MGB Roadmaster

[Moderator]

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...)
http://www.britishv8.org/Other/LanceLaCerte.htm

[BlownMGB-V8]

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

[Citron]

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

[BlownMGB-V8]

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

[MGBV8]

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.

[castlesid]

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

[BlownMGB-V8]

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

[castlesid]

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.

[BlownMGB-V8]

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

[castlesid]

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.

[BlownMGB-V8]

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

[jimbb88]

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.

[Bill Young]

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.

[BlownMGB-V8]

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?

[castlesid]

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.

[BlownMGB-V8]

Thanks Kevin, lots of good info there. Afraid I don't have a fax, the blasted things break and seem generally unreliable so I try to make do with email.

As far as the metalurgy goes I do have some practical knowledge about it, enough to know that a reliable repair would be real tricky. The likelihood of a failure from the damaged area is actually pretty small the way it is assembled, but certainly greater than with an undamaged part. I think we should keep looking for one.

Tie bars: I'm with you on that, absolutely. For the torsion braces though (anti-climb bars) I think crude vector analysis allows us to control the rotation in two separate axis rather than combining them with one link (per side) across 2 or three planes (running at an angle as you described). It seems simpler (to me) and easier to understand and implement, if we take counter-rotation around the drive shaft and separate it from counter rotation about the half shafts. That way we can control the rotational motion about the half shafts via the forward pivot of the triangulated LCA, (although this could arguably induce squat or hop - I don't think it should if the pivot points are on the same centerline) and control rotation about the drive shaft via the top mount if the special top bolts are adequately strong and perhaps with additional small braces from the outer ends of the top mount  to the rear tie bar if not. Admittedly it is not as elegant in terms of engineering by combining functions but at least that way we don't have to deal with calculating the correct angle of the strut in 3 axis. Which I really don't want to do anyway. I guess you could say that the stock cage also has the lateral braces built into the cage itself which then puzzles me as to why the anti-climb braces need to be angled outwards.

But let me reassure you about the top mount. Either the top part of the cage will be used, or a stronger counterpart fabricated instead. The planned fabricated part will be tied into the shock and hanger strap mounts with isolator mounts and have mounts for the coil overs so it should duplicate the stock cage in most respects, but I won't know the exact configuration until I start building it.

I hadn't given any thought to the ride height, that's something maybe we can try to address next weekend. Certainly it influences many other decisions, and is largely decided by factors currently beyond our control such as final engine weight and front suspension configuration, but we can make an educated guess. We also need to accurately measure driveline angle.

Use of the car? Ah yes, that is likely to be quite varied. It is likely to see duty as a driver, show up on a road course here or there, be entered in a few autocrosses and even make a few dragstrip passes. It's basically up to the person in custody of the car at the moment. So we should consider all possibilities as far as it's feasible to do it. Odds are it will end up being a little over built, but that's better than the other way around.

Jim

[castlesid]

Jim,

I may be able to get an old scanner working and hopefully be able to post the drawings and info directly on to this board possibly later today, if I can get my son to help gettting the scanner linked to the computer.

I'm sure you are going in the right direction and some extra visual info may assist.

Kevin.

[Citron]

I will be leaving in the  morn for Alcoa and than Florence.  Anybody who wants to help tear down the 455 and other stuff, I'll invite you to Jim's.

Steve

[BlownMGB-V8]

Steve I will be looking forward to your arrival. Hopefully it won't rain any more and the drive to the shop will stay dry, I'm working on getting some gravel for it but it hasn't happened yet. I got the EIN number from the IRS and gave it to the bank, and there's some paperwork I need to give you. We'll tear town the 455 and see what is needed on it, and maybe if we have time after that we can do a little sheet metal work, or calculate the axle lengths that we need.  Or, I guess we could just sit around and drink beer.

Jim

[Citron]

Sounds like fun.  Will not get there till after 6 pm.  Traffic may make it later. Will leave here at 8 am and should see Dan about 1pm.  I think it is about 4 hours from there to you.

Steve

[BlownMGB-V8]

Hey Kevin, maybe you can answer a question for me. If we assume a stock ride height for a '69 MGB-GT would you be able to tell me how much space there should be between the Jag differential top mounting pad and the floor area of the car above it? (disregarding the differential bulge that is in the panel) That would really be a big help.

Jim

[castlesid]

Jim,

Sorry I've been busy this week and not been able to get the scanner working, the socket for the USB lead appears tp be damaged.

Re you query re the relationship of the diff to the body of the car, frustatingly one of the documents I was going to send, is a diagram covering this subject, tomorrow I will try doing close up photos of the stuff  I want to send you.

The diff height is calculated by setting the rear suspension at its optimum ride height, ie where the geometry of the suspension will be under load and then calculate the required ride height of the car, say 14.5"-15" centre of hub to chrome strip and the difference between the diff and its mount position should be clear. The standard ride height for the suspension itself ie the distance between the coilover top and bottom mounts should be 11.75" under load. you can substitute a piece of angle iron with holes 11.75" apart.. Your problem is going to be that you don't have a top mount position at the moment to use as a reference.

I'll try and send the digrams tomorrow which should help to clarify what i'm trying to describe.

Pic may help to explain what I'm saying.
Hopefully will send other docs tomorrow.

Kevin.

[BlownMGB-V8]

Thanks Kevin but I don't quite understand. At normal ride height shouldn't the half shafts be horizontal, or parallel to the ground? That would seem right to me. (thanks for the measurements btw) Preliminary measurements indicate that the half shafts and LCA's will need to be shortened approximately 4" on each side. Certainly not difficult, but as I've noticed that the two are not quite parallel it would seem that taking an equal amount out of each one would change the camber. Would that be correct?

We've made great progress so far this Roadmaster Weekend. Steve and his brother Eric have been here since Thursday evening and we've got some really interesting information for everyone concerning the engine. I'll give a more complete report later, perhaps Sunday. But as a teaser, we weighed the short block and it came out at 300lbs.

Jim

[castlesid]

Jim,

Sorry if I wasn't explaining it very well, if I was standing next to you with the car it would be very easy.

The angle of the wishbone should angle down from the diff outwards as per the pic of the red car, whether shortening the wishbones and drive shafts equally will have any effect on the geometry I don't know, but this seems to be the accepted way of doing it.
I would have thought that the geometry would remain the same at standard ride height but whether there would be any change under bump or rebound would need calculating,

I have attatached the documents I previously mentioned which hopefully you can read, if they are not clear enough I could re shoot them in high definition so you can blow them up, if you save them to your my pics folder, just let me know.

Re the setting of the diff position, you could mock up the suspension using a bit 3" x 2" timber and use that tomount the diff and the lower wishbone with the suspension height set with the angle iron as suggested,you can then measure from the hub to the chrome strip position to see where your diff should be sited.

Kevin.

[castlesid]

Jim,

Sorry posted a house plan by mistake.




Kevin.