Trailing arm versus pothole

[cliffpeters]

Hit a nasty pothole on the way home from the Chatham Drive It Day event last weekend. Thought I might have damaged my nearside rear damper but was shocked to find the trailing arm damper mount completely snapped off the body of the trailing arm! Ouch.

I'm wondering if there's a way to effectively weld the "ear" back onto the cast aluminium body of the trailing arm? It would seem that it would be a weak weld.

I guess I'll start looking for a replacement.

Cliff

 

 

 

[RogerH]

Hi Cliff,

 it is a surprisingly common failure.  Easily repaired by a trained welder.

When it goes back on ensure to have fillets welded to support the lug.

It will be stronger than new.

When fit it all back together make SURE that the strut is the correct length and the bump stops are doing their job.

 

Roger

[Waldi]

Cliff, pictures can be mis-leading, but does the adjusting knob remain free when the shock-rubber in compressed? Do you see a sign of contact between the knob and the TA?

Waldi

[Dave McDonald]

Cliff,

I had exactly the same breakage when encountering a very deep pothole in the Yorkshire Dales over 20 years ago. Had it repaired by a competent welder using TIG welding and it's lasted for over 20 years. Annoying but not the end of the world.

A Roger has said, check the shock absorber isn't too long causing it to lock up when fully closed ans effectively become a solid strut before the bump stop engages to stop the travel.

Dave McD

[cliffpeters]

2 hours ago, RogerH said:

Hi Cliff,

 it is a surprisingly common failure.  Easily repaired by a trained welder.

When it goes back on ensure to have fillets welded to support the lug.

It will be stronger than new.

When fit it all back together make SURE that the strut is the correct length and the bump stops are doing their job.

 

Roger

Thanks, Roger. That's hugely helpful and encouraging!!

Cliff

[CK's TR6]

In my case it broke like that. Then the gas shock extended to full length. Then when I went to start braking from 65+mph, the whole thing swung forward and the sharp edge of the break cut into the inside edge of my right rear wheel (alloy). Which proceeded to rotate all of this up and jam the cup between the wheel and the frame where it comes out to support the bump stop (down motion) for the lever shock. Just like sticking a heavy stick in the spokes of your bicycle while going fast downhill. Rear wheel immediately stopped rotating (this is at 65 mph!). The pirouette into the jersey barrier did break it loose after the front corner was smashed in, then it caught again and pirouetted the back corner into the jersey barrier. So, by all means just weld it up, and use telescopic shocks. I learned my lesson.

[cliffpeters]

1 hour ago, Waldi said:

Cliff, pictures can be mis-leading, but does the adjusting knob remain free when the shock-rubber in compressed? Do you see a sign of contact between the knob and the TA?

Waldi

I'll have to look at it more closely (I'm not close to the car right now). There were signs of the shock's severe compression.

[cliffpeters]

2 minutes ago, CK's TR6 said:

In my case it broke like that. Then the gas shock extended to full length. Then when I went to start braking from 65+mph, the whole thing swung forward and the sharp edge of the break cut into the inside edge of my right rear wheel (alloy). Which proceeded to rotate all of this up and jam the cup between the wheel and the frame where it comes out to support the bump stop (down motion) for the lever shock. Just like sticking a heavy stick in the spokes of your bicycle while going fast downhill. Rear wheel immediately stopped rotating (this is at 65 mph!). The pirouette into the jersey barrier did break it loose after the front corner was smashed in, then it caught again and pirouetted the back corner into the jersey barrier. So, by all means just weld it up, and use telescopic shocks. I learned my lesson.

Wow, scary. In my case, the car handled fine in a straight line but was handful on right handers. Thanks for the advice.

[cliffpeters]

1 hour ago, Dave McDonald said:

Cliff,

I had exactly the same breakage when encountering a very deep pothole in the Yorkshire Dales over 20 years ago. Had it repaired by a competent welder using TIG welding and it's lasted for over 20 years. Annoying but not the end of the world.

A Roger has said, check the shock absorber isn't too long causing it to lock up when fully closed ans effectively become a solid strut before the bump stop engages to stop the travel.

Dave McD

Thanks for the advice. I'm thinking that damper is trashed so will probably replace the pair.

[Hamish]

I’d try a claim against the highways authority a few pics with ruler in pic for scale of the pothole and pictures of car damage. 
try and get repair costs back. 

[rcreweread]

I wonder if the TA would have broken if a traditional lever arm was being used?

Cheers Rich

 

[Rob Salisbury]

It's worth noting that the big Triumph saloons (T 2000, 2.5, 2.5Pi etc) have a very similar trailing arm set-up and use telescopic dampers, the secret is to insure that the bump stop prevents the shocks from bottoming out, having said there are some monstrous pot holes around these days, and our cars were never designed to cope with speed humps the size of small mountains!! 

Cheers Rob

[Keith66]

1 hour ago, rcreweread said:

I wonder if the TA would have broken if a traditional lever arm was being used?

Cheers Rich

 

 

Hi All

I'm def no expert engineer but logic would tell me there should be way less chance.

So assuming the bump stops don't come into play before the strut bottoms out there would be massive (depending on pot hole size) stresses transmitted vertically to a fixed point, namely the top of the new strut bracket, so pretty strong. Well the ones I fitted seemed to be.

So a locked strut attached to a V strong bracket and a massive road shock leads the weak point failing, i.e. the alloy trailing arm shock mount.

With lever arms there are many areas of flex, both vertically and horizontally, the lever of the lever arm is horizontal so (I assume) wouldn’t transmit the forced so directly, the drop links, though vertical in themselves do not attach to a fixed and strong point and can move both vertically and horizontally.

With all of this err flex in the system I wouldn’t expect this type of failure to be common with lever arms, but as I said I’m no expert so I’m sure someone will confirm it has happened.

Oh I went back to levers after seeing the bridge failure pics on this post.                

https://www.tr-register.co.uk/forums/index.php?/topic/66376-rear-shock-conversion-what-not-to-use/

I think it pays to be careful about mods to 50 year old cars that may put new stresses on components they were never designed to cope with and aren’t as strong as they once were. It may well mean strengthening other areas rather than just whacking the new thing straight on the car.

Not saying don’t mod your car just think about how any mod might affect other areas and sort any potential probs before they happen.

Cheers  Keith

 

 

[15eren]

This is one of the ways to strenghten the trailing arms. It was not broken, but I hope this makes it stronger.

Tage

Edited May 3, 2022 by 15eren

[Mk2 Chopper]

23 minutes ago, 15eren said:

This is one of the ways to strenghten the trailing arms. It was not broken, but I hope this makes it stronger.

Tage

Wow that's neat!

I'm guessing the shock bottomed out before the bump stop in the case of the OP, but shows it could be repaired. 

Gareth

[Motorsport Mickey]

Good work !

Mick Richards

[15eren]

Hi Gareth

No it was not broken. The strengthning was made as a precaution as the trailing arms were already off for cleaning, painting, new bushes etc.

Tage

[Mk2 Chopper]

18 minutes ago, 15eren said:

Hi Gareth

No it was not broken. The strengthning was made as a precaution as the trailing arms were already off for cleaning, painting, new bushes etc.

Tage

Hi Tage.

Yeah I get that, I was referring to the OP (original poster) who's trailing arm is broken. 

Yours certainly looks nicely beefed up with those strengthening gussets welded on. 

Gareth

[RogerH]

Hi Tage

that is impressive.

It does not need to be that substantial. Wow, if only I could weld like that.

 

Roger

[cp25616]

Just put Saffie back onto a nice pair of lever arms last week ironically did this because I was not happy with telescopics and the rebound quality.

Alan G

[stuart]

Typical wrong equipment fitting caused that and as noted by CK`s TR6 you were lucky it didnt do more damage, Careful choice of mountings and shock lengths is needed as this happens often.

Stuart.

[FatJon]

Both my trailing arms had cracks in them when the suspension was rebuilt last year. 50 year old aluminium, work hardened, corroded and pounded. It’s well worth checking them, a TIG repair is cheaper than the alternative.

 

[stuart]

3 minutes ago, FatJon said:

Both my trailing arms had cracks in them when the suspension was rebuilt last year. 50 year old aluminium, work hardened, corroded and pounded. It’s well worth checking them, a TIG repair is cheaper than the alternative.

 

They can be pretty rough sometimes!

Stuart.

 

[PodOne]

Thanks Tage for sharing how you have approached it.

Must say I was a bit surprised how poor the casting was on mine once blasted, no cracks but the spring pans and link arm points looked thin for the job they have to do. I reconciled this with the arms having lasted 50 years then the engineers must have done their sums. Having read various accounts of failures since the next time I come to pulling the TA I'll be beefing them up in these areas.

Andy

 

[DenisMc]

Hi Stuart,

The tear in the casting looks to me like It might have been a casting defect (hot tear), so has perhaps been that way from the start. I'm amazed.

Cliff, 

I had to replace the o/s trailing arm on my TR5 last year. Craig at TRBitz thought that he had one but he was very busy at the time so rather than wait I bought a good one that had been taken off a TR6 from the USA via Ebay. If you decide to replace the arm then it might be worth your while contacting Craig.

Regards,

Denis