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[TheBoy]

With relation to this, as seen on another thread...










They all cleared.  I've done enough checks to be around 95% certain it's not electronically or electronic, or the battery.

I appears the brake pedal is slow to return when foot removed, and most likely those errors and associated codes caused by the brake switch still being activated whilst driving, including a code for Brake/Accelerator pedal signals implausible type codes.


I can reasonably consistently get both brake switches to say pressed without foot on pedal, but very gently touching the brakes, and then gently releasing.  In this scenario, if you put your foot under the pedal, you can lift pedal back to its standard position.

This aligns with the driving symptoms of a feeling the brakes are slow to release, and using gearbox drag to edge forward is inconsistent and difficult.

[TheBoy]

Undo the activation rod from the pedal (though can't remove anything without significant further disassembly), and the pedal pivot feels free, and pedal spring working.

With the nut that screws on the activation rod to clamp to pedal loose, the pedal is free one the allowed movement, but the rod seems to "catch" right at the end of its movement (the end of no braking pressure).


Servo?
Master cylinder?
Something else?

[YZ250]

Can you read live data from the vacuum servo sensor. Not sure I’ve ever seen it, but then again I’ve never been directly looking for it. Although in saying that, lack of servo pressure is usually associated with a hard pedal. 
If the brake pedal pivots are ok, could there be air in the system.   
The inconsistency of gearbox creep would suggest either brake binding or ‘Hill Hold’ being activated, but neither would throw those faults or cause a lazy brake pedal.   
Hope you manage to find the cause.

[YZ250]

Can you read live data from the vacuum servo sensor. Not sure I’ve ever seen it, but then again I’ve never been directly looking for it.........

Had a look on VCDS and it does show brake servo pressure under ABS measuring blocks, so I assume your software would be similar. 

[TheBoy]

Can you read live data from the vacuum servo sensor. Not sure I’ve ever seen it, but then again I’ve never been directly looking for it.........

Had a look on VCDS and it does show brake servo pressure under ABS measuring blocks, so I assume your software would be similar. 

Yes, correct.


As I understand it, there is a plunger from the pedal, through the servo, that presses against the piston in the master cylinder.  The plunger through the servo is not actually attached to master cylinder, it just presses against it.

Given the pedal has a spring, if the pedal isn't returning fully and promptly, it has to be the pedal or the servo?  If the fault was in master cylinder or in the hradraluic system, the plunger would move away from the master cylinder?  Is my thinking correct?

I guess my next step is to undo the master cylinder from the servo, if there is enough flex in the brake lines, and see if the pedal/ servo is smooth, and returns properly.


You would not believe how much JLR want for a servo or a master cylinder!!  Talk about taking the piss.

[Doctor Gollum]

Where does the servo vacuum originate?

[YZ250]

Where does the servo vacuum originate?

Depending on the design, the vacuum either comes from the inlet manifold or on some cars it comes from a dedicated vacuum pump.

[Doctor Gollum]

Being diseasal, probably a dedicated pump...

Could this be at fault?

Also when was the brake fluid last changed?

[YZ250]

Can you read live data from the vacuum servo sensor. Not sure I’ve ever seen it, but then again I’ve never been directly looking for it.........

Had a look on VCDS and it does show brake servo pressure under ABS measuring blocks, so I assume your software would be similar. 

Yes, correct.


As I understand it, there is a plunger from the pedal, through the servo, that presses against the piston in the master cylinder.  The plunger through the servo is not actually attached to master cylinder, it just presses against it.

Given the pedal has a spring, if the pedal isn't returning fully and promptly, it has to be the pedal or the servo?  If the fault was in master cylinder or in the hradraluic system, the plunger would move away from the master cylinder?  Is my thinking correct?

I guess my next step is to undo the master cylinder from the servo, if there is enough flex in the brake lines, and see if the pedal/ servo is smooth, and returns properly.


You would not believe how much JLR want for a servo or a master cylinder!!  Talk about taking the piss.

The servo itself also has a large internal spring that pushes against the diaphragm. That spring is responsible for returning the brake pedal to its correct resting place.

[Doctor Gollum]

Is there a recall on it?

[YZ250]

Being diseasal, probably a dedicated pump...
……..

Correct.   

https://youtu.be/I9LEu6ClKS4?si=zL6nzOyrfc1Fpfbp

[TheBoy]

The servo itself also has a large internal spring that pushes against the diaphragm. That spring is responsible for returning the brake pedal to its correct resting place.

Isn't that what the spring on the pedal does?

This feels like it's catching, or a stiff bit in the movement. You can feel it when pressing, and it gets slightly stuck down on release, at this stiff part.


And, yes, being a soot chucker, will be a vac pump.  There is no issue with the amount of assistance from the servo.

[Doctor Gollum]

In that case the servo is unlikely to be a fault.

Are the brake pedal pivot and connection to the pushrod in good condition?

I ask that as a 'have you actually removed and physically inspected them' rather than 'you think so'...

The clutch pedal pins on the trolley were plastic and so badly worn that they were barely recognisable. And barely functional.

Another random thought, it's not snagging on the lower dash any wiring above it, carpet or mat?

[YZ250]

The servo itself also has a large internal spring that pushes against the diaphragm. That spring is responsible for returning the brake pedal to its correct resting place.

Isn't that what the spring on the pedal does?

This feels like it's catching, or a stiff bit in the movement. You can feel it when pressing, and it gets slightly stuck down on release, at this stiff part.
…..

I was thinking along the lines of the diaphragm or rod catching on its way back out of the servo. The diaphragm (bellows) sits on the rod that attaches to the brake pedal pivot.  The pedal spring aids the return movement, along with pressure from the servo booster. As long as there is no rust/split vacuum pipe etc. the servo would still work fine, as yours is.
So, I’m wondering if the brake pedal was taken out of the equation completely, would the rod still catch on something on its way back out of the servo. 
Of course, this is nigh on impossible to prove due to the location of the servo rod right up behind the dash.

[YZ250]

This is a **basic servo booster** diagram but shows the internal rod return spring. The spring pushes back the diaphragm, which in turn pushes the brake rod back into the car as it’s attached to the diaphragm. Later servo’s have more valves, springs and gubbins inside but it gives a general picture.





**
I know what a basic brake servo looks like inside, although at the time I wished that I didn’t.    I was hitting big numbers along a downhill section of the A30 Launceston bypass and when I reached the brow of the uphill section, I was confronted by stationery traffic. I braked really hard but then heard a loud pop and the brake pedal went rock solid. I did stop in time but it was a close call. On inspection, the pressure had blown a hole through the rusty servo. 
Ever since then I’ve driven really careful.