Toyota Landcruiser Rear Brake Upgrade Package

Transcription

1 May 2007 Toyota Landcruiser Rear Brake Upgrade Package 9 Nevada Ct Hoppers Crossing Vic 3029 Ph Fax hopstop@hoppers.com.au Web

2 2 THE INFORMATION CONTAINED WITHIN THIS DOCUMENT IS PROPRIETY CONFIDENTIAL AND MUST NOT BE DIVULGED TO ANY THIRD PARTY WITHOUT OUR WRITTEN CONSENT

3 3 Rear Brake Upgrade Package 78/79 Series Toyota Landcruiser Introduction Toyota Landcruiser 78/79 Series Vehicles are used extensively throughout the country, and in particular, are favoured by mining operators, many in underground use where conditions are extreme. Whilst the basic vehicle is well respected by the industry, the rear disc brake arrangement has proven to be inadequate for the conditions, with the rear brake pads and hand brake both exhibiting accelerated wear way beyond the rest of the vehicle. In worst conditions, the rear brake linings will wear to the metal backing plates in a matter of weeks, resulting in total loss of rear brakes with accompanying work safety concerns. Handbrakes often fail to hold with days. Analysis of the Problem With this series of 78/79 series vehicles, Toyota moved to a rear disc brake design incorporating a drum type hand brake within the disc. Original rear slip-on disc with small caliper There may have been reasons for this design, but it seems to have been a retrograde step when subjected to regular immersion in muddy and highly corrosive environments. There seem to have been several compromises needed to arrive at this design. Handbrake inside rear disc

4 4 Cause of Rear Brake Problems 1 Combining a drum handbrake and a disc rotor and caliper within the confines of a 16-inch wheel necessitates a small brake caliper and small pad radial section, resulting in an undersized pad area. The standard design has a thin disc and a handbrake of small diameter and swept area relative to the weight of the vehicle. 2 The backing plate and handbrake arrangement allow mud and slurry to enter but not exit, causing abrasives to accumulate and rapidly destroy the handbrake, including its function as an emergency brake. 3 The small disc pad contact area is at odds with the affects of loading under abrasive conditions where rates of wear are parabolic for wear rate versus load. Rear Brake Upgrade Package 78/79 Series Toyota Landcruiser 4 The handbrake design is fiddly and complicated with many small parts that prove to be difficult to assemble correctly. Hoppers Stoppers design solution There appear to be a few possible ways to approach this problem, with a couple of companies proposing designs. Some take unconventional and unusual approaches but appear expensive to purchase and repair; with their application probably only justified if they perform perfectly for a very long time. Hoppers Stoppers' approach is to stick to proven principles and overcome the basic weakness of the existing design. By all reports, the front brakes on these Toyotas work adequately, and considering their environment do not give significant problems in the field. 300 dia by 28 thick rotor fitted to original hub In our view these brakes are not particularly special in their engineering, just the same basic front brakes that they have made for many years. If we built a rear brake set as solid and even better designed than the front it should last as long. This requires a big, thick disc rotor and brake lining swept area similar to the front. Larger revised caliper

5 5 Improved Design By Hoppers Stoppers Handbrake Relocation In order to provide a suitably robust rear caliper and rotor design, it is therefore necessary to go back to the 'old days' and relocate the park brake back to the rear of the gearbox transfer case. Rear view of transfer case As drum brakes accumulate abrasives, it is best to do this with a disc brake design, the disc being attached to the output flange and the caliper of simple mechanical lever type attached to the end of the transfer case. This allows us to utilize the differential ratio to "multiply" the brake effect for an effective park/emergency brake, which is also better located up higher for less emersion in mud. Disc type handbrake installed 1 Rotors Being a full floating rear hub and axle design, restricts the inside diameter of the rotor face, particularly when we try to retain the simple loose fit "slip on" design. In order to achieve a suitably larger swept area, it is therefore better to attach the rotor from the inside in the same manner as the front arrangement. This will require the hub to be removed from the axle housing for disc fitment; this is not a big job and in any case allows repacking of the bearings. In order to facilitate the original conversion, 5 counter sunk holes need to be drilled on the rear carrier hubs, either at the mine's workshop or as a change over supplied by Hoppers Stoppers. The end result is a 300mm diameter rotor; 28mm thick compared to the original 18mm thick and almost double the swept area. No other alterations are required and all standard bearings and seals are retained, with the ability to convert back to the original design if desired, say at time of trading in the vehicle. Hoppers Stoppers Rear Brake Design 78/79 Series Toyota Landcruiser

6 6 2 Caliper Design Within the automotive industry, all common rear calipers are much smaller than the front with usually much smaller pad area. Brake balance considerations dictate much smaller rear hydraulic piston areas, essentially meaning that there is no readily available alternative rear caliper that offers a solution. We therefore achieve our desired large pad area and thick rotor requirements by sleeving an Australian made front caliper down to smaller bore piston of suitable diameter. Handbrake caliper, mounting bracket, disc rotor and carrier plate This also has an added benefit of allowing us to make the sleeves and pistons from corrosion resistant materials more suitable for the intended use. These calipers are plated cast iron, and by specification designed for regular immersion in dirt and water. 3 Brake Pads As the base calipers are originally for the front of a locally made vehicle, the pads are available in many material options. Brake torque applied by a caliper to a rotor is proportional to the hydraulic area and does not change with pad area. It is therefore possible to reduce the specific load on the pad, greatly reduce wear rate and still have correct brake torque. 4 Attachment Caliper mounting to the axle housing is via a 12mm thick steel plate attached to the original backing plate holes using original size 4 off 12mm bolts. For comparison, the original caliper attaches to a 5mm plate. The new caliper cradle attaches to this using 2 off 12mm bolts, which are the same size as original Toyota rear caliper usage. Hoppers Stoppers Rear Brake Design 78/79 Series Toyota Landcruiser Rear Brake Kit ready for installation

7 7 5 Handbrake To attach a suitable "tail shaft disc" we arrange a 10mm thick carrier plate to be sandwiched between the output flange and the universal joint yolk. This requires a small and acceptable movement of the slip joint at the front of the tail shaft. Before This caliper is designed for regular immersion in saltwater with all metal parts being either hot zinc coated or stainless steel. It is attached to the extension housing using six bolts already used to attach the end cover plate. The original hand brake cable is rerouted from its position on the left hand side of the axle to the chassis at the centre of the vehicle where it will work the centre-mounted handbrake. After Note that we have avoided hydraulic actuation of the park brake as any brake fluid leaks would cause the brakes to release, as would any cooling of the hydraulics. Eg. After parking the vehicle with the brakes in a hot state. Summary Hoppers Stoppers rear brake upgrade design principle is based on the fact that known acceptable front brake performance is repeatable at the rear. The basic vehicle remains unmodified in every aspect with existing brake master cylinder and piping, wheels, hubs, gearbox and such kept in standard condition. Fitting is simple and quick with normal tools and no special knowledge. Handbrake Initial kits are not expensive and spare parts similar to that currently paid. The product is provided with an Engineers Report suitable for legal registration so that road going units can be converted and when sold, the new owner can legally continue to use the vehicle. From Inside

8 8

9 9