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Coil sprung axle to leaf spring conversion


Les Henson

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This is how I've converted a coil sprung axle off a 1987 110 to go on a SWB S3. There are a few ways of doing it I think, so this is just one (and the only way I could figure it out).

This is the axle casing alterations only - steering etc has yet to be figured out.

Fortunately, I have a series front axle to take measurements from, so it was just a case of copying distances, diff nose angle, spring seats, etc.

Fortunately - the distance between the chassis rails is the same for 90/110 and series vehicles, so the bump stop can stay where it is, and only clean up and fabricate the spring seats is necessary. Nearly all the metal used is 8mm, with the exception of the bump stop blanks, which are 6mm.

The axle is stripped right down, H/D diff pan was welded on a few weeks ago, guts of the diff are removed, but the housing has been replaced in order to copy across the correct diff nose angle (same as the series).

First - remove unnecessary brackets - leaving just the bump stops.

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Careful removal of the welds/rust takes some time and a bit of care.

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The bump stop mounts are open one end, so are blanked off (6mm plate)

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The bump stops are wider than the spring seats, so it's of no use using them as a reference. Mark the dead centre of the axle, and scribe a line right round it. Measure the seat distance from the centre of the series axle, and also from the edge of the axle end (divide up and discrepencies - I had 2mm). Mark the inner and outer edge of the spring seat on the axle case.

Series spring seats are 4-inches long x 2 1/2" wide.

Correct spring seat location is 143mm in from the axle end, and 336mm in from the centre line (both ends have to be the same). A bare defender axle case is 1088mm long - if you do the maths, there's 3mm not accounted for somewhere, but is probably me tarting things up with an angle grinder/flap wheel.

Easy end first - the long side. The axle tube is 80mm in diameter, so a couple of saddles to fit, plus the spring seat, which has a 12.5mm hole in it for the leaf locating pin.

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Assembled on the bench, welded inside and out, cleaned up on the outside only.

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Note the angle to set the diff nose.

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Clamped in place, angle checked, then welded on - inside and out.

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Awkward little pokey hole, so filled it with weld and then tidied it up.

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Other end next - this is more difficult as it's right on the profile of the diff housing, so no plate on one side, but the other side has a saddle - very similar to the other side. Spring seat first - exact same measurements as the opposite end, and same angle too (I cut this one off twice before it was in the right position).

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Weld into position as far as possible.

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Saddle on the outside - 80mm dia.

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Welder on full chat - max wire and amps :)

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Birds eye view of the diff nose angle.

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Ends blanked off in a similar fashion to the other end.

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The final thing - showing both spring seats and the noticeable angle of them.

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A few important things to remember -

Make sure you are aware of the axle position on the bench - relative to the spring seats at all times (you could set the diff nose angle the wrong way).

Make sure both spring seats are in exactly the same position/angle as each other and also relative to the vehicle the axle is being fitted to.

Don't use less than 6mm plate - anywhere. I used 8mm to be on the safe side and also 'cos Fridge told me to :) (thanks for your help m8)

Measure everything at least twice - if you get it wrong, strange things will happen to the vehicle when you drive it :P

If anyone has done this themselves, then I would appreciate comments on what I've done - right or wrong.

Les.

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I have done it myself - very much as you did Les,except for two differences :

I carefully separated the spring seats from a series axle,and used those,rather than fabricating them.

I wouldn't say one method is better than the other,I just had some scrap series casings around.

I didn't replicate the series diff nose angle,but rather adjusted the spring seats to suit the long military shackles and standard coil spung track rod that i was using.I lost a degree or so of caster.

Very tidy job as usual,and very good write-up.

Cleaning up of the coiler axles took me a hell of a long time.

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I did very similar but ended up cutting my neat welds off and re welding until I had a satisfactory compromise between diff angle,castor and steering drag link clearance,

I have seen on here somewhere someone making longer than usual saddles and compensating with longer spring shackles to give clearance for the steering drag link/track rod.

If I were to do it again I would love to come across a td5 front axle with mountings to enable me to move the track rod to high on the front rather than low on the rear.

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When I did mine I calculated that the diff mounting face would need to be 12 degrees from vertical to give a caster angle of 3 degrees.

Isn't the mounting face on a series axle vertical? Therefore mounting the coiler axle the same would give you 15 degrees of caster.

I used the longer rear shackles so the track rod would clear.

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I think you would lose 2-points? Axle and brakes - rear axle as well would be 3 I think.

I really don't know - I'll be losing all the points :)

Mine was originally tax exempt - registered in Feb '73, but made in Dec '72.

Les.

Thanks Les,

Brill as usual, I am just considering this though I may be removing the old seats from a Series axle for more work!

Didn't think Brakes had points??

As the suspension is the same it is arguably the same as just replacing an axle. No way DVLA would agree I know.

As I keep griping, I have looked at Classic Ford, Total Off Road and Custom Car mags and all the modified motors in them are ilegal on the SVA points system.

Marc.

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just got me thinking,

arent the bumpstop pads supposed to be perfectly level horizontally when the axle is at the correct caster angle/diff nose elevation?

Therefore getting the new leaf spring pads mounted correctly should be easy by just referencing the new pads from the bump pads?

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Well, no. If the bunp stop pad and spring seat were square with each other, then there would be no diff angle, The diff angle is set and at that angle, the bump stop pad should then be in a poition to strike the rubber square on. As it's quite rare for an axle to actually hit the bunp stop - I don't think it matters if it's at a slight angle.

Les.

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Well, no. If the bunp stop pad and spring seat were square with each other, then there would be no diff angle, The diff angle is set and at that angle, the bump stop pad should then be in a poition to strike the rubber square on. As it's quite rare for an axle to actually hit the bunp stop - I don't think it matters if it's at a slight angle.

Les.

I think what Nick meant was that: if you could assume that with the face of the spring seat horizontal the diff axis is at the correct angle (with respect to the horizontal), AND if the face of the spring seat is meant to be horizontal when the angle of the diff nose (with respect to the horizontal plane) is correct, THEN to ensure the correct angle of the spring seat you just need to make sure it is parallel with the bump stop face.

On the otherhand on a coiled axle the bump stop swings through an arc as it is constrained by the radius arms so good design would demand that the face is parallel with the bump stop at the extreme of articulation (fully compressed) and not when the axle is at rest. Which might mean that it is unlikely that the bump stop face is horizontal when the axle is at rest.

Of course I haven't checked any of the above by looking at an axle :D

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I think what Nick meant was that: if you could assume that with the face of the spring seat horizontal the diff axis is at the correct angle (with respect to the horizontal), AND if the face of the spring seat is meant to be horizontal when the angle of the diff nose (with respect to the horizontal plane) is correct, THEN to ensure the correct angle of the spring seat you just need to make sure it is parallel with the bump stop face.

Sounds true except that the bump stop on Les's axle has not been changed and so is I think, not at the correct angle?

A coiler front axle hinges on the rear by the radius arm, a leaf hinges on the front and flattens under preasure, which means that the pad will be angled down at the front edge when the coil axle is transfered to the leaf (I think)??

Add to this the lifting of the diff nose which will make the above even worse?

I guess this really needs to be modelled to see the actual movement of each suspension type. Anyone fancy it?

The only concern I would have is that if the bump stop is at an angle then the gap between the chassis stop and the edge of the pad is reduced thus reducing the available upward travel which aint great to start with.

I am quite happy to be shown that this is incorrect especially if it makes the work less :D

I too would love for Les to offer to do mine :P

Marc.

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Well this is very interesting, technical, and thought provoking.

I just have a really bad headache now :( .

There's no way I'm cutting or altering anything now - it's painted and will stay the way it is - forever

Would you take an angle grinder to such a beautiful thing? :lol:

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Les :)

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