Investigation

At first, I suspected that one of the ball joints may be on the way out, but there are several suspects, so a few checks were necessary.

This week's line-up.

The first check is the easiest; you just bounce the suspension on either side and listen for knocks. While you do this, you feel how smooth the suspension is. If knocking is heard while bouncing the suspension, the problem will be in one of the vertically-aligned joints or the suspension strut. This was not the case for me. On to the next test.

Jack the van up at the lower control arm, until the wheel is off the ground, then try to wobble the wheel from top to bottom and from side to side. If there's any play, or you hear knocking, then the problem will be in a ball joint or laterally-aligned steering component. There was no play in either wheel, so I then jacked the whole front end up at the sub frame and tried turning the steering wheel rapidly (with engine running) to check for play in the steering system. If the knocking was heard during this test, it would be coming from the steering column, tie rods, or even power steering gearbox. This was not it, either.

However, I had a nice clue when lifting the van; the exact knocking sound I'd been hearing during operation occurred once as I lifted the van, and it came from the sub frame bolt at the back end of the control arm. This gave me a place to look and a good idea what I'd find when I did.

We know scissor jacks are the last resort, but mine is tall enough to lift the van at the sub frame, which my bottle jack is not.

The rear bushings on both sides have perished and will need to be replaced. Not only that, the sub frame bolts had come seriously loose. I torqued them back up and went for a test run around the village, hitting the same speed bump that has been giving me the knocking sound, and braking in the usual way at the junction. Not a peep. This confirmed my problem and eBay already had my solution on standby. Parts on order.

This article will be updated with a detailed guide for fixing this problem, as soon as the parts arrive.

Incidentally, the torque value for sub frame bolts in my manual is extremely low. I almost broke a steel pipe trying to get them out when I did the clutch, but the manual claims that 113 ft-lb is sufficient. It's not. I've seen a few other people online discussing this issue with various different cars and trucks, and the agreement is overwhelmingly in favor of cranking those bad boys as tight as you possibly can and then some. I've wound mine up to 180 ft-lb, only because they'll be coming off again when the new bushes arrive, but they'll be going up a lot tighter than that, when they go back on. I can't possibly tell you to overrule your vehicle manual, but I can tell you that 21mm bolts can take a lot more than the 60-90 ft-lb suggestions I've seen over at the Mustang discussion, and given that there are only two of them on each side and they take the weight of most of the engine and drivetrain... well, you get the point.

FYI: Some vans require replacement of the whole arm, which will usually include the lower ball joint and a new set of tie rods. On other vans, just the bushes may be replaceable (as on mine). This is something you'll need to check out before buying parts. In any case, the process will be almost identical (except for the bushing replacement steps), as the entire assembly will need to be removed, regardless of which part you will replace. Stay tuned. Shouldn't be long.