Regular vs Heavy Duty Fan Clutch

(Paul Breen pay palled it) #21

Hi Tony. Bolted straight up. It is a little thicker than the flogged out original but worked. Still have 5/8" to the rad. No parts modified and original steel fan. Will send a bit later rhis week.
I think the link I posted is the one I bought from but may be wrong - ageing. I do now recall pulling down a pdf of the Dayco catalogue to make sure of the dimensions. Good detail on bolthole pcd’s etc - made it easy. I will also check archive. Paul

(Paul Breen pay palled it) #22

I found a picture that I took at the “fit up” stage. Rad is recored but dimensions are similar? Have about 5/8" clearance

(Paul) #23

Nice images and info …Thanks for posting.
I recall your info and help perusing earlier threads while researching.

However the info you added here was not within those, so this is a nice addition for those searching in the future.
And I forgot about that parts list site…never thought to look there.

Hmm…sure, I imagine the fan bolt hole patterns would be different I imagine btw models. If those clutches so hard to find for those saloons, are new clutches and drilling new holes an option?
Interchangeability with other metal fans of the period?

But wow, I’ve owned a Mk2, Mk7, and 3.8S saloon and don’t recall such shallow dimensions … but I can’t remember anything anyway.

Goodness…72mm of space = 2.8 inches.
And 54mm total length is only a shade over 2 inches.

That sure is narrow/close. Are you sure there is not something off there?

I have a 1972 S1, all original, unfortunately all apart now, but I remember making mental note that 3inches (76/77mm) was safe space availability…and that was a quick measurement, there may be a bit more even.

And I am quite certain Paul above, per past posts, has an original S1 too…

Wonder what saloon group would say in their measurements?
I may take a look and search archives to see if it came up.

At any rate, for a mere 1 inch some modification would definitely be justified for the thermal clutch upgrade.
Rebuilding the old viscous ones? I can’t imagine doing that or it being worth trouble.
I’m quite a purist, but the advancements in tech and build quality has vastly improved since those days.

And from all I have read, heard, and seen, they are not recommended over later thermal types, if not shunned.

PS: Remember, the Hayden 2765 is 2.67in (67mm) and used by other S3 XJ6 owners (per past threads)
There is also a viscous fan clutch by Hayden recommended for the S1 XJ6 but I can’t rememberit at moment.

Again, here is their parts list with specs. Take a look.

Also, GMB is respected as well. Japanese.
You and saloon guys may wish to contact them as well.

Their GMB 913-2020 is the Hayden 2765 alternate, and the GMB comes with the pilot hole bushing unlike the Hayden. Needed for the S1 waters pump.
Curious if it is shorter? Worth contacting them I think.
Price is right!

NOTE: Located VISCOUS Hayden options FWIW.
Part nos. 1705 and 1706, at 3 and 3.33inches long respectively.

(tony) #24

good thanks…are you able to measure the radiator to fan hub clearance?

I think the XJ has about 1/2" more clearance than a 420G, which makes a world of difference.
I dont consider under 1/4" to be safe, as the engine may move enough to contact
(and the radiator needs removing so the bigger VC can clear the water pump studs)

I know this mainly helps the MKX/420G guys, but its an issue that regularly resurfaces

(tony) #25

the early cars had a solid (non-disengaged) fan

I have other pics with rulers, the critical dimensions are correct on that diagram

note the 420G & S1 have different part numbers. It is stated in the FSM different RPM for them to fully slip. They have the same dimensions and appearance.

The later S2 ones look similar, but have a visible clock spring in the front

none of the spec sheets I quickly perused had matching bolt hole measurements?

(Paul Breen pay palled it) #26

Hi Tony. Will send as many measurements as I can and some pics by the weekend. Paul

(Frank Andersen) #27

Getting the viscous fluid may also be a problem, Demian, it’s very specific. And then there is the ‘why’ they failed - and the proper fix for that…

As you say; it’s unlikely to be worth the trouble as long as replacements are available…

xj6 85 Sov Europe (UK/NZ)

(Paul) #28

Just a quick update.
Received the Hayden 2765 and I am very pleased with it.
Haven’t installed, but the dimensions are same as the old unit i had on before which was perfect.
…2 5/8 inches in height.

And above all, the movement and feel.
Heated with a gun and stiffened up nicely.
Came with bushing and washers also surprisingly.

In the hand and with heat gun, felt quite similar to the Heavy Duty 2947.
Of course that may change when on the car a bit.

(tony) #29

apparently the process is very much like O/H a torque convertor;

lathe cut it open, replace the (bush I think?), and presumably new fluid, braze back together.

I know this has been done, last price quoted to me a few years ago $A280

an engineer in our club also did this repair himself about 20yrs ago

clearly not economic if a suitable replacement is available

I have a couple of ok spares, and a dud spare, I was thinking of opening it up, but it appears it would need to be cut on the back face, not the edge

(Paul Breen pay palled it) #30

So. I did some poking around and found my origninal receipt details for the Dayco clutch:
Model number: 115765
Sparesbox SKU: 42-115765
Price: $138.95 plus freight
Overall height: 70mm
Fan blade bolt: 82.5mm
O/D: 168mm
Pilot hole: 19mm
Shaft bolt centre: 47mm
Reference to Dayco PDJ cattledog is:

I have about 7/16"clearance at the centre (raised section with the thermal coil in it)

(Paul Breen pay palled it) #31

And. It gets better. Can buy it for less than I paid for it - also at Sparesbox…


(Frank Andersen) #32

Let’s hope the engine moves about less than that, Paul…!

xj6 85 Sov Europe (UK/NZ)

(tony) #33

thanks for that Paul, well today I found something interesting, I have noticed previously a VC on a Isuzu 4wd looked very similar, but didnt check it.

While changing the water pump on a Jeep Cherokee XJ 94-01 the VC looked very much the same…here is the Jeep fan on the Jag XJ viscous clutch…the flange bolt holes dont quite line up, by ~1mm…but could be drilled if needed

75mm is too long for a MKX or 420G, so the search continues on that front
seems like there may be a few with a similar size

for the cheapskates amongst Jag XJ owners, the Jeep VC flange holes could be drilled one size larger in 5mins. They are cheap as dirt

(Paul Breen pay palled it) #34

It’s been two and a half years Frank. She’s on new mountings - gearbox included. I will keep an eye on things but all good so far. Paul

(Paul Breen pay palled it) #35

Hi Tony, I didn’t look though the Dayco catalogue any further than I needed, but I did note that some listed are less than 70mm. May or may not suit - FWIW. I’m not familiar with the MkX etc. Dumb question - must be no chance of packing the radiator forward?

(tony) #36

astute question.

Possibly some forward movement possible, but not much I suspect

I had the radiator out and made some mods that required very minor cutting,
to trial fit a V8 Commodore rad

Unbelievably for such a big car, space is tight in some areas, including the radiator, which is slightly smaller in some dimensions than an XJ.

a few mm may be possible, I will examine my wreck, and check the Dayco catalogue

Luckily I have a good VC in my car at present

relevant to S1 XJ6 owners, as they originally had the “short” 55mm VC, the one in my 420G is from an XJ

(tony) #37

I just scrolled the Dayco catalogue.

The part num you listed is shown as correct for XJ Jags

Hat height is shown as 66mm.

No other VC matches holes, the Jeep is closest, but is is “taller”

You have shown there is enough space in a S1 XJ, but I know for a fact the 4 pre 72 XJ6 motors I have had came with the shorter “same as MKX type VC”

That type has been NLA for many years

So for a MKX or 420G owner, the option is to O/H the one you have,
move the radiator forward 10mm (if possible) for an XJ item,

or fit custom electric fans, which is also difficult with only 2" ( bigger alternator also needed)