Sounds good to me, how can I get ahold of ya?

 

Very informative post. That other thread mentions that 2 inch drop shackles generate 1 - 1.5 negative pinion degrees. Thus 2 inch shackles would be a good thing for traction (assuming a stock vehicle). Am I reading that correctly?

 

if you wish to check pinon angle first you zero your angle finder against your frame - then compare that to your pinion center line and trans output center line - some trans you can use the pan rail but on a 4r100 you can not as the pan is not parelle with the output shaft. There are certain specs of what angle your trans is supposed to be, rear pinion, driveshaft then is compared to those two but all in relation to the zeroed frame.

I however did not bother, i just made sure my front and rear u joints are at the proper operating range. Stock rear (diff) was at 2 deg (the actual angle of the u joint), front (trans) 3 deg. After a 2" drop this changed to 3 deg and 4 deg. This would put me just out of range on the front u joint. This is why some guys can have no vibration and some do with a 2" drop as its so close that they are either in spec or are just over.

When i rotated my shims (sits between spring pack and diff support, i belivie its around a 3deg shim) it then brought my actual rear u joint to an angle of 1 deg and the front to 1 deg wich is a perfect angle for the u joint. (cant be 0 otherwise the u joint needles wont get proper lube as they will not move)

I have not actually checked my pinion angle in relation to the frame but when i checked the initial pinon angle before and after at the same postion and height on the jackstands there was maybe a degree differnce if that, basically not enought for me to realy notice and make note of it. Now the angles of the u joint are even better than from factory, but with that said ford sets their trucks up for towing and hualing so they are usually on the edge of specs for their u joints. This is so when load is added they are perfect. (so they dont shudder when towing, etc)

Obviously there is difference on the way of doing it, i don't drag race my truck and i do drive mostly at highway speeds thus i set it up for the least vibration and wear. (aswell as the least PIA as i could not remove the shim) IF i drag raced or used slicks a lot it probably would have been better for launching if i had left the shim in the factory way as the pinion would be tilted downward more that it is currently. If it bothers me i will get a bigger hammer and take the shim out which will drop the noise of the pinon a bit but not as much as leaving the shim in.

For a 5" drop i would compare the angle of the pinion to the frame aswell as the u joints - if you go to the track then you may wish to run a u joint angle of closer to 3 deg (acutal difference of the u joint not the angle between that and the frame). Basically if your u joints are at the correct angle then your pinon may not be at the correct angle in relation to the frame from that much of a drop, then you may have to adjust the trans angle - this is ofcourse if you are looking for the ideal pinion angle to frame and u joint angles.

 

Thanks to all who have contributed. My knowledge on the issue has like quadrupled. For this and most other mechanical topics, a video or animated GIF would be priceless. Maybe in my next career . . .

But I'm still nagged by a lack of understanding as to how pinion angle affects traction. Can someone explain this? Makes no sense to me.

"The Straight Scoop on Pinion Angles

by Ron Rygelski
Performance Products-Red Line Synthetic Oil
http://www.myoilshop.com
(formerly www.redlineoilracing.com)
rlracing@sgi.net

Myth #1: The pinion angle somehow affects how much traction the car will achieve.

Straight Scoop: No way. The pinion angle doesn't mean squat as far as the rear suspension is concerned. Think about it: why would the suspension care about u-joint angles? What determines the "hit" on the rear tires and the rate and amount of weight transfer is the intersect point of the upper and lower rear bars (control arms). That's known as the "instant center" (IC), and combined with weight distribution, spring rates, and shock valving is what affects traction."

But I see many other people say that pinion angle does affect traction (mostly as in add angle to take away traction for hard-to-launch vehicles).

 

That pic is funny, but so wrong...

 

I agree.....

And I also agree that there is some interesting information in this thread.

Steve

 

Tim,

You are correct is some ways... Traction isnt really helped or hurt with a 4-link style or Upper/lower control arm setup with the wrong pinion angle.

But with a leaf spring setup is a totally different ballgame.

What you are really doing with the shims is keeping the u-joints inline for less drag on the driveline and more power to the wheels. It helps to shock the tires harder which on a heavy vehicle will make it hook harder.

 

Just so we are clear, I do not have an opinion on the matter. I expressed skepticism, but that's it.

And I still cannot see how the pumpkin can rotate with (non-slapper) traction bars installed. The Metcos are way too stiff to compress. And the front leaf hangar is rigid. So the only possibility is that the leafs are getting shorter or longer under pressure -- that's the only way that the pumpkin could move, as the bottom of the axle is solidly located by the traction bars (I have lowers). And there is only so much length that can be added or taken out of the leaf under pressure (i.e., increasing or decreasing the bow of the spring) so as to cause the pumpkin to be able to pivot.

Is that movement there? I guess so. What I am having trouble doing is visualizing a magnitude of twist sufficient to make any signficant difference in the pinion angle.

Sal tells me to "trust him" on this issue, and I have no reason to distrust him. He always seems to know his stuff. I'm just looking for some rational explanation of this phenomenon.

 

So how low can you drove the rear before having to worry about adjusting the pinion angles? Mine is dropped 2-2.5 inches in the rear (Hotchkis leafs).

 

I think if you are a few degrees negative, and you floor it, regardless what type of traction bar you have the rear end will twist a little.

If it twists a little, It will go to ZERO degrees, which is in perfect alignment, resulting in Zero binding of the driveshaft.

(I have no idea, but that is how I understand it until someone explains it)

 

my head is starting to hurt. i understand what needs to be done to check this, but i cant look under my truck right now, to see whats happening. i've read on some of these old links that 2" shackles will give you 1 to 1.5 negative. so would 3" shackles get you a little say negative 2 degrees. also, if you lower the front as well as the rear, does that just cancel out the whole "shackels help theory?

 

I got some 6 degrees that were too much for me, would want to trade um for some 3 or 4 degree shims if anybody has got any. Later

 

this is for Tim, not to go into a big explanation, but the best way I can describe to you what the rear susp is doing is picture the rear springs, then picture an oscilliscope, now add the two together. I am not trying to be coy, that is the quickest way to explain it.

 

I understand axle wrap and wheel hop, thumper.



The issue is how can this happen to any significant degree once a traction bar is installed. Picture the top of the pumkin above rigidly linked to the frame.

 

I have some 4* shims sitting in my garage. Paypal me $15 and they are yours. My paypal is mts77@earthlink.net