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Geko

Trailing Arm bracket failure

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Hi Stef,

you are certainly finding all the known problem areas.

 

What happens about the unknown problem areas.

 

Roger

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What happens about the unknown problem areas.

 

Roger

 

Nobody knows

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I'd require good pics of the fitting angle of the side reinforcing plate. Found this thread with pics provided by Stuart but that was before Photobucket went bonkers...Anyone ?

Edited by Geko

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I will put them up again here Steph they were for a 5 chassis but same applies.

Stuart.

post-3753-0-04046800-1519739650_thumb.jpg

post-3753-0-94269200-1519739655_thumb.jpg

post-3753-0-92998300-1519739661_thumb.jpg

post-3753-0-93142200-1519739667_thumb.jpg

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If you use Chrome as a browser, there's a fix for broken Photstuffit links at https://chrome.google.com/webstore/detail/photobucket-embedded-imag/ogipgokcopooepeipngiikdkpmcpkaon

 

 

Pete

Great stuff, just added it to my Chrome & can now see the photos !!

 

Bob.

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yes, that's what i needed esp 089. I would also require the dimensions of the 3 mm back reinforcing plate which I don't have... Many thanks

I will put them up again here Steph they were for a 5 chassis but same applies.

Stuart.

attachicon.gifMarks TR5 086.jpg

attachicon.gifMarks TR5 087.jpg

attachicon.gifMarks TR5 088.jpg

attachicon.gifMarks TR5 089.jpg

Edited by Geko

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So today I started dismantling the front suspension (yes with my hooked coil spring compressors working a treat). I got stuck with the big bolt going across the lower wishbone arms and the trunnion. Looks like it's firmly rusted in the trunnion, not in the arms. No matter how hard I whacked the bolt, it wouldn't budge. Applied WD-40 liberally and left it for few hours, then pulled with my dynamo wrench up to 300 lbs, no way to get it to move. Heat will be last resort but then i'll have to change the trunnion and the bushes.... In the meanwhile, any sound advices ?

cheers

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Hi Stef,

that big bolt rusts into the steel sleeves. Simply whacking it does no good as the rubber bushes take up the impact.

Remove everything off the car and drill out the bolt as much as possible.

 

Roger

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Remove the whole lower triangle, you should be able to slide the arm (nut side) from its sleeve.

 

Once one arm is removed, cut the bolt with an angle grinder (1.6mm disk) flush to the trunnion, it should move.

Edited by Chris59

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Geko/Stef - I note that you say you are using hooked coil spring compressors.

Do you mean the type which grip the outside of the coil spring?

If so, I suggest that you wear armour plating and be prepared for the possibility of a compressor (and parts of the suspension) flying across the garage and/or doing serious damage to you and your car.

More than one contributor to the Forum narrowly missed serious injury when using external compressors, which are OK for McPherson struts.

There is a tremendous amount of energy within the compressed spring, so good reason for using the correct type of tool, which goes down the centre of the spring and cannot come adrift.

Ian Cornish

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I was about to go for the solution proposed by Chris after removing the whole suspension at once indeed. Ian, I've used these a few times without problem. I believe that the near miss are due to the fact that the coil diameter is rather small, that most hocked type compressors are made for larger diameters and tend to slip out of the coil if not properly secured. Mine is a proper fit and is secured with exhaust clamps on either side. Thanks all.

Edited by Geko

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Folks, back to the initial matter you may remember that I temporarily installed a good spare 2-notch upside down to get the ~ same angle awaiting for the new one to come by HM snail mail. A couple of months and 500 miles down the line I finally replaced both faulty brackets but much to my surprise (not), the temporary spare 2 notch is now cracked bottom up too....

I also replaced the coil springs

 

cheers

 

 

post-11469-0-52312600-1531982210_thumb.jpeg

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Hi Stef,

I wouldn't panic. The temporary bracket, being old, may have been on the verge of cracking before fitting.

 

Roger

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I wish you're right Roger but I don't share your optimism - 3 in a row, same bracket, looks very much like a pattern.

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Hi:

I’ve been following this forum thread with interest and I’d like to put forward theory No: 3.

However, it’s not easy to give a full prognosis based on photos and comments made. So here goes:

Your photo: ’IMG_5886.jpg’ shows a polished surface of the clamped face, and what could be described as de-lamination of the steel. So this is not a ‘regular’ fatigue or brittle fracture.

Your Photo: ‘Bracket_TA_RH_I.jpg’ shows the propagation of the crack. One half of the cracked surface is slightly polished and what looks like brown staining whilst the other half is of a matt appearance. This indicates a fatigue like crack -until the metal is to thin and subsequently snaps (brittle fracture)

Your photo: Image 2018-01-31 also shows similar conditions, and the possibility of an elongated bolt hole (irrespective of the opening up caused by the crack).

RogerH points out that “new bracket is actually bent inwards slightly so the contact area between the bracket and chassis will have a slight gap until it is bolted down”. This is indeed very unfortunate. As the majority of the torque (energy) used into clamping the bracket to the chassis is being used to deform the bent bracket, which results in low clamping force of the bracket to chassis.

Conclusion: The low clamping force caused by the bent bracket allows the bracket to move against the chassis. This movement causes ‘fretting-fatigue cracking’. The de-lamination of the steel is indicative of a breakdown of the granular structure of the steel caused by the fretting of the two surfaces. Fretting between steels also produces corrosion and hence the brown staining as seen in Your photo: ’IMG_5886.jpg’.

I also see that your Chassis seems to have a lot of paint or rust prevention coating on it.

Clamping structural components onto a painted surface is not recommended. The paint collapses and results in zero clamping force.

What to Do:

Firstly, I’d make sure the bolts used are not bottoming out anywhere. Use new high grade bolts. Re-torque after 24hrs.

You could use a very thin paper gasket between the bracket and chassis. Use thread lock.

Of course this could be all bunkum and just be as a result of driving around in 50yr old cars. However three similar failures in quick succesion?

Cheerio (for now)

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very good info TRtrevz.

 

The 3 failures is worrying . Would a bent trailing arm put extra pressure on this bracket ?

 

Roy

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I wish you're right Roger but I don't share your optimism - 3 in a row, same bracket, looks very much like a pattern.

 

Hi Stef, looking at the problem you had on the front wishbone mounts there is obviously some corrosion/ age weakening in parts of the chassis which makes me wonder how sound are the rear trailing arm chassis sections?

Originally these have internal strengthening pieces to stop the box sections collapsing when the TA bracket bolts are torqued up, but over many years these strengthening pieces rot away first and the mounting bolts don't stay up to torque so there is little clamping force holding the brackets to the chassis. If you have to keep reapplying the torque to the bolts this may be part of the problem. Fitting new box sections to the chassis is a lot of work but if they are ok on the outside it is possible to drill out the holes to about 5/8 ins and fit steel tubes with about 1/8 wall thicknes all the way through and weld in place. This works much better than the original and can be done in situ on the car once the TAs are removed.

Chris

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The whole chassis has had it indeed so I ordered a new CTM a couple months back (9 months lead-time, mind you) after several unpleasant experiences. The sleeves in the box section are ok - no signs of rust or crushing and the TA bracket stay firmly bolted on with high tensile bolts and lock nuts. There's no delamination - it's me having removed paint/rust with my grinder for showing. I like the theory of the fretting-fatigue due to the crease in the brackets reducing the clamping force etc... but it doesn't apply in this case as none of the 3 brackets had the crease on them.

The fracture on the new TR shop bracket suggest an incredible torque/twisting force applied on/from the TA which leads me to believe 1/ that the springs (now replaced) may be the the main culprit and 2/ that the polybush fitted on the TAs may not provide enough flex/dampening as rubber bush would do hence rigidifying the assembly TA-chassis.

 

Cheers

Edited by Geko

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Reviving this thread because the mystery of fracturing brackets is now solved. I was suggesting that an incredible force applied on the TA which led to fracturing the RH inner bracket (3X) and indeed... As the story goes, two years ago, I replaced the rear hub bearings and found a spare NOS half shaft in my shed so thought I would replace the half shaft too with the secret hope that I would get rid of a source of "clong". It didn't. Now that I'm replacing the chassis and attending some cosmetic work on the drive train I found that my supodupo NOS half shaft is about 1 inch longer than the original. Needless to explain where the force applied on the TA was coming from... Another lesson learned.

WhatsApp Image 2019-05-09 at 00.18.08.jpeg

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Well done Stef, there is always a reason why, finding it can sometimes be quite difficult. Now we are all more knowledgeable.

Paul

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5 hours ago, Geko said:

Reviving this thread because the mystery of fracturing brackets is now solved. I was suggesting that an incredible force applied on the TA which led to fracturing the RH inner bracket (3X) and indeed... As the story goes, two years ago, I replaced the rear hub bearings and found a spare NOS half shaft in my shed so thought I would replace the half shaft too with the secret hope that I would get rid of a source of "clong". It didn't. Now that I'm replacing the chassis and attending some cosmetic work on the drive train I found that my supodupo NOS half shaft is about 1 inch longer than the original. Needless to explain where the force applied on the TA was coming from... Another lesson learned.

WhatsApp Image 2019-05-09 at 00.18.08.jpeg

So, is the long one going to be Stag/Innsbruck or TVR 2500M

There were shed loads of Stag/Innsbruck shaft assemblies for sale cheaply at one time.  Good way to get a hub and the inner female shaft section.

Cheers

Peter W

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Pete, I had replaced only the shaft and the hub bearing, not the hub itself so don't know about the hub itself. It too begs the question how I could not have seen that the NOS shaft was longer ? Simple enough: When I unpacked the shaft from its greasy wrapping paper it was in full compression whereas when i removed the old shaft it was in full extension with the wrecked rubber gaiter and dangling about so I didn't pay enough attention about the length. My bad.

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On 3/3/2018 at 3:56 PM, Geko said:

Applied WD-40 liberally and left it for few hours,

My experience is that WD-40 is pretty ineffective in freeing seized bolts etc. Plusgas is much more effective. It's also more effective to allow a good bit more time than just a few hours. 

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