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1970-1995 Range Rover Classic
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Discussion Starter #1
Hi

Hard Dash 3.9 Non ABS 1993.

Found a small pinhole leak in the vertical brake line running down from the master cylinder to the flexi hose so replaced it, also replaced all the bleed nipples on the car as some were looking like they were going to be challenging to remove in the future..

Refilled and bleed the whole system and it took a long time to get the pedal to a stiff press but we did manage it eventually, with total resistance at about half travel. The issue is that after starting the engine virtually all resistance on the brake pedal is lost. There are no leaks on the garage floor at all anywhere and this is confusing me.

Could this be a faulty master cylinder? I replaced the servo with a brand new one about 6 months ago and I have no reason to suspect the pedal linkage etc.

I did notice that when bleeding and topping up the reservoir that as I pressed the pedal there was what I can described as a small 'eruption' of fluid at the top of the reservoir level - like some air was pushing up some of the fluid from beneath but it did not look like it was air 'popping' out of the fluid - more like the after effects of dropping a small stone into a puddle.

I'm not sure if that is normal. I'm confused cuz if there is no leak I can only assume no air is getting in so why loose resistance after the engine is started.

Any suggesting welcomed.

Cheers
 

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1995-2002 Range Rover Classic
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I think what you describe is vacuum booster test, you pump the brakes, pedal hardens. leave your foot on pedal and start engine, pedal will go down about 1 inch.
try pressure bleeding where the master cylinder is pressurised to about 10 psi and then you bleed all wheels, thus air is forced out with out
pumping the pedal. here is the tool, https://www.roverparts.com/Parts/9508
 

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1970-1995 Range Rover Classic
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203 Posts
Did you follow the bleed process that is specific to the RRC? these brakes do not function like a standard vacuum boost brake system. these are a hydraulic boost system and have a very different bleed process.
 

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Presumably you've got the "conventional" vacuum brake servo? The big drum shaped type with vac hose running from engine intake.

If so, then it sound's as if the master cylinder may be suspect.

When you first start to push the pedal then the primary action within the MC is to close off the passageway to the fluid reservoir. When this is done, all of the pedal movement pushes the fluid toward the calipers.
If it doesn't completely seal this route (internal seal letting by) you get the fluid coming back up into the reservoir as you describe.

There's no leak, but the fluid displacement is not pressuring what should be a closed system, just filling reservoir from the main cylinder. Let your foot off, and the fluid will drop back down again into the cylinder bore.

I don't know if these are orientated in such a way, but some of the newer vehicles (non RR) you can damage the internal MC seals by using absolutely full stroke on brake pedal when bleeding. For this reason some of them specify vacuum bleed method in which you pull vac via bleed nipple to flush fluid through.
 

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1970-1995 Range Rover Classic
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Discussion Starter #5
Great info many thanks. I did not follow a prescribed procedure even thou i have the WSM - us blokes eh!

RR London - I think you have reinforced my thoughts. I'm going to try bleeding once more using the prescribed method but I think I know where this is going to end up.
Any one repaired the master cylinder with the repair seal kits you can get.?
 

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Over the years I've always stripped and rebuilt any braking system's components as there are generally very simple principles involved in the design, just get everything really clean to reassemble.

There's more nervousness about things like this nowadays with people being fairly circumspect about working on critical safety items.

If you've a good schematic of it and make careful observations about the original components you're taking apart, you shouldn't have a problem.

Sensible bleed and testing post rebuild should verify if it's okay.
 

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Just a further thought from looking at WSM, has the MC got a brake failure switch fitted directly to it?

If so, the routine for bleeding asks for this to be electrically disconnected and then undone by four full turns prior to bleeding.

It looks like this may be needed to clear the piston/seals under full travel. It's tightend to normal position after brake bleed complete.

I've not got this system on mine, so just going from written instructions.
 

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Just a further thought from looking at WSM, has the MC got a brake failure switch fitted directly to it?

If so, the routine for bleeding asks for this to be electrically disconnected and then undone by four full turns prior to bleeding.

It looks like this may be needed to clear the piston/seals under full travel. It's tightend to normal position after brake bleed complete.

I've not got this system on mine, so just going from written instructions.
I recently fitted a new MC to my 1983 (metric Dephy). The brake failure switch you referring works as follows (I took the old one apart): The plastic switch has a springloaded pin which needs to remain pushed in for the light to stay off. The pin rests on a small piston rod at 90 deg which is mounted between the two hydraulic circuits. The piston rod can move "freely" but will remain stationary as long as the pressure in both circuits is the same. The piston rod has two groves machined in it so that if it moves the switch pin will drop into the groove, activate the light and lock the rod in place. To reset the lot you need to extract the switch and reposition the rod back to center (or possibly that might happen on spring load).

So during bleeding you can get sufficient differential pressure to move the rod and activate the switch. The reality is that the rod is not very free and might even be stuck either so stuck it will not move or it will not move back. In any case since the switch will lock the rod when activated removing the switch will be required to reset.

The system sits next to the MC pistons and does not mechanically interact. So bleeding can be successfully without having to mess with the switch. Most likely the rod is locked solid and the whole system is inoperative unless the MC has been renewed recently.

Below picture of concept (picked up from google not actual LR as fitted, credits go to whoever did this: https://www.moke.com.au/in-the-garage/brake-system/106-brake-fail-switches)
 
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