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Ferret Fluid Flywheel Seal


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Have the radiator, fuel pipes/tank and generator oil leak under control but on opening one of the FFW filler plugs there was no oil to be seen (supposed to reach bottom of filler plug hole with the hole at top dead centre). So now replacing the oil seal but don't have instructions and not entirely sure how to do it. I know it's been discussed before but still not entirely clear to me, so please humour me and I'll post pics and my research as penance and to hopefully help someone else.

The fluid is ISO 10 or 15 (warmer climate) hydraulic fluid. Automatic transmission fluid is apparently also OK so long as it's ISO 10 (someone suggested it is ISO 30 but I think that's wrong). Need 5.54 litres, so it figures that it comes in either 5 or 20 litres!

The seal needs to be a high temperature (or pressure? can't recall which) seal. ID 44.45mm, 1.75 inches; OD 63.652mm, 2.5 inches, Thickness 3/8inch, 9.5mm. Bought a seal from a local shop but am advised not to use it, as it is black and therefore not high-temperature enough.

John Deere AT52447 is suggested as a replacement. The other option (that I'm going with) is SKF Bearings Viton seal 17395; that was suggested to a friend by Tim Vibert, who has more experience than most. The seal is apparently fitted to a plate with a lip that pushes into a groove on the back of the seal, so neither of these seals fit as is. Some suggest flipping the plate so the groove is on the outside but my friend warned that the seal might "turn itself inside out" with enough pressure. Not so sure about that but will machine a plate to fit just to be on the safe side. A "genuine" seal is also an option of course but apparently they're a bit hard to source.


1. First job is to separate the gearbox, supporting it (engine lifter and straps) while withdrawing it. So far so good!


2. The seal is obviously knackered so I'm glad I decided to do it before putting the engine back in. (The bolt in the filler plug was to guard against dropping the plug into the housing. Tied a bit of wire to the end but think there's a "proper"  wrench available for the job. 


Came with a resident spider that obviously doesn't (didn't) like my chances of getting it mobile again!


So where to from here? Do I undo the nuts or remove the circlip (or both)? Not sure what the circlip is doing, and the drawing I have shows a bearing housing so don't really want to turn this into a disaster!


Thanks for any advice


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To remove the seal and bearing carrier (there is a ball race behind the seal), remove the 6 setscrews, use 3 of them in the jacking holes and screw in evenly to pull the carrier out. The circlip retains the special lipped washer, take that out and remove the seal. If you want an original spec seal, contact Richard Banister in the UK. They are black seals as original and the lipped washer fits them.

cheers Richard

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Thanks Richard.

Some pics that might help others (and apologies to everyone else!)

Drained it - I guess ATF since it's red and actually lots of it. Perhaps the seal wasn't as bad as it looked.


As per Richard's advice, undo the bolts then screw 3 into the extractor holes and gently screw them in to extract the bearing carrier with seal, seal plate and circlip. The seal is held in place by the circlip with the seal plate in between, however it isn't possible to get the seal out by just removing the circlip because the seal is firmly pressed in.




The bearing carrier snugs up against the bearing and the seal can be seen in the centre:


Getting the circlip out was a challenge - very heavy duty and my pliers are probably a bit light-weight. Decided to wear safety glasses and glad I did because when the circlip came free it flew 5 metres across the shed!


So much for OHS! This shows the bearing housing, circlip, seal housing and "outside" of the seal. 


This shows the lip on the inside of the seal plate that fits into the groove on the seal.


When it is fitted together it supports the lip of the seal, possibly to prevent it pushing out and failing under pressure.


Others have suggested flipping the plate to fit non-standard seals that don't have the groove. If this is done the lip won't have the same support, so at this stage I'm not sure if it's a good idea. Will have a look at the SKF seal when it arrives next week and decide what to do.


I'll have a few questions later. Mainly, the bearing housing bolts were covered in some sort of gunk and I'm not sure if that's just thread locker or some sort of sealant.




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When I worked in REME workshops we had a general guideline that if a fluid flywheel required more than a pint of oil to top up then it should be overhauled, not just seal but outer cover gasket as well as these are known to leak and also cracks have been known to be found in the cover. The total oil capacity is around 9 pints from memory. I always pressure check the flywheel after rebuilding and filling.

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Thanks Richard. 

On draining I filled a 5 litre paint tin, which sneaks in under the 1 pint top-up guide. Surprising that with that much fluid in it I couldn't see the top level trough the filler plug hole.

EMER advises 5.54 litres, which is 9.75 UK pints or 11.75 USA pints. I must say it hadn't occurred to me that UK and US pints were so different!


I'll see if I can find a plug to make up a pressure testing connection.

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Not ready to pressure test yet, however wandered down to the local hardware store and found a couple of fittings that connect to my pump inflator after removing the wand. Plan to use gas tape rather than ordinary teflon tape but it's pretty basic, so if it shows a drop in pressure I'll make something a bit more sophisticated, with proper valve, before blaming the FFW.

So start with inflator and remove the wand


Get your fittings


And it should work, but depends on no leakage from the inflator, which might be asking too much - time will tell!



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6 minutes ago, Codeblue said:

Great, thread. thanks!  

Sorry for silly question but how do you check the level( or top up) of the FFW without removing the engine?

Through the aperture at the top of the gearbox housing where it bolts to the flywheel housing. You really need the correct flywheel plug tool as it has a centre screw to secure the plug, because if you drop the plug down inside the bell housing it means the gearbox will have to be withdrawn to retrieve it.

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Going a bit from memory here, but the Ferret idle spec is around 500 rpm (although we find life easier setting it around 650 rpm). The fluid couplings seem pretty bullet-proof, so if the fluid coupling doesn't start to engage and move the Ferret around 800 rpm, we assume the fluid level is low. I must confess I use this lazy man's way of monitoring level. Since we use ATF in our fluid couplings, red ATF on the hull floor is not a good thing, even if the FC is working well. 

I had a Ferret that had a large rpm drop when put in gear at idle. It turned out it was just an engine tuning problem but leading up to that discovery,  I experimented with fluid coupling oil. As-found was red ATF, which is about ISO 30. Spec is ISO 10 oil. So I switched to ISO 10 oil to see if the coupling would "drag" less at idle when a gear was engaged with the thinner oil. It made no significant difference, so we just use easy-to-get ATF in the fluid couplings. 



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