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Trailing Arm bracket failure


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Folks, so it started last week with a nasty squeaking from the rear end. I jacked it up this evening and found that the inner RH TA bracket had a fresh failure. The crack is all the way on the left side of the bolts which suggests an outward torsion of the TA. I'm now wondering what is the ulterior cause for it? Yes, the brackets are old and original but 1/ I have a lot of positive camber on both sides resulting in wearing the outer edge of the tires (worn to the rope that is) after 10,000 miles and 2/ the rear suspension has always been very saggy even after replacing the Armstrong. I have ordered a set of new brackets but what am I to look at in priority now? Tires are 165/R80/15 on 5.5 rims.

As always

S

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Edited by Geko
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Stef,

 

You say its been very Saggy and you also say you've got positive camber. In your signature pic the rear of the car looks high not saggy...Normally camber goes negative as it 'sags'.

Do you have any Camber/toe measurements for the rear end? is the bad tyre wear because of the static camber/toe or is it a dynamic factor where alignment is changing under power?

I had a bracket pull through a rusty chassis once, the rear-wheel steering effect was strong under power/braking (no mistaking it)

What are the TA bushes like??

Edited by ctc77965o
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Happened to me about 5 year go. Put it down to driving into too many Kent potholes, some really made the suspension bottom out. Did full rear end upgrade this summer. T/A Polly bushes, uprated springs and spax shox. Not only does the rear end feel connected, I do not feel the TA brackets will fail again.

 

Cheers

Simon

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Not sure i was very accurate with my "saggy" bit. I mean the rear suspension is very slack under load and more often than not my tail pipes are scraping the road on startup. For example the bump stop holder on the body is now twisted inwards as a result of the bump stop hitting the TA all the time (RH side only). KL city driving tantamount to potholes and speed breakers gymkhana and it hurts indeed.... Bushes are polybush replaced 3 years ago. I have no idea about static/dynamic toe/camber, it's beyond my knowledge

Edited by Geko
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Sounds like you might wanna replace rear springs whilst you have the TA out. I fitted spacers recently as my short springs were causing exhaust scuffing...much happier at standard ride height.

Maybe the TA bracket is just an old age fatigue failure??

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Stef, sorry to hear that.

 

I took the brackets off my chassis and replaced them with the Rimmer part https://www.rimmerbros.co.uk/Item--i-155502

 

@ Dave Lacey - I saw a picture where the bolts had pulled through the chassis. Attached.

 

Also on the pic is a rough outline of a reinforcement plate I made using the old trailing arm brackets to strengthen it all up.Just guided off the sides of the old bracket and I had a perfect sized reinforcement plate.post-11421-0-88792800-1509086183_thumb.png

 

Seems to have worked out well.

 

Best.

 

Paul.

 

 

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Hi Stef,

the brackets holding the TA at the front will crack vertically through the bolt holes given time.

 

The slack rear end is due to the springs rather than the dampers.

 

Fit new springs (whatever they are) to give you a better rear end reaction/comfort.

 

Go to the Buckeye site and investigate your camber. It should be just a fraction negative. Remembering that it will go more negative with the boot loaded.

 

Roger

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Hi Niall,

if you look at a new bracket it 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 means that the central vertical axis will be under tension and it is working through the axis of the bolt holes.

 

This looks like a very poor design but does give a very positive attachment with the bolts having a built in spring washer.

 

Two years ago my MOT man spotted a very tiny rusty mark on the bottom edge of a bracket.

When I took it off there was a very nice crack - well done MOT man - oh yes they getting rid of that aren't they.

 

Roger

 

 

 

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Gents, As far as i can tell the coil springs are indeed the culprits.

The broken brackets messed up toe and camber but there's no further damage to the chassis.

The Inner LH bracket is on its way out too.

Here are some pics of the offenders

Thanks for the hints !

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Edited by Geko
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Out of curiosity i had a closer look at the fracture and it looks like the bracket is made of bi-layer steel sheets joint together (yellow arrow), one sheet being thinner than the other. The onset of the crack (red arrow) is located on the thinner sheet and then works its way up to the bolt hole or is it from the hole down and up? Once the worm is the fruit, the bracket is weaker and the thicker sheet crack follows. Sounds like a theory, Roger?

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Edited by Geko
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Hi Stef,

sounds like a theory - but sadly a wrong theory. That is what theories are all about.

You assemble all the known knowledge and wait for more knowledge to shoot you down. Science.

 

The bracket is made from one thick sheet and all the holes are stamped out before the sides are bent up.

The thick/thin line you see is simply the effect of the press tool - tends to be clean for 1/2 and slightly ragged for the other half.

 

You are correct about the origin of the crack.

Cracks like to start at edges, they often have sharp corners. Edge of holes are a beauty on aircraft rivet holes. (don't even think about countersink holes :o:o )

Cracks can start in the middle of structures where there are shape changes (in thickness etc) or along weld runs (but they also have other problems)

 

So yours are not out of the ordinary, but to have it in two pieces is quite impressive.

 

As I mentioned in an earlier post the 'flat' part of the bracket where it bolts against the chassis is actually dished.

So the centre line of the holes (with all those edges) is under a great deal of stress from day one.

 

It would be better if the top/bottom edge and all the holes had radius'd edges. It would extend their life from 50 years to 50 years and quite few days.

 

Roger

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Very impressive pictures, interesting learning... thanks' for the sharing, I shall have a specific focus on this area and brackets during the next rebuild next year.

 

Best regards

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Hi Marc,

it is very easy to look at the bottom edge of all four brackets.

Clean all the dirt off and simply look at the centre of the bracket for any sharp edges/ straight rusty line or sign of damage.

 

If in doubt, remove the bracket and use the MK1 eyeball.

 

Roger

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Hi Marc,

it is very easy to look at the bottom edge of all four brackets.

Clean all the dirt off and simply look at the centre of the bracket for any sharp edges/ straight rusty line or sign of damage.

 

If in doubt, remove the bracket and use the MK1 eyeball.

 

Roger

Thanks' Roger, yes not a big deal to have a check but what is a Mk1 eyeball?

Nevertheless, one of the key point you mentioned is the issue w/ the new bracket actually bent inwards slightly ! On my side I shall investigate on the pros and cons and make a decision to change de brackets w/ the adjusted ones

 

Regards

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Hi Marc,

 

what is a Mk1 eyeball? normal eyesight.

 

Roger

Ok I was confused.

 

Regards

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