Dubonnet Suspension
(21/04/2019, 10:42 AM)cbuk2011 Wrote:
(20/04/2019, 08:27 PM)Andreas Wrote: Hello Everyone, I recently found a DY 12 from 1936, see Flutenews March 2019. Now I am desperately looking for any hint how to fix the worn out Dubonnet front suspension units. Maybe someone knows a specialist machine shop? Thank you very much for any Information,

Andreas (new kid on the block) Rolleyes

Give me a ring to discuss your problems, there may be some easy fixes. I have 2 units but both require work
The H and I units are I think different than the Dx type Dubonney type.
Tel 01948880560
Well, the problem is that the needle bearings are desintegrated on both sides. Besides I find it impossible to take the wheel carrier arm apart from the "knee"-thing inside the spring housing. I have never seen a mess like the one I found inside these spring housings: antediluvian oil with bits and pieces of bearing needles mixed with fine metal dust from dry grinding lever action. Impressive!
Thanks given by:
(22/04/2019, 03:27 AM)Mike Swanton Wrote: Personally I find that engine oil makes for too hard a ride, although I've only really experimented with these oils on the last development of the knee actions as supplied on the L model. With that knee action the damping action of the shock absorber is too hard using engine oil. However I would agree with Colin that it does provide better lubrication to the main arm.
I've tried the Penrite Shocker oil no.2 and it is better for the shock absorber action. So without further experimentation I used the No.2 Shocker oil on my DX Stratford Sports where I "need" a firm ride for good road holding.
I also tried the Penrite Shocker Oil No.1 and it gives a lovely gliding ride. It obviously works well with the shock absorber. So for cruising in comfort in a DX, J or LIP I use that thinner hydraulic oil in my knee actions.
I do wonder however about the lubrication of the main arm and whether the thin Shocker no.1 is sufficient as a lubricant, even though it is probably best for the shock absorber. So I've turned to the Penrite Shocker Oil no.2 for the bigger GY models where the lubrication is a higher priority.
I have had most of my knee actions rebuilt and the condition of that main bearing has been shocking in almost every case. Lubrication has not been reaching the main arm. As Chas says, previous owners have not kept the oil level up and with the powerful forces from that strong internal spring lubrication is essential.

I'll try to keep this as simple as possible for the benefit of the members not used to my rambling.

The wording 'shock absorber oil' relates to hydraulic oil.
The Australian Penrite oils are very good, their shock oils 1 & 2 are the equivalent to the UK ISO 46 and 68 hydraulic grades.
46 being the thinner oil and 68 being the thicker.

The main factor in these oils are the 'extreme pressure' loading they can withstand, anti foaming and anti ware additives.
The anti wear area is basically dependant on how much zinc is added. The first two are a load of chemical formula's - don't ask me!

From the lubrication point of view with these oils - consider the pumps and actuators used in hydraulic systems, such as diggers and excavators.
These units are running in a similar configuration to the Dubonnet arm needle bearings, albeit under a harsher environment regarding heat, friction and atmosphere. Same thing with automatic gearbox's, they have an abundance of needle bearings.  They just use hydraulics oils with different additives.  Usual ISO rating used is 32, and that's thinner than 46/68.
The Dubonnet suspensions do not function at high temps so the hydraulic oils used in them have much more lubricantcy.

Engine oils do not contain the additives associated with pressure loading, anti foaming and frictional loads. Well, they do but not to the extent required with hydraulic oils. Therefore they will breakdown very quickly.

Compensating spring (that's the big one inside the housing) loads for H to G are 1.1 to 1.3 metric tons.

A pessimist sees difficulty in every opportunity. A optimist sees opportunity in every difficulty.
Thanks given by: Mike Swanton , BUGAS03
Re post no 11: The rocker arm ("knee-thing") is probably jammed on the splines of the carrier arm with corrosion. You could try soaking in
diesel. Bur where do you go from there?!
Thanks given by:
The rocker arm is pressed onto the shaft.
It's held in place by a interference fit on the shaft, all the way along the spline length.

If you do not have the correct equipment you won't get it off.  Unless of course it is loose on the splines, in which case it's of no use, Period!
Hammering will result in further damage.

For those contemplating disassembling the main spring of the D suspension - DON'T even think about it!
It's held in place with a large curclip. Even if you got to the stage where you could see the clip, attempting to remove it will result in injury due to the retained spring pressure.
Again, it comes down to having the correct equipment.

A pessimist sees difficulty in every opportunity. A optimist sees opportunity in every difficulty.
Thanks given by: BUGAS03

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