JayKay69

I got my coast 1310 for 450 from northridge with free shipping

nthinuf

Ahhh, Canadian money. That makes sense.


Still confused about the front arms though. Everything I have read says that double cardans need different angles (pinion pointed at the tcase instead of parallel to the tcase output) and then play with the front caster/pinion to find the sweet spot between flighty and vibes.







Ohhh, with the lift, the pinion is already pointed up. Gotcha...
Eventually I catch on.

wayoflife

there's nothing to be confused about, just try it yourself. if you set your front pinion so that it points to your t-case, you WILL have negative caster and, among other things, this WILL give you terrible handling. sure, it would be optimal to do this and is required to do this for your rear drive shaft but up front, it's just not something you can do unless maybe you have a prorock 44 unlimited with it's built in caster.

unless i'm misunderstanding you, even with the lift, the pinion will still be pointed in the same direction as before. the only way you can change this is with adjustable control arms.

Northern Wrangler

As it sits my diff is on a slight angle like seen in the second pic (although not as steep an angle).

nthinuf

Yep, that is where I was confusing myself. (and correct me again if this is incorrect WOL, it's just the way I am thinking of it) After the lift, the caster is low, causing flighty handling. So we add adjustable arms to raise the caster (which lowers the pinion). This is where most posts I see start from. Caster is already corrected, which lowered the pinion, so when adding a double cardan DS, they would want to adjust the pinion angle again - which lowers the caster and gets into the caster vs vibe situation.

Since your caster is already low and the pinion is already pointed up a bit, you may not need the arms. Sound right?

neXgen

x 2 call Stan, you can't go wrong with coast.

mkjeep

I would highly recommend you get the ds with yolk replacement vs the one with the adapter for the stock flange. When you use the one with the adapter plate it pushes the double carden farther away from the t-case thus increasing the angle a possibility for vibes. Also when you change bothe the tcase and pinion yolk, its easier to make a trail repair on the u-joints if needed. That is if those bolts you are talking about are the ones on the stock yolk/flange. Hell, I always used a rachet end wrench anyway, couldn't see getting a torque wrench up there anyhow.

Northern Wrangler

So after all the extra reading I've been doing and after being told I shouldn't need the arms I still am left wondering why my DS has gone bad (if I don't need arms to correct the geometry) and what it is in the DS that goes "bad" and causes the drive line vibrations?

Anyone?

wayoflife

your axle, frame and control arms effectively create a parallelogram. lifting your jeep will not cause the position of the pinion to change or, at least not by enough to really matter. rather than rotating upward with a lift, your axle will for the most part maintain its general attitude and this will cause the u-joint at the pinion flange to bend like a wrist. it's not a whole lot but, you would actually see an increase in the amount of deflection at this point and not a decrease. you can see this best when looking at the cv joints on a rear drive shaft of a lifted 2-door with stock arms. it's those severe angles at the joints that cause the cv boots to fail. in fact, one of the selling points of a radius arm design is that it can maintain the postion of the pinion and drive shaft angle throughout the cycle of it's suspension.

installing a set of adjustable control arms to increase the amount of positive caster you have (dropping the pinion even more) will help improve your handling after installing a tall lift and when running big tires but, the increased angle placed on the pinion and drive shaft joint will cause binding - in other words, vibrations. reducing the amount of positive caster you have (setting your pinion to be in line with your drive shaft) will help eliminate this bind and cause your vibrations to go away but, it will make your jeep feel super flighty. this is the balance we all struggle with or, at least for those who don't have locking hubs.

wayoflife

a drive shaft spins really fast and need to be balanced just like your wheels and tires. if you've knocked off a drive shaft weight or maybe bent it a bit after hitting a rock on the trail, that would be enough to throw it off balance and cause vibrations.