Rear damper oil

[Oddjob]

I need to refill my refurbished Marzocchi AG Strada rear dampers, according to the blurb it's supposed to be Special Oil Marzocchi SAE5, you can't seem to buy that now. I contacted a dealer specialising in fork oils and such and he said not to use normal fork oil in dampers as it wasn't suitable. Yet, I've seen quite a few bottles of 5w oil which says it's for use in front suspensions and rear dampers. They can't both be right.

I have some Honda fork oil which I'm considering using, anyone else got any suggestions? I may go for 7.5 or 10w instead of 5w if that is hard to find.

[K2-K6]

I cant think why they'd say unsuitable, I hate it when statements like that are made without them offering reason 

I use Motul for most refills etc, 5 a good start point as the damper valving is usually designed around that to match the intended spring poundage.

7.5 a shift obviously, but you'd of course only find if you like it by trial and error.

[Bryanj]

Its basically a hydraulic oil with anti frothing additive so why not fork oil or atf if its the right grade

[sye]

I had a CBX750 in 1986 that specified ATF for the forks.

[Oddjob]

This is what they said via email.

"Hello Ken,

Thank you for your reply.

I'd not put fork oil in it. They have different requirements and so it would be best to stick with shock oil. Unfortunately, we am unaware of any shock oil we sell that is of 5w."

I'll give the Honda fork oil a try and see how they perform.

[Moorey]

   I would be giving ATF Dexron 2 a try.

[Bryanj]

What do they specify for the old moggy 1000 dampers now. They were refilable

[K2-K6]

What do they specify for the old moggy 1000 dampers now. They were refilable

Everyone is sxared of rotary dampers now after the Suzuki v-twin reputation that was bkamed on that type.

They did use tgem in Schumacher era F1 though, cost about £35,000 a pair apparently  and ran into trouble with material integrity even when made of titanium and stainless steel bespoke billet construction. 

[K2-K6]

In this case Ken I can't really see a proboem with starting off on fork oil.

The "shock" fluid denomination seems to come from needing a very stable oil for shear properties over a wide heat range. Single shock application can be running at 3~4 leverage ratios in which any shock performance change is amplified by that amount at the wheel and putting a very high premium on device linearity to avoid riders complaining.  They use synthetic base oil to do this which is expensive but holds characteristic over wide range of use.
They also use multiple adjustment methods to trim performance, from low and hugh speed compression, low and high rebound, volume shift through shock shaft being more inside or outside damper chamber depending on where in stroke the travel is, compensatory floating piston and valving. Also to ramp up end stroke compression damping abd try to arrest a high speed input that could clatter right through the travel stroke.

The old type like these shock having nothing like this, also being more or less 1:1 in leverage, will be nothing like as sensitive to oil type.

Avoiding starting with too thick an oil is desirable, with too much hydraulic resistance giving a wooden feel on initial compression and not allowing the spring to do it's work if it's correct spring rate.

[Oddjob]

Ta Nige, I'll stay with the 5w the Marzocchi had in them in the first place, I'll see how they perform and adjust if necessary.