walledition

iTrader: (3)

axle pinion is pointing 8 up
trans shaft is pointing 6 down

ok if im looking 2.5-3 down for the axle pinion what about trans shaft?

walledition

iTrader: (3)

Ok lets see if i get this right: you say axle pinion needs to face -3 down, right now its at +8, does that mean i need a 11degree shim? because i see the biggest one i can get is 8 :s

And lets say i shimmed axle pinion down from +8 to -3, does my trans shaft angle need to be changed from -6 to +3? i read u want the same degree on the other side but negative if the other side is possitive and possitive if the other side is negative

just for the record i dont have vibrations now, im doing this hopefully to get better traccion
thank you for your help

TXsilverado

iTrader: (19)

going back to the shocks mounted in front of the rear for a second...wouldn't putting the shock in front of the shock give the shock less leverage? it's not a good/bad thing depending on the shock, and what your chassis needs to work; but from an effectiveness standpoint, the shock cannot do as effective of a job controlling the rear suspension if it's trying to control the weight closer to the center of the truck. I doubt that moving a shock 8" forward would lose enough leverage to make a huge difference, but in theory a shock can do the best job when mounted as far forward (on the front of the frame) and as far back (on the rear end) as possible.

walledition

iTrader: (3)

Ok i have an update, today when i got home from work i made another measurment just to make sure and found out that the axle pinion is really +5 and not +8 :s the flat place where i put the magnet was a little sideways and the needle got stuck i guees, on the same floor without driving the truck i just backed it up an inch or two so the flat surface was facing down, to make sure it was only that i went for a new meassure tool and yeah its really +5

Transmission shaft is still -6

How about i go with a 8 degree shim now, that should set me to -3 at axle pinion, what should i see in the transsmission shaft then?

TXsilverado

iTrader: (19)

a 4* shim should put it about perfect while helping the operating angles of both u joints. the pinion may still be level or slightly up, but under acceleration the pinion should be right in line with the DS. in most cases i measure pinion angle according to the ground it's sitting on, but based on your measurements a -4* pinion angle according to the ground might put the operating angle of your u joint in a bind.

i usually stay out of pinion angle debates because there are 10 different ways to measure, none of them are "wrong"

i helped build a long arm jeep wrangler. good luck getting the pinion to face down 4* with a 2' long driveshaft around 8" suspension lift.

walledition

iTrader: (3)

If i would use a 6 degree shim for the pinion angle that would set me around -1, i could always put some shims on the transmission crossmember to avoid u joint binding or am i missing something here?

thank you for your help

Atomic

iTrader: (42)

I'm no driveline expert, but I have always heard you want -2 to -3 deg on the axle pinion at rest as compared to the driveshaft, so under power its somewhat straight to the driveshaft. You want the angle between the driveshaft and trans to be the same but opposite, so you want +2 to +3 deg on the trans to driveshaft. Picture in your heard you want the lines coming out of the axle and trans to be parallel, which means they have the same angle.

There are 2 things to consider: 1.) Strength of the joint, and 2.) Vibration
The joints will be strongest at 0 degrees, but certainly within their limits (typically 3-4degrees). Vibration is minimized when the angles of the 2 joints are the same but opposite (see video below).

Typically when you launch hard the rear axle will rotate up, and the car will squat. When the rear rotates up it flattens out the angle of the pinion to driveshaft and when it squats it flattens out the driveshaft to trans. In a perfect world all angles will be 0, but because things move and flex under power you have to set it up so it moves as close to 0 as possible under the harshest condition.

Traction bars help make leaf spring suspensions much more controllable, so you can set up the pinion a little tighter (3deg instead of 6-7deg).

Heres a cool demonstration on the subject,

Atomic

iTrader: (42)

As far as the shocks, the shock only cares about its angle in relation to the motion it is supposed to dampen, and this goes by the cosine of the angle between the shock and the motion.

So shock is mounted completely vertical, and truck moves down perfectly vertical, the angle is 0-0=0 and cos(0)=1, meaning all the force extracted (or dampened) by the shock is fully realized. If you mount the shock at a 45 degree angle, cos(45)=.5, meaning the shock will have to be twice as strong to get the same level of dampening as one in line with the motion.

If you consider multiple degrees of freedom in the movement of the axle compared to the body, it makes sense why the shocks are mounted the way they are from the factory. Since we mainly care about drag racing (and therefor only loading in one direction), it usually benefits us to align the shocks directly with the motion of the vehicle during a race, which would be straight up.

George C....

Atomic......not all drag launches are squating

Caltracs tend to "lift" as many what to refer to

Atomic

iTrader: (42)

Right, which is why I said typically

The axle will still try to rotate up regardless of if the car rises or squats depending if it has traction bars or not, which is the important part as far as ujoint angle goes.