Brake Judder

[Pendennis]

Hi Alan, not sure why your dismissing the master cylinder failing? Have you installed a new one ?

It would appear to me an hydraulic issue as you stated in your very first post, only apparent when everything gets warm and up to temperature. If there is an issue with the fluid itself, or seals whether calipers or master cylinder it would only become apparent to you as the fluid is pressurised and warms up.

I had a similar issue which kept coming and going, I always thought it was the fluid as only apparent when it warmed up. Everytime it came I flush the fluid through, each time matters initially improved until eventually I suffered dramatic fade with vibration, I was convinced the feeling the pedal gave me was a leak as the pressure on pedal come and go. When I got out the car and investigated, nothing was evident which made me decide the only cause possible could be the master cylinder, which it was.

I distinctively remember the feeling transferred back through the pedal, it wasn't the spongy feel you get when there's air or fluid boiling, it was jumpy although I did suffer pedal travel. However, my Cat is a race car so appreciate you will not be stamping on the pedal like I am.

Either way your get it sorted, be interested to know what the actual problem is.

[alan c]

I did think about the master cylinder but when we tested the brakes on rollers the problem only occurs with the front brakes. I have therefore assumed, for now, that it cannot be the master cylinder on basis if that was the issue the vibration would be apparent on all wheels.

[Pendennis]

Depends which master cylinder you have, if it's the Uprated type (red cable tie) then there are two circuits (front & rear), but if it's the standard single circuit type then you have a point

[alan c]

So far as I am aware it the standard as would have been supplied in early 90's when the car was built. I will have a look and see if it looks the same as a standard one on CC web site.

 

[7 wonders of the world]

Both std and uprated are tandem master cylinders, connected on a front / rear basis not diagonal as is the case for most tintops.

[Pendennis]

Sorry I thought there was a difference between the two. Thought the Uprated would still work if a failure occurred in the front or rear, thus two different circuits meaning front or rear would initially work, but not continually. Is that the case for the standard set up as well?

[Pendennis]

Sorry I thought there was a difference between the two. Thought the Uprated would still work if a failure occurred in the front or rear, thus two different circuits meaning front or rear would initially work, but not continually. Is that the case for the standard set up as well?

[john milner]

As the brakes were okay but are not after being unused for a while then corrosion is most likely. Discs and pistons corrode so I would start looking at this area first and then look at what else could corrode while being laid up. I can't see how not being used could cause wear or warping.

[7 wonders of the world]

In a tandem set up the two hydraulic circuits are seperate, but the master cylinders are placed one behind the other for reasons of cost and packaging, in the even of one circuit failure the other will still operate albeit with increased pedal travel.

Normal practice is to connect diagonal pairs so in the event of failure to retain one front and on rear brake which reduces the chance of the car swapping ends, however since were more performance based ours are front and rear, thus making it easier to plumb a rear bias valve in too.

NB only tandem cylinders with identical bore sizes should be connected in a diagonal set up.

[alan c]

Ok it might be corrosion of the pistons but cannot be corrosion of discs as i have put new discs on.

if I understand what is being said about the master cylinder it could be a problem with part of that only, testing on rollers confirms it is front brakes only. Is it likely or possible for the master to fail in a way it affects front brakes only?

As the calipers are now with AP I cannot do much more until they are back.

[7 wonders of the world]

If your seeing variations in brake effort on the brake rollers ie the needle rising and falling whilst holding a constant brake pedal pressure it wont be the master cylinder.

Have you checked your tryes for run out, bulges etc as these will cause a variation in loading and radius on rotation which you will feel through the car, since your increasing the loading during braking this will intensify the sensation.

I've seen this several times, likewise localised wear in balljoints can give odd brake judder problems only encounted under a certain amount of steering angle.

 

[Pendennis]

Yes, if the master cylinder is failing it would affect front or rear only, dependent upon which of its seals is failing. But it would affect both wheels whether that front or rear.

Not sure I personally have understood your comment about different brake forces, are you stating the front left is significantly different from front right? If you are then you've either got a caliper issue, however you could have a blockage in the pipe feeding the caliper but that would be unlucky, although you should be able to flush the debris through. Yep wait and see what AP report