Rear inner fulcrum shaft mounts.

[44DHR]

Maikel, Richard - and to answer Simon's initial question on the Part Numbers for these various Fulcrum Brackets. I have looked through some of my records and photos as follows.

Maikel, the early 3.8 E Type bracket is different to the later 4.2 bracket with its little lugs and it has a different mounting arrangement. The 4.2 E type bracket has two threaded blind holes in the bottom at each end to mount the bottom Tie Plate as can be seen in Photo 4. Once these brackets are bolted and shimmed to the side of the diff, this is the "platform" to mount the diff into the lower part of the rear axle cage. In the Ebay photo, the brackets have been removed, hence they do not protrude from the base of the diff.

Richard, yes, by using different bracket castings and mounting these to the two threaded holes on each side of the base of the diff casing, the diff assembly can be used in a variety of applications - with or without a mounting cage - which we are familiar with on the E Type. I show two examples of Jaguar fulcrum brackets which can be bolted to the diff to illustrate how this is achieved.



The top bracket is a 4.2 E Type bracket and you will notice how the mounting holes differ in configuration to the lower XJS bracket - although the distance spacing remains the same between the one of the central holes to the opposite outer hole. The E Type Bracket has its two central holes much closer together. By using the appropriate bracket to suit the vehicle, this gives the diff nose angle relative to the horizontal.



When viewed from the rear of the bracket, interestingly - to answer Simon's question on Part Numbers, despite being different brackets Jaguar still cast the same number of C20480 F on both.

Now if you bolt them to the side of a Salisbury diff, not only is the horizontal angle different when viewed from the side, but due to the spacing of the holes in the castings the length relative to the centre of the diff changed. The following two photos show this as when looking down - E Type to the left, (nearside when the diff is inverted to its usual position) and XJS bracket to the right - in both Photos 3 and 4. so for example a XJS diff with its correct fulcrum brackets attached would not fit a 3.8 or 4.2 E Type rear axle cage as it would have both the wrong angle when bolted in to the top of the cage by the 4 mounting bolts and be incorrectly mounted too far forward.





I trust this assists,

regards, Dave

[288gto]

Very helpful indeed Dave.

After a bit more research, from the 3.8 Parts Catalogue it shows the later type C20481 being fitted from chassis numbers.

850679
879132
861106
888327

The earlier ones appear to be handed with part numbers C16985 RH and 16986 LH

Dave, do you know if the brackets are forged or cast?

Simon

[44DHR]

Simon,
I would think looking at the intricacies and details of the brackets that these would be cast rather than forged.
Cheers,
Dave

[Maikel]

Hello and many thanks to all comments and Dave for his great pictures.

I am still not sure what the the difference is between C20480 and C20481

Now as we have been informed that C16985 RH and 16986 LH are for the early S1 cars, what is the actual difference in geometry? Could I still use the latter type for the earlier cars? Can I install a complete later IRS under an early 3.8. What else is different apart from the design?
OK, hundreds carrier changed in design only
Water deflectors were added
The wishbones changed from hollow style with the rod to those with the rod.
The plate underneath the diff changes in design
The brackets for the rear calipers disappeared.

But all these parts are considered as a continously improvement and not a geometric difference.

I would think I could substitute missing old original parts from a flat floor car with advanced parts from let's say 65.

Even if the parts number changed the newer pairs would still fit. Where am I right or wrong?

Thanks to the more experienced guys.

Maikel

[44DHR]

Maikel,
I wasn't aware that there were any changes to the geometry between the early 3.8 and the 4.2 rear axles. I am also not aware of any changes to the mounting angles in the "chassis rails" or changes to the length of the Radius Arms locating the rear suspension. The Salisbury 4HA diff casing did not change - this gives the top angle where it bolts into the rear suspension cage - so unless the cage differs between the two, the rear fulcrum brackets would both align with the two sets of holes in the bottom of the cage to take the fulcrum shafts.

The "cage" is more correctly called the Rear Suspension Cross Member Assembly, part number C17014, so unless someone knows of any different cage for the early 3.8, I don't really understand why there are two different part numbers for the early 3.8 fulcrum brackets. If there was some differences on these - as part numbers C16985 RH and C16986 LH, (due the lugs ?) - perhaps this was why Jaguar decided to do away with these lugs and have the interchangeable part number C20481 ?

I believe you could use later parts as complete assemblies provided you used their corresponding items if the diff casting is the same. From a complete IRS - to just the later solid drive shafts provided you used the matching hubs, later Fulcrum brackets with the later tie plate, later brakes by dispensing with the earlier brake brackets, etc.

Regards,
Dave

[288gto]

As Dave says, according to the parts catalogue there doesn't seem to be a different part number for the "cage" for early 3.8 cars or any notes about chassis numbers. The lower bracing plate does have a different part number for the early car with a change coinciding with the chassis number change to the later C20481 fulcrum mounts. I suspect, again as Dave mentions, that this was to allow the use of one casting throughout the model range but with the mounting holes machined in different positions depending on the model of car it was to be used on.
Maikel, back to your question, given that we are pretty sure the " cage" C17014 remained the same and that the fulcrum shafts must pass through it at precise positions the diff and wishbones are interchangeable so long as E type fulcrum brackets are used and correctly shimmed up.
This is a tracing of a genuine E type C20481 fulcrum bracket that someone has kindly lent me. I have added dimensions to the nearest millimetre.



Simon

[44DHR]

Maikel,
Having studied my photo of the 3rd February in this post showing the EBay advert for the early 3.8 inner fulcrum brackets, it appears that on the lower bracket in the photo, the centre of the casting only has one countersunk hole present, which is offset to one end of the bracket. In this case in the photo, being shown correctly, as the hole in the centre of the casting is used for the mounting bolt toward the rear of the diff and the outer hole in the bracket is used for the bolt at the diff nose end.

As Simon correctly states, the later castings have provision for - and do then have two holes in the centre of the casting - as in my other photos and in Simon's drawing showing a 4.2 bracket.

If that is the case then these earlier 3.8 brackets would have to be handed to fit using the two bolts per side into the diff case and hence the RH and LH part numbers.

What fun we have learnt about brackets !!

Regards,
Dave

[JagWaugh]

With sufficiently accurate hole locations it might be possible to weld the holes for a "wrong" bracket up and bore/csink new ones.

Here is what c.21977 (s-type/420) looks like:

[Maikel]

Thanks guys?

So, that relaxes me a lot when we can use a later IRS on the earlier cars. OK, not totally original but it does the job.

Will keep an eye open for the original ones until assembly but then I will probably use C20481 is nothing has shown up. Should still try to find the earlier Plate C17023.

But why are the half shafts different, also the yokes?!
Would have expected those remain the same.
Do they have other bore sizes for the UJ?
If that is the only difference I would switch to the newer Mabyn upgraded have shaft assembly.

The wish bones have to match the mounting brackets as I have heard that the distance tubes are of a different lengths between C16985 RH and 16986 LH and C20481.

Summing up 3.8 to 4.2 IRS
Half Shafts are interchangeable but only as a complete unit.
Mounting brackets are compatible but only in conjunction with the corresponding distance tube and Plate underneath the diff. What about the wish bones?
As the wish bones is located outside of the mounting bracket I just wonder if the outside length of the earlier and latter mounting brackets are the same. If not the later wish bones could probably be used also on the earlier brackets and the other way round.

Thank you very much, will help me sourcing the correct parts and will ask for detailed dimensions before buying a half shafts or a wish bones which do actually all look very similar.

Would be nice to have the hole diameter of early and later yokes for the UK
And the length of the earlier and later distance tubes.

Thanks again and hopefully summing up and solving this issue .

Maikel

[Maikel]

To Dave and Simon,

Dave, below one og yout pics you say Jaguar casts on both brackets the number C20480 F.
So could it be that a 20480 could still fit?
I have seen pics of brackets with casting 20480 and 20481 and they both look identical.
And they also have another number on them 16258.

Where is the difference between 20481 and 20480 when they could also be the same.
Could Simon or Dave please visualise that in a picture.

Thank you very much again.

[Maikel]

Have some pics here
http://etype2plus2.com/?p=2508

[44DHR]

Maikel,

Thanks for your photos and to reply to your previous questions.

I did not say the Driveshaft inner and outer yokes differ between the 3.8 Tubular and the later Solid shafts, but it just made sense to fit a complete assembly right through to the matching hub. The U/J Journal Assemblies themselves do not change over the models and are the same bore and size dimensions. If someone chose to use an earlier Flange Yoke onto the diff, followed by the universal U/J Spider, then used a later Solid shaft and then put an earlier Splined Yoke into a later Hub Carrier, it could all be made to work, but why go to all that trouble if you can get the complete assembly in one unit ? To confirm, the U/J joints remain the same as can be seen in any Supplier's catalogue as suiting all 3.8 or 4.2 rear drive shafts.

With regard the dimensions of the wishbones of the earlier 3.8 and the 4.2 where they mount onto the Fulcrum Brackets, the key dimension is the overall width, which I would imagine could not change as they both fit into the same Rear Suspension cage. We have discussed the very early 3.8 Fulcrum Brackets and I believe they could well have a greater length of Distance Tube between the inner spaces than the later more chunky 4.2 Fulcrum Brackets. These tubes are just pieces of thick wall hollow metal tube which serve no function other than to keep dirt out and grease in for the bearings and seals. I can't believe looking at the thickness of the casting that they work in some form of compression to hold the ends of the brackets apart when the Fulcrum Shaft is tightened. These can be cut from any suitable tube to bridge the gap in the brackets.

Finally, on the part numbers, I attach two close-up photos of the Rear Fulcrum Brackets I showed earlier and these are firstly a bracket from a 1970 Series 2 4.2 E type and the second from a 1992 XJS. As I mentioned, both have a casting number of C20480F but can seen to have completely different drillings. I believe that the casting number - as Richard commented - may not necessarily be the part number as these are Universal castings which when drilled to the individual vehicle have a part number allocated to suit the specific drilling for the vehicle. So in the example of a 4.2 E type the casting which shows C20480F is part number C20481 due to it's particular drilling pattern. I don't believe the casting suffix of "F" means anything special.





The photos of your casting looks identical to my top 4.2 Type bracket - which is part number C20481 - irrespective of the number cast into the back of it.

I trust this assists.

regards,

Dave

[288gto]

The plot thickens

I now have for back to back comparison both versions of the E type rear fulcrum shaft brackets.

The blasted, (silver one) is the later C20481 E type bracket.
The black one is the rarer early 3.8 bracket which is actually narrower.
This would lead me to think that the very early wishbones might not be interchangeable with the later brackets.Indeed the parts catalogue change in part number for the wishbones coincides by chassis numbers with the change in fulcrum brackets.

More research required.

In the meantime here are pics for reference and comparison of the two versions.









Simon

[44DHR]

Simon,
Very interesting ! Good to see the early 3.8 brackets alongside the 4.2 brackets.
One thing it does confirm is the bespoke single central drilling in the early bracket making it handed and the probable change to a more "universal" bracket capable of being used on either side and also capable of being drilled to suit other vehicles. The drillings in both confirm they have the same dimensions and produce the same diff nose angle to the horizontal. They also confirm the shorter Distance Tube in the earlier bracket.
I only have the 4.2 E Type parts book, so my apologies on assuming the wishbones were the same as I was unaware of these early part numbers, but one thing I don't understand is how these two brackets could fit the same Rear Axle Crossmember Assembly or "cage", so now we need guidance on what goes on each ends of these early 3.8 brackets in terms of spacers, oil seals and bearings to see if these could possibly make up the same overall width to fit the cage.
If there is a different part number for the early wishbones, is there a difference in the part numbers for the early 3.8 spacers/oil seals/roller bearers and the inner race tubes that the roller bearings have ?
Perhaps some one has a photo of these early wishbones to see if their inner pivot ends are much wider to bridge the gap to suit the cage ?
Perhaps the thickness of later 4.2 wishbones inner ends containing the two pairs of needle roller bearings were reduced in width to match the increased width of the mounting brackets ?
As you say - more research required !
Regards,
Dave

[Maikel]

Good we are discussing it.

To use my original wish bones and other parts, I would need to have the C16985 and C16986.

Anybody ready to swap with the C20481 Set?

Thanks
Maikel

[44DHR]

Maikel,
If you have some early 3.8 E Type rear wishbones, is it possible that you could confirm the inside and outer dimensions of the pivots where they attach to the fulcrum brackets, or even better post a photo so we can compare these to the 4.2 E Type rear wishbones to see if these fit the same E Type Rear Axle Crossmember, (Cage) ?
Regards,
Dave

[Maikel]

Hello Dave,

I will do as soon I am back in my workshop next Friday..
Unfortunately I do not have the later wish bone so I can only measure and take a picture.
By then I should have also received the later brackets and will place them in one picture to snow the dilemma.

Maikel

[Maikel]

Hello again,

I need to add some more pics to this issue and hope somebody has a clou.

Having 4 different diff brackets, I wonder what belongs to which model.

My knowledge so far is. the shorter oat the bottom and the top is for E Type.
But what are the other two for?
The gap between the 3 similar looking brackets is app. 50 mm, 60 mm and 70 mm
The gap between on inner and the opposite outer hole is the same at all brackets.











Thanks for your contribution
Maikel

[Hugo]

Dog bones. That's what they're called, isn't it? I saw some advertised only the other day. It stuck in my mind because I didn't know what they were. Unfortunately what didn't stick in my mind is where I saw them. It will come to me.

[Hugo]

Found it. An ad in the E Type club mag; Dennis Welch motorsport - www.bighealey.co.uk . "Iron" @ £240 + VAT, or aluminium @ £295 + VAT.