MG Sports Cars

Hi Jim, Your quite right about the lower radius arm mainly taking lateral and vertical loads as the base isn't very wide for all the fore and aft loads. That is where the trailing arm comes in to maintain the rear wheels in the correct fore and aft location against acceleration and braking forces. I think the tractive effort as the tires turn will still be taken by the differential mounts with the hub carrier and its lower arm acting purely as a bearing and a means of maintaining the wheel in the correct position. The reason for this is I'm hoping you can get away with the lower trailing control arm alone as there may not be enough room for an upper one as well.
I remember driving a very tired E-type many years ago which would change direction left or right depending on whether you accelerated or braked accompanied by strange clonking sounds from underneath - perhaps the trailing arm had rusted away from the body!! Cheers, Bob.

Well, here's what I'm thinking Bob, as the thrust of acceleration is applied to the trailing arm the point at which it attaches (the upright pivot pin) acts as a fulcrum or pivot for the load that is applied because the force is applied at the tire contact patch, rather than 6 inches higher where the trailing arm is. In other words, there is a 6 inch long lever arm applying the load to the trailing arm pivot. This creates a torque load on the lower control arm equal to the axle torque divided by the radius of the wheel/tire and multiplied by the distance of the pivot above the road. In our example, resulting in 1500 ft/lbs of torque applied to the lower control arm. Attachment of the differential is irrelevant in this case because we are dealing strictly with a linear acceleration load at the trailing arm which is then translated into torque by the offset between the point where the load is applied and the point of rotation. My numbers could be off but the transmission of forces is accurate I believe. Your idea of dual trailing arms is a good one as that would control the torque thus created, in effect moving the rotation axis back to the center of the hub or depending on the geometry of the trailing arms allowing it to be located where it would do the most good. I think that is the basis of a good four link system on a live axle, though in that case it has to deal with rotational loads on the housing also. I don't claim to really have a handle on this, it's been a long time since I studied force vector loads and I'm plenty rusty. Plus there's a lot going on back there, much more than just rotation and counter rotation. However, just taking the basic geometry as a good starting point I think if we do no more than transmit the rotational force created by acceleration to the body of the car we should be able to just about eliminate wheel hop. But the next question is where it gets tricky. If we do that with an additional linkage will it cause the body to go up or down under acceleration? I think that depends on how and where it is attached.

Jim

I found boxes for 2 wheels & will try to get them to the UPS guy this week.

Thanks Jim, that will help a lot.

Guys, somebody needs to step up and find us a wheel flange (photo in above post) as soon as possible. I can buy one but it'll deplete our funds by probably about $75 after tax and shipping. Doesn't anybody know some Jag people who might have a spare lying around?

Roadmaster weekend is coming up in another couple of weeks (Dec. 1 and 2). There well be several people here that weekend. Steve and Margaret are bringing up the 455 engine, Pete Mantell mentioned that he'll try to contact Rick and Dave and see if the three of them can run over, Dan B is coming in, and several local club members are planning on coming to the BCC-S meet Sunday afternoon which hopefully will be a good opportunity to make introductions. A few more weekends like that and we may be able to achieve critical mass.

New shop equipment is on-line.

The new buffer is now operational, it is a 15hp 3 phase large frame motor with a 16" diameter 2-1/2" face buffing wheel. I've tested it out on some stainless I'm using for the control set on my motorcycle and it works well, though I'm not sure I have the right compound for it yet. Very stable and vibration free though and impossible to bog it down. I've nearly completed the foot pedal for the TIG as well and hope to finish it by next month.

Still have a small bracket, the cord and a protective cover to do and then attach the cylinder holder to the welder and wire in the solenoid, pedal and hook up the torch, but with luck that'll be ready for the weekend. We still have some trimming and straightening to do before we need it. Incidentally for those of you who show up, all of the shop equipment is available for your use while you are here so if there's something you need to take care of on your car you can do that. Just another added incentive, courtesy of Blackwood Labs, LLC.

That's some buffer Jim, you could buff a brick to a high gloss with that thing. I like the TIG pedal too, nice idea to use a bass foot pedal, shoud give very good control with a good switch/rheostat attached. I know I promised another contribution to the funds. It will come, but I got bogged down a bit with the purchase of another driver last month and the associated license and title fees. Definitely by this time next month you'll have it, that should make the hub problem easier to overcome.
You mentioned redrilling the hubs, what bolt pattern are you going to use? I thought the Jag sedan bolt on pattern was the same as Chevy and you've already figured out how to do the front hubs on your car. I'd think you'd just use that pattern with the much larger wheel selection it brings.

Indeed, that's the coolest buffer ever.

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I'm reading these posts about IRS... but I keep thinking "Why not deDion?" In theory it could be quite lightweight. Tomorrow I'm scheduled to get underneath a Rover 3500S and photograph its one-of-a-kind "telescoping deDion" rear suspension. It shares a few features with the Jag IRS... inboard disc brakes for example. Some photos are included here (although the ground restricted camera access...)
[www.britishv8.org]

Thanks Bill. Since Jim Stuart has been gracious enough to donate a set of wheels I think we'll just stay with the stock lug pattern, plus it's easier to drill the rear hubs to that pattern than it is to change the front hubs to the Jag pattern. As for the DeDion, not a bad option but again I think it'll be easier to go with what we have now and probably easier to package into the available space.

Call me a penny pincher if you like but I'm very much resistant to the idea of going out and buying a replacement hub when I just know there has to be one sitting in a corner somewhere that could be donated. Same with the tubing, why buy it if it can be donated. I just called Dan B and asked him to check with a buddy in S. Charleston, WV that some of you may know, Dave Chenoweth. Dave used to be pretty heavily involved with Triumphs and Jags and I'm hoping he might still have some parts lying around even though he moved on to BMW's several years back. If I could persuade a few of you to make similar inquiries I'm sure we could turn up something.

I just got a check in from Robert Sisk in Conneticut for $25. Actually I guess I've had it since the 1st of the month but I had inadvertently set a laptop down on it when it came in. I can tell winter is settling in when I start doing that sort of stuff, sorry to not give you credit for it sooner Robert. That brings our total up to $377.40 and I'm saving up for tires and coil-over shocks so that our "roller" will actually be capable of rolling by next summer's meet. I think that explains my reluctance to just buy a hub. As for the tubing, we will need small quantities of some specific sizes, most importantly, a few feet of 1 x 1-3/4 rectangular tubing with a 3/16 to 1/4" wall. 4 or 5 feet sould be sufficient. This is needed for the main differential support. We will also need some heavy wall round tube for the halfshafts but I'm not sure of the size and may have something that will work. Since the stock shafts are center drilled the easiest way to shorten them is to put them between centers and turn the shaft to fit the tube ID and then cut and weld using the tube as a sleeve. This is probably the most common method used on Jag half-shafts. I probably have most of the other needed materials on hand for fabricating mounts and such but I will need some isolator bushings and haven't decided on the configuration for those yet.

Jim

All,
The 455 is now at my house in SC. I haven't gotten a ggod look at it yet, but will over the weekend.
Thanks to Allen for the donation and to my brother for picking it up. It rerally was not on his way, but 500 miles due south.
I will take a look at it and get it re-situated n the trailer for the trip up.
The stuff I pick up in TN need be be in boxes or something since it is an open utility trailer. Don't want anthing to slide off on the way to Jim's.
Looking forward to seeing some of the other crazies in Kentucky.

Steve

What do you guys think about the idea of using both the forward and rear spring mounts as attachment points for radius rods for the Jag upright? I know it would introduce some twist, haven't tried to work out how much yet but it might be little enough for the UHMW bushings to handle. A bracket would have to be welded to the top of the upright. Looking at it all upside down gives you funny ideas. What if the top bracket could be linked to the forward spring mount rather than using the bottom pivot? What if both the top and bottom were linked to one pivot point on the body? What if the standard radius rod to the front spring hanger was used but then a brace to the top of the upright was attached?

Well, none of it sounds really very good, binding is sure to occur. In fact, some binding with the standard radius rods is inevitable. Food for thought though. I'd like to add a triangulated upper control arm personally, but with the fixed length half shaft that's pretty tricky.

Jim

Moderator Wrote:
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> I'm reading these posts about IRS... but I keep
> thinking "Why not deDion?"

The first, and only, time I saw a deDion IRS it was attached to a vintage Lotus 7 race car. I looked it over real hard. I could almost see it in my MG.

Jim,

As suggested in our earlier discussion keep it simple and use the triangulated lower links, once you have the diff location finalised just run a rod through the inner wishbone pick up points to the rear bulkhead of the passenger compartment and you then have the exact location for the inner pick up of the triangulated link. You will probably need to relocate the battery to the spare wheel well but thats not much of a problem

If you use straight radius rods from the original leaf spring front mountings, you will have bind in the suspension and very undesirable bumpsteer unless you build a lot rubber into the link and this will defeat the object.

If you are concerned about the torque reaction on the upright, I have seen a small Watts linkage set up on a Cobra replica that used the Jag rear end, but this utilised there own cast uprights, you could probably still do it by adding a support bracket on top of the jag upright and run the watts linkages for and aft to the chassis rails.

I think the kit manufacturer was Contempory Cobra but not sure they are still in business.

Personaly I would not worry about a top link as the works Jag XJ12 coupes ran without them and the only weak link was the failure rate of the inner bearings which took all the lateral force of the heavy XJ12C and the grip obtained with the wide full race rubber.

Also I wouldn't be too concerned about a little squat, as this is good for traction off the line and grip out of corners.

Regards,

Kevin Jackson

Thanks Kevin, I recall that discussion.Please bear with me, the winter months aren't my most imaginative, or productive either for that matter. You are quite correct of course. The simplest solution is just to axe the boxes, put a torque arm on the LCA that carries the pivot axis forwards to the bulkhead for better torque control and run a diagonal brace to the outer end of the LCA for fore/aft control and let it go at that. Then if the UHMW bushings don't control wheel hop we can put timkens back in it for more rigidity. Use of a fairly stiff set of bushings for the diff should help too.

Jim

No problem Jim, I tend to hibernate when it gets below 5 degrees C.

Just to clarify what parts you will need.

Top and bottom Plates for the diff mounting and lower location points
Two link straps to tie the front and rear wishbone pivots together. Previously done by the cage.
Two triangulated radius arms
Two anti climb bars located at the diff end on the bottom plate and the chassis end angled up to the chassis rails and not to the front spring mounts as this will not prevent the torque reaction.

I realise that you want to make as much of this as possible but most of these bits are quite cheap to buy.
Make sure you use the correct bolts for the top mount of the diff, they are special taper.

If I were you I'd get one the catalogues from one of the Hot Rod companies that use the Jag rear end and that would give you a clearer picture of what you need. I could probably Fax you some info I have from a UK hot rod company if that would be of any help. I don't have a scanner so can't post it directly to the BBS

Kevin.

Thanks Kevin, I can use all the help I can get. By the anti-climb bars do you mean the braces that go from the forward corners of the lower pan to the floor area of the car? I was thinking that I could incorporate that into the LCA by extending it forward and tying the front pivot to the floor/bulkhead. I'll take another look at it tomorrow.

Jim

Jim

The anti climb bars for want of a better name, go from the bottom plate on the diff and are angled up and out to the chassis rails forward of the old lever arm damper position.

If you don't have a Fax I can try and photograph the relevant pages and post them here but not sure if they will show enough detail.

Kevin.

I appreciate the effort Kevin. Didn't have much of a chance to look at it today, but we did have a pretty good discussion about bracing the diff earlier, having to do with it wanting to rotate on 2 axis simultaneously. I'd guess that's the function of the braces you're describing. Is the bottom plate really essential? I was considering doing away with it.

In other news, Jim Stuart shipped us two wheels of the set he has for us and they got here a day or two ago, apparently in good condition. I've not had a chance yet to open both boxes but I'll take a photo and post it, just not tonight. This means we can determine track width and begin narrowing the axle.

Jim

You should have the first pair of wheels- sent UPS last Thursday. As soon as I find some more boxes, I will send the rest. I have a bunch of lug nuts and washers I will send as well.

Jim, I was looking at the photo of the rear hub that's damaged. If we can't find another at a reasonable price, what's the chance of building up the chipped area with weld and then turning the ID and OD back to size in a lathe? It doesn't look like the spline area is involved, so it should be a realtively easy machining job and certainly strong enough to support the inner bearing race.

Jim, in case I forgot, thanks for the wheels!

They look pretty good and they haven't even been cleaned up yet!

Bill, in looking at the broken hub I think I would feel better about using it as-is rather than trying to weld and machine it. That's right where the timken inner race rides so it would be hard to get a proper match after welding, and the race itself will bridge the missing area (shown at the bottom of page 1). Kevin would you care to comment on that?

I mocked up what I had in mind for the LCA. Bear in mind that those are not necessarily the materials that will be used, nor are they in exactly the right positions (the battery boxes will go), it's just an approximation for illustrative purposes, the idea being to extend the forward pivot in line with the existing ones which both are retained and run a rigid diagonal brace to the outer end. This should also take care of any reactive torsion at the differential on the transverse axis, leaving the reactive torque on the longitudinal axis to be dealt with by the top mount. Your thoughts Kevin?

Jim,

Re the damaged hub, I was going to suggest the same solution as Bill Young but do not have enough knowledge of metallurgy to know if this is a satisfactory solution, I think I would keeep looking for an undamaged one. Another thing to check very carefully is the alloy uprights themselves, there have been cases of them with hairline cracks so give them a really good clean and inspect carefully.

Re the diff, you seem to be going in the right direction with the triangulated LCA's but it is essential to use the tie straps on the front and rear wish bone pivots, this job was done previously by the cage.

You are also still going to need the anti-climb bars which fit onto the front tie bar and then up and out to the chassis rail, otherwise the diff will try to rotate under torque loading with dire results.

You will need also to address the required ride height of the car, as this will determine the height that the diff is mounted in the car to maintain correct suspension geometry.

I'm still a little concerned that not using a crossmember is going to cause problems in the location of the diff and not provide sufficient structural strength, and not giving you the top mounts for the coil spring dampers.

Apart from going bloody fast what do you see as the likely use of the car, road,drag, low flying whatever?

I am going to get the relevant pages from parts catalogue and some other illustrations copied, if you have a fax no. let me know, otherwise I will post it to you.

Kevin.