Brakes Hot NO Pedal

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Originally Posted by JDNSW

Its listed as an optional part in the S3 parts book.

John

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thats where i have seen it then :P thanks young fella...

the sump spacer is a form of windage tray I have one in the diesel and apparenly its there to assist in prevention of aeration of the oil and to assist in pick up at wierdo angles....

Im not sure I buy into it but it does sound credable.


Zook while you theory of the stuck master cylinder is sound I have to ask how you account for the fluid loss from the first application and if there wasnt enough loss if the piston was stuck the brakes should be stuck on....when my disco got its brake leak from the master cylinder (i still had brakes they just used 300ml of brakefluid for 200ks of sydney driving) it all came into the footwell..

Im not tempted to buy into the distorting hose theory due to the fact that it would be constant...

[QUOTE=PLR;488689]

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Originally Posted by Tank

John, now that I've slept on it I am tending towards it being the Master cylinder, it seems to be the only rational explanation, I

I don`t understand how both circuits would fail at the same time ?

I don`t know alot about Discos but aren`t they , primary and secondary ?

If as suggested a seal leaked shouldn`t the other circuit still have worked ?

If it leaked where did the fluid go if no loss was noted ?

I`ll be interested to read what you find

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Yeh!, you and me both, Regards Frank.

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Originally Posted by Blknight.aus

the sump spacer is a form of windage tray I have one in the diesel and apparenly its there to assist in prevention of aeration of the oil and to assist in pick up at wierdo angles....

Im not sure I buy into it but it does sound credable.


Zook while you theory of the stuck master cylinder is sound I have to ask how you account for the fluid loss from the first application and if there wasnt enough loss if the piston was stuck the brakes should be stuck on....when my disco got its brake leak from the master cylinder (i still had brakes they just used 300ml of brakefluid for 200ks of sydney driving) it all came into the footwell..

Im not tempted to buy into the distorting hose theory due to the fact that it would be constant...

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Dave, couldn't the fluid have leaked back into the Fluid reservoir, that's what I'm thinking, there seems to be no other explanation. I just went and checked the fluid level and it is normal, yesterday when I checked when the brakes failed it was about 6-8mm higher, I thought at the time it might be from expansion due to heat, but I dipped my finger in and it was only warm. The plot thickens, what do you think. Regards Frank.

G'day All:)

Master Cylinder Check Valve :D there was a similar problem in 1974/5 with some Series 3's with single systems;)

Bung-Tiddley.

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Originally Posted by Blknight.aus

Zook while you theory of the stuck master cylinder is sound I have to ask how you account for the fluid loss from the first application and if there wasnt enough loss if the piston was stuck the brakes should be stuck on....

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Originally Posted by Tank

Dave, couldn't the fluid have leaked back into the Fluid reservoir, that's what I'm thinking, there seems to be no other explanation. I just went and checked the fluid level and it is normal, yesterday when I checked when the brakes failed it was about 6-8mm higher, I thought at the time it might be from expansion due to heat, but I dipped my finger in and it was only warm. The plot thickens, what do you think. Regards Frank.

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what he said.....if the piston is stuck down....it will displace the fluid that it should be pushing.....
hence the higher level in the reservoir.......

masters can leak internally past the first seal and not leak out the back.....
doesnt happen very often......but its not unheard of......


as for the check valve.....my brain isnt switched on at the moment so i cant picture the circuit it will allow fluid to flow through......
may also be a possibilty........

either way...it all points to the master cylinder......and having recently changed the brake fluid
may have caused the problem as the piston and seal gets pushed beyond its normal working zone.......
and into any crud that may be building up....which could have damaged the seal....and it finally gave way when it was worked
hard coming down the steep hill.......

methinks.....

I agree. One doesn't get to hear about it much these days, but boiling the fluid used to be a common-enough problem (and glazed pads but that's not this problem).
How old was the new fluid 3 mths ago and was it a new bottle or one that was opened some time previously?

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Originally Posted by PLR

G`day Folks

Because it seemed like an odd problem , the odd suggestion of the brake hoses came to mind .

It would require a hose on each circuit to do it at the same time to achieve it , which agreed is unlikely but was one of the very few things that came to mind .

Started an apprenteship in around 73 ( can`t really remember when ) and have seen a few odd things go on and things doing what they could not what they should .

I know you`re all keen on the master cylinder but i`m not at all because both circuits would have to do whatever at the same time which is also unlikely and i think there would be a need for external fluid leak .

One circuit fails the other still works and they`re two seperate circuits in the same orifice also it`s very unlikely for the pedal to be pumpable to the floor .

The pedal may go near to the floor slowly but not without any pressure and it would still have some form of braking .

As far as a check valve there isn`t one and as i understand it would either give a hard pedal and no braking or it would cause the brakes to stick on .
There is one on a single as mentioned but not this tandem .

This has been suggested at least 3 times sota and i agree . ( = edit )

I think all that has happened is that the fluid has boiled turned to vapour and acted the same way as air would in the system .

This would account for being able to pump the pedal with no braking occuring .

It would account for the reservoir being higher .

It would account for the brakes working when they cooled down .

The fluid in the reservoir may have been warm but at the calipers it was possibly very hot .

The fix would be to flush the system of all the old fluid and be sure all the old , old fliud is out and if the problem persists check the thickness of the rotors and look for any spotty contact as in warped rotor ( though you`d feel it through the pedal ) or anything else that caused to much heat at the wheels .

Of coarse there would be user overheating as well .

What do you think ?

If someone can explain how the mastercylinder could loose both circuits at the same time , i`m more than happy to learn .

Cheers
Peter

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Peter and Graeme, Dave, Zook and Uncleho and all the others, thanks for the input, I was a truck mechanic before I stuffed my back and Hydraulic brakes are a distant memory, so if the fluid boiled and turned to Vapour, does that mean that the vapour returned to liquid state once cooled. There was no pedal pressure for a good ten minutes, so decided to drive in low range to get some air on the discs and calipers, even though the brakes were Hot they weren't excessively hot, some sizzling when spat on, but spit did stick and evaporate, usually overheated discs will throw spit (or any liquid) off like bouncing a ball off a wall, no discolouration or smoke or fumes. I am still puzzled by this problem and a lot of intelligent people have offered feasible scenarios for why it happened. I will strip the Whole system down and replace all rubbers and seals and whatever else needs replacing, I may also look at some vented rotors, is there any particular reason L/R used solid rotors, like they went out in the late 60's.
I do have a problem with my son's Toyota 4 Runner's brakes, you might be able to help, if you hit the brakes and keep the pressure constant the brakes work well, but if you release just a small amount of pressure (without removing foot from pedal) and then reapply pressure the pedal goes halfway to the floor, a pump or 2 and the pedal is ok, Have bled the brakes but doesn't make any difference, any Ideas would be appreciated, Regards Frank.

I seem to remember a very similar problem in a Series3 I had.It was the master cylinder,a kit and hone with one of those elecy drill hones fixed it.
Andrew

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Originally Posted by DEFENDERZOOK

what he said.....if the piston is stuck down....it will displace the fluid that it should be pushing.....
hence the higher level in the reservoir.......

masters can leak internally past the first seal and not leak out the back.....
doesnt happen very often......but its not unheard of......


as for the check valve.....my brain isnt switched on at the moment so i cant picture the circuit it will allow fluid to flow through......
may also be a possibilty........

either way...it all points to the master cylinder......and having recently changed the brake fluid
may have caused the problem as the piston and seal gets pushed beyond its normal working zone.......
and into any crud that may be building up....which could have damaged the seal....and it finally gave way when it was worked
hard coming down the steep hill.......

methinks.....

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Question time at work today for the brakes guys... This was based on my recolection of the original faults being no brakes, pedal to the floor, good pads in good calipers and good hoses all in a 93 disco, brakes are now back to normal.

the brake gurus art work have discounted a leaking master cylinder... and are (without seeing it and only based on my description) leaning towards a failed vacume unit (which was my long shot since its come back ok) or boiled fluid in the calipers..

there is no check valve perse in a disc brake system (altho there are other valves to be worried about)

there are 2 exlplinations offered that had internal leaks from collapsing seals in the master cylinder but both would have left you with front or rear brakes (based on the brake setup in one of their 94 disco) and the brake warning light on till it was fixed.

There was one suggestion of it may be leaking but its all staying in the pedal tower..

Im still backing my original hunch of boiled off in the calipers...