Chassis Lubrication

 

 

To Grease or Not To Grease
(Chassis Lubrication for the Derby Bentley)

by Ken Lea
 
Most owners will be familiar with the oil lubrication of chassis joints operated from the reservoir on the bulkhead and will know of the frequency of operation.
However, many pundits recommend deviation from the established system, apparently some from fixed ideas and some from not understanding the principles of the design. This was exacerbated some years ago by the non-availability of the components to ensure its proper operation. However, all parts for the complete system are now available and supposition that deviation is required for this reason is not valid.
The original lubricating oil was SAE 30 but the system works equally well with SAE 20W/50 engine oil. The use of grease either locally or in general is not usually successful in maintaining driving characteristics or preventing wear.
I and others have now many years experience in operating the system as designed and it is a proven fact that provided the integrity of the pipework is sound, then little wear takes place on any of the lubricated joints. This is particularly true of the front axle where use of a viscous grease cannot possibly lubricate the king pin assemblies even if separate grease nipples are fitted. For example, trying to force grease through the felt filter or if removed through the 0.030” holes in the lower part of the kingpin and bush.
The original system was designed to balance the flow to all areas so fitted by grading the drip plugs and on the front axle by providing a head of oil to lubricate the bottom bush and thrust washer so critical to enjoyable driving. Furthermore, there are drip plugs fitted internally in each side of the axle/king pin assemblies. One lubricates the outer bush on the brake actuating shaft, one lubricates the top roller bearing of the kingpin and one lubricates the twin bushed actuating brake system. None of these are capable of lubricating by grease. On much of the rest of the system, fitting of grease nipples will suffice except importantly for the rear brake shaft assemblies, but why do this when one pump of the pedal can lubricate all? Oil nipples and the use of individual oiling points can work but no better than the system as designed.
In order to ensure the system is operating correctly there are a number of recommendations especially if work is being undertaken: -
 1. Ensure the pump is not leaking back internally and there is good flow to either side of the chassis. Change both the felt filter and the leather sealing washer if not.
 2. Examine all lubricated points which, after pumping, should show traces of  oil flow. If a joint is dry then either the drip plug is blocked or of the wrong size or the feed pipes system is leaking elsewhere. Furthermore, the passageways after the drip plug may have become blocked and this also should be verified but which will involve dismantling the joint. This is particularly relevant for the spring shackles.
 3. It is essential that the front and rear brake axle mounted systems are also operational. The internally mounted front brake actuating rods are particularly prone through neglect and it is essential that the drip plugs at each end are working and that the plugs are the correct rating. If replacing the king pin, then ensure there is flow through to the king pin and that the drip plugs described above are working. Also that the stand pipe fitted up the centre of the king pin is complete and at full length.
 4. It is always beneficial to check all the drip plugs have their original ratings otherwise the balanced flow as designed is not achieved.
This sounds both laborious and time-consuming but, given proper attention, will be rewarding in both driving and in reduced cost long term. I and others can demonstrate that well maintained systems have given little wear well in excess of 100,000 miles.
One of the secrets of a good Derby is the proper operation of the one shot system and grease will never do!  Don’t use it even with locally mounted grease nipples.

 

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