Pinion angle

[454C10CHEVY]

i hear that if i run 2" drop blocks i have to run pinion angle shims... if this is correct anyone know what degree i have to run?

thanks
jerry

[oldblue1968chevy]

Ive ra 2" blocks for 3 months or so before I had to park it no probs

[CC69Rat]

The only thing you have is 2" blocks? No drop springs?

I'd say with only blocks, you'll be ok. any more and I'd think about shims. If you add the blocks and pick up a vibration underneath the truck you'll know what it is.

[widewhite70]

On my truck I used to have 5 inch drop coils and 2 inch blocks and my pinion angle was off. I could not find any shims for that style block so I found what angle I needed and took my aluminum blocks to the machine shop and they machined the block at the proper degree I needed and it worked perfect, drop block and shim all in one.

[454C10CHEVY]

Ive only put the blocks on so far im doing 3" or4" drop coils also but wanted to try to get pinion angle correct before driving it
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[CC69Rat]

Yep, with that amount of drop (same as mine will be) I will be running about 3 deg shims.

For the most part (and there are old posts on here about it, I'll see if I can find them) On a trailing arm setup. Stock height. let's think about it.

The factory set the trailing arm perches on the axle tube to match stock height. This puts the pinion angle, drive shaft, drive shaft#2, then to tailshaft into somehat of an alignment. (usually 1-2* is fine)

Now, let's put a lowering block under the axle housing and on top of the trailing arm. If that block is square, the angle of the axle pinion (where the drive shaft connects to the rear end) wouldn't change. The rear end simply sits higher in relation to the frame of the truck, of course the truck sits lower. Remember, the axle / pinion angle didn't change. BUT, what did that do to the drive shaft in relation to that joint? The Pinion will now have a slight UPWARD position in relation to the driveshaft and U joint.

Put a 6" drop spring in there now. .. and your pinion is REALLY pointing upward. Understanding the trailing arms will swing up too and correct a little of this.. but still, your axle housing is in the stock position unless you shim it. The shims will 'roll' the nose of the pinion shaft back down and in turn correct the angle where your drive shaft connects to the pinion.

You don't want this to be at zero. About 1-2* "pinion up" if that makes sense. Think about torque and when you pull away from a redlight smoking the tires off.. The rear end torque will naturally roll the rear end down a little too, thus giving you a perfect Drive shaft / Pinion alignment.

I used to work with a lot of lifted Jeeps, and this holds true with them too, just the oposite direction. Getting this angle correct is very important.

On trucks with BIG drops, you can also get into binding if the stock drive shaft length is used. If you hit a big bump the drive shaft can be jammed into the back of the tailshaft of the transmission causing other issues .. just a thought for reference. I would suggest about .5" shorter especially if you're doing a custom drive shaft anyway.

Think about lifting a Jeep. The stock drive shaft would be too short if you lifted it 8" correct? The same holds true for lowering trucks. You can use what's called 'Set Back plates' to move the axle back about .5" and it will correct this binding problem. Again, just BIG drops.. 2" you should be ok. The reason I say this is you dont change the relation of the pinion / driveshaft that much, where 7" drop would, most definitely.

Hope this helps.

[geezer#99]

Actually you want the pinion down 1-2*. Under torque load the pinion always rises.
That's why you use a pinion snubber.

[CC69Rat]

You know what .. you're right. Sorry about that. My bad.

[454C10CHEVY]

So if i get 3* shims i should be pertty close then? wish i had some of you guys closer to me to be able to get some hands on help lol

[davepl]

All that really matters is that the pinion angle matches the inverse of the angle at the transmission yoke (adjusting for pinion rise under load).

You probably all know this already, but the whole reason it matters is because we use U-joints, not constant velocity joints. A U-joint at an angle "speeds up" the shaft at one point in its rotation and slows it down at the other, and so the U-joint at the other end needs to be perfectly opposite to cancel that out. Get the angles mismatched and your axle will be trying to speed up/slow down slightly as the driveshaft turns.

Probably best to verify whatever you wind up doing with an angle finder just to be sure.

[CC69Rat]

Pretty cool write up on it ..

http://www.nastyz28.com/forum/showthread.php?p=2468039

If you get this correct, you will notice a difference in the way the truck drives and just the ride overall. I hear it can rub a couple horsepower too if the pinion angle is off. (kinda makes sense ..)