Narrowing suspension leaves, how much to chop off

[Moseley]

Evening folks. So I'm in the process of fitting a THaus 4" narrowed beam and am at the point where I need to cut and dimple my original leaves. This might sound like a stupid question, but how much do I need to remove? The obvious answer is 2" each side, however, I mocked this up by installing an arm in the beam with the leaves as per standard, this gives a 62mm gap between the end of the tube and the lip on the arm. So by sliding it in 52mm (2") I'm left with a gap of 10mm between beam and arm as per the below:

I figured that this gap is for fitting the beam end seal retainers and seals, however, the seal retainers are too small for the beam and are loose, which leaves me with just the seal to fill this gap (about 8mm) diameter.

So, do I cut the leaves down more to fill the gap? What have others done?


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[Moseley]

Ok I think I may have answered my own question. I guess with the seal in place it should comfortably fill the gap between the arms and the end of the beam tube. I'll assemble everything dry again later, but by my reckoning, I'm looking at about 54mm on each side to narrow the leaves by. The dimples can then be marked up be installing the arms.


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[K@rlos]

If you don't have the seals in the arms should but right up to the end plates, I don't have them in mine for extra tuck. Have your trailing arms got the bearing races on them? They need to come off for beams that don't have the og roller bearings.

 

[Moseley]

The beam has the OG bearings, and so the arms have the races to suit. I'll see how they fit after eating dinner, but I'm presuming that because the races are quite wide, there's a bit of flexibility over exactly where the arms will sit. I'd have thought running without the seals that there's a risk of the beam tube and the arm grinding against each other, or are they dimpled in such a way that there is a small gap between each left?

Can't say I'm keen on the idea of not running any seals, but similarly, it's not worth fitting the seals if they're not snugly fitted. It seems a little bit of a bodge using the OG style seals on this particular beam as the seal 'race' cannot be fitted.


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[K@rlos]

Most people including me don't run the seals on a narrowed beam and I've never had or seen an issue. It's possible the arms are tight on the inner support collars inside the beam which is why they are not seating in the tubes right

 

[tsw]

You've probably got this all sorted now, but just out of interest for anyone else doing the same.

I have a 3" narrowed TH beam that I am in the process of fitting, and I spoke to Alex about this when I noticed that the original seal cups are too small in diameter to fit snuggly into the end of the TH beam tube.

Alex says that he drills a small hole in them and then welds them on to the end of the beam. I didn't fancy welding, so I've bonded them on with some 2-part adhesive.

What size drill bit did you use for dimpling the leaves, if you don't mind me asking?

 

[Moseley]

Yes, I never got back to this thread with what I did. So I ended up installing the seals, but leaving the seal cups off. The shape of the trailing arms means that the seals are held nice and centrally, and they just butt up against the end of the beam tube. I wasn't happy leaving the seals off as it leaves the bearings more exposed to grit and crap thrown up from the wheels - and also risks the trailing arms rubbing against the beam tubes as presumably they would have to be drilled incredibly accurately to leave just a tiny gap between each; again, to minimise ingress of crap.

In terms of drill bits, I ended up borrowing one from a chap at work to use in a pillar drill here. The bit was massive, but the cutting 'blades' were at a 90 degree angle to each other, and it has a nice point to it, so was a good match to the original dimple shape. You basically need to find a bit with the same profile as the locking bolt, and a pillar drill is definitely a must with plenty of cutting fluid to keep the temperatures down.