Brake master cylinder replacement

[jonf]

Hi - need to change the brake master cylinder, looks like its blown a seal. Car is a 2002 ZT 160, petrol.

Can't see a 'how to' guide on it and don't have a Haynes, but I do keep seeing warnings about air and ABS.

Can you obtain seal sets for these ? Replacement units are £100+

Any hints, tips or pointers ?

Thanks !

[COLVERT]

I found this in a post on another thread---------------


On a general point I could not find a solid ‘how to’ for removing the Brake Master Cylinder ( found one but it only explained what to do once you had got to it !) . Anyway , I decided to go through the motions which involved removal of Wipers , Scuttle , Wipers Drive mechanism and bracket next to Master Cylinder that partly held this mechanism too . Open bleed nipples with 11 mm spanner . Use 13mm spanner to unbolt Master from Servo.
This might be of interest to others in the future ?
All the best and thanks


Might help.---

[jonf]

By scuttle, they mean the large plastic part that runs across the car and up to the base of the windscreen presumably ? Some of the bolts securing that are down behind the engine and near-inaccessible !


Thanks

[COLVERT]

Originally Posted by jonf

By scuttle, they mean the large plastic part that runs across the car and up to the base of the windscreen presumably ? Some of the bolts securing that are down behind the engine and near-inaccessible !


Thanks

I don't remember any bolts like those you mention when I took the scuttle off my car. It came off easily.---

[Arctic]

You should be able to get to the servo by removing the front plates from the plenum chamber, few photos below, should give you an insight hopefully.

Inside the car, to remove the vacuum servo you will need to remove the master cylinder, prise out the vacuum check valve from the front of the servo, and keep/collect the seal, remove the drivers lower facia panel, remove the trim panel above the pedals, secured by two screws and push fasteners at the bottom, prise off the clip and withdraw the clevis pin securing the brake pedal to the servo pushrod, then you can unscrew and remove the four nuts holding the servo to the bulk head, it should then be withdrawn from the engine bay area.

I don't think servo are serviceable so it would need changing if not working.

In you opening post you say you think its blown a seal why do you think this please.

[jonf]

Hi Artic - thanks for the reply. It's the master cylinder we think is blown, not the servo.

We think it is a blown seal as the pedal goes hard after a couple of pushes without the engine running, but with the engine running it remains soft and gives full travel with almost no braking effect irrespective of how frequently it is pushed.

There is no fluid leakage from the braking system.

The level of fluid in the master cylinder does not and has not changed.

There is still vacuum negative pressure from the vacuum pump on the cylinder head (haven't checked it at the servo end).

The problem started after the front brake cylinders were changed - we suspect when the cylinders were pushed in to change the brake pads , even though the reservoir was open, the seal was on it's last legs and failed.

Hope that helps !

[Arctic]

Originally Posted by jonf

Hi Artic - thanks for the reply. It's the master cylinder we think is blown, not the servo.

We think it is a blown seal as the pedal goes hard after a couple of pushes without the engine running, but with the engine running it remains soft and gives full travel with almost no braking effect irrespective of how frequently it is pushed.

There is no fluid leakage from the braking system.

The level of fluid in the master cylinder does not and has not changed.

There is still vacuum negative pressure from the vacuum pump on the cylinder head (haven't checked it at the servo end).

It sounds like you have air in the braking system? most likely in the secondary circuit.

Have a good read of this below before proceeding to remove master cylinder. you may have the suffered sinking pedal syndrome.

https://www.the75andztclub.co.uk/for...ad.php?t=63314

[jonf]

OK, thanks

The T4 bleed - presumably a garage job, rather than a home job ?


Apologies - it was the pads only that were changed, not the cylinders - in the same sentence I've stated both and contradicted myself doh !

I'm wondering if the person who did it didn't remove the brake master cylinder cap and just pushed them back to save some time, tho they said they did. I'll be working on it myself in future.

[COLVERT]

Originally Posted by jonf

Hi Artic - thanks for the reply. It's the master cylinder we think is blown, not the servo.

We think it is a blown seal as the pedal goes hard after a couple of pushes without the engine running, but with the engine running it remains soft and gives full travel with almost no braking effect irrespective of how frequently it is pushed.

There is no fluid leakage from the braking system.

The level of fluid in the master cylinder does not and has not changed.

There is still vacuum negative pressure from the vacuum pump on the cylinder head (haven't checked it at the servo end).

The problem started after the front brake cylinders were changed - we suspect when the cylinders were pushed in to change the brake pads , even though the reservoir was open, the seal was on it's last legs and failed.

Hope that helps !

You say the pedal goes hard with the engine not running. Would it do that with a blown seal ???


I go with the air in the system bunch.--

[RoverP480]

If the pedal is hard without the servo it usually means there is no air in the hydraulic system to compress and the master cylinder is working. I would be looking at the servo or less likely ABS modulator. If you start the engine having previously evacuated the servo and still pressing on the pedal, does it go straight to the floor?