Hello!

I just got a teraflex 4" on my jeep and 37's (did the gears, and put a nice warn winch on the front).

What should the front pinion angle look like? Right now the front pumpkin seems level and the drive shaft bends down to it. Should it be tilted up to meet the drive shaft at a similar angle? The rear seems to do just that.

Seth.

 

I'd have the alignment shop check caster, you don't nec. wnat to know what it "looks like", just is caster Ok and are you picking up any vibs.

 

Apparently it is ok. It doesn't bump steer and wanders no more than stock. It trails really well also. Just have to figure out the slight pull to the right.

I came out of the bush and my wheel was 45 degrees off. I adjusted the draglink and it's straight again (it pulled to the right before this happened and it pulls the same amount after it happened, strange).

I just noticed the pinion seemed fiarly level and not angled up towards the front drive shaft.... was wondering if thats how it's done.

Seth.

 

The front axle presents a bit of a problem in this area. In the rear, one usually tries to adjust the pinion angle such that the pinion shaft is pretty close to being in line with the drive shaft (this is for the case when you are using a dual cardan type front U-joint and a standard rear U-joint). I say "pretty close" because most sources suggest that the pinion should actually be about 1 to 3 degrees "flatter" than the driveshaft. This is to allow for the fact that the pinion will rotate up a bit when under power. Setting the correct pinion angle is important to eliminate or reduce driveline vibrations. If the pinion is far off of the ideal angle, you will likely feel driveline vibrations, particularly when the vehicle is under power.

On the front, though, there's a second and usually more important consideration, the castor. Adjusting the castor and the pinion angle are basically the same thing. So if you set the pinion to be sort of inline with the driveshaft, likely your castor will be wrong (usually not enough castor). And if you set the castor to the specs, likely the pinion angle won't be correct (usually too flat).

Individuals may have different perspectives on this but my understanding is that the way it's usually handled is to adjust the castor to the desired amount and just live with the pinion angle wherever it ends up at. Since the front is unsually not powered when driving on the street, the tendency to feel front drive line vibrations is somewhat less than in the rear anyway.

I think a reasonable plan after installing the lift is to have the castor adjusted to the specs you want and then see if you can feel any vibrations from the front. If not, leave it at that point. If you do feel some front vibrations, you might try adjusting the castor a bit (maybe a degree or two) to see if the vibrations go away. If so, are you still happy with the handling (less castor will tend to make the vehicle wander a bit and you'll have less "self centering" action on the wheels).

I had big problems along these lines with my TJ and a 4.5" lift. To be honest, I never could get it to be really "vibration free". I did end up reducing the castor a few degrees and found a compromise that was sort of OK. It did tend to wander a bit, but not bad. And it did still vibrate a bit, but not too bad.

Hopefully you can just set the castor and all will be well!

 

If your axle is rotating 1-3 degrees then you have a problem. JK's have contorl arms so the axle won't rotate like a leaf sprung vehicle.

 

I'm not disputing at all what you said but that's the first time I've ever heard that the front pinion angle should be prioritized over castor. It's curious to me why they would recommend a setting that would likely lead to poor driving characteristics on the road and at high speed, even perhaps a safety concern over possible vibrations. Any idea what the reasoning is? I'm just curious.

 

It depends what article you read, I read a service manual write up that says the castor should take presidence, I tend to agree with that one coming from experiencing castor problems myself.