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  • Technical Help

Important:

The following help and advice is given in good faith.
Brakes International cannot be held responsible for any accidents or claims whatsoever or however caused.
You must not work on vehicle braking systems unless you are competent to do so.

101: Handbrake calipers – Handbrake not working properly.

Cause: Usually because the caliper has not been adjusted on installation or when pads have been replaced. The auto adjusting mechanism is only designed to gradually remove play as the pads wear down, not the major initial adjustment required.

Solution: Disconnect the handbrake cable, unbolt the caliper from its guide pins and firmly force the piston back to remove any play (put slight hand pressure on the caliper lever and you'll feel the play gradually disappear - stop at this point to avoid possible damage to the adjuster mechanism). Then, depending on type of adjusting mechanism (some have a hex key adjuster screw hidden behind a bung), wind the piston out so that the gap is just adequately wide enough to fit over the pads and disc. Refit the caliper and then press the brake pedal several times to let the auto adjuster remove any fine play still remaining. Finally reconnect the handbrake cable ensuring the caliper lever returns fully home when the handbrake lever is off.

Caution!Do NOT use grips on the piston - only use the correct tool.

102: Handbrake calipers – Handbrake efficiency deteriorates over time.

Cause: Failure to take play out of handbrake on installation, then incorrectly adjusting the cable to give a reasonable feel at the handbrake lever, or cables may be binding. Both these faults stop the caliper levers returning fully home and prevent the auto adjusters from working. As the pads wear, the play is not taken up and hand brake efficiency deteriorates.

Solution: Disconnect the handbrake cable, unbolt the caliper from its guide pins and firmly force the piston back to remove any play (put slight hand pressure on the caliper lever and you'll feel the play gradually disappear - stop at this point to avoid possible damage to adjuster). Then, depending on type of adjusting mechanism (some have a hex key adjuster screw hidden behind a bung), wind the piston out so that the gap is just adequately wide enough to fit over the pads and disc. Refit the caliper and then press the brake pedal several times to let the auto adjuster remove any fine play still remaining. Replace damaged cables if necessary and adjust so that both caliper handbrake levers return fully home when the handbrake is in the off position; there should be no play, but both levers must go back to their stops. Press the brake pedal several times and your handbrake should adjust automatically.

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103: Handbrake calipers – Occasional spongy pedal.

Symptom: After releasing the handbrake, the brake pedal is spongy on the first few applications, but then corrects itself. The same problem occurs every time the handbrake is used.

Cause: Air trapped in the piston casing. Pressing of the brake pedal compresses the air trapped in the piston casing. Once pressurised, it uses the self-adjuster faces as a valve and traps the compressed air in the casing. Normal pedal feel occurs until the handbrake is used, this breaks the seal and the air expands back into the hydraulic system.

Solution: Unbolt the caliper housing from its guide pins and open the bleed nipple. Air rises; so, rotate the caliper piston face down (if pipe-work allows) and expel air from the piston casing; then make sure the bleed nipple is at the top and expel any remaining air then tighten the nipple. Refit the caliper to its guide pins.

Note:Budweg vacuum fill all know problem calipers with brake fluid; then they seal them to aid installers.

Printable Version (PDF)

105: Handbrake calipers – Banjo bolt bleeding problem.

Symptom: Real struggle to tighten banjo bolt and impossible get any fluid out.

Cause: Failure to remove the sealing bung out of the inlet hole. Some handbrake calipers are difficult to bleed; so both the original equipment units and Budweg calipers are vacuum pre-filled with brake fluid to assist installation.

Solution: Kick yourself for not reading the instructions and not inspecting the inlet when the banjo bolt wouldn’t screw home properly. Hope that you'll be able to get the crushed bung out and the threads are not damaged.

Note:This is not a manufacturing fault and is not covered under guarantee.

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106: Replaced axle set of calipers – Bleeding problem.

Symptoms: Fitted or replaced both front or both rear calipers and now can’t get a pedal.

Cause: Some calipers have the inlet feed in the middle of the body, pointing to the centre of the vehicle. This can lead to the calipers being fitted on the wrong sides. If this happens, the bleed nipples are at the bottom instead of the top.

Solution: Swap the calipers to the correct hands with bleed nipples at the top. Or you may prefer to turn the vehicle upside down when bleeding the calipers.

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201. Brake pedal creeps – Possible solutions.

There may be fluid loss caused by a leak somewhere in the hydraulic braking system. Urgent attention is required if regular top up of fluid is needed - because this indicates a leak!

Cause: If there is no loss of fluid, the problem will be caused by fluid being forced past a worn seal or a valve. This could happen in the master cylinder, ABS valve block, or pressure regulator valve.

Master Cylinder fault.
On a single circuit system (one outlet pipe), the fault is likely to be in the master cylinder. Pedal creep (with no loss of fluid) is unusual with tandem (twin circuit) master cylinders; but it may happen. The answer is to strip down the cylinder and check for damaged or contaminated seals or corrosion of the cylinder bore-----and rectify. It may be necessary to replace the cylinder.

Note:See separate entry Diesel Engine Vehicles (Tech Note 202)

ABS equipped vehicles.
Although rare, we have found that sometimes the operation of the ABS system solves a creeping pedal problem. Our theory is; due to a lack of brake fluid changes and the ABS never being used, gradual corrosion of the valves and seats allows fluid under pressure to pass the closed valve. The 30 times a second operation of the valve when the ABS is activated removes the corrosion and allows the valve to properly seal again PERHAPS!

Regulating valve fault.
If the regulating valve has a combination of primary and secondary circuit pipes attached, then this valve could be at fault. It is unusual, but it could happen. The solution is to replace the valve.

Fluid Loss.
It is imperative that any loss of brake fluid is quickly identified and corrected, otherwise there is a risk of brake failure.

Printable Version (PDF)

202: Brake pedal creeps – Vehicles with diesel engines.

Diesel engine vehicles usually use a pump to generate the vacuum for servo assistance. Unlike the inlet manifold of a petrol engine, there is no vacuum relief with a pump. If excessive pedal pressure is applied when the vehicle is stationary (and the engine is running) the hydraulic pressures required to stop the vehicle will be grossly exceeded and fluid will be forced past seals that are between circuits. Larger vehicles such as vans and 4x4s are more prone to this problem as they use servos with a higher boost ratio. The phenomenon is known as diesel creep; and it is often incorrectly diagnosed as being caused by a faulty master cylinder. The solution is to stop applying the excessive pressure.

Important!If you can get the brake pedal to creep with the engine switched off and servo exhausted, or actually under braking there is a serious problem that requires urgent attention!

Note:Please see separate note on Pedal Creep (Tech Note 201).

Printable Version (PDF)

301: Brakes bind – Only after driving for a while.

Symptoms: Brakes are free at the start of a journey, but gradually bind or lock on as you drive.

Cause: When braking, heat is generated. This heat is transferred to the brake fluid. As the temperature increases, the fluid expands. Under normal circumstances, this expanded fluid returns to the master cylinder reservoir. If the expanded fluid cannot return to the reservoir, pressure builds up and applies the brakes; and more heat and more pressure are generated. When the fluid cools down, pressure reduces and the brakes release.

Solutions: Take your tools with you and drive the vehicle until the brakes bind on. (The more they bind on, the more time you will have to diagnose the problem). Follow these steps.

Step 1
With the brakes stuck on, slacken, by two to three threads, the nuts that hold the master cylinder to the servo. Then press and release the brake pedal. If the problem persists proceed to Step 2. If the brakes are free after you've done this, the problem lies with the servo or the mechanical links to the pedal. Check that an incorrectly adjusted brake light switch is not holding the pedal on slightly. If the pedal has a link rod to the servo, check that this is well lubricated and moves freely. If the problem is not caused by the brake light switch or by the link rod sticking, it's possible that the link rod or servo push rod has been adjusted incorrectly. Otherwise, the servo is probably faulty.

Note:Just in front of the master cylinder valve seals are small holes; these are compensating ports. With the brake pedal released, the master cylinder pistons should be fully home; otherwise the compensating ports will be blocked by the valve seals.

Step 2
Slacken one pipe at the master cylinder for each circuit in sequence. (Use a rag to stop fluid squirting everywhere because brake fluid works like paint stripper). This will release any pressure in that circuit. If the problem persists proceed to Step 3. If the brakes release now, then it's highly probable that the master cylinder seals have swollen through contamination and are blocking the compensating/relief ports.

Step 3
Feel each wheel and start with the hottest wheel/brake first. Careful, things will be very hot! Slacken the bleed nipple/s on the caliper or wheel cylinder. If the brakes do not release, proceed to the next hottest wheel and repeat. When the brakes release, the problem is a faulty flexible hose attached to that wheel.

Note:It is not uncommon for the inner wall of a flexible hose to collapse. When this happens, the collapsed wall can act like a one-way valve and can restrict the return of fluid.

Step 4

If the brakes are still stuck on, release the handbrake and start again!

Important! Remember to re-tighten all pipes/unions, nuts/bolts and bleed nipples.

Printable Version (PDF)

401: Disc Judder problem - Cause/rectification.

Symptoms: Vibrations are felt through the car with a pulsating pedal when braking. If the steering wheel vibrates also, this tends to indicate the problem is with the front brakes.

Cause: Usually due to variations in disc thickness - DTV.

Note:These variations in thickness are usually the result of excessive disc run-out, caused by mating the disc to dirty or distorted hubs. When driving (brakes off), the pads are normally in close contact to the disc. However, when there is excessive disc run-out, the pads scuff the ‘high’ parts of the disc on every rotation. This scuffing gradually wears the disc thinner where most contact is made.

Imagine a buckled bicycle wheel, the brake blocks would catch the wheel rim (braking surface) at the same ‘high’ points on every rotation. Disc run-out is similar, but the rotation speeds on cars are slightly quicker and brake pads are far more abrasive than a bike’s rubber blocks. So when you’ve driven 2,000 miles, the pads have scuffed the same ‘high’ spots over two million times. Eventually the disc becomes thinner in two parts and causes a judder under braking. Simply replacing the discs without rectification will lead to the problem re-occurring.

Solution: Replace the damaged discs; but when doing so inspect the hubs properly and use a dial gauge to ensure disc run-out is less than 0.1mm (0.004”). This will avoid damaging the new discs. Alternatively, if the discs are only slightly worn, they can be machined on the car so that they run perfectly true.

Facts: If you fit new discs and they’re great for the first 1,000-2,000 miles and then you start to notice a very slight judder developing, you’ve probably got DTV caused by run out.

If you fit new discs and they immediately judder, then it’s probable (although very rare) that they have been machined incorrectly or there was a flaw in the casting.

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801: Fluid Contamination – Master Cylinders.

As part of our quality control, we investigate all master cylinders returned. Of these, 9 out 10 have been on the vehicle for only a few weeks. They worked perfectly on installation; but after a week or two the master cylinder starts to develop problems. Common problems are a spongy or long pedal travel and/or brakes locking on after driving.

Causes of Contamination:

Example of swollen seals (PDF)

Contamination is usually introduced at installation.
With a standard DOT3/DOT4 system, even a drop of mineral oil will cause the contamination, the cause of swollen seals. It is imperative to only use new brake fluid from a sealed container. When a master cylinder is supplied without a reservoir, it is essential that the old reservoir is cleaned thoroughly. As most reservoirs have baffles inside them, only sure way to clean is with hot soapy water then rinse out thoroughly with clean hot water and then air blow dry. Do not use paraffin (mineral) or engine degreaser!

Who should stand the cost of the replacement?
It is to be understood that contamination is not a manufacturing fault. The cause of the fault is not with the manufacturer or the supplier!

Long pedal travel and/or spongy pedal
The valve seals are precision components, designed to allow the transfer of fluid from the reservoir into the hydraulic system as required. (eg, when brake pads wear, more fluid is required in the caliper to take up that wear). If the valve seals swell, they stop working. This leads to a spongy pedal and excess travel. In the case of severe contamination, the seals swell so much that they restrict the movements of the pistons and understandably cause both long pedal travel and brake bind.

See: Brake Bind (Tech Note 301).

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