Fiddle brakes

[red90 driver]

Evening all. Sitting here, post several Leffe's, thinking about next years comps, with particular regard to the use of fiddle brakes on the challenge truck when I decided to throw the question open to derision and ask you lot.....

OK, we have got:

Ashcroft rear shafts, ARB's and 14.50" wide pitbulls, which make for a slightly bigger turning circle than standard!

So, for more manoeuverability, if we fitted fiddles:

a. Would it help in tight sections?

b. What is the best way of installing them?

c. How do they work exactly, if you only have 1 caliper on each wheel?

d. Does the ARB unlock immediately the air is removed, so that if I want to use the fiddle brakes, I can lock up 1 wheel and not both?

e. Best place to install the lever assembly in the cabm and what style of levers (90 or 45 degree)?

f. one caliper or two on each wheel? What calipers to fit?

h. Is this a stupid idea?

[Phil Hancock]

IIRC for a road going truck you will need to add a pair of calipers to the rear axle that are the dedicated fiddle brake calipers.

Or a possibility would be to change the rear calipers (which might mean a disk change as well) to 2 line fronts, use 1 circuit as the service and the 2nd circuit as the fiddle.

[David Sparkes]

As a curiosity, and picking up something I heard (or misheard) at a club night; what sort of locking device have you got for the centre differential?

[GBMUD]

I do not think that it is strictly road legal, but I do know that you can plumb the rear service brakes such that the line to each rear wheel passes through a second master cylinder (for the fiddle brake, in the reservoir port and out through the outlet port) and on to the rear wheel cylinder. This way, when the service brake is used the fluid can pass straight through the second master cylinder in both directions and operate the rear brakes as usual. When the fiddle brake is applied, the reservoir port is closed off by the operation of the fiddle brake cylinder and fluid is directed to the calliper on the wheel in question. If the fiddle brake system has a sufficiently small diameter cylinder and long enough levers, then the standard callipers will be able to stop a wheel. Do not underestimate how much force is needed to stop a wheel though.

An ARB locker will unlock straight away when turned off unless there is any torque across the axle. In other words, only when there is no residual turning force across the axle. It is in fact very unusual for the locker to disengage immediately, usually you need to turn to the left and/or right first to relieve torque across the axle.

Chris

[mmgemini]

I do not think that it is strictly road legal, but I do know that you can plumb the rear service brakes such that the line to each rear wheel passes through a second master cylinder (for the fiddle brake, in the reservoir port and out through the outlet port) and on to the rear wheel cylinder. This way, when the service brake is used the fluid can pass straight through the second master cylinder in both directions and operate the rear brakes as usual. When the fiddle brake is applied, the reservoir port is closed off by the operation of the fiddle brake cylinder and fluid is directed to the calliper on the wheel in question. If the fiddle brake system has a sufficiently small diameter cylinder and long enough levers, then the standard callipers will be able to stop a wheel. Do not underestimate how much force is needed to stop a wheel though.

An ARB locker will unlock straight away when turned off unless there is any torque across the axle. In other words, only when there is no residual turning force across the axle. It is in fact very unusual for the locker to disengage immediately, usually you need to turn to the left and/or right first to relieve torque across the axle.

Chris

Chris.

That's the way we did hydraulic handbrakes on the rally cars.

The downside of that system. DON'T touch the footbrake when you pull the handbrake or you will lock the system. The only way to get it free is to undo both brake lins into and out of that master cylinder.

mike

[nas90]

Evening all. Sitting here, post several Leffe's, thinking about next years comps, with particular regard to the use of fiddle brakes on the challenge truck when I decided to throw the question open to derision and ask you lot.....

OK, we have got:

Ashcroft rear shafts, ARB's and 14.50" wide pitbulls, which make for a slightly bigger turning circle than standard!

So, for more manoeuverability, if we fitted fiddles:

a. Would it help in tight sections?

b. What is the best way of installing them?

c. How do they work exactly, if you only have 1 caliper on each wheel?

d. Does the ARB unlock immediately the air is removed, so that if I want to use the fiddle brakes, I can lock up 1 wheel and not both?

e. Best place to install the lever assembly in the cabm and what style of levers (90 or 45 degree)?

f. one caliper or two on each wheel? What calipers to fit?

h. Is this a stupid idea?

a. Would it help in tight sections? - yes

c. How do they work exactly, if you only have 1 caliper on each wheel? - You need a separate caliper on each rear wheel that is not used for vehicle braking on the road. You can use a mechanical method (bowden cable) or another hyraulically operated rear wheel caliper with master cylinder for each lever, or a hydraulic / pneumatic system. On the nas I do not have room in between the seats to fit 2 levers and have been thinking along the lines of 2 pneumatic valves on the auto select lever to control hydraulically actuated rear fiddle calipers

d. Does the ARB unlock immediately the air is removed, so that if I want to use the fiddle brakes, I can lock up 1 wheel and not both? - Not sure with ARB but on KAM locking diffs when the engagement light goes out I have an open diff, you cannot use fiddles with a locked diff

e. Best place to install the lever assembly in the cabm and what style of levers (90 or 45 degree)? - Depends on vehicle, if possible 2 long levers between driver and co-driver seats operating master cylinder for each rear wheel. My Eagle racer uses 2 levers between seats and each lever has the front / rear locking diff switches, so left hand is always close to the diff locks and fiddles, works well. Left fiddle has rear locker right fiddle has front locker.

h. Is this a stupid idea? - NO! - In use it is best to get the wheel you want to brake with minimum load. If for example you want to turn left but the ground is biasing the weight on the left side of the car maybe a quick blip of the throttle to add some slip will help to brake the wheel. In most cases you will be in low box with plenty of torque going to the axle, if the ground is grippy with big Simex or similar tyres you will need some force in the fiddle brake to stop that wheel rotating. You really need to look ahead and be able to read the terrain to get the best out of fiddle brakes. First time I used them I was rubbish

Edited December 14, 2008 by nas90

[red90 driver]

In reply to David Sparkles - we are using the standard LT230 transfer box centre diff lock. Why?

Thanks for all the inputs from everyone.

Have found the fiddle brakes from Milner, but no prices on the web site. Any ideas of quality/cost for the milner items?

If we have to put another set of calipers on the rear axle, would another set of defender rears be ok, when using big wide tyres?

Is it a good idea to change the discs to a grooved type, or just stay with the standards?

[Guest noggy]

Milner supply very good products, and if you want to talk about fiddle brakes id talk to them!

[David Sparkes]

Sparkles eh, not many people use that adjective concerning me!!

I was told this, by people who don't do this, but who were passing on what they have heard.

In my opinion, the tellers don't have a deep knowledge of how a transmission Viscous Coupling works. This was part of the reason I didn't challenge the detail.

Drivers of vehicles with a transmission Viscous Coupling achieve the 'pivot on a sixpence' behaviour of fiddle brakes by combining application of the normal rear propshaft handbrake with strong application of the throttle pedal (and steering lock).

The rationale, I was told, is that the VC was 'behaving as it is designed to', which based on my knowledge of VC's is incorrect.

This is all I was told.

In addition I'll add that the users of this technique will be running open rear differentials.

My analysis is that the drivers are using the power of modern engines to overcome the natural slip limiting behavoir of the VC. The result, of powered front wheels on full lock combined with unpowered rear wheels is a given.

We can surmise that the inner rear wheel tends to lock, while the outer wheel turns, but I haven't viewed this technique in action.

I suspect the VC won't last long, but I also suspect that second hand ones aren't expensive, and can be changed without the 'heavy engineering' of removing the gearbox.

I don't have detailed knowledge or experience of 'your' type of vehicle, but the thought crossed my mind that by unlocking your centre and rear differentials, at the same time as applying the propshaft handbrake, might give the same effect. I can see that doing three things at once with the left hand might be a little difficult, but I haven't overheard a suggestion about overcoming that problem :-))

Perhaps you can arrange a control that when enabled, means that subsequent application of the handbrake automatically unlocks the two differentials.

I have assumed the technique won't work with a locked rear axle differential, as this would resist the turning effect given by the front wheels on full lock.

Have fun!

[muddy]

With an LT230 if you have the centre diff unlocked with the handbrake on you can get a similer effect although i dont know how much the centre diff or front axle components like this sort of abuse!

[bishbosh]

I was amazed when I first saw fiddles in action (as it were ) Turned a Range Rover on a sixpence.

However, the single pot rear calipers do not have enough oomph to lock a wheel effectively when used as a fiddle. You need front calipers on the back. This is what I was told by the guy who developed his own fiddles and started with rear calipers as you would and then upgraded.

[white90]

Shame that old Bus has gone to meet its maker

But Nigel the builder did indeed use Discovery front calipers added to the rear with totally separate mater cylinders/lines etc.

But at a CSW event he ended up in the modified class.

[Dave W]

With an LT230 if you have the centre diff unlocked with the handbrake on you can get a similer effect although i dont know how much the centre diff or front axle components like this sort of abuse!

In my experience the centre diff explodes in around 30 seconds... or at least that's what happened to mine when I forgot to put the diff lock in and tried driving out of a deep hole... I was putting a lot of power through it but still...

A friend of mine once came up with a great idea for checking the balance of his front wheels on the vehicle - he jacked the front wheels up, applied the transmission brake and, with the centre diff out, brought the front wheels up to speed. He didn't say how long he ran it for but I got the impression it wasn't very long - it was long enough, however, to destroy the centre diff.

The centre diff really doesn't seem to like running like that but then in normal use it would only be expected to cope with minor differences in speed between the two axles.

[will_warne]

In my experience the centre diff explodes in around 30 seconds... or at least that's what happened to mine when I forgot to put the diff lock in and tried driving out of a deep hole... I was putting a lot of power through it but still...

A friend of mine once came up with a great idea for checking the balance of his front wheels on the vehicle - he jacked the front wheels up, applied the transmission brake and, with the centre diff out, brought the front wheels up to speed. He didn't say how long he ran it for but I got the impression it wasn't very long - it was long enough, however, to destroy the centre diff.

The centre diff really doesn't seem to like running like that but then in normal use it would only be expected to cope with minor differences in speed between the two axles.

Dave, I've killed a centre diff doing something similar: It popped out of centre diff lock on the first attempt and then on the second attempt it went bang. I was giving it a little right foot with both lockers and there may have been some airborne so I'm not surprised I broke something However, the broken gears jammed up the centre diff so I did drive home (and for the next few weeks ) with me wondering what the occasional crunching noise was.....

Red90, speak to Adrian Turner about fiddle bakes and large tyres. You need A LOT of power to lock the wheels.

[clbarclay]

I haven't seen in side a LT230 diff, but I suspect they are similar to the standard LR diffs in that there are no bearings between the plannet gears and the cross shaft. Its not just the high torque that destroys the diff in my observations, but the radid movement of the parts against each other. This causes gauling and consequently high friction between the parts effectively turning the open diff into an LSD. Unfortunately this is acompinied by a series of loud clicks as the internals do rotate before the parts finally disinergrate. In normal use the cost of adding bearings to allow for driving like a nutter is not justified

I have considered next time I blow an axle diff to remove the plannet gears out of the middle of the replacement diff, increase the bore diameter and insert suitable bearings to reduce gauling. Probably a lot easier said than done and may not last any longer.

The downside of that system. DON'T touch the footbrake when you pull the handbrake or you will lock the system. The only way to get it free is to undo both brake lins into and out of that master cylinder.

Was this with any particular master cylinders?

I can understand that MC sources straight out a car wouldn't be desinged to work with a very high inlet presure, so may have side effects, but surely it would be theasable to produce an MC to operate with high inlet pressure without locking up.

[FridgeFreezer]

There's always line locks, don't know anyone who's tried it though.

[will_warne]

There's always line locks, don't know anyone who's tried it though.

I haven't but I'm planning too What with steering, gears, lockers, winches etc the last thing you need is to give your hands anything else to do!

[HoggyN]

I haven't but I'm planning too What with steering, gears, lockers, winches etc the last thing you need is to give your hands anything else to do!

In the past I've pondered on a system of (hydraulic) fiddle brakes operated by mechanical linkages attached to the normal steering gear. Essentially the fiddle is activated only when the steering wheel is at, or near, full lock . In the interests of safety the system would only operate in low box with hydraulic valves linked to the gear linkage letting the pressure bleed off to a reservoir when in high box.

Citroen fully powered brake components might lend themselves to the conversion.

A simpler system (on an auto) might be to operate the fiddles with two foot pedals - like on a tractor.

[red90 driver]

So my understanding of the matter is:

If I use fiddle brakes, I will need a secondary set of calipers (Fronts) on the rear axle operated from the in cab levers, coupled with a large application of loud pedal to spin the truck round.

But, by applying the power, I will probably bollix up the centre diff in the LT230 in very short order!

How do the ppl in the CCV class in trials cope with this problem........

Is it really worth putting fiddles on then, in order to break transfer boxes quickly?

(Sorry David, I think my eyesight want checking, I always read your name as Sparkles, and not Sparks. But I think its not too bad a miss-spell....)

[David Sparkes]

"But, by applying the power, I will probably bollix up the centre diff in the LT230 in very short order!"

If using Fiddle brakes, that isn't how I read the comments.

With one fiddle brake applied the centre diff will feed power to both propshafts, so will survive.

It's only if you stop BOTH rear wheels, and thus the rear propshaft, that the centre diff objects to have one output going really fast, while the other is stationary.

Mind you, I also read into the comments that the diffs were not being used in the same circumstances I thought fiddle brakes would be used, IE, to do a sharp turn, either round an obstacle, or to avoid an obstacle. In this scenario I wouldn't expect a fiddle brake to be applied for anything like 30 seconds, maybe 10 or less.

What do people who actually use fiddle brakes say - how long is a typical application?

Cheers

[FridgeFreezer]

From the few times I've seen them in action they've been used to spin a truck round/between trees or change direction against the will of gravity (EG driving along a side-slope then turning to drive up it) and have been used in quick dabs of a few seconds, not necessarily with power on (eg a one-wheel handbrake turn).

Obviously you need to be a bit sensible about the combination of locked wheels & loud pedal but when it's done correctly it's very impressive.

[GBMUD]

But, by applying the power, I will probably bollix up the centre diff in the LT230 in very short order!

How do the ppl in the CCV class in trials cope with this problem........

Is it really worth putting fiddles on then, in order to break transfer boxes quickly?

My understanding is that one uses fiddle brakes with the axle locker unlocked and the centre locker locked, so no danger to the transfer box. This way, with one rear wheel braked 50% power goes to the unlocked rear wheel and 50% to the front axle - this will cause the car to slew round in the desired direction rather like a bulldozer or tank.

(Sorry David, I think my eyesight want checking, I always read your name as Sparkles, and not Sparks. But I think its not too bad a miss-spell....)

Sparkles by name, sparkles by nature.

Chris

[nas90]

So my understanding of the matter is:

If I use fiddle brakes, I will need a secondary set of calipers (Fronts) on the rear axle operated from the in cab levers, coupled with a large application of loud pedal to spin the truck round.

But, by applying the power, I will probably bollix up the centre diff in the LT230 in very short order!

How do the ppl in the CCV class in trials cope with this problem........

Is it really worth putting fiddles on then, in order to break transfer boxes quickly?

(Sorry David, I think my eyesight want checking, I always read your name as Sparkles, and not Sparks. But I think its not too bad a miss-spell....)

No, No, No

Read my piece above, read on to GB Mud, once you have a rear wheel stopped by the fiddle brake then you will go round, the faster you want to go round the more right wellie you give it! That does not mean you need to give it loads each time

You need to be able to read the terrain and estimate when to apply the fiddle, if both rear wheels are gripping it will be difficult to get one of them to stop with a fiddle even using a 4 pot front caliper on the rear wheel. If you can spin-up a wheel or if you can adjust your track position to get weight off a rear wheel it will be easier. Like I said first time out I was rubbish and probably second and third time out

You need an open axle diff - the centre diff MUST be engaged

[Steve Hiatt]

I run them on my racer, a single lever job from Milners (which they source from the States, @ £100) You just plumb it into the rear brake line and then there are two outputs for the brake calipers. I do have twin calipers on the rear, the second set are for the handbrake, but I used the main calipers as I thought they were more likely to be hot and clean than the handbrake ones.

It works very well, even with LSD diffs front and rear. It won't always lock the wheel but it's enough to unsettle the car and you can do the rest with the throtle. Perfect for hairpin bends, showing off doing donuts etc.

[red90 driver]

Thanks gents! (and others...)

After being put right about non exploding transfer boxes, I feel I have all the info I need. Just need to persuede the winch man that I NEED fiddle brakes to make his life easier. And one (or two) of Saley's winches. And Ashcrofts finest front axle candy. And some boggers.. and anything else shiny....

So, a set of front calipers grafted onto the rear axle, a set of Milners finest, and then some practice time with the 205's and a grassy area. I feel a christmas pressy to myself coming on. Don't tell the missus!!