Brake Bias/balance And Iva

[ibrooks]

OK guys this one has been bothering me and I haven't heard or seen any clever answers from the industry yet so I thought I'd throw it in here to see what leaps out.

 

It's one where most of us don't really have a method of testing ourselves and yet one of the safety critical areas where I absolutely agree with the need for the test to be stringent (again partly because it's something you can't test yourself). I thought the SVA method was fairly sensible whereby they would let you set it up on their kit and then lock the settings off in some way. IVA however is a little different here and I don't think it's a step in the right direction.

 

Balance bars - basically have become un-workable. The manual says that they must be rendered permanently un-adjustable and specifies that you would have to weld the threads along their entire length. Not really something you can do at the station after setting it on their rollers and I'm simply not happy with putting that much heat into the components involved. There's also the issue that it renders it impossible to take the thing apart to replace components at a later date which could be construed as a failure on the part that specifies that everything must be accessible for maintenance.

 

Different bore master/slave cylinders or pistons. This one is somewhat hit and miss and whilst every conceivable combination available would probably give you the necessary level of adjustment it's going to be pricey to fit one setup, test and then buy a different size caliper/master cylinder/piston and try again.

 

Pressure limiting valves - now this is the sensible option (and the one the big manufacturers tend to use) since as long as you are in the right ball-park one of these should enable you to get the balance spot-on. However the inspection manual is downright contradictory on these. It says

 

Hydraulic valves that only operate automatically and react to vehicle loading or braking forces are permitted (Load Sensing and Gravity valves) Manually adjusted valves (other than to permit presetting the automatic function of a valve) are not permitted to be fitted even if they are rendered un-adjustable.

 

Now that would provide for the Sierra inertia valve (although when I put the 2B through SVA the tester ignored the one I had in and failed it for too much rear braking effort anyway). It would also allow for the type on an Escort van where there is a lever on the rear axle to alter it's operation according to the ride-height (it assumes the ride-height is related to load on the axle). Both of these have been set for pretty specific operation parameters and for us to start trying to tweak them further for our cars is a bit daft and the results are going to be all over the place. These things react in a progressive fashion that's designed for the weight and centre-of-gravity of the car they came from - we are unlikely to be anywhere near these so even if it's right on the rollers it might be lethally wrong elsewhere.

 

So I'm thinking that leaves the conventional bias valves - and that's where I see the contradiction. In the vast majority of cases these allow a maximum pressure in the rear brake line. The idea is that if you are below the pressurelimit in the system then you aren't prodding the pedal so hard and there isn't going to be enough weight transfer off the rear wheels to allow them to lock with the applied pressure. The set maximum is set at the point where the braking applied to the front wheels would allow enough weight transfer from the rears to risk their locking. When this pressure is reached the valve operates and stops any further increase in rear braking no matter what happens elsewhere in the system. The rules say they are not permitted except where they pre-set the automatic function - surely the type I've described above all pre-set an automatic function. My understanding is that so long as I'm not messing with it whilst driving then it has been pre-set and it's function is from there on automatic. A Rover Metro/100 for example has two pressure limiting valves in the lines to the rear brakes which give a fixed limit based on the pre-load of a spring inside it. So am I right in thinking that a bias valve is just the same (so long as it's not adjustable whilst driving and therfore I have to pre-set it).

 

Any thoughts or other clever ways of complying with this one? Anyone had trouble with it and IVA yet? I hesitate to say any ways of getting around it but I suspect that's what most people would in reality be thinking and the people coming up with this legislation need to be thinking along the lines of giving us ways to comply or people will start looking for ways to avoid. Anyone friendly with a tester who can give their take on it? (wasn't there a tester on here briefly? did we frighten him off?).

 

Iain

[fry61]

Is not the Sierra valve adjustable by way of amount of inclination? That's what I have fitted, with angle at approx. 40degrees above horizontal at present;pipe-work arranged so I can vary this by a small amount either way.

[ibrooks]

Yes you can tweak the operation of the inertia valve a little in this way but you have only altered one part of the system - what I'm getting at is that it works by a ball moving forwards under inertia as the car decelerates. Thing is you haven't changed the mass of the ball and I think there's a spring that holds it back under normal circumstances which also hasn't been altered. To get the setting "right" for your car it might well be that you need the same angle as the original in the Sierra but with a lighter ball and a different spring.

 

I assume the tester tested it by hitting the brakes outside in the car-park and the front brakes lock first?

 

In the wet or dry? and would it have done the same thing. If the brakes were applied whilst cornering would it perform in the same way that it does in the Sierra? (even pointing north-south it will be affected by lateral forces).

 

Unfortunately I can't use the inertia valve as easily as I am going to be running twin master-cylinders with each braking one front and one rear wheel. On the plus side though I also have permanently engaged 4 wheel drive so they won't be testing it on the rollers anyhoo.

 

Iain

[Guest MarkB]

why don't you just ask a nce friendly Mot garage to help set it up on their brake rollers???

[Guest smeghead]

when i got my zero kit from gbs and said i was using a floor mounted pedal box they told me to weld a piece of tube over the exposed threads ie slide the tube on then weld the end which could be grinded off after the test

[Guest gdc]

my experiance is that the tester will only test on the rollers , so the sierra valve wont work .

however i have not failed a brake test on the rollers .

 

i have been at 5 sva tests to date but no iva .

all have been the same .

re the floor mounted peddles , qwerty has made a bit of kit that replaces the bias and is itsellf replaceable

with no damage to the bias set up .

but to make it work with the right pressures we feel it will need limiters in line to the rear brakes .

graham

[Guest smartfazer]

Would one of these work?

 

I presume you would just attach it to the Rear Brake outlet in the Master Cylinder, or somewhere inline???

 

http://cgi.ebay.co.uk/CS-FORD-MONDEO-Estat...=item53daef1487

[ibrooks]

why don't you just ask a nce friendly Mot garage to help set it up on their brake rollers???

 

In my case because I don't want the viscous couplings knackered.

 

That one aside there's also the issue of how to get it there bearing in mind that this needs to be done pre IVA and if it's not right and we can't use an adjustable valve of some sort what do I do? and how many trips is it going to take?

 

I've removed the bias bar from my pedal box and replaced it with a solid bar with circips in machined grooves to keep it central. The ends are turned down and threaded enough so that the rose-joints on the end of the master cylinder pushrods can be held on with a nyloc so I know I've got even effort from each master and I think I'm going to split the pipe from each between one front and the diagonally opposite rear so I'll need to limit two lines accurately to the same degree.

 

Smartfazer - that's the type of thing that a Rover Metro has in the lines to the rear. Assuming it limits to the right pressure then yes it would be pefect but there's no way for us to know whether it would work on a much shorter and lighter car. I was also hoping to stick with the rear discs on mine so I wonder if it would have the same degree of effect as it would on a drum? although I do have a set of stub axles to allow use of the drums with an LSD. Given the price though I might just buy a couple of those and go down the suck-it-and-see route to see if they do the job (wonder which way around they go?). Should solve any posible problems of keeping the limit on the rear pressure equal though.

 

Iain

[Guest smartfazer]

Iain,

 

For the price I was thinking the same.

 

However, I may have to find a shorter Master Cylinder anyway as the Ford "Bendix" is too long, just, and almost fouls the steering column bracket.

 

You see, I have the new 2B chassis with the Pedal Box and Steering Bracket built in by GBS. The Master Cylinder is mounted rearwards, and the brake pipe fitting for the front brake will screw in on its own, but will not allow the brake pipe and 90degree angle as well.

 

I was wondering if one of the newer model Fiesta Master Cylinders will fit that come complete with deceleration valve. Or use a "banjo" and flexi pipe. It would be nice if someone manufactured a 90degree brake pipe fitting into the master cylinder.

 

It would be great to have a complete collection of different Master Cylinders to hand to see which would work best.

 

Will try and get a photo up later to show you what I mean.

 

Trying not to hijack your thread, but the deceleration valve follows my train of thought.

 

Steve

[chris n]

Car Builder Solutions sell a kit to lock the Balance bar in place for the IVA test

 

CBS

[Guest qwerty_100]

Car Builder Solutions sell a kit to lock the Balance bar in place for the IVA test

 

CBS

Hi as GDC says I have made a shaft to replace the Bios bar that does not need to be welded I have not read the regs so am unsure if what I have done is correct. I agree with Iain the best way is to use the pressure reducing valve as shown in ealier thread, I today spoke to a friend who has his own hydraulic parts supply buisness he advised that this type of valve is available in many different guisses and its a case of finding the right one. So what I feel we need to do is to find out the Minitry requirments and then we may be able to find a valve that can be made available to every one.My only reservation is there does not seem to be any consisteny with testers. Iain if you would like to follow this up I am more than happy to help maybe we could find a friendly M.O.T centre that could help.

Regards

Kev (qwerty)

[ibrooks]

Car Builder Solutions sell a kit to lock the Balance bar in place for the IVA test

 

CBS

 

Nope - they make one that locks it in place for SVA. IVA specifically states that this method is no longer acceptable.

 

 

qwerty,

Have a look at this.

 

IVA Manual

 

I'd suggest taking a copy as they keep mucking around moving it despite having said from day one that it would be available online.

 

I'm some way off actually needing this as I have another little project on the go at the moment which is likely to take my time until April-ish.

 

The problem with finding the "right" valve is that all our cars are different. Some have rear dics, some have drums, there are different sizes of front discs (and rears). In the case of my car it will be 4wd (and also have in excess of 200bhp under the loud pedal which is yet another reason I really want to get this right). This is why we really need something adjustable.

 

Iain

[thespannerman]

I run a 3a that passed SVA with good brake balance. Run vented front discs and drum rears on a four outlet master with servo removed. One rear outlet is blanked with bleed nipple, other runs through an old MINI brake limiter with one outlet also blanked off. At the rear of the car a tee piece splits the single brake pipe back to two. As the MINI brake limiter is not adjustable should keep the IVA man happy ie. back brakes don''t lock up first. But the MINI brake limiter can be easily made adjustable at a later date by drilling the end out and fitting an adjustable bolt and lock nut. There not made anymore so need to look for old stock at auto jumbles. No problem testing on rollers either as its not decceleration activated.

[Guest smartfazer]

Spanner,

 

What Master Cylinder are you using?

[thespannerman]

Master cylinder came with the 3a kit(1998). Some one else might know its origins, looks same size as my donor one 1984. Push rod had a U shape clevis type peddle attachment on it, so cut up my old servo to get out the push rod that cliped to my brake pedal.