 | Home > Maintenance & Modifications > Brake caliper stripped thread - OK to helicoil? |
 
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| Dinnu Member Since: 24 Dec 2019 Location: Lija Posts: 3184   
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I have done quite a few helicoil repairs, and all have been satisfactory and better than when the thread was ‘virgin’. BUT those were all in aluminium castings.
Personally I would be hesitant to use a helicoil in such a critical application. Maybe a time-sert (no connection with them) would be better suited, but by the time you do the repair, perhaps it could be cheaper to find a second hand knuckle that is in good condition and fit that. 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing 2012 90 CSW, 2.2TDCI, Santorini Black |
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24th Feb 2022 10:12am |
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| Mossberg Member Since: 29 Feb 2020 Location: Lancs Posts: 552  
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Yes I would look at fitting a timesert but the kit cost is prohibitive. As you say it would be worth looking for a used swivel pin housing. My issue with that is I have just refurbished this and it is one of the 10 spline units so I don't want to loose all the efforts I have put into that if I can undertake a cost effective repair.
 Click image to enlarge Click image to enlarge A before and after photo showing the work I have done. |
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24th Feb 2022 10:26am |
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| rallysteve Member Since: 10 Feb 2014 Location: Cumbria Posts: 2196 
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Why do you want to change the bolt thread pitch? I would get a repair/thread cleaning tap to suit the thread of the original bolts (M12 coarse) and get four new bolts of the correct type (AFU1031) which are also 5mm longer.
Unless the thread in the swivel housing it totally mashed, i wouldnt even entertain using a thread repair on it. If it was, on a critical caliper mount, I would be taking the housing to a local engineering company for them to set a proper timesert in it and then still using the original length and thread of bolt intended. Steve 02' 110 TD5 Double Cab Rebuild Thread 84' 90 3.9 V8 Caged Pickup Build Thread - Now For Sale Mobile Diesel Heater Build Thread |
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24th Feb 2022 10:58am |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 16857 
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There is in principle no reason why you shouldn't fit a Helicoil (or equivalent wire insert) to repair the SPH, but do not attempt to change the thread form unless you have checked that the correct size tapping drill for the insert is larger than the clearance diameter of the original thread form. It probably will be, but if it is not you will have a substandard and weak repair, which is clearly not ideal in this situation.
If you are changing the thread form are you intending to Helicoil all four caliper bolt holes? My main concern with doing this is that the caliper bolts are threadlocked, and I do not know how well that works with a Helicoil insert and whether there is a risk, however small, that the insert will wind out if you try to remove the bolt in the future. I don't think that there would be any particular risk of the bolt unwinding itself in service if correctly torqued. So I think that this is a feasible repair, however it is not one I personally would do. I would replace the SPH, in fact, if both SPHs are of the same age and provenance I would replace both, especially since you don't know why the thread failed in the first place. That fact alone would raise sufficient concern in my mind to err on the side of caution. After all, as Landrover would probably say, if your brake caliper comes off you are likely to experience a reduction in control of the vehicle (just as you do if the end breaks off the axle, apparently). As a side note, in recent times I have done quite a lot of reading on the Timesert versus Helicoil debate, since there are conflicting views on which is "best" and which is "strongest". In the course of this, I have found absolutely no scientific evidence that one is "better" or "stronger" than the other, both tend to be stronger than the parent material. Both are fully secure and enduring when correctly fitted, and outside of a production environment there is no significant difference in fitting time. There really is nothing to choose between them except for three factors.
The second is availability, Timeserts are much harder to obtain, at least in the UK. The third factor, which is the only significant engineering factor I could determine, is that the OD of a Timesert tap is larger than the OD of the equivalent sized Helicoil tap. This may well be significant if the hole to be repaired does not have much material around it. In my case I have two stripped exhaust manifold bolt threads in my Puma cylinder head, which eventually I will get round to repairing by fitting inserts. The holes for the top manifold bolts are disturbingly close to the top face of the cylinder head leaving little parent metal to support the repair, and the head is, of course, aluminium alloy and therefore not particularly strong. For this reason alone I have decided that when the time comes I will Helicoil the hole, and not attempt the Timesert it, since a smaller oversize is required with a Helicoil. |
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24th Feb 2022 11:01am |
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| Dinnu Member Since: 24 Dec 2019 Location: Lija Posts: 3184
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Indeed that is a shame not to repair.
Note that Helicoil also use other alloys, not just stainless. And you only have 1 thread to repair? So still have 50% of the original strength as a minimum. I hope Landrover did not engineer a safety factor of 2. 1988 90 Hard Top, 19J Diesel Turbo, Shire Blue - Restoration ongoing 2012 90 CSW, 2.2TDCI, Santorini Black |
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24th Feb 2022 11:02am |
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