Oil For Shocks

the old time can of ford shock oil is a little higher viscosity than 85-140 gear oil.
the delco love joy type shocks take the thin oil like hydraulic jack oil
 
I bought motorcycle fork oil to use. It has antifoaming agents to help with the application, It comes in various weights.
 
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Who-die shocks like to wear in the wings. The more wear, the more viscous oil is needed. When they were new, the glycerin worked well but the in service life is problematic for it. Modern hydraulic oils are available in a fair amount of different viscosity levels. Cold weather can make the fluid a lot more viscous and that's the reason they used glycerin back in the day.
 
I just rebuilt a Mercedes fan clutch and had to reverse engineer the viscosity of the silicone oil and found the it is supposedly more temperature stable viscosity.
So I got some to test in my shocks.
I was using a model A shock with no wear and all clearances were between.001and.002
I also made the test fixture and weight as shown in the service bulletins.
the 32 shocks are quite similar except for the adjustment valve.
You would be surprised at how stiff they feel when working properly by the timed movement and I tested both at room temperature and freezing temperatures.
previously I had used hydraulic jack oil and thought the shocks worked ok.
I found an old can labeled Ford shock oil not Ford but aftermarket and it made the not worn shock meet the time at the suggested needle valve opening.
Then I compared viscosity with available oils today and the 85-140 gear oil was close but still lower viscosity so I added some shell omala 680 that I use in my transmission (about 10%) that gave me equivalent results to the old time shock oil.
my next shock is going to be the silicone oil test—I got the 1000 cst oil ( used 750 for the fan clutch and it works perfectly)but was as high a viscosity as the old Houdalle shock oil).
 
Here is some info on filling the Houdaille shocks
 

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Tim Ayers said:
I bought motorcycle fork oil to use. It has antifoaming agents to help with the application, It comes in various weights.
Click to expand...

I have fork oils; 2.5, 5 and 10 for my bikes so was curious about how it compares to 85-140 gear oil. The fork oil is an order of magnitude less than 85W - 140 gear oil.

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85W-140 gear oil typically exhibits a kinematic viscosity between 290 cSt and 347 cSt at 40°C. Specific product data points include:

Mobilube HD LS 80W-90/85W-140: 328 cSt
Duragard® Diamond Plate®: 347.7 cSt
AMERIGUARD® 85W-140: 335.3 cSt
Valvoline Classic Blue 85W-140: 333.8 cSt
Ultra1Plus SAE 85W-140: 290.85 cSt
 
glennpm said:
I have fork oils; 2.5, 5 and 10 for my bikes so was curious about how it compares to 85-140 gear oil. The fork oil is an order of magnitude less than 85W - 140 gear oil.

588398


85W-140 gear oil typically exhibits a kinematic viscosity between 290 cSt and 347 cSt at 40°C. Specific product data points include:

Mobilube HD LS 80W-90/85W-140: 328 cSt
Duragard® Diamond Plate®: 347.7 cSt
AMERIGUARD® 85W-140: 335.3 cSt
Valvoline Classic Blue 85W-140: 333.8 cSt
Ultra1Plus SAE 85W-140: 290.85 cSt
Click to expand...

Wow, great info, Glenn
 
Kurt in NJ said:
I just rebuilt a Mercedes fan clutch and had to reverse engineer the viscosity of the silicone oil and found the it is supposedly more temperature stable viscosity.
So I got some to test in my shocks.
I was using a model A shock with no wear and all clearances were between.001and.002
I also made the test fixture and weight as shown in the service bulletins.
the 32 shocks are quite similar except for the adjustment valve.
You would be surprised at how stiff they feel when working properly by the timed movement and I tested both at room temperature and freezing temperatures.
previously I had used hydraulic jack oil and thought the shocks worked ok.
I found an old can labeled Ford shock oil not Ford but aftermarket and it made the not worn shock meet the time at the suggested needle valve opening.
Then I compared viscosity with available oils today and the 85-140 gear oil was close but still lower viscosity so I added some shell omala 680 that I use in my transmission (about 10%) that gave me equivalent results to the old time shock oil.
my next shock is going to be the silicone oil test—I got the 1000 cst oil ( used 750 for the fan clutch and it works perfectly)but was as high a viscosity as the old Houdalle shock oil).
Click to expand...

I believe that Kurt's testing is heading in the correct direction. although a higher center stoke value than 1,000 may be required.

"1000 cSt silicone oil and glycerin have nearly identical kinematic viscosities of approximately 1000 mm²/s (cSt) at room temperature (20–25°C), making them comparable in terms of flow resistance.

While their kinematic viscosity is similar, their dynamic viscosity [most important in shock application]differs due to density variations:

1000 cSt Silicone Oil (PDMS): Has a density of ~0.97 g/cm³, resulting in a dynamic viscosity of ~970 mPa·s. It is chemically inert, has a high flash point (>314°C), and exhibits Newtonian behavior at this viscosity under standard shear rates.
Glycerin (Glycerol): Has a higher density of ~1.26 g/cm³, resulting in a dynamic viscosity of ~1260–1400 mPa·s at 20°C. Glycerin is hygroscopic and significantly more viscous than silicone oil in absolute (dynamic) terms, though it falls within the same order of magnitude for kinematic flow.
Key Distinctions:

Thermal Stability: Silicone oil remains stable up to 150–200°C, whereas glycerin begins to degrade or caramelize at higher temperatures [various comments on the net about variability of viscosity for the Houdaille shocks. Note the Summer Winter adjustments suggested by Houdaille in their literature]

Other good input from Rotorwrench:

" Re: Shock fluid?
That is a question that I still haven't seen an answer for. Glycerin was the original fluid used by Houdaille but I've never heard of a chemical break down of the product marketed later as "shock fluid". I've heard that mineral oil, castor oil, and glycerin were all used in Ford products and some mention the shape of the filler plug was the indicator of type used.

Houdaille shocks originally used leather as the materiel for the wing shaft seals and glycerin will protect the leather. The glycerin stays about the same viscosity in all normal temperature variations. If a more modern type treated leather or some other mineral resistant seal is used then mineral oil can be used. As to what type or viscosity I don't know. The viscosity of glycerin or castor oil would have to be measured to see. Hopefully a shock rebuilder will add their 2 cents.

I still have occasion to to work on an old Bell 47 helicopter with a stabilizer bar set up now and then and they used the late type Houdaille dampers. They have a little window so you can see the fluid level and Mil-H-5606 hydraulic oil was used in them. We had to disconnect and time the drop on them with a specific weighted object attached to the arm each 100-hour inspection. They have a needle valve adjustment to get the time right.
Last edited by rotorwrench; 05-11-2012 at 09:46 AM."
 
Kurt in NJ said:
I just rebuilt a Mercedes fan clutch and had to reverse engineer the viscosity of the silicone oil and found the it is supposedly more temperature stable viscosity.

my next shock is going to be the silicone oil test—I got the 1000 cst oil ( used 750 for the fan clutch and it works perfectly)but was as high a viscosity as the old Houdalle shock oil).
Click to expand...

From what I've found today, the 1000 cSt Silicone may be your best option. As you state, silicone is more temperature stable. Glycerin's cSt values drop quickly.

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From, https://www.super-lube.com/wp-content/uploads/2025/06/Technical_Data_Sheet_Silicone_Oil.pdf

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The table values are at ambient temp of 25°C, typical of what I found. Distinct temp values would have to be calculated.

I'd test and try the 1,000 cSt and if you found it to be too viscous, proportion the 1K with 350 cSt like this:

Assume you want a cSt of 800,

800 = X(1000) + Y(350)
X + Y = 1
800 = (1-Y)(1000) + Y(350)
Y = 200 / 650 or 30.8 % of the 350 cSt and 69.2 % of the 1,000 cSt

The great thing with these shocks is their adjustability which you can use to fine tune the performance.
 
The shocks haven’t increased their temperature much over ambient even after driving fast over rough roads ( for me fast starts over 50) — I was considering the silicone oil for more stability in colder conditions.
 
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