Post Number: 14
|Posted on Monday, 20 August, 2007 - 05:45 pm: |
Hi everyone. 1975 Shadow LRD20648. About a year ago I had the car up on blocks while bleeding the hydraulic system. At one point I pushed the brake pedal down pretty far and subsequently lost all pedal completely, at which time the warning light for the master cylinder came on. I replaced the master cylinder, rebled the system and the brakes then worked fine.
A few weeks ago I was on a drive and the brakes worked perfectly. However, when I pulled away from a stop light I again had no brake pedal at all and the master cylinder light came on. I had the car towed home, removed the rat-trap cover and there was no leaking fluid whatsoever from the master cylinder. It still looked brand new and my brakes are again working normally, although I still have the car up on blocks pending repairs.
I have again received a replacement master cylinder and it will be exchanged under warranty. However, I am wondering if I may previously have misadjusted it ("on" v.s. "off" stops) and wonder if that possible misadjustment rather than a defective cylinder is causing the problem.
Has anyone had a similar situation? I already have my replacement master cylinder (not yet installed), but it is disturbing to have this same catastrophic problem recur, especially since I don't have a clue as to why it is happening.
Any help or advice would be greatly appreciated. Thanks!
Post Number: 65
|Posted on Monday, 20 August, 2007 - 07:22 pm: |
Have you changed your brake fluid recently?
Have you cleaned out the filters in the reservoir ?
As long as there is some free play at the rod that goes into the master cylinder it should be fine. Remember that it can get quite hot down there , so allow for expansion of the rod.
Without a master cylinder the brake pedal will go right to the floor , but if you keep pressing the pedal you should then open the main brake valves and your main systems should work perfectly ( but without 'feel' )
If you have the 'rubber sandwich' type brake pedal stop make sure the bonding hasn't failed and is allowing the pedal to move too far (if the master cylinder is not stopping it ) before opening the main valves. (pedal hits the carpet first.)
You can fix or adjust this to open the valves earlier while you have it apart.
Post Number: 15
|Posted on Thursday, 23 August, 2007 - 09:49 am: |
Thanks for your reply Paul. The brake fluid has been frequently changed and the reservoir filters are clean (cleaned last year).
I'll double check the brake pedal stop, etc. following replacement of the master cylinder. And your point about the free play for the rod that goes into the master cylinder is well-taken, especially since the car was very hot when the brakes failed (idling at a long stop light on a hot Texas afternoon).
Thanks again for your advice.
Post Number: 917
|Posted on Thursday, 23 August, 2007 - 12:31 pm: |
Carl - As it happens I addressed this problem in Issue 65 of Tee one Topics. As luck would have it I had three cars all at once with the master cylinder and needed to get them into service. I suspect the problem is that you have still got air in the system. The master cylinder is virtually fail proof (a million Morris Minors ran on them). As you will see I pulled through about a litre of brake fluid by using a gentle vacuum pump and now have a nice firm pedal. As an aside a year ago I had an early T series that had what the lady driver said was no pedal on the way down a long hill yet she was able to stop. A quick look at the brake fluid colour suggested it was dirty and undoubtedly had water in it. Here the fluid in the closed small circuit of the brake pedal feel system 'boiled' and classic complete failure ensued but as Paul notes only in that circuit!
Post Number: 66
|Posted on Thursday, 23 August, 2007 - 03:51 pm: |
Bill, you mentioning the Morris Minor has just reminded me . . . .
If you use a Land Rover master cylinder instead, it has the same body but has a slightly larger bore size. This has the effect of reducing pedal travel and bringing on the 'real' brakes sooner.
This type of failure is why I am adamant a post Cloud R-R should not be moved without the engine running!
Posted From: client-86-29-84-111.brig.adsl.tesco.net
|Posted on Friday, 24 August, 2007 - 04:51 am: |
The bottom of the lever that pushes the the master has extended prongs that hit on a round spacer ( about 1" dia)> the spacer is clamped between the frames of the rat trap.
Sometimes this spacer is awol which means should the master throw a wobbly then the pedal will go very low before the master bottoms out causing the compensater to push on the brake valves. With the spacer fitted the prongs hit and further pedal movement puts the brake valves on-- usually locking the front wheels when the driver panics.
The spacer is sometimes removed so that the master has full travel and therefore bleeds better.
If a new master is on offer then fit it.
I adjusted my master as follows.
Detecting the free play is a bit akward so---.
I adjusted the push rod so that the rear brakes when applied came off imediately the pedal was fully released then road tested the car within 5 miles the rear brakes were dragging so I backed the rod off untill the car rolled ( on a level road with my wife leaning on the car) As I turned it the car moved so I locked up there and drove 20 miles no dragging.
Then I put the cover back.
To bleed it helps if you drop the front down to the disks touching the floor and the rear as high as possible because of the angle that the master is fitted to the car.
If possible vacuum bleed.
To vacuum bleed get a glass cider flagon seal 2 tubes one to the bottom and the other high up.
Fill flagon with dot 4 until lower tube covered
connect the high one to a vacuum cleaner and the lower one to the nipple.
When all the air is out -no bubbles then the ssytem is bleed.
The high pressure will vacuum bleed via the returns from the brake valves.
continual applications of the brake with engine running will bleed any air before the brake valves back to tank again via the returns.
However I do like to see 250ml out of each calipers (6) under accumulator push.
Never return used/bled fluid to the tank.
I just leave it in the flagon and when half full empty it down the recycle centre.
It is ok to check/flush the system on the cheap stuff dot 4 and when happy change to the expensive stuff.
(Message approved by david_gore)
Post Number: 16
|Posted on Friday, 24 August, 2007 - 05:39 pm: |
Thanks to everyone for their helpful comments. The new master cylinder is installed and I will use Bob and Bill's advice on bleeding.
However, I have one last question on adjusting the "on" stop (push rod) setting for this master cylinder. I can go with Bob's suggestions about adjusting the rod, but would also like to give a shot at the procedure described in the workshop manual which is not making much sense.
A picture is attached where it is recommended that gap "a" should be a bit less than .8 in. between the operating lever (marked as "8") and the "on" stop B. But even with the pushrod adjuster "2" completely unattached, this distance is way less than .8", so pulling the operating lever closer toward the "on" stop via pushrod adjustment doesn't make sense. I don't see any method to move the operating lever the other way to give more clearance.
I'm really missing something here, and if I hadn't had two brake failures over time I wouldn't be so concerned. If anyone has a moment, could you please explain what I am missing?
Post Number: 67
|Posted on Friday, 24 August, 2007 - 06:01 pm: |
Bob, I would like to add / clarify / suggest some things.
The early cars had rubber/metal stops instead of the round metal stops. Metal ones can be fitted instead.
When bleeding the master cylinder : Put a hose clamp on one side, bleed the other side . Swap the clamp and bleed the opposite again. Swap and repeat. This gives twice the available 'moved' fluid to get those little bubbles out. If you have the time, let the bubbles settle in the pipes and repeat the next morning.
We always use two people to bleed the master cylinder. One person pumping and another at the nipple. When clear and about to finish we like to : Push down, open nipple, close nipple release pedal. - repeat 5 or 6 times.
If you still have a low pedal, check the travel with the clamp on each side separately. The side that gives the most travel with the clamp OFF will be the one that needs bleeding again.
Make sure your rear pads are truly free. With the pistons pushed in and the pins removed, you should be able to move the pads with your fingers.
Post Number: 68
|Posted on Friday, 24 August, 2007 - 06:30 pm: |
The free movement at off is at point 1 on the diagram.
There must be a small gap at 1. The faces where the rod pushing the master cylinder and the master cylinder piston meet are conical. Without complicating things ... when the pedal is fully released there must be a tiny gap at point 1 . Screw the rod into 2 until there is a slight up and down movement felt at 1. The piston will then be fully out and there will now be the required gap. Check the movement again when everything is HOT.
Point 3 should not really need touching.
If gap A is too large and the master cylinder fails the pedal will be on the floor before opening the main valves.
Post Number: 920
|Posted on Sunday, 26 August, 2007 - 10:11 am: |
Carl I think you asked about Issue 65 of Topics. This is available on the Victoria Branch of this Club's web site www.rrocavictoria.org.au and the UK site Rolls-Royce and Bentley Enthusiasts www.rrbew.co.uk
Post Number: 17
|Posted on Tuesday, 11 September, 2007 - 10:43 pm: |
Paul, Bill & Bob - thanks very much for your advice. Brakes now work great.
Post Number: 427
|Posted on Sunday, 30 April, 2017 - 03:45 am: |
Can anyone advise which Landrover model master cylinder to use ? I suspect it is a Series 2 SWB late ?
Post Number: 2542
|Posted on Sunday, 30 April, 2017 - 07:41 am: |
If my memory is correct, the master cylinder is the same one fitted to the ubiquitous Morris Minor 1000. When I overhauled DRH14434's hydraulics, I took the master cylinder to a local brake parts specialist who identified it as quoted and sold me an overhaul kit that fitted.
Paul Yorke suggested using the Land Rover master cylinder which has a larger bore to reduce pedal travel - I never felt the standard system had too much travel as it allowed smooth braking and this would probably diminish with the larger bore replacement.
Hopefully someone can confirm.
Post Number: 1306
|Posted on Monday, 01 May, 2017 - 10:15 pm: |
Not a morris 1000 brake master cylinder.
I replaced m/c with RR genuine one on my car years ago when I carried out a brake overhaul with the hole works including rebuilding the spheres and regassing.
Kept the RR old master cylinder and put it in the box.
Pedal feel is still A1, bit of a prob to bleed at the time but once completed has been Ok.
The Girling no is D12/ 310360.
Pix tell the rest hope it helps.
Post Number: 1803
|Posted on Monday, 01 May, 2017 - 11:51 pm: |
Can anyone advise which Landrover model master cylinder to use ? I suspect it is a Series 2 SWB late ?
1 or 2. Single system I think. The single system is the key bit.
Post Number: 429
|Posted on Tuesday, 02 May, 2017 - 12:22 am: |
Thanks Patrick and Paul, the Landrover M/Cyl is about £32 Delphi or £12 Britpart ?!!( I will go with Delphi). The brake system on James car that he is rebuilding appears to have had a fortune spent on it, but the m/cyl circuit has no pressure. Could be air but will change the M/cyl as a precaution.