IRS design problem

[Ant]

I have just discovered a design problem with the mounting of the T/Bird spindles on the end of the bottom arms, which have 5/8" spherical rod end joints, one on the outside of each end of the spindle, then a bolt with a small sleeve going through the joint and down to a smaller size for the sleeve in the standard Ford rubbers. Then the perceived problem starts the bolt just has a nut on the inner end against the inner metal sleeve, so the other side of the rubber bush is unsupported, I can put a ring spanner on it and lever it and movement occurs (I would wonder what it would be like under heavy load!)
The rod ends are for adjustment of camber/toe in toe out, as the rest of the suspension is urethane bushed, and the top arm has no adjustment available!
I can only see one option that might be feasible, which is to run a long high tensile bolt all the way through the two rod ends and spindle, to try and stop the individual shortish bolts wandering in the rubbers, and for good measure make a nice fit sleeve to go in the middle and bolt solid? Then fit a urethane bush kit to reduce movement further bearing in mind this car is mainly for the road. I see some cars have four lugs welded on the arm so the rubber joint
is supported both sides, maybe I am being to critical until I test the car, but I have huge reservations on this design - help.
Any suggestions gratefully appreciated - Ant

[Bumpster]

I wish I knew enough about rear suspensions to know what you are talking about, especially since my car will have an irs from a Lincoln Mk. VIII, which is similar (or the same?) to yours. That brings up this question: Is there a GOOD book, or preferably a video, that really explains rear suspensions, and the differences between the several choices we have with these cars? I need good pictures with good explainations. The few books available at local bookstores haven't been much help.

Bumpster

[Bart Carter]

There is a place offering poly bushings for Ford IRS. Vintage Performance

Check to see if they have the right ones for you.

[Ant]

Bart:
Thanks for the tip to go to Vintage Performance, had a look - good website!

I have had a talk to the manufacturer he suggested I go to solid bushings in the upright, due to the fact that my setup which is (Bumpsters posting) Lincoln or T/Bird not really sure on that, but it looks like all the others I have seen on the forum!

The problem I have is that the rubber bush has nothing on the inside but the nut to secure the bolt, no flange or locater, so the bolt goes through the rod end outside the upright then into the bush and thats it - big flex area, urethane aint going to make any difference unless both ends of the bolt are supported, hence make the upright solid with alloy bushes, but the top and bottom inners are good wide urethane bushings!

I was going to try and fit a long bolt so as the rod ends were on the same plane, a bit like the Jaguar IRS, but the CV intrudes in the middle - bugger!
I am also going to upgrade my RM10 Rod ends to chrome-moly/teflon items, and run bigger bolts than the metric OEM items, so hopefully this will stabilize the system?

Ant

[427SSSS]

"Currently building an Almac Cobra, no engine yet!"

Ant, what is an "Almac Cobra", give us details, pictures?

[Richard Hudgins]

Hi Ant,

JBL uses the Ford alloy upright. If you go to Chassis photos you will see some detail photos of the rear suspension and the mounting methods.

Jbl replaces the rubber inserts with urethane inserts and captures both sides of each leg with the A Arm.

I would not trust the single shear mounting that you are describing.

[Ant]

427SSSS
Its a New Zealand made car by Almac Cars in Wellington.

Richard:

Not sure whether I like the single mount on the outside but I am hoping by solid bushing the bottom eyes, as long as the upright is strong enough, it should take it. The manufacturer isn't concerned about, but its questionable to me!

Ant

[John A. Simpson]

I think you'll like the solution these people came up with, looks very professional and well executed.

http://eaglewoman.simracing.dk/cobra/index.htm

Look at their spherical bearing conversion link

Good Luck

John

[mr bruce]

The settup mentioned above is still the single strut upper, not a proper A-arm design. Only a matter of time until the hub carrier's fatigue cycle is reached, and then possible breakage, maybe with disasterous results.

[Ant]

Hi Richard

Thanks for your post and your suspension looks very nicely designed and built!

As I intend on solid bushing the bottom eyes, using chrome moly teflon, top of the range 5/8"X3/4" Rod ends that are rated a lot higher than the steel items, as mentioned on the outside, and of course using high tensile 5/8" bolts this should be strong, but I realise that if there was a flange on the inside of the upright then that narrows the loading of the upright down somewhat, or as you put it alters it from a single sheer force to better location, I suppose the question is how strong are the uprights and over engineering is better than under engineering. Maybe I could fit a brace on the inside between the eyes that is bent slightly to clear the CV Joint, but I don't reckon it will do that much!

It would be hard to change the outside of the arm to your method, but I wouldn't have any adjustment for camber and toe in!
My inside bushing is quite wide apart urethane and fitting rod ends there isn't going to achieve much apart from a camber adjustment.

Unfortunately I haven't a digi camera, but I will try and borrow one and post some picts

Ant

[Richard Hudgins]

Ant,

The upright pickup points need to be in captured in double sheer.

Single sheer will not work for long. The material of the upright is quite brittle and will not stand Annular loads.

Also, the stock bushings will migrate in the mounts and are too soft for your use.

Put the mounts in double sheer as shown in the photos that I posted before.

Please listen, this advice is from experience with these uprights and much testing. JBL does it this way for very good reasons.

.Ant, Please note that I posted the above before I saw your post. Internet timing, Hey?

I think that you can make your system work if you do a couple of things.

1. Make hard urethane bushings for the pickup points (90 shore A or above)

2. Have the inner bushing have a flange that stops the migration of the bushing through the pickup point.

Note: I still do not like single sheer on this upright, it is a 356 casting and does not like to put in a "bend" loading.

I can send you photos of the system that JBL uses if you would like. It would be much better than me typing forever in an effort to explain.

Let me know if you would like this

[Ant]

Hi Richard

Thanks for your advice, I am quite annoyed that I have spent a considerable amount of money for a rear end that was supposed to be an improvement over the older Jaguar type, it certainly is lighter as claimed!

I have looked at your upright mounting through the link in your post, but would appreciate looking at a couple of photos if you would like to email them to me:

ajnewton@xtra.co.nz

I see on the back of the bottom arm that you have a nice track arm for toe in adjustment and as pictured the top A arm does the camber adjustment, all this keeping the upright mounted as well as possible!

1. I could try and modify the bottom arm, which looks almost identical to yours apart, from urethane inners wider apart by making the back brace adjustable with rod end, and flange the lower bushings properly!

2. There aint a lot of room to fit a top A arm, he has make a strong single strut, with a very wide inner bush as mentioned in earlier post, that when I lever it there is hardly any detectable movement. I will have major difficulty doing the top!

I managed to get a digital camera from my wifes boss today, but it is a new fangled one without the floppy disc and only had a connection for PC Computers, so I cannot download it on to my old Macintosh G3!

One thing is for sure I am going to end up with peace of mind on this so when I go out to the classic meets 2 -3 times yearly I dont have to be conscious of a potential weakness, but having said that the car wont have BB power and I dont intend on running slicks - at this stage!

Kind regards Ant

[Maxstang]

Mr. Bruce, I'm not sure I understand your answer concerning the FFR IRS setup. Are you saying they are eventually doomed to fail? I'm interested as I'm considering using their IRS for a project.

[Ant]

I have found a way to fit lugs and give my T/bird upright support each side of the lower bushings, but there is one questionable piece of engineering, I have the rod ends on the outside of the Upright mounting plate where the outer flange would be, so I am leaving that and welding a 5mm flange on the inside to make the inner flange as JBL and FFR do, but with a neat horizontal slot to match the bolt/rod end travel, you might say silly but I can still adjust camber and toe in, that will give me double sheer as the flange can't move and if I secure bolt shaft with machined washer with slot lugs, mind you I will have to change that when I do an adjustment, but its a way out of my problem,
Having said all that no one probably knows what I am talking about, I will show some photos soon!

Mr Bruce a well made single top arm which has a wide bush area can provide quite a bit of rotational control/side loading control, and help to support the bottom bearing areas, I would be very surprised to see it break even under hard circuit use. Mind you put some sticky drag slicks on it BIG BLOCK cubes and 7000rpms, and anything can happen. There is one word I have to remind myself as being a perfectionist once I recognise a so called grey area of concern is COMPROMISE, even motor manufacturers do this all the time.

I will feel better when I have made the bushes and redesigned the arms.

Thanks for listening to my problems guys - Ant

[mr bruce]

will the hub carrier fail? Eventually. When?, testing is being done as we speak, to determine when.Aluminum behaves very differently than steel. Look at the panic raised when they found out you don't use aluminum rod ends. Why is there a horizontal shock mounted to the upper strut? To control fore/ aft movement under acceleration/breaking, and control wheel hop. That fact tells you rite there that something is moving. The stock T-bird strut has wide bushings and a channel type design, as Ant has suggested. But ,the T-bird was designed to be a regular passenger car, not a "race car" with big sticky tyres, and big brakes, and boocoo horsepower. There was a double fatality accedent a month or so ago, was that car using the single strut type upper? Hope the investigators checked the hub carriers.

[Ant]

mr bruce

This hub carrier isn't over engineered as you mention, and the mounting is all important, but two things here for general use and a few laps, the standard rear brakes should be okay, if not I will uprate them, but I have run some quick laps on no better rear brakes than these, the front brakes are a different story, I have circuit use 48 fin curved vein rotors with large Billet calipers!
The Cobra is much lighter than a T/Bird or a Lincoln, but obviously there is a lot more power and maybe G Forces in the Cobra, so how strong does the Hub carrier need to be?

I am now modifying my bottom arm for much better mounting, as similar to JBL, the top arm is questionable whether its okay or not I would imagine that with the better bushing and the single "wide" bearing strut it has! - that it would move a lot less than rubber bushes, if I am concerned about it I could run a radius arm back on to the upper rear chassis rail for horizontal loadings!

I guess some people think as my supplier does that the upper hub carrier bush is for camber or in and out forces, but I think the upper bush takes fore and aft plus some rotational loads!

Thanks Ant