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Brakes Issue
Daddylonglegs - 26/7/12 at 01:11 PM

I'm just wondering if my issue with the IVA fail on rears locking before fronts might be simpler to cure thatn fitting a bias valve?

I have been searching round the forums for inspiration, and came across one with questions regarding the connection of the MC.

My Ford Master Cylinder has 3 connections on it and my brakes are connected as follows:

Rear connection to rear axle and T-piece off to the rear slaves

Front lower connection off to another T-piece which then feeds left and right calipers.

Front upper outlet just has a bleed nipple fitted.

I know the ford MC has a 2-piston setup with one feeding the rear and one the front. I am wondering what effect changing the front so one side comes off one of the front outlets, and one off the other?

Anyone give me an idea as to what would be the effect on the front brakes, i.e. would it make them more efficient and therefore help with the front/rear balance issue?

Thanks guys.

loggyboy - 26/7/12 at 01:16 PM

My donor sierra had somesort of valve that the rears went through prior to leaving the engine bay, could that be a restrictor?

Daddylonglegs - 26/7/12 at 01:19 PM

Yep, that's the bias valve that reduces the rear brake force under deceleration, and that's the bit I was going to fit if I can't sort it any other way.

I just wondered what effect moving the front brakes to run off seperate outlets at the front of the MC would have. Not sure if it would give better front braking than with both coming from a single outlet as I have at the minute.

John

robinj66 - 26/7/12 at 01:23 PM

I have mine with the two outlets each feeding one side of the front. That's how Mr Ford set it up but I can't see any logical reason why your setup should make much difference

JAG - 26/7/12 at 01:35 PM

By all means do this but it will make no difference to the brake balance.

Both of the front ports come from the same m'cyl' piston - hence the same pressure, hence no change in balance Sorry.

Best thing to do is fit the Bias Valve

Daddylonglegs - 26/7/12 at 01:38 PM

Fair play. Well, sounds like Robin may have the answer to my woes anyhow, I wait with baited breath

whitestu - 26/7/12 at 01:38 PM

quote:

I have mine with the two outlets each feeding one side of the front. That's how Mr Ford set it up but I can't see any logical reason why your setup should make much difference


That's how mine is connected as well.

Stu

robinj66 - 26/7/12 at 04:23 PM

quote:
Originally posted by Daddylonglegs
Fair play. Well, sounds like Robin may have the answer to my woes anyhow, I wait with baited breath


Blimey!! I had better get a move on before you turn blue (Still at work atm)

robinj66 - 26/7/12 at 09:00 PM

John - Here's a photo
[img][/img]

Not in the garage so I will have to search the shed tomorrow (luckily I have booked a day off

austin man - 26/7/12 at 09:56 PM

quote:
Originally posted by Daddylonglegs
I'm just wondering if my issue with the IVA fail on rears locking before fronts might be simpler to cure thatn fitting a bias valve?

I have been searching round the forums for inspiration, and came across one with questions regarding the connection of the MC.

My Ford Master Cylinder has 3 connections on it and my brakes are connected as follows:

Rear connection to rear axle and T-piece off to the rear slaves

Front lower connection off to another T-piece which then feeds left and right calipers.

Front upper outlet just has a bleed nipple fitted.

I know the ford MC has a 2-piston setup with one feeding the rear and one the front. I am wondering what effect changing the front so one side comes off one of the front outlets, and one off the other?

Anyone give me an idea as to what would be the effect on the front brakes, i.e. would it make them more efficient and therefore help with the front/rear balance issue?

Thanks guys.



Definitely the teo fronts to each front wheel and 1 to the rear with a T connected to feed both rears I didnt fit the valve on mine and no problem with SVA as it was or MOT now

Daddylonglegs - 27/7/12 at 07:47 AM

Robin, not seen that sort before. The one I have been told that is used is the one shown below:

Bias Valve
Bias Valve

Not sure what your one is off, wonder if there is anyone who can tell me and also how it is connected?

JB

whitestu - 27/7/12 at 09:00 AM

JB, the one in your pic looks like a Sierra one. There is a slim chance I still have the one that came with my donor car. I'll have a look over the weekend and I I can find you are welcome to have it.

Stu

robinj66 - 27/7/12 at 09:26 AM

The valve I have is the earlier type according to Haynes. It appears to work by way of a ball bearing. Does anyone know if this is OK to cure John's problem. The photo put up by john is the later type valve and I'm not sure if there is a difference in how they work and more importantly if the earlier type will work on the roller test at IVA.

Any thoughts......

whitestu - 27/7/12 at 10:06 AM

I thought such valves worked to limit pressure to the rear brakes under heavy braking due to the braking G force closing the valve a bit and so limiting pressure.

Some cars have valves linked to the rear suspension that limit pressure when the rear end lifts under braking, which has the same effect.

As such, it wouldn't make much difference on the rollers, but would when the car is being braked from any speed.

Stu

britishtrident - 27/7/12 at 10:21 AM

A "G" valve is a very clever bit of kit but not the way to go it just show any effect on rollers. what is required is either a pressure limiting valve or a pressure proportioning valve.


Pressure limiting valves are the type that was fitted to early BL Minis the simple shut off any increase in pressure to the rear brakes once a pre-set pressure is reached in he supply pipe from the master cylinder.


Proportioning valves are similar but smarter after the the pre-set limit is reached a proportion ( could be about 50%) of the increase in pressure above the shut off still goes to the rear.

britishtrident - 27/7/12 at 10:36 AM

quote:
Originally posted by whitestu
I thought such valves worked to limit pressure to the rear brakes under heavy braking due to the braking G force closing the valve a bit and so limiting pressure.

Some cars have valves linked to the rear suspension that limit pressure when the rear end lifts under braking, which has the same effect.

As such, it wouldn't make much difference on the rollers, but would when the car is being braked from any speed.

Stu



Load sensing valves linked to the rear suspension (usually either the centre of the anti-roll bar on IRS or axle beam) are mainly used to increase the shut off pressure to compensate for carrying loads over the rear wheels. They are more often found on estate car and van variants of pre-ABS models Ford used them on some Escort MK3 variants and Peugeot and Fiat use hem on several models. The Uno/Panda/Ritmo/Strada/Lada valve is of this type and only requires the addition of a bracket with screw thread for a set screw to make the actuation pressure pre-setable. The Fiat valve will however function perfectly without the adjuster and the good bit is it a new one can be found for between a £10 and £20.

[Edited on 27/7/12 by britishtrident]

Daddylonglegs - 27/7/12 at 11:06 AM

OK guys, I think I need to clarify the fail point.

The car passed all the static brake testing fine, he used the pressure pad under the foot etc. to test under different loading for both front and rear. The efficiencies were fine, he told me that the rear was showing 75% and IIRC the minimum allowed was 60%.

When I asked him if there would be an issue with the valve fitting (which he advised) and he said that there was enough efficiency to 'play with'.

The part the car actually failed on was the drive at about 25-30mph then hard braked. The rears definitely locked up before the front and the rear started to step out. The fitting of the inertia type valve should sort this out, all I have to do is play with the mounting angle.

So as far as I can see, fitting the vavle will work OK and if I can get to bed the front discs/pads in a bit mmore then we should be fine. (As I mentioned before, the fronts are Cortina calipers with new discs & pads, the rears are 9" used drums with new shoes).

John

whitestu - 27/7/12 at 12:25 PM

quote:

Load sensing valves linked to the rear suspension (usually either the centre of the anti-roll bar on IRS or axle beam) are mainly used to increase the shut off pressure to compensate for carrying loads over the rear wheels.


And when there is little load on the rear i.e when you brake, the pressure is reduced to prevent the rears from locking first.

My old Alfasud had one (connected to the Panhard rod IIRC) and when the valve failed and allowed full pressure to the rears the car tried to swap ends every time you did an emergency stop!

What fun!

britishtrident - 27/7/12 at 02:06 PM

quote:
Originally posted by whitestu
quote:

Load sensing valves linked to the rear suspension (usually either the centre of the anti-roll bar on IRS or axle beam) are mainly used to increase the shut off pressure to compensate for carrying loads over the rear wheels.


And when there is little load on the rear i.e when you brake, the pressure is reduced to prevent the rears from locking first.

My old Alfasud had one (connected to the Panhard rod IIRC) and when the valve failed and allowed full pressure to the rears the car tried to swap ends every time you did an emergency stop!

What fun!



No the Bendix load sensing valves dont work in quite that way they can't reduce the pressure once the pressure as already been supplied to the rear brakes. The base pressure at normal ride height is set low enough to prevent locking under all load conditions, the valve sets a higher shut-off pressure when carrying a load, in the normal ride height condition there is a small clearance between the the vave plunger and the actuating link mechanism. When the load on the rear suspension is increased the clearance is taken up then the valve plunger is pushed in allowing increased pressure to the rear.

What happens when the go wrong is the piston sticks in the bore and first time the car is loaded up or goes over a bump the plunger is forced in and seizes in the full on position result when the load is reduced and car is returned to normal rideheight far to much pressure is still alowed to the rear brakes and an instant spin first time the brakes ar used in anger.


With the Lockheed valves old the BMC Mini with single circuit brakes we used to find the opposite problem the internal spring would loose tension over the years and the shut to the rear brakes would occur too early resulting in virtually zero prssure to the rear brakes.

whitestu - 27/7/12 at 02:09 PM

quote:

What happens when the go wrong is the piston sticks in the bore and first time the car is loaded up or goes over a bump the plunger is forced in and seizes in the full on position result when the load is reduced and car is returned to normal rideheight far to much pressure is still alowed to the rear brakes and an instant spin first time the brakes ar used in anger.


That makes sense! Being an Alfasud there was certainly some rust involved!

Stu

steve m - 27/7/12 at 02:24 PM

My locost rear brakes lock up before the front, and in my opinion has nothing to do with setup/balance or ay other out of the ordinary reason, put purely down to weight distribition

My 7<< weighs about 1/3 rd of the original donor, and the weight distribution even with me in it is going to be somthing like
75% front and 25% back original configuration i believe for a ford escort would be nearer 60/40

I have noticed that having a full 6.5 gallons of fuel, and tools spare water etc and other bits of clutter, in the boot, my rear brakes are much less likley to lock up

Also two up, the rears have NEVER locked

This point is also very valid when the car has its mot, as if the mot guy uses the rollers, my car skips and bounces around, and will never get the rears to work, just lock, untill we get two of us to sit on ther rear

I was going to fit larger rear wheel cylinders, as that would reduce there effectivness, but thankfully, realised the problem, and how to fix it, properly

Would it not be a better idea to carry two bags of sand in the boot, ?

Again this is only my opinion !!

regards

steve

whitestu - 27/7/12 at 02:41 PM

quote:

My locost rear brakes lock up before the front, and in my opinion has nothing to do with setup/balance or ay other out of the ordinary reason, put purely down to weight distribition


That sounds really dangerous!

Given the different positioning of the engine compared to the donor, weight distribution should be nearer 50/50 in the locost, so should be less likely to lock the rears.

stu

Daddylonglegs - 27/7/12 at 07:42 PM

I have to agree. After feeling mine step out at the test and only doing around 25-30mph, I would hate to think what would happen at 60-70mph or even worse, in the wet

I had no question that the tester was right, even though it is a PITA having to re-test. I would sooner have that than end up backwards in a ditch or worse!

AdrianH - 27/7/12 at 07:47 PM

What is your rear brake set up? Sorry if missed it.

Adrian

Daddylonglegs - 27/7/12 at 08:21 PM

@adrian, 9" drums chap. Fed from one outlet on MC and T-eed at axle.

AdrianH - 27/7/12 at 08:30 PM

Then I would suggest you reduce the size of your brake cylinders in the rear drums from 22mm to 19mm, get the ones from the escort.

See my IVA fail page
http://www.tamarisktechnicals.com/pages/iva.html

I had all sorts of suggestions from cutting down the friction material to using oil on the edge, and such stupid ideas it was laughable.
Adrian