Grinding At Certain Rpm

[Mike Walker 0]

Just seems to be problem after problem with the car at the moment got a grinding noise between 3000rpm and 3500rpm in all gears, any other revs and the engine is sweet.

 

When this happens the gearstick also shakes badly so whatever it is is obviously sending the engine/g'box into a spasm!

 

Things I can think of are engine mounts, alternator bearings, big-end/main bearings, gearbox or diff shagged but I've got the feeling that someone here will be able to pinpoint the problem more precisely from the description......

[jackherer 543]

it could be a driveshaft... also check the gearbox is firmly bolted to the engine.

[Mike Walker 0]

it could be a driveshaft... also check the gearbox is firmly bolted to the engine.

 

If it were a driveshaft would it result in there being some play in it? All seems pretty tight under there.......

 

I'll check the gearbox is bolted to the engine fine just wondering why it would result in the vibration only at certain RPM?

[PumaRacing 2]

If the engine itself is running ok at those rpms then the most likely thing to be very specifically rpm dependent would be an exhaust resonance. You might have lost a mounting and the system is moving about and touching the gearchange linkage.

 

Does the correct answer win a fiver ?

[C_W 3 1 Cars]

It's either that or some other thing resonating; the metal cambelt cover on my 8v used to rattle at certain revs (although usually lower rpm than this) but I wouldn't describe this as grinding. The exhaust DOES make a scary noise if the gearlinkage touches the exhcuast.

[Mike Walker 0]

If the engine itself is running ok at those rpms then the most likely thing to be very specifically rpm dependent would be an exhaust resonance. You might have lost a mounting and the system is moving about and touching the gearchange linkage.

 

Does the correct answer win a fiver ?

 

Yes you most certainly do get a high five®

 

It would make a lot of sense if it was the exhaust as it makes the gearstick vibrate as well, i'll check that tonight

[Mike Walker 0]

It's either that or some other thing resonating; the metal cambelt cover on my 8v used to rattle at certain revs (although usually lower rpm than this) but I wouldn't describe this as grinding. The exhaust DOES make a scary noise if the gearlinkage touches the exhcuast.

 

Now that the exhaust resonating and touching something else metal has been mentioned i've realised that this describes the sound perfectly and that the 'grinding' description was merely a poor effort by myself

[steve@cornwall 100]

It's either that or some other thing resonating; the metal cambelt cover on my 8v used to rattle at certain revs (although usually lower rpm than this) but I wouldn't describe this as grinding. The exhaust DOES make a scary noise if the gearlinkage touches the exhcuast.

 

Had similar with a neighbour's gti- suspectd n/s driveshaft, so changd it and it was much better- until the battery tray snaped because it hadn't been bolted to the vertical side of the chassis leg-only at the top! Causing the g'box to hit the driveshaft. Check the g'box mount under the battery, just in case it's got a loose nut,allowing the 'box to drop slightly

[Mike Walker 0]

Had similar with a neighbour's gti- suspectd n/s driveshaft, so changd it and it was much better- until the battery tray snaped because it hadn't been bolted to the vertical side of the chassis leg-only at the top! Causing the g'box to hit the driveshaft. Check the g'box mount under the battery, just in case it's got a loose nut,allowing the 'box to drop slightly

 

Erm, so does the battery tray have some critical fixing points or am I reading that wrong?

[ORB 227 1 Cars]

I think I am correct in saying that the battery tray has four bolts.

 

two that you see as soon as you take the battery off and two that are sort of under the battery tray that bolts towards the wing.

 

The battery tray is vital as it is this that holds the gearbox mount and thus makes it a structural part of the car.

[Mike Walker 0]

I think I am correct in saying that the battery tray has four bolts.

 

two that you see as soon as you take the battery off and two that are sort of under the battery tray that bolts towards the wing.

 

The battery tray is vital as it is this that holds the gearbox mount and thus makes it a structural part of the car.

 

Wow, thats mental!!

 

Kind of quirky as well which I like!

[Simes 248 2 Cars]

Unless I've mis-read something, you don't need to remove the battery tray to check the gearbox mount.

[steve@cornwall 100]

Unless I've mis-read something, you don't need to remove the battery tray to check the gearbox mount.

 

Yup it says "under the battery", that HAS to come out!

[Mike Walker 0]

Well, it's definately not the exhaust I can't make it hit anything under the car by shaking it about and it's held on securely and in the right place.

 

Also had another look about at the driveline and all seems well there so all thats left is to take the battery tray out and have a ganders at the bolts, if thats not the problem i'm sure i'll be back for some more probing

[C_W 3 1 Cars]

You'll probably find out that it's not an easy job to take the battery tray out!! I don't think it needs to any way, make sure that at least the 2 top bolts are tight and that the batter tray doesn't moved if levered.

 

You can with the battery and rubber top mount removed, check the tightness of the pin in the gearbox which the 18mm nuts goes on to.

 

But I doubt this would be the cause of the grining, unless there is a lot of engine movement which is sometimes difficult to replicate when not being driven.

[steve@cornwall 100]

DON'T take the battery tray out!!!!! as said, just check that it's tightly fitted and that the tray is still flat on top!

 

unlike this one

 

[Mike Walker 0]

You'll probably find out that it's not an easy job to take the battery tray out!! I don't think it needs to any way, make sure that at least the 2 top bolts are tight and that the batter tray doesn't moved if levered.

 

You can with the battery and rubber top mount removed, check the tightness of the pin in the gearbox which the 18mm nuts goes on to.

 

But I doubt this would be the cause of the grining, unless there is a lot of engine movement which is sometimes difficult to replicate when not being driven.

 

To be honest I think i'd notice if there was a lot of engine movement as surely it would be felt to an extent in the car or would be visible looking at the engine whilst at idle or reving it?

 

I 'wiggled' the battery tray last night and i'm not happy that its fixed on there tightly enough at all so i'll just remove the battery itself so I can see whats going on.

[Simes 248 2 Cars]

Have you thought that the grinding and shaking could be unrelated?

 

Does the grinding noise happen when you depress the clutch?

 

Could it be the intermediate bearing in the RH driveshaft?

[Mike Walker 0]

Have you thought that the grinding and shaking could be unrelated?

 

Does the grinding noise happen when you depress the clutch?

 

Could it be the intermediate bearing in the RH driveshaft?

 

Well, the shaking of the gearstick only happens directly in conjunction with the noise so that kinda rules them being unrelated out.

 

If you mean does the noise happen every time you depress the clutch then no, it only happens as described and i'm not sure whether its exactly the same sound but you get a quick 'blip' of it immediately after starting the car as the revs pick up for the first time.

 

I could well imagine it being the intermediate bearing as (don't laugh) its currently only held in with one of the bolts, dunno where the other ones gone!