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Trailing Arm Hub Studs

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    Trailing Arm Hub Studs

    I started to replace the offside drive shaft and in the process of removal managed to strip two of the studs. I can helicoil the holes quite easily. I plan to go for 5/16” UNC studs in the aluminium trailing arm with 5/16” unf stud ends for the hub. This is rather than the standard 5/16” unf at both ends on the standard TD 812 Triumph studs.

    Does anyone have a part number and source for a suitable stud with combined unc/unf 5/16” studs, that are the right length?

    Thanks in advance.
    Chris
    Magenta Stag TV8 MOD

    #2
    Search 3/8” studs as supplied by Classic Car Developments. Stainless stepped stud 5/16 unf and 3/8unc, much stronger and longer stud but removes less of the precious ally than drilling for a 5/16” helicoil. Not the cheapest way but peace of mind and loan of jigs for little more than a tank of fuel.

    You can get manifold studs with different threads at each end but I wouldn’t be too worried about my manifold falling off.
    Last edited by KOY 23; 16th March 2019, 04:22.

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      #3
      I turned my own from ⅜” UNC bolts, took only a few minutes per. As koy23 said, putting a ⅜” UNC thread into the trailing arm is more secure than Helicoils.
      Mabel is a white 1972 Mk1½, TV8, ZF 4HP-22 auto,
      2016 RBRR finisher. 400 mile C2C 21/22 April 2018!

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        #4
        Thanks for the advice guys, that makes a lot of sense.
        Chris
        Magenta Stag TV8 MOD

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          #5
          As has been said above, the 3/8 th UNC removes less material and gives a stronger thread root than a 5/16th Helicoil, (the Helicoil is a 5/16 thread inside a larger outside thread), and VERY importantly you need to use a jig to tap the 3/8 unc threads into the hubs (the 3/8th UNC only needs 5/16th Dia tapping hole, and you've already got them...stripped, check, it's the right size already). If you've stripped a couple of studs it's likely there's some more only just hanging on and may strip upon being torqued up (sinking feeling as the nut continues to turn without torque figures being met), if the hubs are off repair ALL the holes in both bubs to prevent future problems.

          BUT the clearance on the 5/16 holes in the hub flanges to the studs is very close (about 5 thou to the studs dia) if you don't use a jig and get the tapped new holes exactly at 90 degrees to the trailing arm flange the hub won't pass over the studs because the studs will have a lean on them, and then you have to open up the hub holes which means when you tighten the studs (only 16 lb ft remember) it imparts a bending motion onto the studs, not good practice.
          Whether you use helicoil or the technically better 3/8 UNC (my choice) use a jig to prevent leaning the tap when tapping the hole, either make your own jig or use the CDD studs and use the loan of the jig he offers to make sure holes are tapped correctly.

          Micky

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