Problems after changing brake pads

[Rob Bell]

Hi chaps,

Got a real problem having just changed the pads on my ZTT. It all went straightforwardly enough - even managed to replace the brake pad wear sensors without difficulty.

BUT...

... now the brake pedal is very soft, and there is a whooshing noise with pedal depression from behind the bulk head.

Read on another thread this bit:

Originally Posted by Grey Ghost

The danger with pushing the piston back is flipping the sealing rubber in the master cylinder. Having watched an expert do mine today, he explained that if you push the piston back very slowly there is no danger of this happening. That is exactly what he did without a problem.
The other issue is that with the new pads there can be an overspill of fluid as there will then be more than is required in the system. Definitely better to have it exit through the bleed nipple than into the plenum below the master cylinder and then have to wash it out with clean water as we did today.

I avoided problems with fluid overflow by strategically positioning an old towel to collect the excess fluid. And I did push back the pistons reasonably slowly.

But I am now worrying that I didn't push them back slowly enough??? So if the sealing rubber has flipped, anyone know how I can correct the problem? Is this a dealer only task?

Help!!!

[T-Cut]

Originally Posted by Rob Bell

... now the brake pedal is very soft, and there is a whooshing noise with pedal depression from behind the bulk head.

That will be the servo activating when you press the brake. You can check this by pressing and releasing the pedal several times WITHOUT the engine running. This action exhausts residual vacuum in the servo and takes it out of the equation as far as the noise goes. You will hear a whoosh/hiss as the air goes into the vacuum chamber. When this stops, you should now hear virtually nothing and the pedal will be rock hard each time you pump it.

Now, with your foot still hard on the pedal, start the engine. The pedal will sink. In fact it may sink to the floor! Pump the pedal again and you should now hear the whooshing sound, which confirms the above. It's the servo activating the brakes.

Don't worry about the master cylinder seals. It's unlikely you've abused them in the slightest.

The sinking behaviour of the brake pedal is a mystery to me and needs a discussion. I'll open a separate thread.

For easier recall, I'm calling this SPP (Sinking Pedal Phenomenon).

TC

[Rob Bell]

Hmm - bad news.

I took it to a local MGR specialist in Holloway who confirmed my worst fears That'll teach me - one small IDY job is now going to cost a small fortune in replacing the master cylinder...

Yep, the pedal can fall to the floor - and did several times, and even did during a test drive. Very worrying behaviour. I am assured that the odd 'whoosh' noise is in fact normal, but frankly, I haven't heard it before, but I guess I could be being extra conscious of things on finding the pedal excessively soft and spongy.

I am now uttering more expletives and challenging ancient anglosaxon than could ever be posted in an open forum. Arrrrgggghhhh!

[podge]

Would it be worth asking your local freindly M.O.T tester to put the car on the rollers and see what brakes you have.P.

[Rob Bell]

Originally Posted by podge

Would it be worth asking your local freindly M.O.T tester to put the car on the rollers and see what brakes you have.P.

It's ABS equipped.

[mayor]

I am a little concerned about the recent posts on this subject since I have bought 2 rear mintex discs and pads to fit myself this week sometime. Like a lot of the members I have done a lot of brake pads/discs over the years with various cars and I have never had the master cylinder flip its seals but now I am wondering if its an issue with 75/ZT?

[T-Cut]

Originally Posted by mayor

- - - -I have never had the master cylinder flip its seals

Me neither. In 40 years of servicing the 'usual' way, it's never happened. I don't recall reading of anybody having this problem either, which has all the makings of a myth to my mind. How can applying hydraulic pressure to the compression face of the seal cause it to flip? I'd like an explanation as to how it happens.

- - -but now I am wondering if its an issue with 75/ZT?

As above, these issues can be nice earners for some garages. The owner fears the worst after reading Mr Haynes and they're more than willing to confirm his fears. New master cylinder £300. Just bleed the brakes properly £50. Go figure.

TC

[dgreaves]

T-Cut is right I've worked on brakes on my cars all my motoring life never heard of this, for instance I have 2 Saab's with Teves brakes,changed the pads frequently over the last 10 years without a problem. Have the brakes bled to make sure and if you can, watch whoever is doing the job to make sure you are not getting your leg lifted.

just a thought I haven't got a Haynes but do they mean caliper seal that can flip not master cylinder?

Dave Greaves

[rovermech]

Hi
Having owned my own garage untill retiring, I never had any problem pushing the fluid back through the system when renewing brake pads till ABS came in, now I hear it all the time people finish up with a spongy pedal.
I still keep my hand in with a few repairs but when I change pads , I always clamp the flexable hose to stop fluid returning and open the bleed nipple to release the fluid as I press or wind back the piston, never had a poor pedal doing it this way and alot cheaper than a master cyl or ABS system

[WeeMan]

Agree with Rovermech....that's the way to do it!