Brake Master Cylinder Upgrade????

[NTEL]

Having installed 4 pot WMS brake calipers on the front of the Taz Racer(280i) I now find that I have a lot more pedal travel then before. It stops well enough but I have to press the pedal down further. I'm assuming that this is due to the system having to move more fluid than before.

Does anybody know of a larger bore master cylinder that can be fitted to replace the original and am I right in saying that the original is a 13/16" girling unit.

Ta

Dave

[Brap_Brap]

NTEL said:

Having installed 4 pot WMS brake calipers on the front of the Taz Racer(280i) I now find that I have a lot more pedal travel then before. It stops well enough but I have to press the pedal down further. I'm assuming that this is due to the system having to move more fluid than before.

Is there any sponginess? I know it's stating the obvious, but is there any chance an air bubble remains in the system?
For the time it takes and potentially the time and money it might save, I'd bleed the system again, back wheels too, furthest from the master working your way to the closest.

Edited by Brap_Brap on Wednesday 27th May 18:00

[NTEL]

Brap_Brap said:

Is there any sponginess? I know it's stating the obvious, but is there any chance an air bubble remains in the system?
For the time it takes and potentially the time and money it might save, I'd bleed the system again, back wheels too, furthest from the master working your way to the closest.

Edited by Brap_Brap on Wednesday 27th May 18:00

That was the first thing I checked. There is definately no air in the system and no spongyness. Its just got a longer pedal travel and I'm sure that this is due to moving more fluid.

Edited by NTEL on Wednesday 27th May 20:01

[Brap_Brap]

That makes sense.

[350zwelgje]

Upgraded to 4-pots as well (ok, hi-spec not your supplier).
It is for me not required to upgrade the master on mine, as pedal travel is normal. But this is a 350i from '87 and it has a standard Cortina 20,6mm bore master. Happy with it, and no requirements to upgrade.

Pad out (due to disks size and not running true) can occur and push the brake pads and pistons back. When you brake the first time, more fluid is required to push the brake pads on to the disk. But you would notice as the second time braking quickly after the first time would need less pedal travel.
If this is happening two solutions:
- Get the disks true (mounting them to the front stub axle as best as possible)
- If disks run true, install pressure valves in the brake line to maintain a bit of pressure. Steve Heath is using this method on his wedge.

Rob

[deetes]

I had the same problem on mine when I went to four pots. Bled it every which way and in the end adjusted the Master cylinder push rod. Obviously you have to watch and not over adjust it as the brakes wil bind.

[NTEL]

deetes said:

I had the same problem on mine when I went to four pots. Bled it every which way and in the end adjusted the Master cylinder push rod. Obviously you have to watch and not over adjust it as the brakes wil bind.

How is this done Deetes?

Thanks for all the replies, I'll have a good look at the discs tomorrow and check that the pads are wearing evenly.

[GreenV8S]

There is always a small amount of dead travel between the pedal and the master cylinder. This is essential in order to allow the piston to return fully and open the transfer ports to the reservoir. The more dead travel you have the further you have to push the pedal before the master cylinder starts to apply pressure to the brakes. Once you have taken up the travel, everything else you feel is the hydraulics. So if you start to feel resistance on the pedal but the brakes are spongy when you push harder, that's a problem with the hydraulics. But if you just have to shove the pedal a long way before you get any resistance, it's possible you have too much dead travel.

The dead travel is adjustable by a screw in the end of the pushrod at the master cylnder. Normally you need to set this before installing the m/c.

Don't adjust it too tight. If you take out the dead travel completely so that transfer ports don't open, the hydraulics become a completely sealed system. As soon as you get the slightest thermal expansion in the fluid, the brakes will start dragging and then get tighter and tighter until they seize on.

Edited by GreenV8S on Friday 29th May 09:22

[chedder]

Hi Dave, WMS four pots on mine and no noticeable extra travel on the brake pedal, a lot more 'feel' though.
The rear brakes take an awful lot of messing around to completely purge the pipes of air, approx 2L if I remember correctly, used cheap fluid until completely free of air then pushed decent fluid throughout the system, 'Eazybleed' pressure system helps a lot.
GreenV8S is right about the brake push rod, don't over do the adjustment unless you like the smell of burnt pads

[NTEL]

chedder said:

approx 2L if I remember correctly:

I use Castrol SFR at about £70.00 per litre!!!!!!!!!!!

Thanks for all the advice guys. I'll give it another bleed through tomorrow and see how it is.

[TVR_owner]

NTEL said:

chedder said:

approx 2L if I remember correctly:

I use Castrol SFR at about £70.00 per litre!!!!!!!!!!!

Thanks for all the advice guys. I'll give it another bleed through tomorrow and see how it is.

Dave,
My 4 pots on the M are fed with a 3/4" piston so I would think the problem lies elsewhere.

You should remember just how important brakes are and that adequate time should be spent getting them right. If you have some brakes at the moment (even with the odd pedal) I would leave well alone until November say, when you and the long winter nights to sort the problem. Best not to rush these things.

[GreenV8S]

NTEL said:

I use Castrol SFR at about £70.00 per litre!!!!!!!!!!!

If you've got the system clean and just trying to displace air then there's no reason not to reuse the fluid. When mine has been drained I dump the bled fluid straight back into reservoir and pump it round for a few minutes to help pull any any bubbles out.