Increasing engine vibration

SamWise · Post by **SamWise** » Sun May 24, 2009 10:45 pm

I'm noticing a greatly increased engine vibration. This tends to occur in 3rd and 4thm between about 2000 and 3000 revs (from memory), and only when accelerating fairly hard. It's enough that my satnav mount wobbles all over, and the gearstick is all over the shop too. Any thoughts as to what might cause that?

DLM · Post by **DLM** » Mon May 25, 2009 12:34 pm

Between 2-3k rpm on a TD? That's where there's most torque being generated.

Have you done initial checks on the mounts?

The lower "mount" (really a bush to restrain the rotational forces generated by the engine and drivetrain) can become oil-soaked, perished, and broken. It's under the front offside of the engine, held in the casting through which the o/s driveshaft passes. If completely KO'd, you may hear a dull clunk on startup as the engine bashes the front subframe. A careful visual check while someone else starts the car can give a good idea how well it's restraining rotational forces. Check for damage and sponginess on the rubber of the bush, and if the metal mount and rubber bush have parted company.

The rubber-and-through-bolt part of the upper engine mount, also on the offside, can also fracture - a jack placed under the sump ( wood between sump and jack to protect sump) will tell you if there's gross damage: if it starts to do more than just support the engine on very careful raising, the
rubber-and-through-bolt section may be u/s.

Also check the nearly-pyramid-shaped rubbers which restrain fore-and-aft movement of this mount.

The lower n/s gearbox mount is a bit more inaccessible - I've personally never had problems with one.

DavidRutherford · Post by **DavidRutherford** » Mon May 25, 2009 12:50 pm

I'm guessing that the frequency of the vibration is not the 50-ish Hz that would be caused by an engine at 3000rpm, but is more like the 10-15Hz, co-inciding with a wheel at 200-300rpm, and three arms of a Tri-axe joint.

In short, sounds like a driveshaft inner joint to me.

Whilst dead engine/gearbox mountings will amplify any vibration like this, I don't think that "just" a soft engine mounting can be responsible for vibration like this: There has to be something to generate the vibration in the first place.

Is the vibration any worse if you try accelerating with a bit of steering angle on? Also, if there's a nice bit of smooth road around somewhere, try accelerating with the car in high. If the problem is indeed driveshaft related, then this should make it even worse, as the driveshaft is now having to go through a much greater angle, thus amplifying the problem.

Kitch · Post by **Kitch** » Mon May 25, 2009 1:49 pm

My valver's started doing this, and it's since I changed the driveshaft for a used replacement. Gear lever wobbles around whenever you load it up. It's not the engine mount, thats tight and the gear lever doesn't move around when youpush and release the throttle suddenly.

SamWise · Post by **SamWise** » Mon May 25, 2009 8:57 pm

Sounds exactly like what I'm getting, Kitch. Could well be a driveshaft then.

SamWise · Post by **SamWise** » Thu May 28, 2009 9:51 pm

I'm pretty sure it IS the driveshaft, now I've observed that it is in fact between 40 and 60 mph regardless of gear that the vibration occurs (though it's gradually spreading wider). I tried a little hunt for driveshafts, and was shocked to find that £140 was the only price out there! How long can I get away with driving like this? I'm doing collosal mileages at the moment, typically over 800 per week, and it's worrying me.

mountainmanUK · Post by **mountainmanUK** » Thu May 28, 2009 10:23 pm

I'm assuming that you're running a TD?

Would this be any use to you.....?

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... 0291689903

Certainly a lot cheaper than £140

I bet they will also sell the shorter LH shaft too.

SamWise · Post by **SamWise** » Thu May 28, 2009 10:28 pm

How did that not come up when I searched? Thanks! I need to find out now which is the problem shaft.....

DavidRutherford · Post by **DavidRutherford** » Thu May 28, 2009 10:46 pm

Jack up, axle stands, wibble wheel back and forth and it should be obvious which shaft is the issue, as I would expect there to be a fair bit of play in whichever joint it is.

The only other alternative is that it could be a knackered driveshaft intermediate bearing causing the long shaft to whip. Worth 5 mins under the car to inspect.