XJ Coil Swap Questions

[motopete]

I'm swapping to Xj coils, but I have some questions. Some might seem dumb but I need to know why I'm doing it.

I see that some guys use a npt plate and nipple, Why? Isn't the tappered end the same size as rbv coils? Why use 1 1/2" pieces when the lower bolt is 1 1/8, is it because it's needs adjustability? The isolators are for the the big coil end because they're inverted, they still fit the small end?

Also I'm going to use Bilstien 5125. Is one 255/70 enough or is two 175/60 better, are two 255/70 too much?

Thanks

 

[JOSEPH169]

check the technical library

http://www.therangerstation.com/Magazine/Fall2003/MaximumFlexForTheTTB.htm

 

[4.0B2]

One of the 255's should be fine

 

[motopete]

YES, I checked the tech library. Thats were I got the info for the questions. I know how, I want to know what and why. And yes I search the forums for hours.

 

[JOSEPH169]

For more flex while rock crawling, softer spring ppi than RBV springs.

 

[4.0B2]

Just be careful bc some XJ coils are stupid soft. I had some 4" lift XJ coils that were so soft my b2 compressed them completely

 

[motopete]

OK, thanks Joe...


Someone else with experience?

 

[motopete]

I've done quite a bit of research. I've got BDS 6.5" 240 in/p waiting at the parts shop for me, I just want to know what (and Why) other parts I need before hand so I can complete the job in one go.

Nice BII by the way I just went through your build

 

[4x4junkie]

The small end of the XJ coil is certainly bigger than that of the RBV coil (and is why the need for the plumbing stuff).
FWIW, I only used the flange, not the nipple, as I found it too large and didn't seat all the way down or something (I forget exactly, this was over 8 years ago). Instead I welded a washer over the top of the flange to keep it centered around the stud.

As for shocks, I was running single 255/70 Bilsteins up until just recently. It was a bit soft, but certainly livable. I would recommend going duals if you have the space for them (or do what I just did and get custom-valvable shocks such as Fox. Worth every penny).

 

[motopete]

Thankyou 4X4junkie. Is the reason for a 1 1/2" npt plate for the diameter then? Is the small end of the spring so large the ball joint is in the way like EB springs? Also would two 255/70 be overkill?

 

[4x4junkie]

EB springs don't have a small end on them at all, so that's why the need to modify a F-150 retainer to clear the axle housing C.
For the XJ coils, I recall only having to grind a slight chamfer on the edge of the pipe flange for it to seat down flat. The spring then sits down on the flange. (you can see they pretty much sit flat in this pic)
The dished washer that goes on the top I modified to be a little bigger by welding some metal around it's perimeter, it looked like it might be able to pull through the spring if some tension were put on it.

Dual 255/70s shouldn't be overkill at all, especially if you want to tap into your suspension's speed potential at all. Unless you get them used though, you'll probably pay just as much or more for 4 new Bilstein 5125s than you would for a pair of Foxes (and you wouldn't be able to tune them if needed either).

You haven't mentioned anything about your steering yet, have you got something planned out for it?

 

[4.0B2]

What are the plans here?
Daily Driver/trail rig? prerunner? rock crawler?

 

[motopete]

For my steering right now I have a extreme drop, with 5.5 Stuperlift brackets and 6" BDS TTB coils (410 ppi). They sit static at 16.5", it has a bit of bump steer. I'm swapping to SJ drop brackets and 6.5 BDS XJ coils (240 ppi) (I'm thinking) and if my math is correct it should sit at 15ish" til I get a winch. So that will bring the steering pretty close to level, plus with some decent shocks I should be pretty good. What do ya think? If that doesn't work I'll look at other options.

I want it to be a versatile rig that can be driven on the street. The island I live on is mostly rock, and it rains 50% of the time, so not much high speed stuff.

 

[4.0B2]

After my dealings with the stock steering, I think you should look at upgrades. Stone crusher, Superrunner, crossover. You'll be a lot happier with the way it steers and drives.

 

[4x4junkie]

The extreme drop (#FA600) arm should be fine if your suspension sits at 4" lift exactly. If those BDS Jeep coils are like my Skyjackers though (22" free length), you're gonna end up with about 5.5" lift out of them (the winch might get you down maybe ½-¾"). Be prepared to raise your coil buckets up a little (or swap them) if this ends up being the case and you don't want to mess with the steering linkage.