_kelly
Prolific User
Username: h_kelly

Post Number: 231
Registered: 3-2012
Posted on Saturday, 07 October, 2017 - 06:39 am:   Edit PostDelete PostView Post/Check IP

Geoff the master cylinder can be a pain ...
What I did in past to establish if master cylinder was working or faulty, I disconnected the outbound line (to calipers has smaller line and nut) put a bleed screw in its place, kneeling on ground I was able to depress brake pedal and open bled screw to master cylinder to purge any air. With this done you should have a very tall pedal.you can assume from this master cylinder is good.
TO DO ABOVE NEED TO DEPRESSURISE the system.

Now you know the high pressure system is okay Geoff, don't bother charging same till master cylinder situation sorted.

I found the bleed screw the only way to ensure master cylinder good.

If you dismantled the master cylinder have a real good look at the photo in manual re replacing seals to ensure in correct order, I got cough out on same.

Good luck, keep us posted
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richard george yeaman
Grand Master
Username: richyrich

Post Number: 842
Registered: 4-2012
Posted on Saturday, 07 October, 2017 - 08:08 am:   Edit PostDelete PostView Post/Check IP

hi Geoff seeing that you have gone to the trouble of renewing all of the other stuff it might be a good idea to install a master cylinder kit or to replace it.

Richard.
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1811
Registered: 5-2012
Posted on Saturday, 07 October, 2017 - 12:04 pm:   Edit PostDelete PostView Post/Check IP

Thanks for the help

David - I checked the manual and it said the pressure limiting valve had been moved to the high pressure circuit after car 1899. So I can rule this out.

Hubert - I really like your idea of blocking the out line using a bleed screw. This is a great way of checking the master cylinder. I hadn't thought of it.

Richard - the thing about the master cylinder is I just wanted to make sure I've diagnosed the fault correctly before proceeding. Nothing worse than replacing a part to find the original fault is still there. Having said that, it is very much looking like a master cylinder problem. I pulled the rear brake pads earlier today and thankfully everything looks good - no sign of a leaking seal which is good news.

It's looking like a master cylinder problem. I'll run Hubert's test this weekend.

Geoff
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David Gore
Moderator
Username: david_gore

Post Number: 2683
Registered: 4-2003
Posted on Saturday, 07 October, 2017 - 03:21 pm:   Edit PostDelete PostView Post/Check IP

"I checked the manual and it said the pressure limiting valve had been moved to the high pressure circuit after car 1899."

Geoff, is this chassis number correct? The pressure limiting valve on DRH14434 was definitely mounted above the rear of the master cylinder.

I have always thought the pressure limiting valve would have been moved to the high pressure circuit or deleted when the master cylinder was replaced by the rubber cushion.

I will be happy to be corrected if I am mistaken.
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1878
Registered: 6-2006
Posted on Saturday, 07 October, 2017 - 03:43 pm:   Edit PostDelete PostView Post/Check IP

This is typical behaviour I'm afraid.

There should be a few threads on here where it's covered.

Briefly. . .

Clamp one sides hose - bleed the other. Swap clamp over and bleed the second side. Repeat. It's a two man job.
Pump down hard release more slowly.
The master cylinder is just a little too small for the job.
If you replace it use the next size up. Land rover s1 single circuit brakes.

You may also want to try pushing the pads back and wedging them in.

Something you imagine sould be easy but never seems to be :-(

David - they never moved the valve just altered the pipes. Can't say when though.
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richard george yeaman
Grand Master
Username: richyrich

Post Number: 843
Registered: 4-2012
Posted on Saturday, 07 October, 2017 - 08:00 pm:   Edit PostDelete PostView Post/Check IP

good tips Paul, that would suggest a change of pads and upgrade the master cylinder would give a better feel for the brake pedal.

Richard.
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Alan Dibley
Frequent User
Username: alsdibley

Post Number: 94
Registered: 10-2009
Posted on Saturday, 07 October, 2017 - 08:14 pm:   Edit PostDelete PostView Post/Check IP

I did the modification on my T after a couple of happenings when the pedal went to the floor (a quick pump made them work so no harm done, except to my pulse-rate). I had been through all these hints and the system seemed perfect but there was still "something". After removing the M/C, making a rubbery thing to give some feel and swapping the limiting valve to the big caliper pistons I now have peace of mind. Can't recommend enough.

It's written up somewhere. Who knows where - I've forgotten?

Alan D.
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Martin Taylor
Frequent User
Username: martin_taylor

Post Number: 89
Registered: 7-2013
Posted on Saturday, 07 October, 2017 - 10:55 pm:   Edit PostDelete PostView Post/Check IP

Connect a vacuum bleeder to it. I had to pull a liter or more through before it got all the air out. The land rover master cylinder makes it feel like a modern car but this is not necessary (but a good upgrade).
The air gets caught in the deceleration valve and the pipes as mentioned above
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 1544
Registered: 5-2015
Posted on Sunday, 08 October, 2017 - 12:20 am:   Edit PostDelete PostView Post/Check IP

try this.

Open nipple and retract pistons so fluid and any air is injected out into a jar.

Pump pads back against disk and repeat.
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1812
Registered: 5-2012
Posted on Sunday, 08 October, 2017 - 04:33 am:   Edit PostDelete PostView Post/Check IP

Looks like I just haven't pumped enough fluid through, 200 mils. I realise that pumping 1 litre will probably get things sorted but I have decided to upgrade to a Land Rover master cylinder. I really like the idea of the better feel that it gives, having never been that satisfied with the longer pedal travel of the current setup.

I nearly didn't put this question up, on the basis of "I'll muddle through somehow". Just shows how useful and helpful discussion can be. I knew about the Land Rover mod but had never given it much thought, thinking the only advantage was easier bleeding of the system. Having seen Paul's and Richard's comments about the enhanced "feel" and also having checked some related threads on this forum I am sure this is the way to go.

Many thanks to everyone for the help

Geoff
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1813
Registered: 5-2012
Posted on Sunday, 08 October, 2017 - 04:12 pm:   Edit PostDelete PostView Post/Check IP

I've been checking out Land Rover master cylinders. The best I could find is:

http://www.ebay.com/itm/Land-Rover-Series-2-2A-3-SWB88-3-4-Bore-Center-Valve-Brake-Master-Cylinder/282621225870?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D41451%26meid%3Dae3adb2b596d4489a
35668932b1c23ff%26pid%3D100011%26rk%3D1%26rkt%3D8%26sd%3D282308417658&_trksid=p2047675.c100011.m1850


However, it is listed as for a series 2 land rover, not the series 1 as specified by Paul. Has anyone used this master cylinder or know if it will fit, without modification?

Geoff
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1883
Registered: 6-2006
Posted on Sunday, 08 October, 2017 - 05:16 pm:   Edit PostDelete PostView Post/Check IP

It looks right.

Out of interest, why is it the best one?
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h_kelly
Prolific User
Username: h_kelly

Post Number: 232
Registered: 3-2012
Posted on Sunday, 08 October, 2017 - 08:55 pm:   Edit PostDelete PostView Post/Check IP

Geoff,
Paul may be able to advise you on this, will the length of the master cylinder rod adjustment remain the same as original one?. The reason I mention same is, if adjustment is out, the back brakes can stick on, when brakes become hot etc..
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richard george yeaman
Grand Master
Username: richyrich

Post Number: 844
Registered: 4-2012
Posted on Sunday, 08 October, 2017 - 09:03 pm:   Edit PostDelete PostView Post/Check IP

Good point Hubert, I had this happen to me by over adjusting the hand brake pads, ended up with a cloud of smoke trailing behind me.

Richard.
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1814
Registered: 5-2012
Posted on Monday, 09 October, 2017 - 03:03 am:   Edit PostDelete PostView Post/Check IP

Paul,

The reason I used the word "best" is that during my searches I found Companies selling these master cylinders for as high as 300gbp. I then found your link from a previous entry on this forum:

http://www.ebay.com/itm/Land-Rover-Series-2-2A-3-SWB88-3-4-Bore-Center-Valve-Brake-Master-Cylinder-/282308417658?hash=item41bae4987a:g:-jMAAOSwux5YNct4&vxp=mtr

However the master cylinder was labelled as sold, but on scrolling down I saw one for $38 and another at $23. The $38 one looked to be better quality.

I was thrown simply because you referred to the master cylinder as "s1" in an entry above on this thread. I just wanted confirmation before ordering the part. If you know of a better source I would be grateful if you could let me know.

Hubert and Richard - Good point. However, the one way I can make my own mod is to extend the thread using a die, if required. If the rod is too short, then I'm stuck - it's the chance you take in using a substitute part, however given all the information on this, I'm confident the S2 - S2A master cylinder will fit.

Geoff
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1891
Registered: 6-2006
Posted on Monday, 09 October, 2017 - 08:28 am:   Edit PostDelete PostView Post/Check IP

Looks good.

Just swap the rods over if they do not have the same thread.

Simple :-)
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1815
Registered: 5-2012
Posted on Monday, 09 October, 2017 - 08:37 am:   Edit PostDelete PostView Post/Check IP

Thanks Paul - I really appreciate the help.

Geoff
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 1560
Registered: 9-2004
Posted on Wednesday, 11 October, 2017 - 09:29 pm:   Edit PostDelete PostView Post/Check IP

Modification for bleeding the low pressure master cylinder on the later cars without the PL valve.
using an old cap.....do this bit first



Solder up the breather hole and block off the other cap.

Low pressure bleed system.
Make sure low pressure hoses and pump seals are ok.
Use no more than eight lb pressure.
open bleed screw n/s first.
o/s next.



Am needed by the wife. More later.
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 1562
Registered: 9-2004
Posted on Thursday, 12 October, 2017 - 05:52 am:   Edit PostDelete PostView Post/Check IP

So the bleed screws are on the lower cylinder on the rear calipers for the master cylinder circuit.



Have a bleed pipe to collect the old fluid into a container.
For the air pressure use a large spare wheel pumped up to eight lbs.
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 1746
Registered: 9-2004
Posted on Friday, 02 February, 2018 - 06:53 am:   Edit PostDelete PostView Post/Check IP

Never finished the outcome on bleeding the original type of master cylinder under reservoir pressure.
The use of a large wheel set at 8lbs was not really the best quick way.
Pressure in the tyre would soon deplete so I set up the small compressor with a water condensation trap with the adjustable pressure setting to 8lbs.



A good bleed from both sides starting with the NS/R and wow what a pedal feel, job done with the original type M/C.
Did RR carry out this type of way at factory assemble?
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gordon le feuvre
Prolific User
Username: triumph

Post Number: 230
Registered: 7-2012
Posted on Friday, 02 February, 2018 - 08:29 pm:   Edit PostDelete PostView Post/Check IP

The other point to remember is if you do not actually know how clean your reservoir is, remove top and check mesh on top of master cylinder circuit (it stands higher than HP meshes)to make sure it is not sludged up. From 1001-1898 "G2 valve was on master cylinder circuit AND used UPPER pistons on rear. From 1899-22072 master cylinder had been moved to LOWER pistons on rear AND "G" valve piped into HP circuit. From 22073 up to end of Shadow production the master cylinder was dispensed with and a rubber cone and spring substituted. Follow Paul Yorke's advice, I was at a dealer from when Shadow came out. For 30 years had problems getting decent pedal, cars that stand around are worse because original rust/dirt on pads push them away from disc and .625 cylinder uses too much volume to get them back to disc, hence pedal travel!
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 1749
Registered: 9-2004
Posted on Saturday, 03 February, 2018 - 05:42 am:   Edit PostDelete PostView Post/Check IP

New rear pads will need to be bedded in for the precise pedal feel with the original type master cylinder.
Also the wheel bearing must be in first class order!
Shame the dealer ships did not work out how to do a simple low pressure bleeder!

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