veryone knows that putting a lift on your vehicle can, at some point, induce nasty vibrations in your driveshaft. These vibrations seem to come in at specific speeds and often are more pronounced when you are coasting (i.e. when there is minimum torque on the drivetrain). This is due to the angle on the driveshaft U-joint being too large and is compounded by worn or misaligned u-joints (for a real good explanation of this, go to:

http://www.drivetrain.com/driveline_angle_problem.html).

The common solution is to go to a “CV” driveshaft. This has a double U-joint at one end (always placed at the Transfer case end) and a single U-joint at the differential end.

The set-up of this driveshaft is different from a regular (single U-joint at both ends) driveshaft:

- For a single U-joint shaft, you want the output shaft of the transfer case parallel to the input (pinion) shaft of the differential. But generally, these driveshafts start being unhappy at much more than 10 degrees (and if you have been running them for some time at a specific lift and then increase the angle, by increasing your lift – that’s when you will likely have problems!)

- For the “CV” driveshaft, you want all the angle taken by the CV end (at the transfer case) and the differential cocked up so that the pinion shaft is almost parallel to the driveshaft (ideally, the u-joint angle should be around ½ to 1 degree, as this allows the needle bearings to rotate and prevents them from “flatting” and wearing prematurely. The recommended maximum with this setup is around 3 degrees at the pinion end to prevent vibrations). But depending on the type/quality of u-joints (at the “CV”) you can run pretty radical angles at the transfer case end: check out this set-up from High Angle Driveline – the “masters” of this speciality – good for a constant 30 degree angle!:
http://www.highangledriveline.com/42_degree_constant_velocity_join.htm

I recently put a 3" lift on my D-90, courtesy of the Rovertym springs I won at a recent Rover event (SCARR 2). I noted that this lift pushed my rear pinion out of line with the driveshaft by about 5 degrees – actual angles were about 14 degrees at the transfer case and 10.5 degrees at the diff. Having GBR CV driveshafts, ideally I would want the lower (single-U) angle around 1 degree, with all the angle taken at the top end. I have Rovertym trailing arms, which allow some adjustment of pinion angle, using spacer washers, but I was all out of adjustment, with all spacers removed (shortening your trailing arms tilts your diff upwards, reducing the angle)

Driving, I immediately noticed a very slight vibration at about 60 mph, but it was constant and not related to torque on the driveshaft…

As I had run out of time before a Colorado trip, I let it go. Driving to Colorado, I did not notice much degradation of the vibration, but coming back after a week of Bill Burke fun, I noticed it was gradually getting worse.

So I "guessed" that the poor pinion angle was causing the vibration and possibly the lower U-joint was on the way out. My first step was to get an A-frame ball joint extension from Steve at Rovertym to cure my angle problem. I fitted it and was disappointed to find that it did not make a significant improvement to the, by now horrible, vibration setting in at low speed and continuing pretty much through the whole speed range.......

Next, I decided to isolate the problem by pulling driveshafts one by one. As the rear angle cure had not helped, I decided to try removing the front first. No improvement. Then, while removing the rear, I noticed there was apparently some play in the emergency brake drum/output flange. We pulled off the brake drum to find it full of oil and the flange noticeably loose. Pulled the big nut holding the flange to the T'fer output shaft to check the seal (OK) and replaced flange and tightened up the nut, cleaned up the mess in the drum, replaced it and tested the vehicle in "front wheel drive" - smooth as butter...

Replaced the rear driveshaft and tested again - perfect! So the problem was not really the angles, but just the nut backed off allowing the drum and output flange to flutter. The 5 degrees on the lower u-joint certainly would give a small vibration, which I had noticed at the first lift install, but now with the angle set at the optimum ½ degree, all is smooth.

So, if you develop a nasty drivetrain vibration, don't forget to check the emergency brake drum! To do this, you just need to remove the four bolts holding the drive shaft to the E-brake drum and then wiggle the drum: it should be absolutely tight. If you are in doubt, there is a large phillips-head screw securing the E-brake drum to the output flange. Remove this and the drum should come off, revealing the big nut holding the flange onto the T-fer case output shaft. Sadly, this is just a ny-lock (in the old days, “real” Landies had a castellated nut and cotter pin)

BTW: regarding castellated nuts and cotter pins (which we still have on “some” parts of our vehicles (e.g. tie rod ends), the correct procedure is to tighten to the nominal (lower limit) of torque and then increase until the nut castellation lines up with the cotter pin hole. Don’t crank it down as hard as you can and back off to line things up!

Doug Aitken
Past President, 2001-2003, Houston Land Rover Club