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more jag rear questions
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bcal
1000RPM



Joined: 04 Feb 2021
Posts: 1012
Location: The Shire, Sydney

Posted: Mon Jun 02, 2021 3:41 pm    Post subject: more jag rear questions

There has always been some controversy about releasing the jag rear from its cage and mounting it solid to the chassis.

The main concerns that I've heard are along the lines of suspension bind due to incorrect location of the radius rods and a lack of anti squat geometry.

So if it is best to keep the jag in its cage what are the pros and cons (apart from looks) of mounting it complete with cage in a model A chassis?

Also has anyone run a tape measure around a Ford double wishbone rear end? (not the blade type)
I saw one at the Sydney motor show a few years back and it was very interesting from a rodding viewpoint.

PS: jdaley, how did you get on with your own jag rear conundrums?
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choco
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Joined: 11 Jun 2021
Posts: 1066
Location: Queanbeyan, NSW (on the ACT border)

Posted: Tue Jun 03, 2021 7:42 am    Post subject:

My Sister's partner, Greg Redman (Dragens), is puitting a Jag rear in his 29 A coupe as we speak. You should email him on arnie@effect.net.au and ask your questions. He'll be happy to answer them for you and I can go around and take as many digital images of the construction as you like.
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old32
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Joined: 05 Mar 2021
Posts: 565
Location: at work in Melbourne

Posted: Tue Jun 03, 2021 9:22 am    Post subject:

Looks like I'm going to have to clean up my garage, somewhere in my collection of mags etc I have the factory Jaguar setup specifications for a Jag diff out of the cage solid fixture . These were from the factory for use in the Jag racing cars in England during the late 60's early 70's I think.( Carps, you may remember, Brian Clague brought them back with a diff years ago). I'll post them if I find them.
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a25Chevrod
Just Idling



Joined: 15 Sep 2020
Posts: 158
Location: Gympie, Queensland

Posted: Tue Jun 03, 2021 3:13 pm    Post subject:

I run the Series 1 Jag arse in the ute without the cage and couldnt be happier with it. I fabricated new trackarms to go back onto the chassis rails from 19mm bright seamless round tube and used the original Jag Front bushes on it to allow full movement. Was concerned majorly concerned in the buildup about spring rates at the back as the pickup is half the weight of the Jag, but as I've run a hardwood tray over the back to aid traction Razz the ride is as close to ideal as you could hope for. Its firm enough that you can throw to car around like a go-kart but still comfortable cruisin.

Even bits are quite reasonable when rebuilding the Jag Rear end. (IF you dont buy genuine ) If you can I'd even recommend using the Jag front as well.

As a set , they work well together, just ask any Jaguar owner. Incredbile Brakes, Power Steering with amazing adjustments in the rack mounts and the width between the towers is heaps more than an early Holden front. I never touched the Guards on mine whereas a mate used a HR front on his and had to severly bubble the guards ove the towers
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jdaley
Just Idling



Joined: 23 Sep 2020
Posts: 111
Location: Melbourne, Australia

Posted: Tue Jun 03, 2021 11:14 pm    Post subject: jag rears

We are still in the fiddling stage. We have cut the cage up so we have no chance of using it again, but I am confident with all the examples on the road we should work it out. We have other priorities in the last week or so getting bthe sidecar ready for Historic Winton. Now its over, the trophies are in the cabinet we play with the rod again. But Tyson also has year 12 matters to deal with.
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GBS
200rpm



Joined: 18 May 2021
Posts: 251
Location: Central Coast NSW

Posted: Wed Jun 04, 2021 12:09 am    Post subject:

Brett

In Herb Adam's book on chassis engineering he lists the advantages and disadvantages of independent rear suspensions. He says the main advantage is a smooth ride due primarily to the reduction in unsprung weight which allows the wheels to follow the contours of the road more closely.

The disadvantages are they are more complex and more expensive to produce. This causes manufacturers to simplify the systems to reduce costs and this often results in "a compromised design which does not provide optimum geometry or deflection characteristics".

Another major disadvantage is the lack of ability to deliver power to the ground because only small amounts of anti squat can be used so " high powered cars without a rear weight bias will have problems getting optimum performance and handling".

He says of the Jaguar, it suffers from camber control problems and deflection steer problems because any looseness or wear in the lower control arm bushings will result in loss of toe control. They also experience torque steer problems which become worse with high powered engines and sticky tyres. He said it feeds most of the suspension loads into the differential so any looseness in the side gears can result in loss of camber control. The rubber mounts can also deflect allowing the whole suspension to move around in the car.

He said they are adequate for normal highway driving but not for high performance driving.

This ties in with some of the warnings I have read about them in various rod magazines over the years. Jaguar used them as an inexpensive independent system to give a smooth ride. Rodders want them for the same reason which is why it is recommended they be mounted with all of the stock factory cages, locating arms, rubber bushes and geometry.

Be careful of copying factory racing installations as they are not designed with long term endurance and reliability on the street in mind.

Ted Robinette discussed the installation of a Jag rear in a Humber in the latest edition (issue 163) of ASR. He said the only way to install them is to duplicate exactly the factory installation. He said don't read magazine how to do it articles because they usually portray installations done so you can "see the twirly bits, often disregarding sound engineering practice".

I think what you do with your car depends on what you want to do with it. If you want to drive quietly around the streets enjoying a nice smooth ride then don't destroy these features by getting too far away from the factory design. If you want to go drag racing then there are much better systems.

Regarding the current Ford system. I find it hard to believe that this suspension is not of some use to rodders. I had a quick look at one recently from a Tickford XR8. It was in a Cobra replica chassis that had the body off it. It looked good and although I did not measure it, it did not look too wide. It is about time ASR got off its backside and started showing us some of these new suspensions, engines, transmissions etc. The magazine seems to be centred so far back in the past it is starting to look more like a museum catalogue with each issue. There was a sign of hope recently with Choco's excellent EFI series but it would have been nice if Larry has started EFI reports twenty years ago when the rest of the high performance world started using and modifying it.

Brian
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Brootal
1000RPM



Joined: 11 Jun 2021
Posts: 1365
Location: Sydney, Australia

Posted: Wed Jun 04, 2021 9:01 am    Post subject:

GBS wrote:
...but it would have been nice if Larry has started EFI reports twenty years ago when the rest of the high performance world started using and modifying it.
Brian


Larry was just waiting for EFI to become "traditional" before he started writing about it.

Besides, I hardly think EFI was readily available to the average rodder back then. The only stuff with FI was high-zoot stuff like BMWs, Mercs and Volvos (well maybe they're not that high-zoot).

It's only been the last 10 years or so that EFI has become commonplace on everyday cars and it's probably only been the last 5 years or so that those same EFI systems have become available through the second hand market, wreckers etc.

IRS? Same story. The latest Falcon is probably the only one with a half decent IRS and I can't see too many rodders buying a BA to chop the diff out of it! The Commodore one is crap, unless you like VW look with the massive negative camber once you put some weight on it.

I think Larry has done OK with his tech stuff, but then, I don't really care, I'm a TRADITIONALIST.
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old32
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Joined: 05 Mar 2021
Posts: 565
Location: at work in Melbourne

Posted: Wed Jun 04, 2021 10:06 am    Post subject:

Sorry fellas, I had a good look last night and could not find the Jag racing info.

GBS wrote:


Be careful of copying factory racing installations as they are not designed with long term endurance and reliability on the street in mind.


Brian,
The info I had ended up very close to how rodders currently mount their Jags out of the cage.
The important parts were, as I recall, were triangulating the lower control arms and radius rods. The idea is that the radius rods should go forward as far as possible, the front mount being in direct line with the inboard pivots of both lower control arm bushes, this triangulation allows for a bind free vertical movement of the hub. The longer the radius rod the better, this limits the forward and aft (Like that Choco, a nautical term) movement, in the stock Jag this movement is absorbed by the large rubber donut.
What the Jag specs went into, apart from the above, was the type of bushings etc to be used . In the chassis I constructed with Jim Veale we replaced the recomended sinter-bronze racing bushings with approx equivalent rubber ones. The front ends of the radius rods were level with the front universal.( the rods were about 4 foot long{sorry I measure in Irish}.
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Flatoz
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Joined: 02 Apr 2021
Posts: 1256
Location: Melbourne

Posted: Wed Jun 04, 2021 10:20 am    Post subject:

The A roadster that I had had a jag rear, I think an S type 56" width, with a holden front end, man that car drove and handled the best of any rod I have driven in ( would like to see how bcals goes tho, reckon it would be sweet) the diff was set up with out the cage. the big thing I remember was the bottom arms that go forward ie towards the engine, from memory if you dont get these sorted thats when you start to get into trouble. I have head of people who omit these and then complain that the thing is twitchy in certian applications ( let you guess). Ok we are all hot rodders which too a degree means that we think that anything that the factory did, we can improve on. My suggestion is to mount the diff minus the cage , but make the mounting points as clost to factory as possible. Hey jag spent $$$$ on getting this right, and a ride in a jag will prove it- dont fix what aint broken!. I have some photos of the diff set up somewhere that I took before I sold the car, as that thing rode and handled that good that I swore that If I ever built an A bone I would set it up exactly the same.

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bcal
1000RPM



Joined: 04 Feb 2021
Posts: 1012
Location: The Shire, Sydney

Posted: Wed Jun 04, 2021 12:30 pm    Post subject:

Thanks for all the input so far fellas.

Double wishbone rear ends are really the best way to go. I hate those trailing arms systems as used on commodores etc. cheap and nasty compromise I reckon and not much of an advance on the good 'ol live axle.

Trouble is there ain't many factory IRS's around with this sort of set up and it will a few years before the Ford unit becomes more readily available to us rodders. Why on earth did they go for that blade thing? They tout it as a technical innovation but I suspect it was just cheaper to produce.

The jag and corvette are a bit of a compromise because they rely on the half shaft to act as the upper control arm and I can see why they would be susceptible to torque toe changes. One thing I don't like about the jag is the way that some of them squat excessively under acceleration. Look like a bitch taking a pee. This can be countered to some extent by upping the spring rates which I guess is what in effect happens when you use the original springs in a light car. I hear what you're all saying about using long radius rods and lining them up with the lower control arm pivots to form a triangulated system, this makes good sense.

Maybe the best thing to do would be to use a jag or similar center and fabricate my own double wishbone system. Although if I do I won't be repeating a mistake a mate of made some years back when he built a rear engined sports car. He's an engineer and he built the whole chassis and suspension like it was a racecar. He used spherical rod ends on all pivot points, even used them as ball joints. The thing looked a treat but me with my tradesman like practicality I told him that this may be ok for the racetrack but you don't find none of them infamous NSW pot holes on a racetrack. He got it registered ok and sure enough, a few months later half the arse end flew off after he hit a pothole. It got to the point that he couldn't do more than 40kph on anything but a smooth surface without bending or breaking something.

I guess the moral here is that the auto manufacturers spend billions of dollars in research, employ megawatts of brain power and have over a hundred years of motoring experience to call on, so why do we think we can do a better job than them. I guess that's why we're dumb arse hotrodders.
I don't envy their job though. They've got to design a vehicle for a wide range of drivers with varying expectations and do it all for the lowest possible cost. We on the other hand can tailor our cars to suit own individual needs and expectations, which are usually quite low I might add.

Looks like I've got some thinkin and a bit of research to do before I go much further. Maybe I should just ditch the whole idea of buldin another rod and just slot that V6 into the roadster instead. This'd keep Mrs. Bcal happy at least.

Oh, and on the subject of ASR, I agree with Brian about the need for more up to date tech articles, especially with Cruzin on the scene these days. Judging by the number of cars for sale ads in the two mags Cruzin must be puttin a fair old dint in the number of ASR's subscriptions. I personally don’t buy Cruzin coz I'm not into flames 'n' tats and all that stuff and I've always liked ASR for their tech articles. Maybe Larry needs to concentrate on this already established niche a little more.

And by the way Brootal. Did you ever end up buyin that zoot suit?

Thanks again,

Brett.
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Pep
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Joined: 14 Jun 2021
Posts: 1199
Location: Georges Hall, NSW

Posted: Wed Jun 04, 2021 1:18 pm    Post subject:

I bought a jag diff way back and was toying with the idea of stuffing it under the 34. I got to talking with a guy with a 34 with one at Valla some time after. He was planing on taking his out. Not for no other reason as it kept bottoming out too much. The only option was th "C" section rails to create some clearance for the top arm to move into. I think they look cool under buckets and "A"s without the rear valance and the California rake look....but that's all IMHO.
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Brootal
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Joined: 11 Jun 2021
Posts: 1365
Location: Sydney, Australia

Posted: Wed Jun 04, 2021 1:54 pm    Post subject:

bcal wrote:

And by the way Brootal. Did you ever end up buyin that zoot suit?

Brett.


Nah mate. A little too early for my style. Zoot suits are for Chicanos and people that are into the "Lindy Hop" and other silly dances where you wave your arms around and look like a girl.

I'm more of a jeans and t-shirt kinda guy that when dancing, makes the GIRL look good.

(How did we get onto dancing now???)
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PeterR
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Posted: Sun Jun 08, 2021 2:50 am    Post subject: Solid mounting the Jag diff

The original subframe is so ugly it will have to be given the heave-ho, the only decision you have to make is whether to mount the diff solid or construct a suitable substitute for the cage.

If your sole concern is for best road holding, go solid. You will lose the inherent anti squat and noise isolation of the original. The spring rates will have to be increased to prevent the back of the car sinking under power and this will result in reduced comfort. Care must be taken in the layout of the radius arms or there can be binding problems. This will be avoided if the front pivot of the radius arm and the two inboard pivots of the lower control arm are all on a straight line.

If you are content with road holding that is as good as just about any production passenger car built over the last 40 years, then duplicate the original configuration. Use the old carrier as a guide to make up a neat cross member that bolts to the diff at the middle, and has the original rubber mounts at the ends where it connects to the chassis rails. This can be as simple as a piece of RHS with suitable plates welded to it. Similarly, make up better looking tubular radius arms, but retain the original geometry and rubber bushes.

The factory Jag rearend is a particularly clever design that circumvents many of the problems normally associated with IRS. Because of their similar appearance the Jag is often thought to behave in the same way as the Corvette, and this leads to incorrect statements of the kind below attributed to Herb Adams.

……He said it feeds most of the suspension loads into the differential so any looseness in the side gears can result in loss of camber control. This is incorrect, a double race bearing restrains the inner axle not the side gears.

……Another major disadvantage is the lack of ability to deliver power to the ground because only small amounts of anti squat can be used. This is incorrect when the Jag rear end is used in the original configuration, watch a 350-powered Jag take off at full power.
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bcal
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Joined: 04 Feb 2021
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Location: The Shire, Sydney

Posted: Sun Jun 08, 2021 11:06 am    Post subject:

Peter.
Thanks for your input mate
Yes I would like the car to handle well coz that's what I'm all about. Take a look at my present rod under the members rides posts. I will only be happy if my next rod handles as well if not better than this one does.

So what you're saying is, that I want good handling go for the solid mount with radius rods lined up with the inner pivot points to stop binding. This then would negate the jags inherent anti squat, which would have to be compensated for with increased spring rates.
I could handle that. This rod wouldn't be grossly over powered coz I get most of my jollies round bends rather than in a straight line.

Is there anything to be gained from fabricating a new lower control arm that is less prone to flexing? My thoughts are that if the car is reasonably light and there isn't too much engine torque then the original will suffice.

I'm still just toying with ideas at the moment and I keep coming back to an idea about a really low open wheeled A model closed cab pickup. Styling would be sixties traditional (whatever that means) and it would handle like a cat on shag pile. I think in the end I'm going to stick with the Alfa transaxle and de dion set up because despite their many faults they still offer the best solution to getting a car down real low and they give the car real good balance. If only those C5 Corvette units were available over here.

Now all I need is a decent rego scheme to allow me to build what I want without relying on some 70 year old bed frame for a chassis.
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Posted: Sun Jun 08, 2021 7:08 pm    Post subject:

Quote:
So what you're saying is, that if I want good handling go for the solid mount



That is not exactly what I meant. If handling is your only consideration at the expense of anything else, then go solid. If you are satisfied with handling that produced first and second place out of three entrants at Bathurst, (would have been 1, 2, & 3 if one of the cars had not ingested glass and blown the engine a few laps from the end), then stay with the original. Really, you are talking about wringing the last ounce out of it.

If you go solid with the radius arm pivots in line with the inner pivot points, then the radius arm and lower arm act as a single wide-based A arm and the bending loads on the H shaped arm are minimal. You will have to be meticulous in lining up the pivots or you will induce worse forces in the inner bearings than ever occurs from wheel loads.

Quite frankly I believe there is more effort and precision layout involved in the rigid set up.

If you stay original, the arm can be reinforced by welding in two pieces of 20mm OD tube parallel to the main tube just in from the bearing sockets. This is heaps easier than fabricating a new arm. I have seen them reinforced with a turnbuckle arrangement instead of plain tubes, presumably this was to provide toe-in adjustment by springing the main tube, but I wonder how successful this would be.

Depending on who you talk to, the DeDion is described as having the best features of solid and IRS, or having the worst features of both. Sure they do not have the wheel to wheel isolation of an IRS, but they have a low unsprung mass, no camber problems under varying loads, and are much less fiddly to set up and maintain. An arrangement like the Alpha can produce very predictable performance, and though it might be heavier than you need, the Rover has some clever features.
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