Oil for Ferret Fluid Coupling?
 

At the Oshawa Museum, I found Dexron ATF in the fluid coupling of the Ferret I am working on. I notice significant creep/drag when in gear at a relatively low idle speed of around 400-500 rpm.

ATF has a viscosity grade of around 30 whereas the tables I have seen on various sites recommend a ISO 10-15 viscosity grade oil, based on the OM13 military spec. Seems logical the much more viscous oil we are using is the cause of the creep. What are you Ferret owners using?

EDIT: A second attempt at searching found a site that says, "DO NO USE ATF!" And to drain it, "you need to remove either engine or gearbox". Oh dear. Is there no other option? For example, where does the oil drain when the seal leaks?

Oil
 

Drain out the ATF via the filler plug. ATF is too thin.
I used normal hydrolic oil as in hoists, rams etc with no problems.
Wayne.

Ferret fluid coupling
 

Check out this link - scroll down to the bottom for the chart with the list of fluids, and a second diagram showing what goes where.

http://www.ferret-fv701.co.uk/useful_info.htm

Hope this helps.

Cheers,

Chris Preston,
Victoria, BC

Chris, That's the link that says I should be using ISO 10 or 15 viscosity grade oil in the fluid coupling, which is a very thin, quite specialized oil for high speed spindle bearings. It's MUCH thinner than the ATF that's in there now, which has 30 grade viscosity.

I did some more searching and the consensus, especially over on HVMF, is that OM-13 spec oil is indeed ISO 10 or 15 viscosity grade.

I suspect the heavier ATF is contributing to the quite high drag I get from the fluid coupling, especially when engaging 1st and 2nd gear at a standstill.

Anybody know how I can drain the fluid coupling without having to split the engine and gearbox?

You are correct, ISO10 is one of the thinnest hydraulic oils. The common grade for plant machines, cranes, etc. is ISO32, so you can see there is a difference.
I spent many years working on British Army military vehicles (41 actually) and have dealt with fluid flywheels in everything from the 1940 Daimler Dingo to the CVR(W) Fox. The Dingo originally had engine oil in the flywheel but postwar this was changed to OM13 (ISO10), there would have been drag I suspect with the engine oil, but they would not have had anything more suitable in their inventory of oils at the time.
If you really want to drain the oil, it will make one wholly mess, the oil capacity is about 9 pints and that will flood out all through the base of the vehicle before any of it could be drained from the hull. Better to wait until you have to pull the gearbox, then it can be drained in to a container, without too much mess.

Does the fluid flywheel / torque convertor shares the same oil supply??
Does it also have a trans cooler?
In a car you disconnect a hose from the cooler and the trans pump pumps it out while you top it up with the new oil. I was party to a feret trans (Mr Wilsons brain child) rebuild many years ago (army mechanic recon course), but have forgotten most all of it.

A Fluid Flywheel and a Torque Convertor are two wholly different drives. The FF is self contained, no pump or cooler.

For your better understanding here is my fluid flywheel apart.

Hope it brings some understanding.

This is the oil I have used

R

Thanks, Richard. That's a bit disappointing. I really wanted to get some thinner oil in there because right now she almost stalls at idle when first or second gear is engaged from neutral. I've got the idle mixture screws set on the lean side so I'll try setting them a bit richer to see if that helps. The idle is around 400 rpm and I can change forward/reverse quietly at that rpm so I'd like to keep it low.

She runs too cool as well. The new thermostat may improve the idle stability.

We have a spare engine and gearbox so I'll take a look just to see where the fluid coupling oil would drain out of the bell housing and to confirm I can't get a drain trough up through the gearbox drain hatch to direct the oil. The oil could be drained quite slowly by rotating the open fill plug hole gradually downwards.

Also I might be able to suck some oil out with small bore tubing through the fill plug.

Thanks, Robin. That shows sucking it out with tubing would be a tedious process requiring topping up and sucking again to gradually dilute the ATF.

I think your idle at 400rpm is a bit slow, you may find the regulator is cutting in and out at that speed too. I find it best around 550. Shifting from forward to reverse has to be done in one swift movement and can be done without it being at 400, but you need to select and engage Neutral. Also, never leave the engine running in gear while stationary for a period as oil will overheat.

You say you think the engine is running too cool, let me know what temp it is showing on the gauge please.

Regarding draining oil, if you don't want a mess then the only way is to pull the gearbox back from the engine.

regards, Richard

Honestly, pulling the gearbox off the engine and thereby allowing you to remove fluid flywheel is a relatively easy job especially when you consider you are dealing with Mk1 vehicles and have a decent shop and overhead lifting abilities.

You are making more problems for yourself if you don't in my humble opinion.

I fear what is happening is Aquino is looming large on the horizon and the pressure is to deliver a running vehicle.

There are a few cheats to allow you to skip a few steps but honestly if you don't know when the fluid flywheel was last rebuilt then you have no idea when the seal was replaced. I think you are better to start from a known point and move forward with a trouble free vehicle for years to come.

I know you may feel it is easy for me to sit at this vantage point and pontificate but honestly if you want a smooth fluid flywheel its worth the extra effort.

I know when I get mine back together it will be one area I will have no concern over.

Robin

Richard,
I'll double check the idle with a laser tach as the mechanical tach bounces around at low rpms (will oiling the cable help?) and I'm estimating the idle speed. I'll raise it to 550 and try that.

Do you mean the generator regulator? This Ferret (and in fact all our Ferrets AFAIK) has the updated alternator that was installed in the early 70's, so that wouldn't be a factor, right?.

Interesting what you say about selecting forward/reverse. I can get a very clean, grind-free forward/reverse shift by selecting and engaging first gear first. It is damn near impossible to select forward/reverse with neutral selected and engaged because of nasty high-frequency tooth grinding. I attribute that to the excessive drag in the flywheel combined with normal drag in the gearbox causing the gearbox output pinion to rotate the transfer case bevel gears much faster in neutral than it does in first. In first, you get the advantage of the 6:1 gear reduction to significantly reduce the flywheel drag rpm.

It'll be interesting to see what effect the thinner flywheel oil will have on this.

I knew the engine was running too cool because of IR gun readings, the fact I could also hold the thermostat housing comfortably with my hand, and the fact that the upper rad line heated up after a cold start at the same rate as the thermostat housing.

Today, I now know why it was running too cool - there was no thermostat installed. I have installed a good t/s and I'm in the process of replacing all the old hoses.

The temp gauge doesn't work. That's high on my list of priorities. I measured 95 ohms across the disconnected sensor at room temp which makes me think a) it's not a modern NTC sensor and b) the fact I have a resistance at all means it may be OK.

The obvious reason it's not working is because there is no voltage across the 2 pins on the sensor connector with ignition on. More troubleshooting required.

Malcolm .

Robin,
It's a big job pulling the gearbox even with our good facilities (we just installed a hoist!) and I have so many other things to fix. I'll leave that for a winter project.

I'm going to try 3 or 4 suck-outs and refills with ISO 10 oil. That should get me down to the ISO 15-20 range. I'll see what difference that makes.

By the way, where do you get your spare parts from? Any Canadian sources?

Malcolm

Dear Malcolm,

I understand and accept why you are doing it the way you are, enough said mate.

I hold my own spare parts supply as I have elected to sacrifice my second vehicle as the long term spares for the first. I might trade with you guys, we can do that privately off the forum.

As far as spares being sourced locally, I sourced all the parts for my gearbox rebuild from this side of the pond, seals and bearings just by matching OD / ID / Height and style. We made our own gaskets etc and used industry accepted sealants of an equivalent quality.

I need a garage stood before I can go further.

Things like brake shoes I will have relined if I need to when I get there. I am having a Land Rover master cylinder stainless (for work's vehicle collection) sleeved at John Stuart Power Brake in Ontario. There is a lot more that can be done without UK sourcing than people imagine.

Glad to hear your making progress.

I am actually a member of the Ferret Club in case you didn't know!

Regards

Robin

Malcolm,

as far as the transfer case change, of all the different Ferrets I have driven, I think it is 9 in total now, the change has always been done in neutral.

What I have found is that it does have to be a swift movement made with purpose.

I would say about one in 100 times it doesn't happen corrrectly and a shut down of the engine enables the change to be made.

I have not proved it but I always have suspected that the failed changes are because the vehicle has been allowed to roll back or forwards ever so minutely while the change is being made and something is now out of alignment.

To counter that I always have my foot on the brake during changes.

Robin

To follow up with this thread, I drained the ATF from the fluid coupling and replaced it with ISO 10 hydraulic oil. The results were disappointing. It is still impossible to change into forward or reverse with neutral engaged. The only difference I noticed with the thinner oil was that the rpm drop when a gear is engaged from neutral (with the transfer case already in forward or reverse) is not so large.

What puzzles me is the old hands here who have been driving these Ferrets since we got them circa 1980 tell me they have always had to select forward/reverse with first gear engaged. It won't work in neutral.

Since my thinner oil experiment didn't work, I can only see two reasons the transfer case input shaft is rotating too fast in neutral to prevent forward/reverse from being selected - the fluid coupling is binding for some other reason than oil, or a band in the gearbox is a bit tight and partially engaging a high gear when in neutral.