Catastrophic Steering box failure!

**Tank** · 3rd March 2012, 02:37 PM

Originally Posted by rick130

Frank, as you've said in Vlad's thread you've never bent a standard tie rod but plenty of us have, and when you compare the size LR use to, say a GU Patrol it's minuscule and not fit for purpose IMO.
In about '02 Nissan upped the size of the arms again to at a guess >32mm (and also changed to female tie rod ends)

When I first bought the 130 ten years ago the very first parts I bought were a tie rod and drag link (as well as a pair of axles and drive flanges) from Mal and Paula Story to replace the standard rods.
Mine was bent and jamming in the silly channel under the diff.

I was aware that this was a problem and went looking for it after being advised to either make my own large diameter ones or buy some Maxi ones by my mate Mark who was an ex-JRA and LRA engineer.

All the Perenties built at JRA Moorebank had HD large diameter steering arms.

He said that Solihull wouldn't believe there was a problem with the standard ones, then, when they had a few too many bend in the UK they came up with, in his words the pathetic aluminium channel under the diff.

His old 110 had over half a million km on it when he sold it and it had OS steering arms that he'd made by cutting the ends off the stock ones and sleeving them with large OD tube.

BTW, a split tube and clamp holding the tie rod is preferable to a jam nut as it doesn't fatigue stress the thread near as badly.
The jam nut concentrates the loads at the root of only one to two threads whereas the split clamp spreads the load over more area, increasing fatigue life, so LR did one thing right compared to a lot of other vehicles.

Tony Southgate, the designer of the all conquering TWR XJR-9 and 12 Le Mans Jags in the late eighties/early nineties bucked the motor racing industry trend (we all used jam nuts, even aircraft do) and made split clamps for their cars as they had to survive a 24hr race while clobbering ripple strips the whole time.

Rick, I'm not disputing LR track rods are too soft, as I said I've never bent one, other than a slight bow that could be pushed back with both feet from underneath, talking about an inch here.
I have been modifying cars most of my life and every time I have modified a part to make it stronger I have found all I have done is transfer the problem elsewhere.
Example H/D springs on different vehicles caused cracks in the chassis, H/D poly bushes caused cracks around A arm mounting points, strengthen those areas and the problem moves somewhere else. Was building a car for Bathurst and was chasing problems all over the car (starting from the Poly bushes in front end), finally thought everything was fine the whole car was as stiff as the owner wanted, then the windscreen started cracking and popping.
Was the same in Stock car racing, no sooner strengthen a weak spot and it would show up in a spot where there had been no problem before.
I'm a firm beleiver in "For every Action there is an Equal and Opposite Reaction", Regards Frank.

**Dougal** · 3rd March 2012, 05:06 PM

Originally Posted by Tank

Dougal, I'm not saying it isn't, what I wanted to know was if you have some expertise in this area (i.e. cause of the break in the sector shaft), as an engineer/metallurgist or some other qualification so as I as I can take your advice.

I am a mechanical engineer. Failures and fatigue (fracture mechanics) are an area I have both studied and remain highly interested in. But that shouldn't matter, either the explanation makes sense or it doesn't.

The root cause of of fatigue is repeated stress that is too high for that material and geometry to survive. It starts with a surface flaw yielding and grows into a crack. From there the crack grows with each cycle until the remaining material reaches a critical stress level and fast-fractures. It has to be higher than 1000 cycles to be classed as fatigue. Less than 1000 cycles and it's a common garden screw up.

High occasional loading actually delays fatigue failure, it overloads the crack tip which on removal of the high load leaves a compressive stress which takes more of the normal cycles to break through. This is the same mechanism used to destress bike spokes, lifting gear and pressure vessels.

In this case the high cyclical loading is caused by bigger wheels and tyres. Simply put the working loads of the sector shaft are a lot higher than normal and every bump or steering input causes higher material stress.
There are several ways to avoid it.
1. Reduce the load (i.e. smaller tyres)
2. Improve the geometry (i.e. bigger shaft, bigger radius, remove stress concentration)
3. Improve the surface finish of the shaft to prevent a crack starting.
4. Make the shaft from a material with a higher fatigue limit.

**uninformed** · 3rd March 2012, 05:39 PM

Tank, as you know I am no expert. What is your definiton of expert?, is it experience or eductaional training, and if so what institues do you acept as being of sound information?

In my trade I have seen guys that have been doing it for over 30 years and they are using bad techniques and bad practice. I also know people that have degrees and they dont display a great knowledge of their field. Then there is the guy that has no degree and made a successful business out of good products he designed and maufactured himself. I trust his jugdment...self taught and all.

As far as saying that if Dougal or anyone else for that matter isnt a so called expert, then their thoughts arent any more correct than yours is BS...someone is correct and some one isnt. MD alone sold 100's of HD track rods. If you want more info go onto LR4x4 and ask how many people have had HD track rods and how many of those running stock tyres have had sector shaft failures....the numbers will tell you the answer.

**Tank** · 3rd March 2012, 06:26 PM

Originally Posted by uninformed

Tank, as you know I am no expert. What is your definiton of expert?, is it experience or eductaional training, and if so what institues do you acept as being of sound information?

In my trade I have seen guys that have been doing it for over 30 years and they are using bad techniques and bad practice. I also know people that have degrees and they dont display a great knowledge of their field. Then there is the guy that has no degree and made a successful business out of good products he designed and maufactured himself. I trust his jugdment...self taught and all.

As far as saying that if Dougal or anyone else for that matter isnt a so called expert, then their thoughts arent any more correct than yours is BS...someone is correct and some one isnt. MD alone sold 100's of HD track rods. If you want more info go onto LR4x4 and ask how many people have had HD track rods and how many of those running stock tyres have had sector shaft failures....the numbers will tell you the answer.

You're the one saying that the numbers are minscule, show me some proof that that is so and I will take it onboard, but to make a statement that you made because it fits your belief is BS.
I would class Dougal as an expert as to his statements in the above post(post #42), I am basing my comments on basic commonsense, experience in the field and basic Physics. Can your statement be backed up or not, what are these numbers you talk of, Regards Frank.

**uninformed** · 3rd March 2012, 07:04 PM

well I can find out pretty much how many HD track rods and drag links MD sold. This will be for all LR vehicles: series, LR 90,110,130, defender, RRC RRP38, Disco 1 and 2. I could also ask how many reported sector shaft failures they had, and how many they had come through their workshop in over 30 years of servcing just LR products.....Now MD are only one of many companies to make HD steering links. That is why I sugested you go to LR4x4. Alot of UK guys on there. They also upgrade to HD steering links. You will get another set of numbers of these and sector shaft faliures to compile with your data. I could also direct you to pirate4x4 and see how the LR section feel about stock links, HD links and sector shaft failures.

Now no proof is not proof as they say, but given the number of reported failures of different things LR wise here on Aulro, sector shaft isnt coming up that often. Now compare that to the number of contributing members here that have HD links, and then compare that to the number of sector shaft failures and see how many of those had HD links installed and how many didnt. Also count how many HD link fitted vehicles have not had a sector shaft failure.

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