Bumping and lurching

[PeteB]

Just back from trip to France and Italy - all was good with the van (apart from the amount of petrol it guzzled) until the final stint back to Calais, then I started to get a vibration a bit like a wheel that is out of balance, but maybe slightly slower vibration - we were doing 65-70 at the time. Thought it was one of the front wheels, until I looked in the mirror and saw the parcel shelf bed was bouncing up and down, so it was obviously worse at the back.

Once we were off the motorway, it seemed that it was worst when accelerating up hill in 2nd and 3rd gears - it would reduce if I came off the power - but it could still be felt a bit at all speeds. On accelerating, it felt like a forwards and backwards lurching, as if the power was coming in surges. At speed it felt like a vibration like a missing wheel weight or damaged tyre. On braking to walking speed, it felt like a gentle side-to-side wiggle of the whole van. It was still present with the clutch down or in neutral. Felt it through the seat rather than through the steering wheel.
I tried to work out if the vibration varied with engine speed or road speed - it was hard to be sure, but I think it varied with engine speed, as it felt about the same in both 2nd and 3rd when accelerating up a hill.

I checked all tyres - tread and sidewalls - and all wheelnuts - everything looked fine. I jiggled the driveshafts for good measure, but that made no difference, and there was no knocking noice to go with the vibration / wiggle / lurch anyway.

One possible indication - one the big leg down to Italy, I didn't check the oil at every fill up, and we went a bit below the bottom mark. Once I noticed, I topped it up to the bottom mark with the oil I was carrying, and then did about 10 miles before I was able to buy more oil and top it up to the top mark. After this we did about 250 miles before the vibration started.

The other is that the engine mountings are old and worn - hasn't caused any trouble before now - sometimes just a slight dog-dog-dog judder when pulling away, but not all the time. Maybe these could have got worse and led to the problem? I shook the engine by the exhast - the range of movement felt about the same as it always has, for whatever that's worth.

Any ideas what it could be??

[kevtherev]

sometimes just a slight dog-dog-dog judder when pulling away, but not all the time. Maybe these could have got worse and led to the problem? I shook the engine by the exhast - the range of movement felt about the same as it always has, for whatever that's worth.

Any ideas what it could be??

and did the engine move ...when you shook it?

cos it shouldn't.

[PeteB]

A bit! Maybe 2 or 3 inches of vertical movement at the exhaust, but against fairly firm resistance - not just flapping about

[kevtherev]

A bit! Maybe 2 or 3 inches of vertical movement at the exhaust, but against fairly firm resistance - not just flapping about

ok, well the mounts are shot.. I would be thinking about replacing those asap
they shouldn't be able to move at all by hand (ok may be a 1/2 an inch with serious effort)

as for whats causing it well, there are some things to consider.
misfire
wheel imbalance.
clutch slip

the latter is my bet as it's worse under load.

[PeteB]

Thanks Kev,

Finally had chance to jack it up today - thought I would check the easy things first - left rear tyre distinctly non-round - but without any defect you could see other than by spinning the wheel.

Still suprised by the forward/backwards feeling it gave accelerating - still next time I will jack it up rather than keep driving - very glad the tyre didn't fail catastrophically on the motorway!

Cheers,

Pete.