Join Date: Jul 2017
Location: Nobel Ontario Canada
Bullitt Year: 08
Bullitt Color: DHG
Bullitt Serialized Number: 4404
1 PC, 2 PC driveshaft. What's the Diff?
Rosebud posted a query today about one piece aluminum driveshafts. A timely post since I'm writing about driveshafts today. Hmmmm?
Let's start with the basics. Universal joints like to operate on a 1-3 degree angle, 2 degrees preferred. If the angle is greater or less than recommended, then you will cause early wear or failure of the u joint, driveshaft yokes, or the pinion bearings and gear.
The 2001 and 2008 Bullits have two piece steel driveshafts. This allows for smaller angles on the yokes, u joints and pinion. The downside is that they are quite heavy and clunky because of all the movement of four u joints and a hangar bearing.
If you change to a one piece aluminum driveshaft, you reduce the weight by about 10-20 pounds and therefore reduce the rotational mass and can modestly improve acceleration and shift quality.
The good aluminum driveshafts will usually just bolt up to the existing pinion flange and plug into the back of the transmission, and have a booted slip joint. A 3.5" diameter shaft is ideal (some are 4") because that diameter will usually not contact the floor of the car even if it is lowered a bit. (read ~1")
Here's the concern. The pinion angle and the trans. output shaft angle should be equal and opposite for best operation. Example: Pinion angle negative 2 degrees (up), trans. output shaft positive 2 degrees (down)
If there is a large difference, then you bind the u joints and lose power. The reason you want ~2 degrees angle is so that when you take off and the suspension squats, then hopefully you zero out the angle.
But how can you adjust the pinion and Trans. shaft angles? If you have adjustable UCA's and LCA's then you can rotate the axle slightly and dial in the angle. If no to the adjustable control arms, then you can shim the rear trans. mount a bit to help out the angles. Hopefully you can get the two angles close to equal (within 1 degree) and opposite within the 1-3 degree angle which will optimize your power delivery and u joint life. If you don't, you will likely wear out the rear u joint prematurely and put extra strain on the pinion gear and bearings. Unintended consequences await you with every modification.
The diagram is not to scale. For example only.
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In my defense, I was left unsupervised.
Last edited by bullit4404; 05-20-2019 at 08:51 PM.