This weekend I wound up removing the Belltech lowering shackles I had installed a few weeks ago because they caused a vibration I couldn't get rid of. Luckily I have access to a machine shop so I was able to make different shim sizes and didn't have to buy shims, but nothing I tried up to 2.75 deg shim would work. With no shims at 2" the vibe was strong. With a 1.5 deg shim it was reduced. Dropping the lift to 1.5" and going to 2 deg reduced it a little more, and more shim beyond that made no difference. I got tired of jacking that beast up, so now I'm back to stock and vibration free again.

I found several websites through a google search about pinion angles. They all said that a vehicle with leaf springs should have a 1.5 - 2 deg angle between the driveshaft and pinion. I measured mine lowered 2" with a 2 deg shim (Belltechs recommended fix) and the driveshaft to pinion angle was 4.5 deg. According to these websites u-joints are only meant to operate with a 1 - 3 deg angle, and anything more will cause possible vibes and premature wear.

I know most of you have lowered without shims and had no problem and shims seem to have fixed the rest. I was wondering if anyone else has encountered a vibe like this and if anyone else has actually measured the pinion/driveshaft angle.

 

I'll be Mr. Obvious here, you did install the shims correctly, didn't you? There was some confusion awhile back on here about which way the thick part of the shim faces (the rear).

 

I did read all the discussion about the correct installation and I really don't want to open that can of worms again. I installed them thick side to the rear, so increasing the thickness flattened out the pinion/shaft angle.

 

OK, I just wanted to be sure you didn't get mixed up by the confusion. I wonder what the specs are from the factory for the pinion angle? Anybody have access to the shop manual or similar info.?

 

I'm sorry for your trouble, but this is interesting. I recently installed the groundforce shackles along with the shims. I had ZERO vibe issues prior to the install so I paid the xtra $ for the shims up front so I would stay vibe free.

After the install (yes the shims are thick end toward the rear) I now have the low speed (20-30mph) vibe. Pi$$ed me off........I called groundforce and they suggested I take the shims out and see what happens. I haven't had time to do it yet, but I may have a set of shims for sale soon.......

Jeff

 

I installed the Suspension Max drop shackles about 2 weeks ago and I've driven about 1500 miles since then ranging from 0-100 mph and never noticed any vibrations but after I installed them I started wondering about how that would affect the pinion angles. How do I measure the angle? Would drop leaf springs be a better option?

 

If you google "pinion angle shims" you will find several sites that explain this. I found the classicbronco site the most helpful with the measurement and the carcraft.com one explained what the angle should be and why the best.

I measured mine with a machinists level, where you have a flat surface and a rotating center piece with a bubble level that is marked in degrees. I put the flat surface on the drive shaft and found a 3 degree downward tilt to the back.
For the pinion I measured the angle at the flange that where u-joint bolts and found the front to be tilted down 1.5 deg. Added together that gives you a 4.5 deg angle. This was lowered 2" with 2 deg shims installed. I haven't measured it stock.