Thunderbird Coils

I installed the 94 Thunderbird coils last week. They provided 3-1/2 to 4 inches of lift (its uneven side to side) with 1/2 inch of that coming from the adapter plate and thin TBird rubber isolater needed at the top of spring. I expected something closer to 2" of spring lift versus the 3" to 3-1/2 that I got. The TBird spring is straight wound and flat ground at the top so the adapter plate is needed to keep the spring centered and transfer the load to the stock isolater pad. Its a tight fit over the lower spring pad (it was an easy fit on two junk yard Cherokees) but it does fit with a little persuasion and the stock retaining clip will fit too.

Since the TBird spring is only a 1/2 inch taller than the stock spring most of the lift comes at the expense of articulation.

I added Durango springs to the rear (stock XJ main, durango 2,3,4) to even out the lift (4 inches rear lift). After driving it around below 45 I had all the usual problems, vibration, a light wobble (not full blown DW). SYE and lca drop brackets are in order if I keep this in.

John

How's the ride with those coils though? A higher spring rate is nice to force the rear to move more, but from the sounds of it I would assume that it's fairly rough.

The calculated spring rate was 300lb/in versus 200 lb/in stock. As a comparision the F-150 springs oftern used come in around 450lb/in. I added a 4 degree shim on the rear and a 1" transfer case drop, reworked the rear spring pack to lower it to 3-1/2 inches lift (20-1/2 inche lip to axle center line). This cleared up the vibrations so I got to drive it around a bit today and the front lift settled in to 3-1/2 inches (21 inches lip to axle center). The ride felt softer but most of that is perceptual due to a softer rear with more arch and less rate (changed rear spring pack stack today too). I like the Durango springs, lots of arch, thick leafs. I hit a bunch of dips and the front felt fine. Not to stiff at all.

For anyone interested the adpater plates are two discs, one 3/8 thick, 5" OD and 2-1/2 ID. This is the top plate that transfers the load to the stock isolater. The lower plate is 3-3/8 OD, 2-1/2 ID and 3/4 inch thick. The lower plate is welded to the upper and fits inside the spring to locate it (use the stock 1/8 rubber isolater between the spring and adpter plate). I tapered the hole in the upper plate using a die grinder so the stock XJ isolater nested tightly. A 3/4 piece of pipe with an OD of 3-3/8 or a little less could be used instead of the lower plate.

After driving it around some more today I am very happy with this combo. Coils cost $30, Adapter plates $50 (mom & pop shop made them for me) Leafs $40, bump stop exentions & Xfer case drop, sway bar drop (home made) $8 for square tubing cut to length, 4 deg shims $13, center pins $4, spring clamps (8) $6.50. I picked up a set of adjustable LCA's instead of drop brackets but I am not sure these are essential ($205). $175 excluding the LCA's. I need to get new shocks and will try some of the cheaper alternatives identified elsewhere on the fourm.

John

Forgot to mention I added YJ brake lines front and rear (~$60 from car quest).

John

John,
Very nice info for those who might want a cheap alternative.

Very Nice.

You should be able to adjust the Castor and front drive line angle reasonably well with stock length control arms up to about 4.5" of lift. Over that is really pushing it (although I have heard and see some people do it, it is really not optimum).

Just thought I would include this for anyone not considering doing this due to not wanting to invest in Adj LCA's.

Michael

Found some spring rate info on line. Helps to explain why they felt so soft on the street.

The springs are variable rate. This explains why they were not noticably stiffer than stock. The installed height is several inches greater in the Cherokee than it was in the Thunderbird so the spring rate was less than 270lb/in intial rate (I used the V8 springs).

Front: 223-282 lb./in. 3.8 liter
Front: 349-403 lb./in. 3.8 liter SC
Front: 270-330 lb./in V8 (The springs I used)

John

I spent 10 hours off road with these coils over the weekend and a couple hundred miles on the road. The lift has "settled out" to 3-1/2 to 4 inches, no change. Thats an advantage of used coils, the are already settled out.

Off Road
For running down sandy washes (25-45 mph), going over dirt moguls (10-20 mph), slow work over ditches, and "green horn" rocks (0-2mph) these springs are great. I dont bottom out when the front end gets light (either on purpose by to much enthusiasm) and I have all the stock travel (stock shock limited). Yes the front end can be bottomed out but it takes some air to do it. When I crawled the Cherokee up on two diagonal wheels (feel the rocking) the front compressed to within an inch or so of the bump stop so it stuffs pretty well. It not all wine an roses however. Washboard surfaces flat out stink. It was bad enough stock but its worse now. With the tires (P235-75R-15) "aired down" at 17 PSI stuff still flew off the seats and bounced around the floor. Part of this is due to the steeper control arms, part of it due to the stiffer initial rate of 270 lbs/in versus 200lbs/in stock. Bushings, shock valving and geometry play a big part on how wahsboards feel, but the stiffer springs sure dont help.

On Road
Its great, better than stock until you come up on a speed bump. I have to treat 4" speed bumps with a lot more caution than in the family mini van. It has a tight and marginally over sprung-under damped feel to it but handles emergency maneuvers just fine and has good turn in characteristics despite being a bit underdamped.

Summary
I think I am going to try out a set of the V6 T-Bird Springs 223-282 variable rate versus the 270-330 variable rate of the V8 springs. Its nice not to bottom out on the moguls an with small air but I would rather back down a bit and not suffer the washboards and speed bumps so much. Loosing half an inch or so up front would help the geometry too.

John

Here is a picture of the spring adapter plate

And here is a picture of the end result in action.

Should've turned the camera vertical to see where the spring bolts into the axle.

that shop did a pretty good job on the disc too.

and uh, what is that little flap hanging round under the top plate?

I was torn about putting the V-6 springs in place of V-8 springs. Spent about 30 hours wheeling on the V-8 springs and I really liked the way the behaved on faster runs down washes, over whoop-t-do's and when occassionally getting airborne. However I was really starting to get annoyed with small bumps and my last trip to Superstition Mountain and playing on the rocks sealed the deal. Heck they were only $20 and 4 hours labor to install.

The V-6 are progressive rates like the V8 springs but have an initial rate of 223 lb/in versus 270lb/in. The free height is about 18-3/4 versus 18 for the V8 spring. While changing to these springs I wanted to increase the lift to 4.5" so I added a second stock Cherokee spring isolator.The 5/8 thick stock isolater pad along with the 3/8 thickness of the adapter plate provide a total of 1" of lift. The V6 spring alone provides 3-1/2" of lift. Hit 4.5" on both sides so I am happy. The photo below show the F-150 coil (commonly used) the stock spring, the V8 TBird spring and the taller V-6 TBird spring. In the foreground is the adapter plate and the TBird rubber spring isolater.



Its a new vehicle when it comes to speed bumps. Taking 20% off the initial spring rate made a huge difference. I am sure it will wheel better but I will need a little more throttle control down the washes and high speed stuff.

John

bringing this guy back from the dead because these coils fawking rock. hands down. DO IT!!!

nosigma said:

I was torn about putting the V-6 springs in place of V-8 springs. Spent about 30 hours wheeling on the V-8 springs and I really liked the way the behaved on faster runs down washes, over whoop-t-do's and when occassionally getting airborne. However I was really starting to get annoyed with small bumps and my last trip to Superstition Mountain and playing on the rocks sealed the deal. Heck they were only $20 and 4 hours labor to install.

The V-6 are progressive rates like the V8 springs but have an initial rate of 223 lb/in versus 270lb/in. The free height is about 18-3/4 versus 18 for the V8 spring. While changing to these springs I wanted to increase the lift to 4.5" so I added a second stock Cherokee spring isolator.The 5/8 thick stock isolater pad along with the 3/8 thickness of the adapter plate provide a total of 1" of lift. The V6 spring alone provides 3-1/2" of lift. Hit 4.5" on both sides so I am happy. The photo below show the F-150 coil (commonly used) the stock spring, the V8 TBird spring and the taller V-6 TBird spring. In the foreground is the adapter plate and the TBird rubber spring isolater.

Its a new vehicle when it comes to speed bumps. Taking 20% off the initial spring rate made a huge difference. I am sure it will wheel better but I will need a little more throttle control down the washes and high speed stuff.

John

Click to expand...

I must mention, you dont have to make those coil thing like nosigma did, just grab the top of the mcphearson strut and drill the center holl out to 2.10", it will fit around the stock bump stop shaft and it will hold the coil perfectly. its a good ride and cheap!

I've checked out this thread before and seeing your endorsement just further convinces me this is my route, that and S10 leafs, should be a direct swap and nearly even lift front and back right?

avnsteve said:

I've checked out this thread before and seeing your endorsement just further convinces me this is my route, that and S10 leafs, should be a direct swap and nearly even lift front and back right?

Click to expand...

Direct swap? No. you have to cut the eyes off each end and measure the rest you'll need to cut but they do noy direcctly swap into the pack, you have to mate them with your current leaf pack and in order as well.

But yes, with these coils and those leafs mated, you're looking at a junk yard 4" lift.

yeah, I dig the bastard pack method, it's simple enough, of course I probably should not have said "direct swap" but you get my point, 4" woohoo! I've priced those parts around here and it's a total of about $75 for all the parts...

What route did you guys go for shocks? I may give this a try soon...

I'm assuming you're running a SYE?

Just a quick note to everyone. It's not only the newer Tbird coils that work for lift, Cougar's and Tbird's from 83 up will work just the same. Makes me think I should have pulled the ones from my old 86 v6 cougar before I scrapped it.

Selarep,
Wow. Kinda nice to see one of my first postings brought back to life.
Good idea on using the MacPherson strut parts instead of the adapter plates. That should make this an easier swap since not to many folks have access to metal cutting and welding equipment.

I still run the V-6 springs over 2 years later and dont have any complaints about them. I ran them all ove SoCal and now beat up the slick muddy rocks on the East Coast. While I am always searching for the perfect rear bastard pack (rebuilt a dozen times) I dont have any desire to mess with the front coils.

John

Thanks John for venturing out and finding this setup, I appreciate it and its fun learning tips and trick like these.

As for the shocks, everyone listen up. You can use the front shock from a YJ and get them new from Kragen for $17 each. You're going to need a good vice or use a press and get the stock sleeves out of the YJ shocks since the diameter is way to small.
as for the rear shocks, use ford f-150 from a 95 and make sure you use the Longer shocks since 2 different sizes were used back there together.

Just wondering, i just sold my 88 pioneer with the f150 coils in the front w yj shocks, and 3 inch blocks in the back with the f150 shocks...sold it for 500, wish i didnt, but i had to get rid of it...i need of cash...now im looking to do another lift on another cherokee...which set of coil springs/leaf packs(dakota or s10) will i get the most lift out of regaurdless of ride quality????

thanks