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Moving holes by 1/2 dia in a flange.

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  • Moving holes by 1/2 dia in a flange.

    I am converting my classic land rover to discovery axles, for several reasons, one of which a more suitable diff ratio for the range rover engine.
    This requires 'moving' the holes in the flanges on the ends of the axle by 8 degrees.
    This means that the holes are moved around so that the new hole is 1/2 in new metal and 1/2 in the original hole.
    I've machined up jig plates to drill the holes with.
    I started out by filling up the old holes with mild steel allthread bar, welded up at the back, I did this as drilling/tapping weld is not something I wanted to do which would be the case if I just fully welded up the old holes.
    Problem is tapping 1/2 allthread and 1/2 steel is very tricky I think the allthread bar twists a little from front to rear as I turn the tap gripping it, I did one side but now its time for the other side.
    Are there any little tricks I can do to make this easier, or shall I just tackle the job the same as the previous side.
    I didnt want to remove or make new flanges as I dont have the measuring facilities or equipment to postion the flanges square, so re-drilling is the only option.

    Last edited by dr pepper; 12-07-2010, 07:07 PM.
    Build it, bodge it, but dont buy it.

  • #2
    I must be missing something. Why didn't you just clock the holes further to drill into solid material?


    • #3
      That would have made things easy, the hubs have to be rotated 8 degrees to get the corect castor angle, and the correct diff drive flange angle, thats why its like it is.
      Could do with some means of locking the front end of the allthread to the flange, I dont want to weld it as the casing wont go in my mill to reface it, the back edge isnt a gsket surface so doesnt matter as much.
      Maybe a 3mm or 4mm grub screw screwed in on the edge of the 10mm plug opposite the new hole might do the trick.
      Last edited by dr pepper; 12-07-2010, 07:45 PM.
      Build it, bodge it, but dont buy it.


      • #4
        Couldn't you just wedge the spring pads 8 deg and achieved the same thing?
        It's only ink and paper


        • #5
          Originally posted by Carld
          Couldn't you just wedge the spring pads 8 deg and achieved the same thing?

          Good idea. Also I recall from my hot-rodding days that spring shops have those tapered shims or wedges if you will available in different angles.


          • #6
            yes I spose I could.
            8 degrees is a fair old setting, and also I have spacers under the axle to lift it up to clear the different steering track rod, the angle plate would angle the axle in the opposite plane bringing the track rod closer to the springs which would require even more spacing under the axle losing ground clearance.
            Its been head scratching all the way, and a few have said why bother.
            I dont think theres a way of avoiding the drilling, more a case of doing it so that the holes will tap easily.
            Build it, bodge it, but dont buy it.


            • #7
              A permanent locking Loctite or just an epoxy such as JB Weld might give you enough additional holding to keep the inserts tight. You would have to be sure the threads are clean and oil-free. Don't let the adhesive get hot when drilling. I would try this first as I have done similar work repairing holes that were stripped and drilled crooked. Strength is rather remarkable if there is a lot of good clean contact area.

              If you have the capability you could turn up some inserts with a slightly oversize thread so they would screw in tightly, but they might loosen when you drilled the new hole. Something like tapered pipe plugs might be another possibility.

              Would it be feasible to relocate holes or studs in matching part so they can all be in totally new material?
              Last edited by Don Young; 12-07-2010, 09:21 PM.
              Don Young


              • #8
                Thats a good idea, I have some structural strength loctite adhesive, and some quick metal, might just make a dummy jig and see if it works.
                I have a thread cutting lathe, with the correct back gears, what kind of oversize would you turn it up to +0.05mm?, I cannot go really tight as screwing it in would be an issue, I have to screw them in with a flat blade 'driver.
                My backup plan is along the lines of relocation, if a forbidden tap breaks or hole screws up then I'd make a thick washer cut into 2 c shapes, with the holes tapped in the right places and put this behind the axle case flange and drill out the original flange holes.
                I have a rough but effective spark eroder built from junk for demolishing broken taps and bolts.
                Last edited by dr pepper; 12-07-2010, 09:55 PM.
                Build it, bodge it, but dont buy it.


                • #9
                  Drill and tap an 8-32 hole in the edge of each inserted part on the side away from the hole. Twist in a set screw.

                  I see it was mentioned earlier. I think it is a good idea.
                  Last edited by Evan; 12-07-2010, 11:12 PM.
                  Free software for calculating bolt circles and similar: Click Here


                  • #10
                    my free advice

                    Dont' use allthread. It is the lowest grade possible. Unless you have specifically asked for a grade

                    Drill out the old holes, insert a plug and weld them at both ends. Grind smooth on the ends. Center drill, drill and tap.

                    Buy a new tap. Seriously. This is an important job. Buy a damn good tap. Not the pepboys or Canadian tire one. KBC, SOWA, FULLER, etc.

                    Good luck DR Pepper,



                    • #11
                      I used a new tap on the other side, a dormer as used by aerospace, spiral taps as used by cnc's are a little expensive.
                      Maybe I did the wrong thing with the allthread, I didnt want a high tensile bolt as I was concerned about the drill wandering into the softer flange metal, as is allthough not perfectly square the hole is parallel right through.
                      I dont know what the flange is made from it doesnt look flame treated or anything.
                      The screw opposite the hole is what I'm going to do different on the other side, welding the outside edge of the flange is a preffered not to do as if I atack it with a grinder afterwards I'm gonna get leaks.
                      Last edited by dr pepper; 12-07-2010, 11:27 PM.
                      Build it, bodge it, but dont buy it.


                      • #12
                        About the leaks, fill the housing with about a cup of wheel bearing grease. That will mix with the oil and make it much less likely to leak. I rebuilt the front end on my Series II including the u-joints and all the seals on the Swivel Pin Housing back in the 1970s and it hasn't leaked yet.

                        Which model is that?
                        Free software for calculating bolt circles and similar: Click Here


                        • #13
                          Never heard that one before, done that on chains but never on an axle.
                          Mines a kid compared to yours its a '80 series 3 long wheel base with a mil hard top back.
                          Was a petrol, now a diesel with discovery axles.
                          I wouldnt butcher a series 2 or 2a.
                          Glad to see yours is still running.
                          Mi dads old '70 swb is still going, and my mrs had a lwb mil petrol '71 for 15 years, thats still going too.
                          Build it, bodge it, but dont buy it.


                          • #14
                            is it just me that does not like the look of that?


                            • #15
                              It'll work just fine. The old Rovers are built like a tractor. In fact, that is one of the uses it was intended to fulfil. Mine is over 50 years old and the engine has never been rebuilt. It could use some new valve guides and maybe some oil rings but it runs just fine. I started it without trouble at -15 the other day without auxiliary heat. I use it regularly on the property all year long.

                              The body is aluminum and the chassis is hot dip galvanized as are nearly all othe steel parts. The entire thing is bolted together and can be stripped down to a chassis in a day. The tranny lifts out from the top after removing the bonnet, folding down the windscreen, unbolting the hood and removing the seat base.

                              It has a 45 hp engine and in the lowest gear the total drive ratio is around 44 to 1. I can lift off the driver's door so that I can walk along beside whilst steering so I can see what is going on better. It has a hand throttle to set rpm's and is rated at a full half ton cargo even though it only has an 88 inch wheelbase. It will pull stumps, pound posts and grade my driveway in summer. I plow snow with it in the winter and the heater even works.

                              Free software for calculating bolt circles and similar: Click Here