Damper oil options

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Andy W
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Damper oil options

Postby Andy W » Mon Oct 31, 2016 2:06 pm

I want to improve the handling a bit...
I read somewhere that putting 40w oil in the suspension dampers makes the Minor less bouncy.
If I put some of the 80w gear oil I have left over in them, is that overkill?
Also, is taking an inch off the front rubber stoppers a good idea?

Thanks.
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panky
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Re: Damper oil options

Postby panky » Mon Oct 31, 2016 3:37 pm

I think the gear oil is a bit too heavy, Roy used to talk about it being used in his rally Minor but for road use straight SAE40 is just right and makes a big difference. If you're riding on the front bump stops then the suspension is set too low, in normal driving the suspension should be well clear, but many advocate trimming the rear ones down an inch.
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oliver90owner
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Re: Damper oil options

Postby oliver90owner » Mon Oct 31, 2016 6:56 pm

Bouncy is a relative term and the car will bounce at extremes. No oil, very bouncy! Too thin oil - bouncy. Correct grade - could be bouncy if the dampers require overhaul. Too thick and the dampers may be bouncy in the opposite fashion - bump, bump, bump rather than beeyooong!

philthehill
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Re: Damper oil options

Postby philthehill » Mon Oct 31, 2016 10:23 pm

The 80 grade oil will make the dampers near solid which will put severe strain on the damper mounting bolts which may lead to failure.
I would advise that a straight 30 grade oil is used and definably no more than a straight 40 grade oil.
Taking an inch off the front bump stops is not recommended as the internals of the damper may come up against the end of the piston chambers and get damaged because of the additional travel. It should be remembered that the front bump stop does squash/shorten when the suspension comes sharp up against it so the suspension does travel further than the clearance between bump stop and top trunnion at rest.
There should be adequate travel of the front suspension and if the front suspension is to be lowered it should be no more than 1 1/2" or 1 spline.


Andy W
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Re: Damper oil options

Postby Andy W » Tue Nov 01, 2016 9:23 am

Great, thanks guys! :D

I will start with straight 30 & see how it feels.
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MikeNash
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Re: Damper oil options

Postby MikeNash » Tue Nov 01, 2016 8:44 pm

Um, regarding oil viscosity, you'll find that gear oil of SAE80 grade is almost the same viscosity as SAE 30 grade engine oil. The numbers mean NOTHING apart from indicating that one is different to another. (And certainly the numbers have NOTHING to do with "weights" that so many American sites describe, e.g. "30 weight" or 40 weight". Engine lubricating oils are practically all the same density and therefore the same "weight" for any given volume. Life would have been so much easier if the Society of Automobile Engineers (SAE) had used letters instead!)

To conform to SAE standards, the viscosity (the measure of its internal friction i.e. to us its reluctance to move) of SAE 30 engine oil at a temperature of 100C must be between 9.3 and 12.5 centistokes (abbreviated to cSt). SAE 80 gear oil at the same temperature must be between 7 and 11 cSt. So its practically identical in viscosity, even slightly thinner.

There's acres on the interweb about this but a good straight forward description is here http://www.kewengineering.co.uk/content ... -explained

And if you're addicted, there are millions of charts and tables here https://www.bing.com/images/search?q=en ... &FORM=IGRE

So, overall, you can use your SAE 80 gear oil for the dampers but I suggest you keep to engine oil unless you are sure that the SAE 80 oil you have is definitely gear oil and not back axle oil with EP additives (EP = extreme pressure). If it is the latter the can will have "EP" written on it and these additives can attack bearing materials such as bronze, etc. I don't know if the dampers have these in them but I wouldn't risk it.

Best of luck, regards, MikeN.
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philthehill
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Re: Damper oil options

Postby philthehill » Wed Nov 02, 2016 9:17 am

Mike
As you point out - the viscosity of the oils mentioned above at 100C are near the same but the oil in the dampers will get nowhere near that temperature.
A more natural and realistic way to compare oils used in dampers would be to compare their 'flow' (viscosity) rates at say 20C.
The oil in a damper does not specifically lubricate but has to flow transfer/past the pistons/valves and through small apertures. A straight 10 grade oil will flow/transfer quicker than a straight 80 grade at at say 20C.
For example - If you fill a Minor damper with straight 10 grade oil the lever arm can be moved quite easily - fill the damper with straight 80 grade and the damper arm is near impossible to move - that resistance to move is transferred to the four 5/16" BSF damper mounting bolts which may then start to move and ultimately fail.
The alloy body of the damper is made from quite soft alloy and it does not take much to enlarge the bolt hole so starting a chain of enlarging holes and loosening bolts.
With the normal damper oil installed there should only be moderate resistance required to move the arm (quoted from the wksp man).
I have tried most viscosities of oil in my dampers over the years and unless you are running on a billiard table surface the maximum grade oil I would use/reccommend is a straight 40 grade oil but preferably a straight 30 grade oil.
The BMC wksp Man Sect L3 recommends using a SAE 20/20W mineral oil as an alternative to the Armstrong Super (Thin) damper oil and a pointer to my comments about viscosity/flow at less than 100C - the manual states that the SAE 20/20W oil should not be used in low temperatures (specifically because it thickens up - my additional words).
Phil


MikeNash
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Re: Damper oil options

Postby MikeNash » Wed Nov 02, 2016 8:52 pm

I'm not wishing to cross swords with m'learned friend Phil, but if you see here https://www.bing.com/images/search?q=oi ... ajaxhist=0
the viscosity of SAE 30 engine oil is practically the same as SAE 80 gear oil at both 40C &100C. (Hence me referring above to these charts.) I think a comparison at 40C is close enough to the damper working temp to prove my point, but if my Trav passes it's MOT tomorrow I'll try to get some actual measurements. (The under bonnet temp on mine is typically 60-80C and the dampers' action itself will heat them up.)

Using the interweb, I tried to find some data on SAE 80 but of those who supply it (Mobil, Comma, Shell, etc) none now have a straight 80 grade but all are multigrade either EP80-90 or EP75-80. The same is true of SAE 30 engine oil with none of those who supply figures now having a straight 30 grade - all are multigrade. There seems to be few suppliers of straight SAE 30 grade engine oil and I couldn't find any of them who offer 40C viscosity data.

But all that said, while I still assert that Andy W could use his SAE 80 oil with advantage I suspect it's an EP80 which I fear might do the dampers' internal a mischief and therefore should be avoided. But even then, for any straight SAE30 or 40 engine one obtains now one seems to have take on trust regarding its viscosity at 40C.

Regards, MikeN.
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philthehill
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Re: Damper oil options

Postby philthehill » Thu Nov 03, 2016 7:44 pm

Mike
Thank you for your reply and links.

Having tried various grades of oil in my dampers over the years and from that experience I think that I will stick to my original advice to use a straight SAE 30 oil and at max a straight SAE 40 oil.

Suitable straight SAE oils are available through the links below.

https://www.machinemart.co.uk/p/clarke- ... l-1-litre/

https://www.machinemart.co.uk/p/compressor-oil-sae40-/

But of course it is ultimately up to the person owning or maintaining the vehicle to decide what oil is right for them.
Phil


Andy W
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Re: Damper oil options

Postby Andy W » Thu Nov 03, 2016 8:27 pm

Wow! Awesomely detailed & learned replies folks...I am awestruck once again with how much knowledge
& experience is on this site.
I think the 80 grade oil I have to hand is an EP so I will avoid using that anyway & get me some Clarkes 30 & try it out...
I need to change the oil in my compressor anyway so it's a result all round! :D
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IslipMinor
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Re: Damper oil options

Postby IslipMinor » Fri Nov 04, 2016 11:43 pm

The SAE viscosity grades for engine oil and gear oil use 2 different scales.

Very roughly, the viscosity of engine oil SAE 30 is similar to gear oil SAE 80, and engine SAE 60 is similar to gear oil SAE 140. EP and Non-EP gear oils use the same viscosity scale.

For dampers engine oil SAE 40 is the best, but not a multigrade. It should be a 'straight' 40 grade.
Richard



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Re: Damper oil options

Postby amgrave » Sat Nov 05, 2016 1:29 am

Has anyone tried hydraulic oil 32 and if so how does it perform. In theory it should perform nicely as it is a single grade and is designed for hydraulics as in dampers and thicker than original spec.


Trickydicky
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Re: Damper oil options

Postby Trickydicky » Sat Nov 05, 2016 10:39 am

Since reconditioning my rear dampers over two years ago I filled them with SAE40 and they are performing well. Before then it was like driving a space hopper! :lol:
Filling them with too heavier an oil will put strain on the the other areas of the suspension which could result in failure.
Richard

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IslipMinor
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Re: Damper oil options

Postby IslipMinor » Sat Nov 05, 2016 11:21 am

Hydraulic oil 32 is much thinner than even a straight SAE 20 engine oil. The purpose of using SAE 40 is to firm up the damping and take up some of the wear in older dampers. It does work very well!

The hydraulic oil equivalent of SAE 40 is 150, about the thickest available.
Richard



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Re: Damper oil options

Postby Nickol » Sat Nov 05, 2016 3:56 pm

Whilst on the subject, the Manual says that to fill the rear damper, you Need to take them off first. The othe rday while changing a rear wheel it seemed that it would be perfectly possible to unsrew the cap/bolt and refill without taking one off first. Is there however, another reason for having to do so?
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Trickydicky
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Re: Damper oil options

Postby Trickydicky » Sat Nov 05, 2016 7:27 pm

Nickol, it's to stop dirt and grit getting into the damper causing failure.Plus you need to disconnect the drop link to allow you to "pump" fresh oil around the damper.
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Re: Damper oil options

Postby Nickol » Mon Nov 07, 2016 10:05 am

Thankyou Richard - Sounds quite Logical.
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Andy W
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Re: Damper oil options

Postby Andy W » Sun Nov 20, 2016 6:53 pm

I finally got round to changing my front damper oil....I opted for straight 30 grade engine oil & it is certainly vastly better than before.
On the rear I shaved an inch off my bumper stops & fitted a s/h DMG old skool Spax kit (set quite firm as I often have a drum kit in the back :lol: )

All in all, a much better drive for very little £ outlay! :D
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Re: Damper oil options

Postby GavinL » Sat Aug 01, 2020 8:44 am

I've used motorcycle fork oil in my Midget dampers on the basis that it is designed for dampers and has antifoamong additives, although not probably really necessary in car dampers. I used SAE20 ( as recommended in the workshop manual) but having read this thread I realise it is too thin as the front is a bit bouncy, probably due to wear, so will be replacing with 30 or 40.


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