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DE model servo

Posted: Mon Jun 25, 2018 1:43 pm
by Roark
Thanks to the good offices of Peter Grant I have been in contact with someone in Australia who has made new seals for the Clayton deWandre servos fitted to DE models.

On that basis I decided to strip the servo on my car in order to clean it both inside and outside. It's a strange item. The main body has a large and long but soft spring attached to the piston which, one presumes, must have some oil around it to lubricate the seals. However, the owner's handbook does not mention what lubricant should used or even how much should be used.

There is a bellows on the top through which one rod moves and there is a rubber sleeve on the other. Apparently there are also some smaller seals in the brass block on the top. However, while there is a drain plug at the bottom I do not have any idea of what oils to use and how much. Does anyone have any idea please?

Re: DE model servo

Posted: Mon Jun 25, 2018 5:12 pm
by Roark
The servo is now stripped to a bare shell and i have spent a lot of time cleaning the various components. However, on top of the servo is a small brass block with a shorter length of studding sticking out. It appears to be sprung loaded and while I have removed the securing nut on end end I cannot find a way of removing the piston in order to replace the seals inside the block.
Does anyone have any clues please?

Re: DE model servo

Posted: Wed Jun 27, 2018 9:10 am
by Christopher Storey
If the seal is rubber the seal lubricant will be red rubber grease . You can buy a lifetime's supply for about £10 :D :D

If by any chance however it is leather, as in the larger lorry type Clayton servos, then light hydraulic oil will be the preferred lubricant .

As far as dismantling is concerned, I imagine that the brass block should be unscrewed up the studding . The nut you have removed will probably be merely a locknut for the brass block

Re: DE model servo

Posted: Wed Jun 27, 2018 9:47 am
by Roark
Thanks to some help from Mark Bearman in Australia it seems the seal and the whole servo is lubricated by the chassis lubrication system. However, that doesn't give any indication of how much oil should be in the servo. If it's fed by that system one would suspect that the servo would need to be drained occasionally.
The main piston seal is a curious construction and made of leather largely. There are companies who specialise in spares for the lorry type servos and the DE models have one that could have been used on a lorry. The braking system is the same as for the 4 ton ERF and Ford of the early fifties.
I have managed to remove the pistons from the distribution block but have muddled up the re-assembly of the operating rods. Hopefully Mark will be able to supply some diagrams

Re: DE model servo

Posted: Sun Nov 04, 2018 11:09 am
by Stan Thomas
I don't know the specific model servo you have on your car, but the Clayton Dewandre service manual I have is for (quote) "single Unit or Monoblock Type" servos for my 1931 Daimler says in the section for lubrication:

"Normally, the rear or lever end of the servo cylinder should be about one-third full of oil and to prevent over-oiling a drain aperture is provided about two inches from the base of the servo cylinder. The oil in the servo cylinder should be drained off occasionally by means of the drain plug and fresh oil supplied".

As the manual refers to earlier units having cast iron postons before the introduction of leather and rubber pistons, it would appear the units varied little in basic design and service requirements - although there is no reference to specifically what oil should be used.

Perhaps a start therefore would be to look for the "level apperture" two inches from the bottom of the chamber to see if we're on the right track, and I would assume an ordinary 30 grade engine oil is all that is needed to keep things lubricated etc.