First look at JBL 4.6/BB touring car chassis

[mylesdw]

Originally Posted by Richard Hudgins

Which ball joint are you referring to?

If you mean the spherical unit on the race chassis, I think that we have different opinions about dodgy.

The bearing that I use has a radial load rating of 55,696 lbs. and an axial load rating of 19340 lbs.

I'm sure you know a lot more about this than I, it was a rather flippant remark; I have no doubts about the strength of your bearing but feeding all the suspension forces as a cyclic bending force through the threaded portion of the bearing does make me wonder.

[jmarsey]

Yeah Richard! What were you thinking????

[Richard Hudgins]

Originally Posted by mylesdw

I'm sure you know a lot more about this than I, it was a rather flippant remark; I have no doubts about the strength of your bearing but feeding all the suspension forces as a cyclic bending force through the threaded portion of the bearing does make me wonder.

Myles,

You are absolutely correct. The threaded bit is not at all optimum.

But the loads were considered and the threaded bit is adequate for the application as long as the chassis is subjected to loads below 25G's.

I really doubt that fatigue will become a problem with this joint as the teflon will cold flow and fail well before cyclic material failure occurs.

In other words, the joint will become loose and vibration will occur, hopefully prompting the driver to look into the reason for the above.

There are units out there with >50k miles and the joints are just like new.

I am amazed!!!!!!!!

Really!! You would think that the life would be much shorter.

But there you are.

[Aussie Mike]

Hi Richard,

I changed my tie rod ends to 5/8" teflon lined 4130 rod ends. My main concern about them was keeping the dust and dirt out of them. Do you use any kind of dust cap or seal arrangement on the rod ends in your suspension or is the dust and dirt not a problem?

Cheers

[Richard Hudgins]

Originally Posted by Aussie Mike

Hi Richard,

I changed my tie rod ends to 5/8" teflon lined 4130 rod ends. My main concern about them was keeping the dust and dirt out of them. Do you use any kind of dust cap or seal arrangement on the rod ends in your suspension or is the dust and dirt not a problem?

Cheers

Mike,

I have not seen any wear from dirt as of yet. But these cars are not used in really bad/dirty environments.

I have seen these same rod ends in off road race vehicles and they do not seem to wear excessively but they replace them after every race, therefore poor data about wear.

I think that some of the sprint car guys here will have much more history on these units as they run in the worst conditions for a spherical bearing.

I know that there are a few companies that sell dust shields for the sprint car crowd.

[mylesdw]

Originally Posted by Richard Hudgins

There are units out there with >50k miles and the joints are just like new.

Surely the nature of fatigue failure is that the part can appear 'just like new' right up until the point that it fails.

I guess that some things like this may look wrong 'on paper' but in practice the failure never occurs; The proof of the pudding is in the eating and >50K is a pretty good practical test.

On the subject of 'that' front suspension: why did you go for rocker arms and inboard springs? I always thought that was for aerodynamic reasons on open wheeled cars. Just interested.

[Richard Hudgins]

Originally Posted by mylesdw

Surely the nature of fatigue failure is that the part can appear 'just like new' right up until the point that it fails.

I guess that some things like this may look wrong 'on paper' but in practice the failure never occurs; The proof of the pudding is in the eating and >50K is a pretty good practical test.

On the subject of 'that' front suspension: why did you go for rocker arms and inboard springs? I always thought that was for aerodynamic reasons on open wheeled cars. Just interested.

You are correct that the nature of fatigue failure is that the failure point often looks normal until it fails.

As you know, metal fatigue is caused by repeated cycling of of the load. It is a progressive localized damage due to fluctuating stresses and strains on the material. Metal fatigue cracks initiate and propagate in regions where the strain is most severe.

The process of fatigue consists of three stages:

1. Initial crack initiation
2. Progressive crack growth across the part
3. Final sudden fracture of the remaining cross section

I have had a number of the rod ends magnafluxed at varying points in their life and have yet to find any stress cracks in the units.

Even after some fair shunts that left the rod ends bent, there has been no cracking. However, I do stress that these joints as well as all rod ends on the chassis should be inspected between each session for damage or wear.



As to your second query.


1. Packaging. Look at all of bits and see how everything is centrally located and quite compact. Think polar moment. The new cars have pull rod rear suspension for the same reason.

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2. Motion ratios. Over-square to produce high damper shaft movement.



3. Aero. When a splitter is fitted, air needs to flow through the wheel well as cleanly as possible to insure accelerated flow on the underside of the splitter. This was also a consideration, but it is really much like gilding the lily.

[Aussie Mike]

Thanks Richard, That's given me a bit more confidence.

Cheers