How tough is it to replace the ball joints on a 1967 340? Is it easier in the long haul to remove the complete suspension first? I've never done either of these jobs.

 

The ball joints are easy to replace. You just need a ball joints remover that breaks the hold they have in the tapered hole they mount in. They come in many shapes & sizes.

 

Before starting, check the whole front suspension for wear and free play. This includes the wishbone bushes and wheel bearings as well as the ball joints.

For the top joint, take note of the shims that control castor angle (and camber to some extent) and don't lose any. Put them back in the same position, if you don't want to alter the suspension geometry. The bottom is the more awkward to remove. In a many, but not all cases, if the joint has been regularly greased, the wear is restricted to the railco socket that sits in the cap on the underside of the wishbone. It's easy to replace this and then adjust for tightness with the appropriate shims. I'd buy the whole kit and then swap what's necessary.

The work definitely need one of Glyn's splitter tools plus some carefully judged, simultaneous blows from a pair of half pound hammers, one each side of the taper. And finally, for the safety of the car and yourself make sure it is redundantly supported on axle stands.

 

I just thought I should throw this out there- the lower ball joints can be replaced by the same units for the xjs and the xj40s. I used the newer lowers and uppers both on my S-type when I rebuilt its front end. The lowers' number is JLM11860. The uppers have a different part number for the 340 than the s-type, but (please correct me) I believe the front suspension for the mk2 series and the s-types are same, unless their steering knuckles are different.....
regards Jerry

 

The front end suspension was not changed from Mk2 to S Type. Some convert to the 420 front end because pads are more readily available & cheaper because the front brake calipres were changed/improved on the 420.

 

Don't bother trying to replace the old-type lower ball joints that date from 1955. Instead, fit the Lemforder all-in-one balljoints that first came out with the XJ40 series of the XJ saloons. These last forever, (or almost !!), and are a doddle to fit.
This is a British supplier, but there are US suppliers as well.
https://www.jagshop.co.uk/product/41...int-cac9937lem
Here is Moss
https://mossmotors.com/cac9937lem-lo...emforder-brand
You'll probably need the top ball joints too
https://www.jagshop.co.uk/product/41...int-cac9938lem