Fork Oil Weight?

[Mikep328]

I've seen several threads on this but probably due to poor searching on my part, I haven't found what I'm looking for... 

As background, when I bought this CB400 last year, receipts show that new fork seals had been fitted a couple of years prior.  Obviously some sort of oil was put in the forks at the time but there is no mention of what oil - ATF or fork - was installed.  The fork action is OK and no leaks/seeps but I want to drain/refill the forks so I know what's in there and that the levels are appropriate/equal in both forks.

The service manual specifies ATF which is simple/easy/cheap enough but there are several types of ATF.  Also, I don't know if ATF available today corresponds with the ATF that was in use back then.  IOW, putting today's ATF in the forks may produce a different result than "yesterday's" ATF.  For that matter, AFAIK, in the 70's there were two types of ATF, Dexron or Type F; CB400 service manual doesn't state which one to use. 

I'm not sure that fork oil, per se, functions any better than ATF since they are both essentially "hydraulic" oils but fork oils have specific weights listed on the bottle whereas ATF does not.  SO, my question is: what weight fork oil seems to work best in the 400 forks?    I see that DSS sells 10W so I ASSume that is his "recommendation" but would like to hear what actual riders have found works well.

[McCabe-Thiele (Ted)]

I believe the use of ATF has now been superceded by the availabilty of bespoke fork oil.
I used Castrol 10W in my 400.

Back when the 400's were new there was not the variety of ATF's that there are now.

I can't really comment on how well the 10W oil performs as I have not done the mileage to give an informed opinion.

[Johnwebley]

I use ATF,

Basic Dexron,as my car used it,

Nice even,smooth feeling when riding,



Sent from my SM-A546E using Tapatalk

[Skoti]

Always used ATF cos it's cheap and readily available.


But recently had to use Repsol Qualifier 10w fully synthetic fork oil.

https://lubricants.repsol.com/en/products/lubricants-search-engine/detail-of-lubricants.RP_9000B/

Can't really tell any difference, except my wallet's a bit lighter...

[McCabe-Thiele (Ted)]

I use ATF,

Basic Dexron,as my car used it,

Nice even,smooth feeling when riding,



Sent from my SM-A546E using Tapatalk

When you say basic Dexron is that 1,2, or 3 all old specs pre- synthetics?

[Skoti]

I use ATF,

Basic Dexron,as my car used it,

Nice even,smooth feeling when riding,



Sent from my SM-A546E using Tapatalk

When you say basic Dexron is that 1,2, or 3 all old specs pre- synthetics?

The newest ATF Dexron oil is backward compatable. Anything that took Dexron II will now take Dextron III.
All oils of the same grades are designed to be mixed as per industry standards.

[McCabe-Thiele (Ted)]

I use ATF,

Basic Dexron,as my car used it,

Nice even,smooth feeling when riding,



Sent from my SM-A546E using Tapatalk

When you say basic Dexron is that 1,2, or 3 all old specs pre- synthetics?

The newest ATF Dexron oil is backward compatable. Anything that took Dexron II will now take Dextron III.
All oils of the same grades are designed to be mixed as per industry standards.

That is true for use in an automatic gearbox - not sure if the different grades are the same viscocity though and what the temperature gradient might be?
I do know they have more plasticisers in the later grades - there must be however some performance differences in the oil itself. Hard to find actual viscocity rating - might be 5W depends where you look some are a 5W/10.
https://en.wikipedia.org/wiki/DEXRON#2005_-_DEXRON-VI_(J)

[Skoti]

Ted,

I'm getting well out my depth here, maybe we have an oil expert on this forum that can answer your questions?

Anyhow the lubrication requirements of our old Honda forks are probably far less than that of modern automatic transmission systems.
So maybe the latest spec ATF should be more than adequate for us.


 

[Bryanj]

The main reason for using ATF is that it supposedly does not froth when pumped which hapens a lot in forks.
When Mr Honda designed these bikes ATF was about the only oil with this property, specialist fork oils did not exist.
My opinion is use any ATF as the specs wont matter to what it is being used for OR use specialist fork oil but as to what grade now that depends on the owners weight, how it will be ridden and level of comfort required, i seem to remember 7 worked out about same as ATF

[McCabe-Thiele (Ted)]

On automatic gearboxes the older Dexron grades took longer to change gear at optimal times until they had reached a normal working temperature assisted  by a shared radiator oil cooler arrangement.

Be interesting if this is reflected in it's use on a motorbike are they firm when cold becoming softer after a few miles.

[taysidedragon]

I use Silkolene 15w fork oil in mine. The fork action and ride quality is fine for my 14stone lump. 👍😁

[Mikep328]

I ordered some Castrol 10W; we'll see how that works.  I'm a bit under 12 stone.

[Mikep328]

GRR...   Using the correct size box end wrench I could not loosen either of the top fork bolts!  When I go to the bike next (a 1/2 mile walk from our house) I'll take a socket set but that will require removing the handlebar to get access.  I can't imagine that the fork bolt is supposed to be anywhere near as tight as these are.  Maybe I'll try the wrench again and give it a good whack with a rubber mallet to see if I can break the bolts loose without removing the bar.  Out of curiosity I looked in the service manual to see if there was a torque setting for the fork bolt, wondering if it was supposed to be much tighter than I think but I couldn't find a setting for that bolt.

Oh well, if things went smoothly it would be boring.

[K2-K6]

They aren't too tight in their assembly requirement, but can just be awkward to get them to undo easily. There's quite a bit of drag in turning them with their seal inside the fork tube.

I find them easier with good six sided socket and long breaker bar or big torque wrench, either of these you can apply decent consistent pressure downward to avoid slipping off, that while easily using the long lever so that there's no need to struggle with much rotation force, usually makes it all a little calmer.

Putting them back in, same method but while holding pressure on the top, turn it backwards (undo) to find the lead of the thread as it "clicks" down into place and then you can easily turn the right way to pick-up competent engagement in getting the thread started.

[taysidedragon]

GRR...   Using the correct size box end wrench I could not loosen either of the top fork bolts!  When I go to the bike next (a 1/2 mile walk from our house) I'll take a socket set but that will require removing the handlebar to get access.  I can't imagine that the fork bolt is supposed to be anywhere near as tight as these are.  Maybe I'll try the wrench again and give it a good whack with a rubber mallet to see if I can break the bolts loose without removing the bar.  Out of curiosity I looked in the service manual to see if there was a torque setting for the fork bolt, wondering if it was supposed to be much tighter than I think but I couldn't find a setting for that bolt.

Oh well, if things went smoothly it would be boring.

Slacken the pinch bolt in the top yoke first.