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88 4Runner - Help me figure out my rear 3-link

ScaldedDog

Well-known member
Joined
Nov 26, 2020
Member Number
3082
Messages
61
Situation: '88 4runner with front 4WU 3-link, and leaf springs in back. Front axle forward 3" with 42" lower links. 111" wheelbase. 39.5" Pitbulls wheeled at 4psi, so they wheel really small. 66-65" Diamond axles with 8" 3rds.

Project: I love the way the front works, and have found the extended leaves in back frustrating, so I'm 3-linking the rear, also with 4WU stuff, and looking to slightly extend the wheelbase - to 112" - in the process.

Question: I'm trying to figure out where the lower frame mounts should go, and what length lower links to run. The photo below has the rear axle at 112" and at ride height, with the frame mounts pushed as forward as far as they'll go. Rear links are 43" long. My concern is that the link brackets hang really low, and the center point between the axles - where breakover angle would be measured - is pretty well back on the bracket. In other words, I'm concerned about hanging up a lot.

20240814_180034.jpg


I'm thinking I'll move the brackets back, but the question is, how far?

1" back - nets me 1/4" vertically at the breakover point, and makes the rear lowers 42", which matches the front. I don't really care about sparing links, as I'd never carry a spare link on the trail.

3" back - nets me 3/4" vertically at the breakover point and makes the rear lowers 40".

5" back - nets over an inch vertically at the breakover, and largely removes that from being a consideration (other than the fact that the brackets have to be low somewhere, but that's not avoidable). It makes the links only 38", though.

What's the right compromise? Any real-world functional difference between a 38" and 42" link? Are the anti-squat numbers going to get better, or worse, as I move the frame mounts back while keeping everything else the same? (I have to confess to not understanding that part of suspension geometry very well.) Do any of you guys run a 4WU 3-link? What's your experience with hanging up on these brackets?

Talk to me, guys...

Mark
 
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4wu rear kit, correct? Curious what Brian suggests and how you like it overall.
 
LOL! Yeah, I'll call him tomorrow. Still interested in other folks' opinions and experience, though.

Mark
 
ScaldedDog said:
LOL! Yeah, I'll call him tomorrow. Still interested in other folks' opinions and experience, though.

Mark
Click to expand...
No clue here. But glad you still have the 4Runner and still bummed I didn't buy it. :flipoff2:

Take pics, etc.. Very curious how it goes together
 
First thing I'd do is learn how to use a tape, because no fucking way those are 43" long :flipoff2:

When you say 43" you must be referring to the length of tubing, because those look like 60" eye to eye :flipoff2:

For a trail rig, there is no real benefit to super long links. I'd move that mount way back where you like it, make some pvc mock up links, cyle it and see if it does anything funny like shoot the pinion to the sky (it won't, but it's easier to make the steel shorter than longer)

General rule is eye to eye length equal to tire size, but that's just rough. Lots of jeeps with short arms (like 28"?) out wheel shitty long arm kits. Guaranteed you'll noticed hanging up on those mounts 100x's more than any characteristic of a short link.
 
rockota said:
No clue here. But glad you still have the 4Runner and still bummed I didn't buy it. :flipoff2:

Take pics, etc.. Very curious how it goes together
Click to expand...
Can you believe it was 24 years ago next month? I bought it from Scott on a business trip to the Bay Area, canceled my return flight and drove it home to CO. We were young men then. You may still be. :grinpimp: At 66, I expect this will be the last big project I do on this thing. I will post pics!
YotaAtieToo said:
First thing I'd do is learn how to use a tape, because no fucking way those are 43" long :flipoff2:

When you say 43" you must be referring to the length of tubing, because those look like 60" eye to eye :flipoff2:

For a trail rig, there is no real benefit to super long links. I'd move that mount way back where you like it, make some pvc mock up links, cyle it and see if it does anything funny like shoot the pinion to the sky (it won't, but it's easier to make the steel shorter than longer)

General rule is eye to eye length equal to tire size, but that's just rough. Lots of jeeps with short arms (like 28"?) out wheel shitty long arm kits. Guaranteed you'll noticed hanging up on those mounts 100x's more than any characteristic of a short link.
Click to expand...
LOL! I promise the rears are 43" eye-to-eye, as shown in the photo. The presence of the wheel in front, and absence of same in the back, causes the rears to look freakishly long. I was thinking 40" would be about right, but am not certain that would move the bracket back far enough. I could move the axle back more, of course, but I think 112" is on the long end of optimal with my smallish 40's.

Mark
 
That frame bracket is insanely large. I'd be figuring out a way to make that much shorter. I get the theory about why they designed it to be a long ramp but it still seems extreme.
 
Making it shorter won't give him more clearance though. But ya, it does look gigantic.

What size shock in the back?

I still say go less than 40, like 35-37" unless Brian has a major reason not to.
 
Yeah, I don't mind the length, and wouldn't mind the depth if I was on 42" stickies that I could run at 10psi, but that's not what I have. It's pretty low when aired down. I'm thinking back 5" for 38" links may be the ticket. If I talk to Brian I'll let you know what he says.

Mark
 
Oh, I forgot to answer the shock length question. 14" FOX coilovers, just like the front. 5-6" uptravel at the shock.

Mark
 
burn them in when the wheel base matters, bridge the the front and rear brackets, flat skid plate a crossed.

you are overthinking this
 
I heard back from Brian at 4WU. He said the rear lowers were designed to be run in the 38.5-41" range. In the meantime, I moved the brackets back so they'll yield a 112" wheelbase at 38". That seems close enough to me, and I don't want the brackets any further forward.

20240826_190814.jpg


I can't work on this for a few days, but will post more pics as things progress.

Mark
 
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$500 isn't terrible, but I'm guessing you have to add other pieces to make it work for you?

I was picturing something like this, but for a Toyota. I put this kit on my father in laws jeep and it was really nice.

motobilt.com

4 Link Suspension Mount Skid System for Jeep YJ

Building high quality fabricated products for offroad vehicles is the mission. The Motobilt Jeep YJ Four Link Suspension Kit consists of an assembly that mounts ot the frame and houses both the upper and lower links for the front and rear 4 link suspension. This kit was designed to make it...
motobilt.com motobilt.com
 
Exactly. About $800, all in.

That YJ system is pretty slick.

Mark
 
I'm still - yeah, I know - working on this, and have another question: Can I still run my driveshaft unmodified? Here's a photo at ride height with the new setup, followed by some numbers:

20241016_115058.jpg


I moved the rear axle back an inch, and you can see there is now some of the shaft exposed that was not before. Here are the numbers:

  • Max extension leaves just a fraction over 3" of thin shaft visible.
  • Full droop on both sides leaves 2 5/8" of thin shaft visible, so at full droop I have 1/2" of driveshaft extension available
  • Ride height leaves 1 3/8" of this shaft visible, which is shown in the photo above, and is 1" less that what I used to run
  • Full stuff on both sides leaves 3/8" of thin shaft visible

The gist is that I used to run with roughly 2.5" of the shaft engaged, and would now be at roughly 1.5". Is that enough?
While I'll rarely be at full droop on both sides, and almost never there and under power, can this be safely run in those situations with only 1/2" of engagement?

What say Irate?

Mark
 
How many inches are the splines on that drive shaft? I took mine out and marked with paint pen on the female yoke where it sits at ride height and full bump. As long as its got enough plunge you should be good
 
chays2464 said:
How many inches are the splines on that drive shaft? I took mine out and marked with paint pen on the female yoke where it sits at ride height and full bump. As long as its got enough plunge you should be good
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That's a good question. The female part is 5", including the cap. Assuming the male part is, too, (and it can't be longer), and I can see 3" of it when fully extended, and none of that is splined, then that would leave only 2" of spline. That doesn't seem like enough, but perhaps it is. If the entire length of the female part is splined, then the drive shaft would be fully engaged no matter whether it was fully compressed or fully extended.

Is that how these work?

Mark
 
You really want to make sure it doesn't punch out the tcase output at full bump. I laid mine out and marked it with paint pen to see how much it plunges at ride height vs full bump. Not sure if the pics help but Im visual so seeing it laid out helped me. Sounds like you have plenty of spline egangement so just shoot for it not bottoming out at full bump and thats gonna tell you where it lives at ride height and full droop if that makes sense
1729274597388.png


This is the shaft at ride height
1729274656741.png
 
I think I'm good at full stuff, as I still have 3/8" of shaft visible. Not a lot of margin, but should be enough.

Is that a broken stock shaft on the right? It looks kind of like mine, but is different.

Mark
 
ScaldedDog said:
I think I'm good at full stuff, as I still have 3/8" of shaft visible. Not a lot of margin, but should be enough.

Is that a broken stock shaft on the right? It looks kind of like mine, but is different.

Mark
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Thats a trail gear long spline builder kit. I broke 3 of them in the exact same spot so I finally upgraded to 1350 ujoint with Ford splines to get a thicker female splined portion. A lot of that was from axle wrap but ive got 5 trips on the new shaft with no issues so far
 
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