hey guys I'm not really sure what angle my drive shaft should be at, its slopping forward to the front, and it looks like a lot? car is dropped with sport line springs and has and has a t56, but I don't think that should matter? maybe its just me but can someone chime in with some info or pics? thanks

 

You mean downward at the front? No worry. This is more a concern for those who buy aftermarket adjustable torque arms.

 

Yes it's down forward, and thats what I have is a adjustable torque arm! What angle should I set it all at? Thanks

 

In the old days of leaf springs, a bit of pinion down was desirable, but with the torque arm, you want the pinion shaft parallel to the transmission output shaft, whatever the driveshaft angle.

 

Angle of the driveshaft means nothing. The pinion angle is in relation to the engine/trans angle. Measure the angle of the crankshaft. Measure the angle of the pinion shaft. Those should be at the same angle however you can angle the pinion down 1-2 degrees from the crankshaft angle to help under hard acceleration.

Once those angle are set, your pinion angle is set. The angle the driveshaft sits has no relation to the crankshaft/pinion angle unless the angle between the driveshaft and both yokes is extreme.

Watch this

 

This is exactly what I was referencing. In the days of leaf springs, this was true. But for our torque arms, it's not, so the adjustability is just a way to turn more profit. Nothing else. If the aftermarket would offer us lightweight tubular arms that aren't adjustable, then those might be worthwhile. The stock arms are heavy.
Besides, since most of us will be cruising 99% of the time, and WOT first gear less than 1% of the time, there's no sense destroying parts and suffering vibrations for that 1%.

 

thanks guys! that video put thins in perspective for me, get that done now!!

 

You can buy non adjustable torque arms but that's just to provide something that's a little better than a stock replacement. It still won't correct pinion angle geometry if it's wrong. The only way to know if your pinion angle is correct or not is to measure it. A factory suspension still may not be perfect.

 

Ok so I think I done something wrong, I have my t56 pointing down towards the rear and my rear end pointing down towards the front, that is wront right? I going to adjust my rear end up and maybe drop my trans down to get them parallel? But no more than 6° right

 

Yes, that is wrong.

Imagine looking at the crankshaft / transmission centerline, and the pinion centerline. In a perfect world, you'd have the 2 centerlines parallel but not in line with each other, which would then leave the drive shaft at a slight angle to both, equal at both ends. I.e. equal but opposite angles between the drive shaft and the other things at each end. The engine sits at an angle, usually something like 7°, down toward the rear (up toward the front); therefore you'd want your pinion to also be 7° up toward the front. Maybe put the pinion angle slightly lower than that since it tends to raise itself under hard acceleration, as Alky alludes to; so, maybe 6° or so.

To a certain extent you just end up having to accept whatever angle the U-joints articulate through, since you can't easily raise or lower the entire engine or rear end. You can however adjust the trans tail location somewhat, which might help... for example if you raised the tail 1", you might reduce the crankshaft and pinion angles by a ° or 2 and at the same time make it point somewhat closer to straight at the pinion, which in turn might lower the angle the U-joints articulate through. I seriously doubt you'd want to lower the rear of the trans, especially in a lowered car, because that would make the crank/trans angle even greater and consequently require the pinion to point upwards that much more and also make the U-joints articulate more.

 

Thanks for your help! I have a founders adjustable torque arm, I ended up with 3° trans down towards the rear and the same for the rear end upward towards the front, so thats a total of 6°, is that alright? Or should I go for like 3-4 °

 

Don't bother with the "total" thing. It's WRONG.

If the crankshaft and the pinion centerline are parallel (same angle w.r.t. gravity) then you're just about right. Like Alky pointed out, a few fractions of a ° different, with the pinion somewhat downwards from what you measure with it sitting still, is probably desirable; the more traction you have, the more downward you'd want it, and the more floppy (stock) your TA is, the more down. With a good solid aftermarket TA setup and moderate street power, you probably don't want more than 1 ° of difference, and probably a good bit less than that.

Draw out your angles on a sheet of paper. Doesn't have to be real elaborate, just DRAW IT, including drawing the angles, and make it match what you measure. Just DOING that is a magnificent exercise toward getting it right. Go DO IT, and come back and tell us what you found out in the process.

 

Never think of the downward pinion angle as actually pointing down. A downward pinion angle can still be pointed upward.

Downward pinion means it's a lower angle than the engine/trans angle.

If your engine/trans is point down at the rear with a 3° angle and the diff is pointed upward at the front 3° then the pinion angle is zero because they are parallel angles. If you brought the diff down to 1°, it would still be pointed upward but would have a 2° downward angle in relation to the engine/trans angle.

For the majority of street cars zero to 1° down angle is just fine.

I drove a multi driveshaft truck last week that I know had really bad driveline angles. Driving down the highway it sounded and felt like I was driving down rumblestrips. I corrected the driveline angles with a ride height adjustment (air ride suspension) and the driveline vibration went away.