Master cylinder on zx td?

Twiss · Post by **Twiss** » 11 Dec 2006, 10:26

Hello

Can the master cylinder on the zx td be changed for a better one, a more responsive one? if so which one do I need? and what other parts do I require?

Thanks Vaughn

jeremy · Post by **jeremy** » 11 Dec 2006, 17:35

For a faster response you need to move more fluid quickly - which means a larger bore - which means more effort - which may mean that the servo isn't big enough . . . .

James.UK · Post by **James.UK** » 11 Dec 2006, 18:22

When I swopped my front brake calipers for those off a Volcane, and fitted new, bigger vented disks my mechanic had to fit a larger master cylinder.. So they do make at least two sizes..

Twiss · Post by **Twiss** » 12 Dec 2006, 09:19

James.uk you wouldnt know what master clyinder he used ?

Thanks Vaughn

James.UK · Post by **James.UK** » 14 Dec 2006, 17:44

Sorry I don't, but I think it was the same as the one off a 2ltre Volcane..

.

uhn113x · Post by **uhn113x** » 18 Dec 2006, 17:20

Vaughn
What, precisely, do you mean by "more responsive"?

If the brakes are working as they should be, they are more than adequate. Modification will not fix faults.

I had to change the master cylinder on my ZX TD because it was leaking into the footwell; not an easy job, and the pushrod adjustment in the Haynes BOL bore no resemblance to what it should be; when I adjusted it like the book, the brake pedal was nearly on the floor, so I had to remove it and readjust by using a depth gauge.
Brakes are really good on it then (drums at rear)

HTH

Twiss · Post by **Twiss** » 19 Dec 2006, 20:44

Well I mean more responsive like something to happen a little quicker.

What happens is I can press the pedal half and almost nothing happens, then alittle further and I can feel the brakes starting to slow the car down. So I would like to bring/shorten the pedal travel if possible.

I have had all the brake pads and shoes replaced in the last year plus the rear drums have had new adjusters, both hand brakes cables replaced. and both wheel cylnders replaced. and I have fitted Brembo max discs on the front -- they made a difference in stopping the car.

What do u mean uhn113x you had to use depth gauge to adjust it ?

Thanks Vaughn

uhn113x · Post by **uhn113x** » 20 Dec 2006, 07:29

Vaughn

Ah

now I think I see what you mean - it is just the amount of pedal travel that is excessive, not the actual braking efficiency, yes?

So, a few more questions!

Has it ever been any better on this car?
If so, did the problem happen suddenly or gradually?

I think the only way that the pedal travel can be too much is by excessive rear brake clearance or the pushrod on the master cylinder needing adjustment. Nothing to do with fitting different discs, other non-standard mods et al.

OK - I always thought that mine was a tad too much; if you pressed the pedal with your hand (stationary!!) you could feel that nothing was felt for a few cm.
So, when I had to swap the m/cyl for leakage, I checked the pushrod coming out of the servo against the HBOL and found the book had a glaring error, so no good there.

I measured the flange on the m/cyl and the depression where the rod pushes using a depth gauge - the sort there is on a vernier caliper.
Same on the servo flange and its rod.
I adjusted the rod to leave about 1mm clearance.

Also - the rear brake adjusters - I was told that it is better if, after you adjust them, you go through the stud holes and give them both an extra click.

The ZX is not renowned for its tight prake pedal, but a pal who has worked on Cits for years said mine was very good now; about 2cm on the pedal before brakes are applied. With the engine off, it is nearly at the top, so the clearance must be due to the design of the servo.

Make sense?

HTH

jeremy · Post by **jeremy** » 20 Dec 2006, 09:15

I entirely agree with uhn 113x - and having a ZX 1.9D with the bendix brakes I know exactly what you mean.

One of the problem with braking systems is that the pedal provides maximum mechanical advantage over a very small range - like the top bit of the pedal travel - so as the brakes wear and the pedal sinks - they don't work well. - Nice high pedal - nice sharp brakes.

So chances are a high firm pedal will give better brakes. - So why is it slack after all the work you (and I) have done.

I think there are 4 possibilities:

Slack rear brakes - like my car yours has new adjusters etc and presumably the handbrake works well and on both sides (one side will drop more than the opther if one side only is working when you drive off against the handbrake.) However although my car seems OK I did have to tighten the brake cables up a long way - and wonder if all is OK.

So to test for slack in the back brakes gently apply the handbrake a notch or 2 and see if this tightens the pedal. (Sort of instant adjustment!) (Safety warning - don't drive for more than a few yards like this)

Air in the system - unlikely - pedal probably spongy, possiby uneven braking - also brakes would improve with pumping - but they do to some extent anyway due to the back brakes taking up the slack and not returning before the next pump.

Master cylinder-pedal mechanism slack. This is what uhn is referring to and I think is the likely culprit. Care must be taken when adjusting this to make sure the master cylinder pistons release adequately - which is so that the holes between the cylinder and the pistons (recuperator ports) is uncovered when the pedal is released. If this does not happed the system will not function and you may even get locking brakes. You may be able to feel some slack when you operate the pedal by hand - try it with the servo collapsed as well.

Flexy hose stretch - will cause problems - all cars have this to some extent - but have tight brakes - so unless yours has very poor spec hoses (unlikely) this isn't likely to be the main problem. ZX don't seem to have excessively long flexys either. Expensive braided ones may be better if they are made with tight braiding but I think there are other more significant improvements to be made first.

Twiss · Post by **Twiss** » 20 Dec 2006, 17:12

Thanks for your replys Guys

I'll have to get my head round it but I think I got it.

If not I'm sure Ill be asking more questions, if thats ok ?

Thanks Vaughn

G4EIY · Post by **G4EIY** » 20 Dec 2006, 17:35

Hi Twiss,

Another possibility, although very unlikely, worn wheel bearing.

This can move the caliper cylinder to one side, thus pushing brake fluid back into the reservoir.

If this happens, extra volume of fluid is required before all the slack is taken up.

jeremy · Post by **jeremy** » 20 Dec 2006, 18:06

Did wonder about wheel bearings when posting above but I know you've had the car for several years and always complained about this problem - and I would have expected the things to have started making noises by now!

If the bearings are slack it will show when you shake the wheel - and generally go if you try and shake it while the brakes are applied. You will also generally get some noise on cornering. Thats the easy bit - working out which one is noisy when you cant find any slack is more fun.

G4EIY · Post by **G4EIY** » 20 Dec 2006, 22:58

Relatively easy to check, but it does require removing the wheels.

Just inspect the position of both the pads in relation to the disk face.
If no gap between the brake pad and the disc face on both sides, then that's nornally ok...

If small gap is visible on one side, that could be the problem...

Best of luck...

Twiss · Post by **Twiss** » 22 Dec 2006, 17:11

Well Had a check and by the looks and feel of it the wheel bearings are ok. So I think its just that pedal travel thing.<--- I know very technical

Vaughn