Front fork oil

[kaysystems]

Hi

What fork oil are you folks using now? I used to use brake fluid, but that was not kind to the paint if it managed to leak out.

Should I use a regular fork oil? 10W?

thanks

David

[ducwiz]

Oh no, how dare you !

Brake fluid is not based on mineral oil. It is not recommended as a fork oil. It destroys any rubber part like fork seals, O-rings, etc. made from the most common "NBR". Hence it produces leaks rapidly. It needs a special rubber grade (EPDM).
Afaik the fork oil grades are given in the Ducati user manuals.

Hans

[themoudie]

I used to use brake fluid, but that was not kind to the paint if it managed to leak out.

OH! Really? Are you sure that you don't mean Automatic Transmission Fluid (ATF)?

I have a '74 450 MKIII, with Marzocchi 35mm forks that is used on public roads, the majority being small backroads with potholes, ripples and manholes etc. The ambient temperature when I am out riding the bike is in the range from 5°C to 25°C, the majority in the range 10°C - 20°C. If your ambient temperatures when riding your motorcycle are higher than mine, you may need to use an oil with a thicker viscosity.

I have found that Castrol ATF suits my riding style and roads fine. Using a 10W fork oil produces a pneumatic drill/pattering effect from the forks. Not enough to cause problems on the road, but sufficient to be noticeable.

Enlarging the damper holes (be careful) increases the flow rate of the damping fluid and hence may make for a more plush ride than standard, IF the same damping fluid is used.

Fork oils manufactured by differing manufacturers using the same "weight" label e.g. 10W, have differing viscosities (Resistance of a fluid (liquid or gas) to a change in shape, or movement of neighbouring portions relative to one another. Viscosity denotes opposition to flow. The reciprocal (opposite) of the viscosity is called the fluidity, a measure of the ease of flow. Molasses, for example, has a greater viscosity than water. Britannica_definition

The manufacturers of fork oils/damping fluids use of the oils "weight" e.g. 10W is meaningless. Differing manufacturer's fluids labelled as 10W have differing viscosities, so you are not comparing like with like, but an unripe lemon with a ripe banana! I would suggest a study of the linked table, the manufacturer's owners manual and consideration of your combined weight, with that of your machine and the ambient temperatures that you ride in.

Dynojet_Co_Table_of_fork oil_viscosity_by_manufacturer

Make sure that everything is spotless when re-assembling your forks, I use brake cleaner to clean all the internals before assembling and no rags to "give it a wipe", workshop paper towels if you must wipe it.

I hope this helps you make a choice.

Good health, Bill

[graeme]

Bill, I agree with you that ATF works well in Mazocchi scrambler forks.
As nice a front ride as it gets without changing any standard bits.

Graeme

[kaysystems]

Thanks guys - I started using brake fluid in the UK in the 70's based on a dealer recommendation. ATF was never mentioned. I guess that since brake fluid is a hydraulic fluid it seemed OK.

So I'll make my choice. A good ATF does sound like a good idea. I was looking into the Belray 10W that I have and it seems a bit viscous.
How about Mobil1 synthetic ATF?
That is interesting stuff. My Ford RV transmission was very rough when the converter clutch kicked in. Apparently normal ATF can burn into the clutch plates. About 5000 miles with Mobil 1 it is as smooth as the day it left the factory! Supposed to dissolve the burned gum.

Thanks again

David

[themoudie]

Aye Dave, a pleasure.

Perchance, you weren't a fishing mad forestry student near Penrith in the mid 1970's, were you? PM me if you would prefer.

As for the "Mobil1 synthetic ATF?", I would give it a go and see how you like it. It certainly won't rot the seals and disolve the paintwork like the brakefluid will!

Good health, Bill

[kaysystems]

No, not Penrith. I did an apprenticeship at Rolls Royce in Derby during the 70's. A great place to learn a lot about engineering, and the real world.

Just read the original Ducati shop manual - AGIP F1 Shock Absorber Oil (Hydraulic Brake Fluid).

Yes I think I may try the Mobil1, as I have some left over.

David

[themoudie]

Aye David, thank you for your reply.

All I can say about the description in brackets "AGIP F1 Shock Absorber Oil (Hydraulic Brake Fluid)" is that it appears to be a bad translation from Italian into English!

Google translations!

"Hydraulic brake fluid" = "Liquido freni idraulici"
"Hydraulic controls oil" = "Olio comandi idraulici"
"Shock absorber oil" = "Olio ammortizzatore"

The DUCATI owners instruction manual for the 450 is written as follows:

"The front suspension is composed by the telescopic - hydraulic long-stroke fork, with steering stop.
DUCATI model for 450 MARK 3 and DESMO: each fork leg contains 100 ÷ 110 cu. cm. (cu. inch. 6.1025 to 6.7127) of AGIP F.1. oil.
SHOCK ABSORBER - MARZOCCHI model for 450 SCR:
Each fork leg contains 180 ÷ 185 cu. cm. (cu. inch 10.98 to 11.29) AGIP F.1. ROTRA ATF oil., for hydraulic controls viscosity 3-4 Engler at 50°C"

No mention of "hydraulic brake fluid". Mobil1 synthetic ATF would be my choice as a starting point, as you already have it and see how you find the front forks respond.

Good health, Bill

[kaysystems]

Thanks Bill
My only problem with Mobil1 is the smell. It’s really bad!

All the best

David

[themoudie]

You are doing SOME stoppies, if you are worried about the smell of the fork oil!

Bill