Prop shaft alignment

This is an outline of procedure to reduce or eliminate syncro propeller shaft (drive shaft) vibrations.

Symptoms

Often these vibrations occur at road speeds of around 50-70 kph (30-45 mph).

Prerequisites

Assumption is made that the propeller shaft is not bent or otherwise damaged, and that rear transmission and front differential are in good working order. Also this procedure is geared towards the stock VW propeller shaft, not after market shafts with slip joints, double cardan joints, etc.

Procedures

• Make sure the u-joints have no play at all. Try and move the bearing cups and yokes. The yokes should be snug and smooth moving.
• If u-joints need replacing due to worn or frozen bearings, then Precision brand, part #813 will fit if grease nipple port is plugged with short bolt.
• Make sure the internal bushings at guibo end (rubber damper end) are not worn out. U-joint yoke should be a tight fit with no slop (and shaft greased). If bushings and or yoke shaft worn, then take to machinist to fit new bronze (or Oilite) bushings and have yoke shaft machined to remove wear and to fit. There are two bushings, one at the end and one deeper inside driveshaft. They can be removed with a 1" tap. In the UK there is a replacement poly bushing available for the end bushing.
• Guibo should be intact with no rips, tears, rubber degradation, and bolted to proper torque.
• Measure flange angles on both trans and front diff; they should be equal and probably best if 4 degrees from vertical or less. I *believe* the stock set up is having flange faces angled down at 4 degrees or less. Don't shim to have flanges perfectly vertical. The joints should have some angle on them to allow the needle bearings to wear evenly.
• Adjust front diff (or trans if needed) with shim(s). For example, add shims to front diff. front mount to make input flange face down more.
• Measure lateral alignment and adjust transmission and or front diff to align, centre on centre.
• Recheck flange angles.

Install propeller shaft and test drive. If vibrations persist, try loosening the front differential mounting bolts a bit and drive for a few miles. This may allow the front differential to align itself to shaft. Tighten bolts back up.

References

• Herman's Blog with propshaft info
• Another blog with alignment and propshaft info (author's blog)
• Link to polybushing