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Strut tube opening out of round.

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  • Strut tube opening out of round.

    I had a spare strut tube I was planning on fitting after I replaced the shock absorber.

    So I took it along to a small local garage to ask if they could free off the top cap for me. They placed it in a vice and used a pipe wrench on the aftermarket cap.
    It freed off with little effort, no heat was needed on it.

    So I return home to remove the shock only to find it won't come out. Taking a closer look revealed that the tube is no longer concentric and is clamping the shock tube inside. Unsurprisingly the threads are damaged in the flattened area. It's hard to say if the damage occurred in as I looked on or not, I'd like to think it didn't but that's a moot point anyway.

    Is there any hope of this being salvaged? I dare say the flat could be heated to extract the shock tube, but is it possible to restore it's roundness and the threads?
    Has anyone had any experience of this before?

    Thanks for any tips on how I might go about fixing this. I don't have a camera to hand to share a pic.

    Thanks in advance.
    Last edited by Nuvo; 21st February 2018, 21:13. Reason: many typos

  • #2
    Are you sure it is the out of round keeping the insert in place? I recently spent 2 hours trying to remove an insert from a strut that was round. I suspect corrosion was keeping it in. I couldnt use that strut afterwards i would be surprised if a small amount of squash at one end would hold the insert that tightly, i was using hammers, heat and all my body weight and it didnt move. Insert being 'pinched' at one end withstanding that?... I'd suggest heat or immersing it in citric acid. It will creep in and attack corrosion wherever and do an alright job of derusting the outside! Give it a few days soaking.


    • #3
      You make some very good points.
      There is certainly a good deal of corrosion evident all around the area between the inner tube wall and the shock tube.
      I'm unable to get the strut cap to reengage the thread more that about a single turn, which made me think it was caused by deformation of the tube, I now realise it's more likely caused by damaged threads than the flat itself.

      Based on the difficulties you've experienced, I think this could strut could be toast. I'll try as you suggest consigning it to the tip.

      PS. How do you rate the B6 Bilsteins shocks compare to stock Boge items (assuming that's what you had)? This is what I have lined up to fit myself if I don't hit any further snags like this to contend with.



      • #4
        Usually only the very top of the shock is a tight fit into the strut, probably about 40mm. I'd usually not clamp the strut but wedge it in a vice so it can't turn then use stillsons on the nut, that way you wouldn't crush the strut, usually just scratch the nut.

        First give it a good soak, then heat the top of the srut as much as you dare, then try putting a nut on the shock, clamp the threads below the nut in a vice and use a large hammer on the strut to persuade it to separate.

        I run B6's with stock springs and find them to be very good.


        • #5
          I've not put my b6 shocks in yet but they look and feel quality. I've not heard a bad word against them so can't wait to fit! Im waiting for some warmer weather so i can spray my spare struts...

          Just for info - any bag of catering grade citric acid will work. Ive dissolved a bag into an old black plastic bin. It works better warm so mix with hot water. It will still work cold, just takes longer.

          Not sure if a big enough thread die is easy to get hold of but, depending on the damage, maybe a thin needle file will clean up the squashed bits?


          • #6
            Try getting an appropriate thread file. I bought one and it made quite a difference to the thread on top of the strut

            Ragussa green avant RS2+ spec
            Racing blue Octavia VRS mk2 estate-Remapped now to 250 bhp
            Audi coupe gt-slow as hell but loads of character-sold


            • #7
              Something like this

              Ragussa green avant RS2+ spec
              Racing blue Octavia VRS mk2 estate-Remapped now to 250 bhp
              Audi coupe gt-slow as hell but loads of character-sold


              • #8
                Thanks for all the great tips and advice. I feel a bit more positive about the prospect of saving this from the skip now


                • #9
                  Well this wasn't half as bad as I first thought. Having several applications of penetrating fluid work its magic over the course of a few days or so, I thought I'd try refitting the spring with the strut cap off. A single tap with a hammer to the lower half of the strut tube and POW! The shock shot right out.
                  I hope this helps someone should they face the same problem.

                  The interior of the strut tube needs a good clean out, there's oil and light corrosion in there. What would you recommend for this?


                  • #10
                    I have used a rust penetrating oil in a tube with a long bottle brush, to remove rust. Clean out he strut with MEK to remove the oil. Use the same brush to apply rust converter to the inside of the tube. When you go to put a new shock in the struts, add a light weight oil. These strut tubes came from the factory with oil in the struts around the shock. This does 3 things. One, it transfers the heat from the shock to the outside of the strut keeping the shock cooler. Two, it prevents rust from forming in the strut. Three, it keeps the shock from moving around in the strut housing. Now I use this method with Konis. I know some Bilsteins are in inverted and you may not be able to use the oil method.
                    They can have my car when they pry my cold dead fingers from the steering wheel.


                    • #11
                      Thanks for the tips Greg.

                      Just a wee update to this.

                      A thread restorer file removed most of the snagging so that I can now screw the cap on by hand.

                      I used a 5% mix of Surfex HD and a 50mm diameter nylon flue brush to remove the sludge from the strut tube and rinsed thoroughly with water.

                      Next I created a 5% mix of Deox-C and filled the tube and let it work its magic for a few hours, emptying the contents into a temporary container and then agitating the work surface using more degreaser and the brush, then rinsing with water again.
                      I then refilled the tube with the Deox-C mix for a further few hours.

                      I just repeated these steps as necessary to achieve really good results.

                      I'm thinking about spraying the interior tube with some AFC-50 as a final step.

                      Last edited by Nuvo; 10th March 2018, 21:09.


                      • #12
                        Deox-c = citric acid but much less ££££. Both work really well but noticeably better if heated to 60-70deg c. I think acf50 would work well but doesn't it 'work' by sacrificing itself rather than the metal under it? I've got some and the recommendation is reapply every tear. Tricky on the inside of a strut! How about spraying an etch primer / epoxy primer in there?


                        • #13
                          Ah, I didn't realise that Deox-C is citric acid, I guess that's what the C stands for! I would have bought the catering grade stuff as you had suggested.
                          Sadly I don't have an immersion heater available for this task.
                          I'm not entriely sure how ACF-50 works, I'd need look into that. Same goes for the primers you mention.


                          • #14
                            Don't tell the missus but I reheat my derust solution in a big pan on the stove pour it into the tube and it will have done some of its business by the time it cools.

                            I also don't have cylinder head parts on the dining table when she is out


                            • #15
                              One of my fave before and after shots using citric acid though to be fair - this was actually Deox-c before I read what the c stood for!