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Trailing Arm Corrosion/Repair


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Hi everyone

 

About to start restoring the rear suspension on a 4A and have a potential issue with the trailing arm as per attached photo.

 

It appears the casting lug accommodating the mounting stud in the trailing arm has corroded away leaving part of the stud visible - the item was sandblasted about 35 years ago before I acquired it and the corrosion must have taken place prior to that, if indeed it wasn't like that from new - there is no evidence of recent corrosion.

 

Question is, can this be repaired by alloy welding and then recutting the thread? If not, are there any other options (longer stud with a nut on the end??) or is it scrap?

 

Cheers

Rich

 

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The casting is quite thin around the hub stud holes and break through isn't unheard of when reworking stripped threads. That T/A looks very badly corroded and if it were mine I'd be looking to replace it.

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Hi Rich

 

Alloy castings can be welded and then and drilled and tapped, and I had a gearbox drain plug hole repaired in this way. However, the alloy was in far better condition overall than your suspension casting. Unless it is a flaw in the photo, is there also a crack around the adjacent bolt hole?

 

If that's the case you might be better of looking for another casting as Pete also says, as you will find its not cost effective to have someone carry out a repair.

 

However, it's still an OEM original part, so I would say hang on to it, or pass on to another TR owner or autojumbler, as someone somewhere with tig welding experience might be able to repair it for future use,

 

Regards

 

Kevin

Edited by boxofbits
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By the looks of it I would definitely replace, the rest of the casting doesnt look good.

Stuart.

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+1 with the above comments.

 

I realised that the "Innsbruck" arms were shared on the suspension systems of the independent IRS Trs, also Triumph Stags and the large saloons, however I didn't realise the Titanic was equipped with them !

 

Quite spectacularly eroded, corroded and generally past it's use date, there a plenty of other trailing arms available, I paid £25 for a very nice pair almost ready to put straight onto the car about 5 months ago. As itemised above the breaking through of the thread of the hubs studs isn't in itself a problem but as Kevin points out it looks like there's a crack in the trailing arm wall which says these components have had enough. Save somebody some grief and put a hammer through both of those arms and throw into the recycling bin, in all conscience I couldn't sell or even give those away, they could end up killing somebody.

 

Mick Richards

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Been Heli-coiled I think.

 

Could salvage but wants quite a bit of weld build up. These are OK welding material I think.

 

You could try asking John Mills. He does jobs like this. Watch this from about 7.5 minutes.

 

 

Would make a nice video!!

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Thanks for everyones input

 

I'm no David Bailey so my photos are **** and probably don't do the trailing arm justice.

 

What looked like a crack on the next lug was actually a hair!

 

Just been and cleaned it up a bit - some more photos attached - I thought the trailing arm was quite good in actual fact but I will bow to more experience, unless views change in the light of the better (?!) photos.

 

I have to say it does look like the tapping is off centre to start with - presumably all the stud tappings are equidistant and jigged so if one is out, then the rest would be - no other lugs are showing the same but then some of them are much larger lugs ( what is the correct term?) to start with - bit strange.

 

Cheers

Rich

 

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I have to say it does look like the tapping is off centre to start with - ....no other lugs are showing the same but then some of them are much larger lugs ( what is the correct term?) to start with - bit strange.

 

Nope the new photos don't dissuade me, I'd be finding much better examples.

 

Regarding the breaking through of the studs check out Trailing arms on the search facility (always worth checking there first) you'll find at least 6 or 8 threads and how to reclaim any threaded stud holes that are awry.

When these castings were done at the foundry the firm allowed their year one apprentice with 2 months experience to place the alloy blocks around the circumference in the mould jig. Mostly it worked ok but he occasionally turned in drunk ! hence the haphazard block placement which sometimes allows the stud threads to break through the walls outer edges. If you have any studs which are at an angle or the threads diffuse into a grey powder when the studs are twisted out you can reclaim them. The studs are 5/16th UNF which doesn't carry enough material at it's root thickness to stand more than the 16 lb ft that Triumph specified (there are 6 of them after all). To get a better grip the studs are often replaced with 5/16 UNC threads (coarser threads so bigger root thread dimension) into the trailing arm with the original 5/16 UNF retained on the Hub end. These need Helicoiling or fitted using inserts (Wurth or Timeserts are a couple of examples) trouble is the hole diameter needs to be increased to take the thread within a thread items which then can lead to the breakthrough of the side walls as you've seen.

Check out the Search threads all is explained there including fitting bigger dia studs with a smaller hole size required ! all knowledge is on this forum, however I'd save any reworking of trailing arms for better examples than these.

 

Mick Richards

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Hi Rich,

things can be repaired and your stud lug could be sorted. But!!! it would be wise to helicoil ALL the studs. AND then you have what looks like a badly weathered casting.

It will cost you money to refurb. It would be cheaper quicker to buy another TA. Have a word with 'Ray Gill' on this forum. They are fairly close to you in Essex.

 

Ali and its alloys have a nasty habit of the surface corrosion eating into the subsurface structure.

Grain boudaries break down and then you have a kit of parts at the wrong time.

If you decided to go with the TA thenafter all the repairs it would be wise to 'grit' blast anbd then have it coated in Alochrom1200 to protect - more expense.

 

Roger

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Mick - thanks for your comments - I am aware of the other posts about trailing arm threads, in fact I've copied them into a specific file - this query was not specifically about studs/threads but rather corrosion, which I don't recall being covered previously, hence the question - as it happens, I have got another pair but I haven't looked at them closely yet.

 

If your contact has another pair for £25, then I'll buy them as well!

 

Given that these items were acquired in 1982, already in bits and blasted, and dry stored since with no evidence of any subsequent corrosion, I am surprised they are is such bad condition, and it makes me wonder how good other second hand units are likely to be which have been in use for much longer.

 

Roger - I haven't had a chance to start the rebuild of this car in earnest yet, so haven't started dismantling parts any further than they are already, so don't know what the insides are like - do you take out the rubber grommets to do this and is it then easy to see the corrosion or do you need a camera probe?

 

I'm using the intervening time to investigate and resource known issues ( rotten boot lids and repair panels spring to mind!).

 

Thanks for everyone's advice as always

 

Cheers

Rich

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Hi Rich,

 

Trailing arms were from a Stag autojumbler at the years Stoneleigh Triumph and MG parts day.

 

Mick Richards

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" Given that these items were acquired in 1982, already in bits and blasted, and dry stored since with no evidence of any subsequent corrosion, I am surprised they are is such bad condition, and it makes me wonder how good other second hand units are likely to be which have been in use for much longer."

 

Reasonable point . . . . . but.

 

The quality of t/a castings seems to have been variable, and some appear to have deteriorated at a much faster rate than others. I can recall skipping heavily corroded trailing arms back in the mid/late 70s simply because they were fit for nothing else, whereas I have seen other arms that have survived decades on the road in all weathers and yet still look decent enough and are going strong.

 

Cheers

 

Alec

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  • 9 months later...

Hi all

 

Just in the midst of my full restoration on my 4A, I've cleaned dates Trailing Arms and painted them then realised one looks to have a casting flaw in one of the mounting bush holes. I've attached some pics showing it. The TA casting is un identified other than on obscure part number, whereas the other one which seems ok has a Stanpart marking. I'd appreciate the collective thoughts on there flaw, is it a scrapper, or still good, I'm leaning towards a scrapper, but welcome your thoughts. Thanks.

 

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Ian

 

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Hi all

 

Thanks for the feedback, yes Pete I was also going to mention the Shock Absorber hole, the other TA shows a similar amount of wear. Is it worth having a Washer made to reduce the hole size?

 

Sorry Andrew I don't know what the finish is, it was applied by a local engineering company who specialise in cleaning & repairing Valve Body castings for the Gas, Water & Oil Industries.

 

 

Cheers

 

 

Ian

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Hi Ian,

you could easily repair the odd shaped hole.

Using a piece of round Ali bar get it to the correct diameter for the hole and then file a flat on it to align with the original hole.

 

It will probably want to wear again but it will take time. I've seen quite a few looking like that and they are still around.

 

Roger

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Thanks Roger, you set me thinking about the other TA, which I'd noticed had an odd shape to it in the shocker mount area, sure enough it looked like someone had let a piece in, unfortunately it had dished as you can see and had been glued in, which I suppose is fair enough, once the shocker is in it isn't going anywhere but the dishing doesn't seem good.

 

A bit of gentle prodding and out it popped.

 

 

 

Ian

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Not all Triumph Trailing arms are the same as Trs.

I was offered a replacement which I think came from a saloon, dont know which year but it was definitely different. Ended up getting one from TRGB which was fine.

Chris

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  • 2 weeks later...

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