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armstrong pear shaped shock absorbers - help anyone?
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MattF



Joined: 29 Mar 2013
Posts: 86
Location: Christchurch, NewZealand

PostPosted: Sat Apr 20, 2013 7:09 am    Post subject: armstrong pear shaped shock absorbers - help anyone? Reply with quote

Hey guys, need to know what sort of hydraulic oil i can use in the shock absorbers of my 36 morris eight? They are the pear shaped ones as apposed to the 38s that had a more modern armstrong shocks, don't know if that changes much. im 99% sure they are ok but just empty Sad
Cheers, Matt
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peter scott



Joined: 18 Dec 2007
Posts: 7113
Location: Edinburgh

PostPosted: Sat Apr 27, 2013 10:03 pm    Post subject: Reply with quote

Hi Matt,

This man will know.

Company: Vintage & Classic Shock Absorbers Ltd
Address: 203 Sanderstead Road
South Croydon
Surrey
CR2 0PN
Contact: Graham Brown
Telephone: 020 8651 5347

Peter
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whiteshadow



Joined: 24 Jan 2011
Posts: 78

PostPosted: Sun Apr 28, 2013 1:16 pm    Post subject: I've got some!! Reply with quote

Hi,

I've got some of the pear shaped shocks on my '33 Singer Saloon...... Still doing it up, so I have taken them apart to re-furbish them (at some point!).

I brought some 'Millers' oil for them .....I think I got the info somewhere in my manuals.

If you still need the info or photos of the internals, just let me know!

Mark
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Kelsham



Joined: 18 Jan 2009
Posts: 349
Location: Llandrindod Wells Powys

PostPosted: Sun Apr 28, 2013 3:55 pm    Post subject: Reply with quote

Where has the oil gone ? in my experience the seals begin to leak and when the oil is replaced it soon leaks away again.

I had an Austin Atlantic years ago that I would top up with 30 grade every couple of weeks.

If i had it today I think I would try to refurb it.

kels.
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goneps



Joined: 18 Jun 2013
Posts: 601
Location: Auckland, New Zealand

PostPosted: Tue Jun 18, 2013 11:51 pm    Post subject: armstrong pear shaped shock absorbers - help anyone? Reply with quote

whiteshadow wrote:
Hi,

.....I think I got the info somewhere in my manuals.

If you still need the info or photos of the internals, just let me know!

Mark


Mark,

If you do have a reliable source stating the specific grade of oil I, for one, would be very glad to have that information. For the Morris Eight, official sources are not helpful: the handbook states "replenish with Armstrong fluid", which of course is no longer available; the early chassis lubrication chart doesn't mention them at all; and the post-war Castrol chart instructs the hapless owner to "replenish with correct fluid", which is about as helpful as a parachute that opens after the first bounce.

Since I'm currently overhauling a number of these units and will be fitting them to the car in due course (currently on telescopics), reliable information on the correct grade of oil would be a big help.

Richard
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Rick
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Joined: 27 Apr 2005
Posts: 22429
Location: UK

PostPosted: Wed Jun 19, 2013 7:52 am    Post subject: Reply with quote

Somewhere in the garage I've got an old Armstrong shock absorber oil can, I'll see if I can find it and see any specs on it.

RJ
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Wed Jun 19, 2013 11:24 am    Post subject: Reply with quote

Apparently it should be an SAE 140 grade for the pear shaped

The next point to bear in mind is that SAE140 oil is not really that viscous . This is a matter not commonly understood by the layman, including myself until very recently—when it was raised on another forum. The fact is that the SAE grades applied to gear oils and engine oils are not on a common scale, so for instance an SAE90 gear oil has equivalent viscosity to SAE40 or 50 engine oil. The chart below explains this graphically:

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goneps



Joined: 18 Jun 2013
Posts: 601
Location: Auckland, New Zealand

PostPosted: Wed Jun 19, 2013 5:11 pm    Post subject: Reply with quote

Hullo Dave,

I thought this had a familiar look—you've quoted part of what I posted on the 8MVS a couple of weeks ago! Nice try, but it hasn't advanced the debate much! At the time I was just throwing out ideas—thinking aloud, as it were—in the hope of provoking further debate.

In fact, during the period since, the trend of my thinking has been that 140 gear oil is probably rather more viscous than ideal or even desirable. Penrite and Millers both produce hydraulic damper oils of ISO46 and 68 which, as the chart shows, translates to SAE75W and 80W gear oil equivalent and within the SAE20 range on the engine oil scale.

According to a contemporary technical manual, Pears were designed to allow leakage past the plungers, the lower cylinder being slightly larger than the upper. Without leakage the whole thing would lock solid, trying to fit a quart into a pint pot. Having now had an opportunity to measure these components, in round figures the upper plungers are 21mm OD and the lower are 22mm. The OD of each plunger is approximately 0.2mm less than the ID of its respective cylinder, so while not a precision fit the oil has to squeeze past long plungers with minimal clearance, in addition to working its way through the galleries and valve at the sharp end of the unit (to employ nautical terminology).

Rick,

Many thanks. Any light that can be shed upon this subject would be welcome indeed.

Richard
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Wed Jun 19, 2013 5:22 pm    Post subject: Reply with quote

Hello Richard Smile

What a small world we live in these days!

I had lifted a response that Richard posted on a Morris forum thinking it may help Smile not realising that Richard had posed the question!

Welcome to the forum, I know we will all benefit from your advise & experience, you will be able to view my MGA thread (the excuse I have been using on Morris forums for not contributing recently!!! )

Cheers

Dave
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whiteshadow



Joined: 24 Jan 2011
Posts: 78

PostPosted: Sun Aug 04, 2013 8:25 am    Post subject: sorry, sorry..sorry Reply with quote

I have to apologise a couple of times....

First I wasn't aware that this thread had kicked off again otherwise I would have replied sooner!!

Secondly, I guess I must have that false memory syndrome!....when I dig through the Singer paperwork, they either ignore topping up the dampers or as you say "add the specificArmstrong damper oil".
I've brought a couple of bottles of Penrite shocker Oil #1 damper oil as it states its suitable for armstrong lever dampers......if I remember right, I planned to refurbish the dampers modifing it for modern oil seals (not the current felt ones!) - without disturbing the adjustment nuts, then see how close to being 'Critically Damped'....possibly switching to the thicker Penrite #2 oil.

Hope this is of some help?!
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whiteshadow



Joined: 24 Jan 2011
Posts: 78

PostPosted: Sun Aug 04, 2013 8:29 am    Post subject: sorry, sorry..sorry Reply with quote

I have to apologise a couple of times....

First I wasn't aware that this thread had kicked off again otherwise I would have replied sooner!!

Secondly, I guess I must have that false memory syndrome!....when I dig through the Singer paperwork, they either ignore topping up the dampers or as you say "add the specificArmstrong damper oil".
I've brought a couple of bottles of Penrite shocker Oil #1 damper oil as it states its suitable for armstrong lever dampers......if I remember right, I planned to refurbish the dampers modifing it for modern oil seals (not the current felt ones!) - without disturbing the adjustment nuts, then see how close to being 'Critically Damped'....possibly switching to the thicker Penrite #2 oil.

Hope this is of some help?!
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goneps



Joined: 18 Jun 2013
Posts: 601
Location: Auckland, New Zealand

PostPosted: Mon Aug 05, 2013 12:30 am    Post subject: Reply with quote

Having extensively pestered both Penrite and Millers Oils, the latter came up with what seemed a fairly confident recommendation for their ISO32 "Shock Oil", and I'm inclined to go with this—at least as a starting point. Note that this product is of somewhat lower viscosity than Penrite's "No.1", which is ISO46.

As can be seen from the viscosity chart posted by ukdave, ISO32 is equivalent to the top of the 10W engine oil range, whereas ISO46 sits roughly at the mid-point of the SAE20 range.

One factor usually overlooked when discussing this topic is that of working temperature of the oil. Standard oil viscosity charts establish flow rates at nominal temperatures of 40° and 100°C, and it goes without saying that while such temperatures are usual in engines, and at least the lower range in transmissions, it's unlikely suspension dampers would ever become more than warm to the touch. According to one graph I've found, an ISO32 oil at 20°C has the same kinematic viscosity as an SAE30 engine oil at 45°C, which for an engine is well below normal operating temperature. What I'm getting at is this: if the oil never gets hot we surely need a relatively "thin" oil to start with.

Early versions of the Pear were fitted with adjustable valves, which might be a useful modification to incorporate when undertaking necessary engineering work prior to reassembling the units.

Another factor to bear in mind is the weight of the car. These units were used on a wide variety of vehicles from the lightweight Minor and Eight upwards. I have a pair of front units (not yet dismantled) from a Morris 12, considerably heavier than my Eight with Tourer body, but there's no discernible difference in the strength of the valve springs. It's possible the holes in the base of the cone-shaped shuttle part of the valve are slightly larger, but it's virtually impossible to measure them accurately. If anything, I would have expected them to be smaller and thus more restrictive for a heavier car.

Sorry if the above is a bit rambling—look upon it as thinking aloud.

Richard
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