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Stripped thread ..


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Hello.   Bit of a saga.

I have various past threads on related issues on all this work, and received a lot of good advice along the way, but the bare bones are:- the rear damper upgrade on my TR4a didn't work properly - kept bottoming out.  Decided to replace with original lever-type.  Got some off a fellow member back in November,  left them with Stevsons in Brum who refurbed for me -   still to be fitted. While they were off the trailing arm bushes were all corroded so  I took everything off the back, had the arms cleaned and powder coated, fitted new adjustable trailing arm brackets and bushes, replaced all the brake pipes and cylinders, new springs. Put all back together -careful with the torque on the  6 axle nuts,  found the brakes didn't work properly, informed on here that the handbrake levers had probably worn grooves in the backplate. Took everything back off, bought an IGBT welder, filled in the back plates. Today - put everything back together, new axle nuts, careful with the torque,   and one of the studs stripped the trailing arm socket . Arrrrrrrrrgh.   I thought I was at the end of a very long process,   and now I have a stripped hole.     

 

On close inspection I have just unscrewed what looks like a spring from the stud thread.  The stud thread is all good and this spring thing is mainly in one piece.  Is it a helicoil, I wonder, from a previous fix?   Any suggested remedies?

 

Dave

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Hello Dave

Some time ago I fitted both sides with the 3/8 UNC threaded studs that I got from this company

https://www.classicdrivingdevelopment.co.uk/category.asp?cID=24&carID=7&pID=118&page=TR4A+3%2F8+UNC+TRAILING+ARM+STUDS

They hire out the jigs to fit them. Was a bit unsure at first but soon got the hand of fitting them. I also bought a low range torque wrench and only use about 12 ft lb to tighten the nuts. So far they have been fine.

If you already have helicoils then not sure what to suggest.

Keith

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Sounds like a helicoil, which should be stronger than the original thread if fitted correctly

you coild try a new helicoil, or maybe go for larger studs from someone like Classic Driving Developments

i fitted these a few years ago and with the rented jigs its an easy job

good luck!

steve

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Hi Dave,

very carefully peel off the thread that was stuck to the stud when it came out.

Now, can you easily break it - if yes then it is the Ali thread from the TA. If you can't break it with your fingers then it sounds like a Helicoil thread.

If it is Ali then simply fit a 5/16 Helicoil - I have a kit&jig you can borrow.

If the debris is an old helicoil then you have trouble. There is not a great deal of spare material to play with. You may need to get the whole lug welded up and then cut a new hole.

 

Roger

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Could be the remains, but it is very spring-like. I will try the helicoil route I think. 

 

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3 minutes ago, RogerH said:

Hi Dave,

very carefully peel off the thread that was stuck to the stud when it came out.

Now, can you easily break it - if yes then it is the Ali thread from the TA. If you can't break it with your fingers then it sounds like a Helicoil thread.

If it is Ali then simply fit a 5/16 Helicoil - I have a kit&jig you can borrow.

If the debris is an old helicoil then you have trouble. There is not a great deal of spare material to play with. You may need to get the whole lug welded up and then cut a new hole.

 

Roger

Hi Rog,

I was just going to suggest re Helicoiling the thread already in the trailing arm, it should just wind straight in if the thread has been Helicoil cut.

Mick Richards

Edited by Motorsport Mickey
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Roger. Our replies crossed. I just broke it easily with my fingers. So I guess it's the aluminium. Looks very shiny inside the hole too 

 

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13 minutes ago, dpb said:

Roger. Our replies crossed. I just broke it easily with my fingers. So I guess it's the aluminium. Looks very shiny inside the hole too 

 

If you want to use my helicoil kit and jig just ask.

 

Roger

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FWIW The torque for the nuts is 16ftlbs Only small torque wrenches will go down that low and be accurate so be careful.

Stuart.

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hi Stuart,   I had it set at 14.5 so should have been fine.  In fact I had done them all then had to redo after welding the back plates, again at 14.5, and 11 of 12 were fine.  I am somewhat miffed with it,  and now seems I have to do it all again.

 

Cheers

Dave

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On 3/18/2022 at 7:57 PM, RogerH said:

If you want to use my helicoil kit and jig just ask.

 

Roger

HI Roger

 

Thanks for the offer. I may well take it up.   Too annoyed to do anything about it right now!

 

Dave

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Hello.

 

Thanks Roger,   but not needed right now.   I have tried a Loctite Thread Repair kit,    and it seems to have done the job for now.   If I take it all apart again I think I will replace all the studs with the bigger threads/studs as suggested above.

Thanks for all your help, until the next time...


Dave

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41 minutes ago, dpb said:

 I have tried a Loctite Thread Repair kit,

If its LOCTITE PC 3967 that is   nowhere near strong enough

trq.jpg.f84442f1c9fa0aa2e6b4cc1744723fe4.jpg

That is only good for less than 4 ft lbs.   You need more than 16.

 

 

Edited by RobH
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Hi Ro

I think the part number may be slightly different, but the torques are similar.  So far it has torqued to 14.5 lbft,  (better than the aluminium that failed last week). I aim to take the nuts on and off a few times to see if it stands up,  if not then the coarser threaded studs are likely where I will end up.


Dave

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Well, it torqued up 3 times and failed on the 4th.  So now its helicoil or coarser threads.    Any favourites?

 

Dave

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If you want to do want a racer does tap the 3/8th UNC straight into the trailing arm parent metal, using the stripped out 5/16th holes. It's the tapping size for 3/8th UNC.

Drill out those that are still ok (if any ) to match the stripped holes. You can go deeper by 2 or 3 threads into the trailing arm on all these holes if you wish, using the virgin undrilled trailing arm material underneath (gaining maybe a 25% increase in threaded length at the same time...not to be sniffed at). Then drill out the 5/16th clearance holes in the hub, taking them up a size to clear on the 3/8 th holes needed for you to fit cap head bolts with a short shank through the holes into the trailing arm. Because you are not using studs you don't have the same problems with keeping the drill and taps at 90 deg in both planes when drilling or tapping. 

The cap heads can be fitted individually allowing you to "squirm" the hub around using the clearances on the individual holes to get each cap head in as needed. I've used an anti loose washer under the heads but still use the 16 lb ft as a torque. The UNC thread is stronger than the UNF studded original thread, it having more material left across the "throat" of the threads. 

Mick Richards

Edited by Motorsport Mickey
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Thanks both.    I like the idea of not having to be perfect with the drilling. 

 

Are those cap head  bolts hexagonal, or have a hex socket? Does it make any difference?

 

Dave

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2 minutes ago, dpb said:

Thanks both.    I like the idea of not having to be perfect with the drilling. 

 

Are those cap head  bolts hexagonal, or have a hex socket? Does it make any difference?

 

Dave

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Cap head have a hex centre so for ease of fitment you want socket driven Allen keys. Like these Allen key drivers

Stuart.

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Hi Dave,

I have a 1968 TR5 so somewhat similar. The right hand arm had split at the point the upper bump stop is mounted to the arm (It is mounted on the body on the TR4A) and there were some other peculiarities about the casting so I bought an arm from a seller in the USA via Ebay that had come off a 1972 TR6. The arm was in great condition but one of the six studs was not very secure and the hole had clearly been tapped deeper as the drill had broken through the boss at the rear of the flange. I bought a 5/16" UNF Helicoil kit that reinstated the thread really well. If you go this way a note of caution. Make sure that when you drill out the remains of the old thread with the Helicoil tapping drill that it is square to the flange. If you don't the stud will end up out of square and you may then have a problem getting the hub flange over the six studs. In my case whoever had drilled the hole deeper in the US had not done it squarely so I was a bit stuck and my stud ended up slightly out of square. I got around this by fitting the hub flange over the 5 studs and then screwed in the 6th stud.

Regards,

Denis

Edited by DenisMc
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That's fine Denis, provided that if it ever comes to removing the hub you can remember which stud you first have to remove!

Tim

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Hi Tim,

A good point but I had bought a new stud from Rimmer Bros so I know that it is the new looking bright and shiny one!

Regards,

Denis

Edited by DenisMc
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