The New Jost SDR Diffuser is Now Available at JMR
The New Jost SDR Diffuser is Now Available at JMR

The Jost SDR diffuser is mounted on the back of the trailer or rigid truck; it compresses air flowing over the roof and pushes the high pressure air into the low pressure area which would normally be created behind the trailer.

The SDR diffuser turns this low pressure area into high pressure area smoothing the air flow to reduce drag, this makes the workload lighter on the truck to easily maintain higher speeds and reduce fuel consumption. The SDR diffuser has no moving parts and requires no maintenance and can be fitted to any box type trailer or rigid truck body.

The Jost SDR diffuser can be installed to new or existing rigid truck bodies and reefer type trailers, the installation should take no more than an hour. Once the turbulent low pressure zone is created at higher speeds it drags the truck and trailer back.

In order to keep a constant speed more power and more fuel will be needed to overcome this drag. Other advantages of the Jost SDR diffuser includes a more stable vehicle, the SDR also supresses dust and rain spray increasing visibility and safety for other road users. The rear end of the trailer stays cleaner on vehicles fitted with the SDR.

Where will the Jost SDR diffuser give the best return on investment?

The Jost SDR diffuser starts working at 40km/h, but gives the best results at 80km/h. In other words, a long distance line haul application is where the Jost SDR will give the largest return on investment.

The first Jost SDR diffuser fitment was done at JMR Trailer Service Centre in Alrode for Vaal Milling by Gert de Lange JMR Alrode Workshop Manager. The first installation with training took less than an hour and future installations are expected to take no more than half an hour to complete. Vaal Milling will be fitting another 2 trucks with the SDR002D-R in the next two weeks as the vehicles are made available to JMR for fitment.

Fuel consumption has a major effect on the profitability of running a transport business and fuel savings will directly benefit the bottom line. We will be keeping a close eye on consumption and we expect to see some comparative figures from March/April 2013. Watch this space for updates and further information.

To make an appointment to fit your first SDR002D-R please contact Kevin Tucker at JMR Alrode.

Jost Part number: SDR002D-R

Hub Failures - What to Look For
Hub Failures - What to Look For

There are four main causes for hub failures:

  1. Lack of Lubrication
  2. Overloading
  3. Tight (over-torqued) axle nut
  4. Loose axle nut

Usually, hub failures are progressive and will produce some evidence of the failure. This will very often include damaged hub seals (leak), abnormal tyre wear (diagonal across), steering wheel problems, as well as the 3 “S” – smoke, smell and sound.

The bearing pre-load is adjusted by tightening the axle nut against the two cone-shaped bearings. While tightening the axle nut the complete hub assembly will get tighter and until there will be no more movement. As soon as the bearing pre-load is adjusted a cotter (split) is fitted at the axle nut to prevent the axle nut from moving.

Fault finding:

A loose axle nut will allow the hub assembly to move side-ways (laterally) on the axle journal. The bearings will wear and the hub will become looser. The looseness of the hub will now allow excessive movement of the bearing rollers, causing roller cage wear and uneven race wear (scalloping). If this damage is not seen in time the play will increase and will eventually lead to hub failures.

If the hub axle nut is adjusted too tight, the lubricant between the bearing rollers and bearing races will break down. This is the same like a lack of grease, and the bearings will overheat causing bearing fatigue and hub failures. Subsequently this will cause a “bearing lock-up”. Further investigation will show fatigue marks on the bearings and severe heat discoloration.

Overloading the axles is the same like overloading the hub and like over-tightening the axle nut. The lead on the axle/hub forces the grease (lubricant) from the bearing rollers and bearing races causing heat and fatigue. Running on bad roads with big pot-holes will have the same effect like overloading.

Not enough lubricant causes metal to metal contact between the bearing rollers and bearing cages. This will result in excessive bearing and bearing race scoring with subsequent fatigue.

Please note:

On hubs with a large outer bearing the oscillating hub can cause the axle nut to be pulled off the axle during a hub failure. In other cases where the axle nut is pulled of the axle, the thread will be ripped off the axle nut while the thread on the axle is normally undamaged.

On hubs with a small outer bearing hub failure, the hub can slip past the axle nut and the remaining parts of the outer bearing.

For more details on how to handle hub failures, contact your closest JMR branch.

Did you read the article Brake Linings on Trailers - How it works ?

A How To Guide for Doing Brake Adjustments on a Trailer
A How To Guide for Doing Brake Adjustments on a Trailer

The most important part of any braking system is the foundation brake. If the foundation brake is not in correct working order and properly adjusted, even the best designed air braking system won’t be able to stop the vehicle.

Brake adjustment is often neglected. The reality is that brake failures and runaways that result in crashes are almost never caused by an air system failure, but by the lack of routine brake maintenance, or by the driver failing to check brakes on a daily basis.

Drivers may be held responsible if the brakes are incorrectly adjusted or not working properly. Drivers must check manual and automatic slack adjusters daily during the pre-trip inspection.


When the brakes are adjusted by slack adjusters, the shoes are moved towards the drum. This brings them as close to the drums as possible minimizing the amount of free travel when the brakes are applied. It also reduces the volume of air used to apply the brakes. Brake adjustment (push rod travel) must be checked as part of the pre-trip inspection.

The following is a guide to checking manual slack adjusters:

  1. Pull the push rod out of its limit using your hands or a pry bar.
  2. Measure the distance the push rod travels (the “slack”). If the slack is 1 inch (25.4mm) or more, you must adjust the brake.
  3. Turn the adjusting bolt until you feel solid resistance.
  4. If you are turning the bolt in the right direction the cam will turn in the same direction. Watch the chamber push rod and slack adjuster arm. If you detect outward movement (away from the brake booster) you are turning the bolt the wrong way.
  5. Back off the bolt one-quarter to one-half a turn to restore running clearance.
  6. Re-check push rod travel.
  7. The angle between pushrod and slack adjuster should be 90 degrees when the brake is on.
  8. The angle between pushrod and slack adjuster should be 110 degrees when the brake is off.

Checking Automatic Slack Adjusters:

Automatic slack adjusters are entirely different to the manual types, once properly installed, automatic slack adjusters should not need manual brake adjustment. Automatic slack adjusters are designed to self-adjust, but sometimes they fail or are incorrectly installed. They have to be checked during pre-trip inspection. The pushrod/slack adjuster angle should be the same like on the manual adjuster.

WARNING: Adjust automatic slack adjusters only as an emergency measure, so that you can get the vehicle to a service depot. Repeated manual adjustment will wear down the slack adjuster’s internal components which could lead to a brake failure.

Contact JMR today for high quality, reliable machines, parts and workmanship that ensure that your braking system is taken care of.