944 3,400 RPM gearstick vibration

[davieg]

When driving along in my 1991 944 S2 Cab, if i keep the revs at exactly 3,400 RPM, i get a vibrating noise coming from the gearstick. Any revs above or below and the noise disapears straight away but this happens in any gear at 3,400 RPM. Anyone have any idea's what would be causing this and how serious it could become over time and what would be required to rectify the problem.

Cheers
Dave

>>> Edited by davieg on Tuesday 20th July 12:00

[diver944]

It could be you have something loose in the linkage under the gearstick, maybe even the metal clip that holds the top of the gearstick to the shaft.

The leather gaitor is held in place by a thin plastic frame at the bottome of the gearstick gaitor. This can be CAREFULLY lifted out and will expose the workings underneath. It is very thin and fragile

Once the gaitor is up you should see the metal clip and also the linkage down below a second rubber gaitor. Hopefully you will spot something loose

[studog]

On my admittedly older 2.5 lux I had exactly the same problem. This was caused by wear in the connection between the lever and the linkage. There is a pin welded to the lever which was quite badly worn away.

Refurbished ones are available I believe. I made and fitted a new pin for mine. It may be best to look up a local engineering shop as it wouldn't cost much to have one made.

[davieg]

Now i do have a lot of play in the gear leaver, moving from side to side and there is a slight wearing sound when changing gear which made me think the gear leaver holding pin may have gone but i wasn't sure if this would cause the vibrating noise at 3,400RPM or if this would have been something else. I'm going to try and get the holding pin looked at shortly and hopefully that will solve the prob as well. Any other sugestions welcome tho

~dave~

[domster]

It's the balance belt being one or two teeth out.

Bet you a fiver.

(I had a 944 S2 Cab with exactly the same symptom, you'll probably notice a slighter vibration at equal intervals in the rev range, ie 1700 rpm, 5000 rpm etc.)

[Spyke]

domster said:

It's the balance belt being one or two teeth out.

So what's the solution? And does it mean shoddy service work if the belts have been done recently (for recently read six months or so...)

Spyke

[domster]

The solution is simply to get the belt refitted, or replaced if worn. The belts should be done every 40k miles or something anyway. IIRC it was a couple of hundred quid when I had it done (a few years back). You may find it cost efficient to check/replace the water pump etc. at the same time.

Remember, it is the balance belt that is a bit out by the sounds of it - not the cambelt. Did you have one or both done?

PS Re shoddy service, well, if you didn't go back and get the belts tensioned after 800 miles, then that may be the problem, or the cause of the problem (even toothed belts can slip, by jumping teeth, if not tensioned correctly). But yes, if the balance belt was fitted a tooth or two out of alignment then this could cause vibration. I suspect mine had been poorly fitted rather than slipped, but it was a german import (imported by me!), so who knew the history of it?

>> Edited by domster on Thursday 22 July 16:40

[domster]

PPS The vibration shouldn't get any worse over time, but you are driving your engine 'out of balance' and that probably isn't good for the crankshaft bearings etc.

>> Edited by domster on Thursday 22 July 16:45

[nick_968]

If your balance shaft is out of alignment then it should be fixed immediately, it can only be correct or 180 degrees out if I remember correctly. The vibrations from this can cause the oil pickup to crack, potentially causing much more serious problems with oil pressure. However I dont think it is possible to diagnose it as a misaligned balance shaft just from the symptoms you describe. It could just be wear in the linkages. Get it checked by someone who knows their stuff to put your mind at rest.

[Spyke]

Cool - thanks all.

(I haven't actually got one yet - but have noticed it in a couple of test drives since it was pointed out on here)

[davieg]

Hmm, well there is vibration higher in the rev range as well so you may be right about the balance belt. Going to get it checked this or next weekend now i have the repair cash. Anything else that should be done at the same time (along with the gear leaver pin which must be loose with so much play in the gear leaver)?