Suspension help/advice (1 Viewer)

[nor_cal_cyclist]

Greetings -

Got my FJ40 @TRAIL TAILOR 's shop for a body off frame cleanup/resto-mod, and trying to get my suspension figured out. Primarily a rock crawler/trail truck that will be driven (on 37's) to and from events/runs (ie highway miles). My last 40 was SOA/SR, but was thinking of going linked after watching countless hours of YouTube and reading MUD & Pirates. I know Proffitt's likes the SOA front/linked rear for the type of truck I'm designing. Not sure on links at all, seems like more stuff to break, but Trail Tailor seems to like the idea and keeps nudging me in that direction.

I figured I'd add a little WB with the SR, but planned to keep the rear in the same place (at least that's my initial thought).

Questions:
1) Can I link the rear without cutting more than a fender flare opening - looks like most guys really open up the rear wheel well?

2) Benefits or problems to running a 4-link with parallel control arms and a panhard vs a triangulated 4-link?

3) Other suggestions - yes, I know this is a can of worms

Thanks - looking forward to getting this figured out and ordering a pair of ProRock D62's to wrap up the "major parts" needing to be ordered (drivetrain got yanked this weekend, so the process has begun)

 

[peesalot]

worst issue is with stock width axless you have no place for the coilovers or shocks.
some cut frame and tube it, some use the Genright frame towers that section into the frame, somego full width.

 

[69LC]

One option to consider for the lack of space referred to above could be avoided with neatly tucked coilovers between the frame and lower rear links by angling them forward. Find someone to help you calculate spring rates and shock valving.

A single or double triangulated 4 link, or three link with an upper wishbone will give you good movement without the side shift that using a track/panhard bar does.

A disadvantage of parallel links is that they don't allow for anti-squat tuning, or for pinion pitch for the rear. If you want a lot of travel, the more you axle rolls (like a swingarm) the less angularity the rear u-joint will need. Most of the common fj40 traction bars are good in this way. Then you rely more on a cv at the tcase.

Another thing to consider while designing where to mount the springs is that the further outboard you mount them on the axle, the less forced articulation you will get.

 

[mr jits]

I would have most of this worked out in my head before ever dropping my rig at a shop to be built. The amount of money you're going to spend on "development" time, is going to make a dent in your budget.
For your plans, I think an 80 series frame swap would be perfect. I wish I'd have gone that route when I'd first started my last 40. The drivability, and modern ride are just awesome. Add to that serious offroad abilities with even a stock 80 suspension and it's a nice starting point.

 

[nor_cal_cyclist]

I would have most of this worked out in my head before ever dropping my rig at a shop to be built. The amount of money you're going to spend on "development" time, is going to make a dent in your budget.
For your plans, I think an 80 series frame swap would be perfect. I wish I'd have gone that route when I'd first started my last 40. The drivability, and modern ride are just awesome. Add to that serious offroad abilities with even a stock 80 suspension and it's a nice starting point.

I thought I was going to go SR/SOA again...just strated exploring options when they were presented

 

[TRAIL TAILOR]

I would have most of this worked out in my head before ever dropping my rig at a shop to be built. The amount of money you're going to spend on "development" time, is going to make a dent in your budget.
For your plans, I think an 80 series frame swap would be perfect. I wish I'd have gone that route when I'd first started my last 40. The drivability, and modern ride are just awesome. Add to that serious offroad abilities with even a stock 80 suspension and it's a nice starting point.

@nor_cal_cyclist I still hold to my suggestion of the coil conversion based on the 80 design...

J

 

[nor_cal_cyclist]

worst issue is with stock width axless you have no place for the coilovers or shocks.
some cut frame and tube it, some use the Genright frame towers that section into the frame, somego full width.

Figured I'd go FJ60 width (gain 3" overall) for the coil buckets. Also adds a little stability. Not too sure about 80 width - seems like a LOT of extra width I'd be adding.

No comments on the rear wheel well cuts? Honestly, that might be the deal breaker on a linked rear - personally don't care for the look of the stretched rear/extended wheel well.

Thanks!

@nor_cal_cyclist I still hold to my suggestion of the coil conversion based on the 80 design...

J

@TRAIL TAILOR - I hear ya...as an Engineer, I am probably the MOST resistant to change personality you'll come across. Conservative by nature, and more so on this build after spending so much time on my last FJ40 re-doing stuff I "thought" I had figured out. Just making sure I/we get it done "correctly" the first time - for driveability, wheeling capability, durability, maintainability, and overall looks (bothering to resto-mod, better look good, to my eyes, in the end).

 

[deliverance]

37’s in the stock rear wheel location will be tight and most likely limit up travel. I pushed my boy’s back about 3-4” with fj55 springs and kept the original contour of the opening while enlarging it up and back, which to me is just as aesthetically pleasing. I’m not a fan of the “comp cut,” where it’s opened to the back of the tub. But again, that’s my subjective opinion.

 

[74fj40]

You don’t have to comp cut for a stretch. Sitting at 105”. Plans for links down the road.. but kept Leaf springs for now. Fzj80 rear. Widened fj60 front. 4.5” backspacing on wheels

 

[cseitz]

When I originally moved my rear axle back, I moved the stock rear curve of the fender back the same amount as my axle. It kept more of the original fender look. I was unhappy with the front portion of the fender, so I ended up moving the front portion of the curve back as well. Similar to what @74fj40 did above.

 

[cseitz]

Also, I didnt see it mentioned, what power train are you using? That might also dictate some of you suspension design choices. Automatic? Manual? Single t-case? Doubler? All stuff that should be included early. I know I might sound like a broke record, but "Do it right and do it once". I didn't take this advice and it cost me a lot of time.

 

[nor_cal_cyclist]

Also, I didnt see it mentioned, what power train are you using? That might also dictate some of you suspension design choices. Automatic? Manual? Single t-case? Doubler? All stuff that should be included early. I know I might sound like a broke record, but "Do it right and do it once". I didn't take this advice and it cost me a lot of time.

Crate LS3 tied to a NV4500 and an Atlas (2-speed). Axles were planned as ProRock 62's. I figured I had some time on the suspension, as my Atlas is still at least 4-5 weeks out.

 

[SuperBuickGuy]

I did a 3 link front, triangulated 4 link rear. Only move the axles 2 1/2 forward and rearward from stock. I do a lot of suspensions and think that stretching anywhere where you need to turn really isn't worth it. calculate your instant center correctly and you'll climb what longer wheelbases will struggle climbing. ... how to is in my build Shipwreck... good luck.

 

[Dimples]

If your considering parallel with a panhard you could do trailing arm lowers and move the springs/shocks/coilovers forward to eliminate issues with tire clearance issues at the axle. Just a thought.

 

[Mace]

Questions:
1) Can I link the rear without cutting more than a fender flare opening - looks like most guys really open up the rear wheel well?

2) Benefits or problems to running a 4-link with parallel control arms and a panhard vs a triangulated 4-link?

3) Other suggestions - yes, I know this is a can of worms

1) Yes, but you may be sacrificing the link length and adding other issues.
2) parallel 4 links don't flex much at all. The problem is that the axle has to rotate to flex, and that is severely hampered with a parallel 4 link. That is why three links are more common. Dual triangulated 4 links are really the way to go. Less axle walk, and as much flex as you want.
3) Lots of ideas, need to know where to start.

 

[nor_cal_cyclist]

I got "gun shy" on the suspension and am dropping back to what I know and am comfortable with for wheeling: SOA w/an anti-wrap/traction bar for the rear.

That said - any suggestion for a starting point on my front axle if wanting to go SOA? Diamond is recommending/guessing at raising the pinion 5* for a good starting point. It will have new Alcan springs - about stock amount of arch, so not much additional lift other than the 5-6" from the SOA.

Final decision to go with Diamond, since Dynatrac wanted more measurements/dimensions than I could get without having axles to mock up the suspension first. Seemed like a chicken-egg situation. MUCH harder to get this project really going than I thought it would be - even without the delays COVID/social unrest has caused.