Measuring DIY Lift Kit Height on 1977 FJ40

[gashalot]

I found and bought a lightly modified 1977 FJ40. Early owners did some period modifications: Chevy 350 swap w/ Advance Adapters gear, extra tank, winch, and a lift. They were also good at keeping notes and receipts, with one exception: the front lift. The first owner was a pretty talented metal worker, so he custom fabricated his own front lift with something akin to an anti-inversion setup.

I need to estimate the lift height before I order new shocks. Based on the measurements below, I think I'm looking at a 2.5" lift (primarily based on rear shackle), but I'd welcome second opinions before I learn the hard way.

Data and parts I can confirm:

• Front Shock: old Rancho RS5113. Modern part# RS55113, works with 2-3" front lift.
• Rear Shock: old Rancho RS5116. Modern part# RS55116, again a 2-3" lift.
• Rear Shackle: ~5.2" bolt center-center. (Approx using calipers, picture below).
• Front custom welded anti-inversion-style shackle: ~5.1" from center of bolt to bottom of frame rail (approx). No idea what dimension to measure here.
• Front rear attachment also custom welded. Unclear what dimensions to measure here or if they matter.

Pictures of all key parts below. Thanks in advance for anyone who might help me with the mystery!

 

[franklin40]

are you doing just shocks or springs too? if just shocks take them off and find a ditch and stuff one corner and measure the compressed distance between shock mounts. then measure the ones that are drooped and that’ll give you the most accurate measurements

the shackle reversal you have will make for variables that will be too inaccurate to guess. best to just measure

 

[Rocky_LC]

Are you going to keep the front shackle reversal?

 

[B y r o n]

I appears you have a shackle reversal on the front. Here is some additional information on it.

 

[gashalot]

I appears you have a shackle reversal on the front. Here is some additional information on it.

Extremely helpful! Having read, and to @Rocky_LC 's question, I think the answer is yes, keep the reversal. Thank you both for the gentle nudge to understand WTF I was looking at.

That decision is entirely pragmatic. My use case is rough and poorly maintained forest roads in the Pacific Northwest. Reliable fun. Given this setup has lasted ~30 years, I'm inclined to keep it so I can divert my rebuild funds to drivetrain reliability and some other creature comforts.

To @franklin40 : thank you! I'll do that measurement tomorrow. I already "own" said ditch. Once I confirm loaded / unloaded lengths, is there any other "reason" to study the attempted lift height? Later spring replacements?

 

[rlong]

It is probably most reliable to flex the suspension fully with a floor jack on one side of the anxle and measure at the shock pins on both sides; one fully compressed and the other in full extension. Then confirm shock lengths that won’t bottom out in either direction and have a little room for error

 

[jim land]

You have 2.5" lift spring, with the shackle reversal it give 1.5" more , so it is a 4" total lift , longer rear shackle is to make level

If you flex it and the shock are not limiting the articulation, just buy some same lenght shocks
Or remove the shocks and flex it to the max to see open and close ideal lenght you need

 

[pb4ugo]

For a compression measurement, you can measure pin to pin then subtract the distance between the bumpstop and axle will get you close. The extension is s little more difficult. Using a floor jack may not have enough height to get the opposite wheel off the ground. You might be able to get close at full droop the add some. Best is to put the suspension in a bind to get a tire or two off the ground. Maybe find or make some type of rti ramp or a log. Most shock manufacturers give extension and compression #'s