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Servo Issues


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#1 petey81

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Posted 13 November 2020 - 06:36 PM

Hi all

I don't usually post on here for technical issue as I pretty much search and do my own work but the below has stumped me.
I was driving to get my car mot and the brake pedal hits the floor!
The brakes have been bled fully 4 times, new front pistons and seals. No visible leaks and once I block the vacuum end the brakes work fine..
Could this need a servo repair kit?

#2 cal844

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Posted 13 November 2020 - 06:57 PM

Sounds like you need to replace the master cylinder. Loss of servo would just give a firmer pedal but shouldn't give a longer pedal like you are experiencing.

I have had this previously on 2 minis, replacing the master cylinder solved the issue both times

#3 petey81

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Posted 13 November 2020 - 07:14 PM

Sounds like you need to replace the master cylinder. Loss of servo would just give a firmer pedal but shouldn't give a longer pedal like you are experiencing.

I have had this previously on 2 minis, replacing the master cylinder solved the issue both times


Brakes work fine with servo bypassed which would still use the master cylinder?

#4 petey81

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Posted 14 November 2020 - 09:06 AM

Forgot to mention it bleeds fine and brakes work without the servo connected and with the engine running.
If I connect the servo up with the engine running the pedal goes to the floor and I have no brakes.

#5 cal844

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Posted 14 November 2020 - 10:47 PM

You do have the brakes adjusted correctly? I usually get all 4 wheels to bind pretty severely so they can only just be moved with alot of force. I usually fit a road wheel to set this so it's easier to grip.

You could try a known working servo to rule it out but personally I think the issue is elsewhere, but without being with the car it's a longer process of elimination

Edited by cal844, 14 November 2020 - 10:48 PM.


#6 weef

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Posted 14 November 2020 - 11:00 PM

Remove the outgoing pipes from the master cylinder, let the fluid run out of the ports whilst you blank off these outlets. This now leaves only the servo and the master cylinder in circuit. Now check again and see what symptoms you have. 



#7 petey81

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Posted 15 November 2020 - 09:09 AM

Cheers all.

I have definitely bleed the system correctly.

#8 timmy850

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Posted 15 November 2020 - 09:27 AM

Have you adjusted the drums properly? There is a good guide in this video

https://youtu.be/M02bqqNOlkY



#9 petey81

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Posted 15 November 2020 - 09:43 AM

All drums adjusted perfectly.

Brakes work fine without servo connected.

I'm absolutely certain all the brakes are bled correctly as this is a basic thing that I would always check every few months anyway. I had instant brake failure not a gradual problem

#10 cal844

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Posted 15 November 2020 - 10:15 AM

Are the wheel cylinders OK?

#11 petey81

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Posted 15 November 2020 - 10:17 AM

All fine as I have stripped it down straight away
Checked-
For leaks
Adjusted drums
Handbrake adjusted correctly
Re bleed brakes
Checked servo pins and brakes pedal
Brake fluid topped up
No air leaks from servo
Brakes work with servo disconnected

Edited by petey81, 15 November 2020 - 10:21 AM.


#12 sonscar

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Posted 15 November 2020 - 10:35 AM

Just my view,for the pedal to go to the floor the fluid has to squirt out of somewhere which would be obvious or bypass the seals in the master cylinder.The servo is a red herring it only presses the master harder.The vacuum could be pulling the fluid out of the cylinder past the seals but I think it unlikely,but this would indicate shot seals.I would change the master.Good hunting,Steve..

#13 petey81

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Posted 15 November 2020 - 10:40 AM

Going by all your help I will rebuild the master cylinder.
I'm not loosing any fluid so very odd.
I have fiesta calipers upfront with green stuff pads so no issues without the servo connected.

#14 cal844

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Posted 15 November 2020 - 01:35 PM

As I said previously I had the same issue and replacing the master cylinder cured this. As there are no leaks anywhere is change the cylinder

#15 petey81

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Posted 15 November 2020 - 02:58 PM

As I said previously I had the same issue and replacing the master cylinder cured this. As there are no leaks anywhere is change the cylinder


Did you change the whole thing or rebuild kit?




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