110 Chassis datum

[uninformed]

Hey all,

I found this diagram in the WSM, it’s useful for the work I’m doing. Does anyone know with any accuracy what the two datum points are for Chassis Datum BB? I’m guessing the highest points of the chassis rail at each axle. On the actual chassis box section, not on brackets or such?

 

[Paul C]

It would look to be the top of the rails, if you check the measurements they give you off that datum it will verify it, I can only see 4 measurements given off of it, the top hole of the panhard rod mount, the front radius arm mounts and the rear crossmember height and the top of the front outrigger 100-103mm.

[Snagger]

The datum can only be from the tops of the chassis rails - there is nothing else present to set the initial alignment in the jig.  I would expect the datum to be on the flat tops of the sections, not the raised weld, as the weld will have variable thicknesses from one chassis to another.  The spring seats would be added after the main rails were secured (inverted) in the jig, so they won’t be the datum.

[uninformed]

1 hour ago, Paul C said:

It would look to be the top of the rails, if you check the measurements they give you off that datum it will verify it, I can only see 4 measurements given off of it, the top hole of the panhard rod mount, the front radius arm mounts and the rear crossmember height and the top of the front outrigger 100-103mm.

So much of my chassis has been cut and shunt nothing original left to verify both ends lol…

[uninformed]

32 minutes ago, Snagger said:

The datum can only be from the tops of the chassis rails - there is nothing else present to set the initial alignment in the jig.  I would expect the datum to be on the flat tops of the sections, not the raised weld, as the weld will have variable thicknesses from one chassis to another.  The spring seats would be added after the main rails were secured (inverted) in the jig, so they won’t be the datum.

That’s a fair assumption and that’s what I’ve gone with. The inner C  section of chassis is higher than the outer and at those points, higher than the welds so all good. 
 

Now I’m also hoping the body line is parallel with that. It appears (as accurately as that drawing allows ) that all the rear load points are… that’s what I’m going with anyway 

[Snagger]

Ah, yes, they have different sized C-section rail sides rather than the joggled flange for the seam of the SIII 109, so the weld depth or unevenness of the joggling is not a factor for you.