cut/turn angles, spring perch location

[Benjitis1]

For those of you that sell cut and turned FJ-40 axles, what is the exact amount of degrees you turn your knuckles and your perches. If i start with my stock Spring under perches at 0 degrees, or level, then i rotate the entire axle up how many degrees?? When i get the pinion pointed at the right angle i weld the new spring over perches perfectly level. Then how many degrees do i turn the knuckles? I would like some definate angles, because ive read so many threads and everyone says a different angle and they give approximates. This will be sprungover on stock springs. I'll be running 36" TSL's, in case that makes a difference on the caster angle, or whatever. Thanks.

 

[Mark W]

In my opinion there is not one angle that is right. You want the pinion pointed at the T/C. Or actually at the front of the double carden joint. What angle this is depends on the amount of arch in the springs, any mods to the mounting of the springs (shackle reversal, wheelbase extension by moving the hangers, or???) whether the springs have been reversed, what engine and tranny combo you are running (and how mounted if not stock). Don't forget that you may want different caster (within reason) than someone else.

I know that there are guys selling pre-turned housings, but I personally feel that the *best* way to do it is to fit the turn to the rig. That means that no one can give you an exact number

I did an FJ60 a couple of weeks ago that wound up turned to 15 degrees more than stock. (Most '40s will be less than this BTW.) I did an FJ60 a couple of years ago which had a double T/C setup. Didn't need to turn it at all to have it pointed at the T/C and use a double carden driveshaft. My point is that every setup is different.

 

[woody]

Mark is spot on...my front axle was in/out of the rig 5 times over an evening while we tweaked the cut-turn angles and perch angles....and since I'm now on my 3rd driveline revision since then, it's likely no longer correct.

All there are are rules of thumb, and educated guesses....

Andre's writeup on the SOA in the Tech Links is an excellent start....

Edit: IMO, there are two key elements...first is caster angle....positive 3-5 degrees for steering and larger tires (guess +3 or so for 36's, more for larger tires). The other key is pinion at the t-case to eliminate bind at the joints....for offroad use, I've never sweated the CV at the t-case or ensureing they are parallel, at least in front. It never see's speed use with the lockouts locked or in 4wd, ever. Once those two are set, the perch angle will have 100 permutations since no two shackle reversals (or non reversals...) are done identically....spring sag, etc also plays a part.

 

[Mark W]

The other key is pinion at the t-case to eliminate bind at the joints....for offroad use, I've never sweated the CV at the t-case or ensureing they are parallel, at least in front. It never see's speed use with the lockouts locked or in 4wd, ever.

Just so that this part of the above comments are not misinterpeted. This only works for off road only use of 4wd. Those of use who drive rthe rigs on the street and lock the hubs in October to unlock them again in May have to be pickier about this.


Mark...

 

[Benjitis1]

Alrighty then. Thanks. Im on the right track i think. Ive called a couple shops, and so far, i plan on making an index mark on the axle tube and on the knuckle, then rotate the knuckle 5/16" to 3/8", which should put the pinion where it needs to be for my application, being stock motor, stock springs, no shackle reversal, just your basic SOA w/cut/turn. Hope she turns out alright.

 

[Mark W]

Don't like that idea. It is pretty tough to be accurate enough with index marks. Especially keeping both side matching. Buy (or borrow if you can) a bubble level with an adjustable degree marked bubble on it. These can be picked up for about $50 at any welding supply shop or store which caters to machineshops and other fabricators. Use the knuckle bearing race as you measuring point. You can easily keep everything accurate to within one degree and keep it identical side to side.

This is too major a mod, and one that you will wind up living with to just get it "close enough".


Mark...

 

[Benjitis1]

You dont like the index mark idea??? Seems like it would be just as accurate, maybe the width of a chisel blade off in one direction or the other. This rig will rarely see the street and never go over 45mph. Shes a trailer queen being built for the trails.

 

[woody]

The cheap $10 units from any hardware store suffice...we used a nice digital model, but only cause it ws available.

Mark emphasized me correctly...trail rig versus street rig....

 

[Mark W]

If it is just a trail rig then the accuracy is not as vital and index marks should work fine so long as you are a bit obsessive about it.

 

[peesalot]

the index mark plan will work but should be double checked with a angle finder.
IMO here are the answers you asked for.
On a SOA 40 with stock springs and 36 hawgs
Did like you said for pinion ( at 10*) with perches reset to 0*
You should find the knuckle ends to be just a little different in caster from factory( like 1 * more on pass.)
Cut em and roll em back by your index plan but I would say 5?16 is the #
That left a caster of just less than 4* on driver and just over 4* on pass.
1 finger , saginaw , unbalanced , straight at 70. very stable, no wierd chirping , lots of pavement miles and no unusual tire wear.

 

[peesalot]

Forgot 1 crucial element , shackle reversal with the thru the frame method moving the stock rear hangers out front and extending frame horns 1.5 ".

 

[Benjitis1]

Okay, im gonna get an angle finder and double check with the index marks.