Why are torque specs varied?

[ManzanoNissan]

Hey everyone. So couple questions, 1) Haynes manual is the best buy for all the torque specs I need to work on my 1991 D21 4 cylinder 4x4? Or is there something better I'm not aware of?
2) I'm doing some work and I've found the torque specs that I've gathered online suspect. I'm about to do the upper and lower ball joints and here too I find torque specs that are varied for example:

upper balljoint to knuckle spindle - 58 to 108 ft-lbs
upper balljoint to upper control arm - 12 to 15 ft-lbs

lower balljoint to knuckle spindle -87 to 141 ft-lbs
lower balljoint to lower control arm - 35 to 45 ft-lbs

I'm not used to varied torque specs, I've been learning this mechanics craft on an old Mercedes where the torque specs are precise. Can someone explain why the varied specs (almost double in a couple instances) and which number are you supposed to settle on?

Thanks all.

[VStar650CL]

There's no '91 FSM here in Nico but there is a complete '90, see FA-5 here (pdf page 1047) for the front end torque specs:
https://www.nicoclub.com/service-manual ... k_1990.pdf

Nissan puts almost all their torque specs into the exploded drawings. There's a legend at the bottom of the diagram, lbs/ft is the second number in parens. So your Haynes is correct, the upper is indeed 58~108 and the lower 87~108. For ball joints the only concern is having the tapered shaft fully seated into the tapered hole, so in practice the absolute torque doesn't make much difference as long as it's "tight enough". The same is true of almost all tapered front end parts.

[ManzanoNissan]

There's no '91 FSM here in Nico but there is a complete '90, see FA-5 here (pdf page 1047) for the front end torque specs:
https://www.nicoclub.com/service-manual ... k_1990.pdf

Nissan puts almost all their torque specs into the exploded drawings. There's a legend at the bottom of the diagram, lbs/ft is the second number in parens. So your Haynes is correct, the upper is indeed 58~108 and the lower 87~108. For ball joints the only concern is having the tapered shaft fully seated into the tapered hole, so in practice the absolute torque doesn't make much difference as long as it's "tight enough". The same is true of almost all tapered front end parts.

Thank you again for the education and the resources Vstar. I've downloaded a copy for my files.

The question about why it's varied comes from installing the front lower shocks. There's a single bolt that ties the shock to the lower frame by going through the frame into a framed nut. There's a limit to the torque there in that you can't tighten past what the frame will allow. I mean I guess there's people out there strong enough to keep turning the screw head until it snaps but for me the bolt tightened to the frame before the lower torque spec. I moved to using 'tight enough' from there on and I still don't get why unless I was using ratios not for my truck.

[VStar650CL]

Shock bolts are a little different for reasons I expressed in your other thread, but it's the same in one way, which is that in both cases, there's almost no dynamic load on the fastener which would tend to loosen it. With a ball joint or tie-rod end there's zero turning force applied to the nut as long as the ball doesn't bind, for a shock retainer with a transverse eye, almost all the applied force is perpendicular to the bolt or stud with no rotational component. So in both cases the torque spec is likely to be wishy-washy, simply because no engineer wants to put "tight enough" into a service manual.

[ManzanoNissan]

Shock bolts are a little different for reasons I expressed in your other thread, but it's the same in one way, which is that in both cases, there's almost no dynamic load on the fastener which would tend to loosen it. With a ball joint or tie-rod end there's zero turning force applied to the nut as long as the ball doesn't bind, for a shock retainer with a transverse eye, almost all the applied force is perpendicular to the bolt or stud with no rotational component. So in both cases the torque spec is likely to be wishy-washy, simply because no engineer wants to put "tight enough" into a service manual.

hahaha I get it. Well I've learned something new out of this process. Thanks again VStar!

[VStar650CL]