Grinding noise on acceleration.

[aclwalker 3]

Ever since I got my car over 3 years ago I would occasionally get a grinding noise on acceleration.

 

Recently this has got worse, such that I can reliably repeat it now.

 

EDIT: forgot to say it's a 1994 VR6

 

Here are the details:

 

1 It only really happens in winter or cold days, but it's now happening more often so might persist this summer.

2 It happens after long fast runs at motorway speeds when I come off the motorway and then start driving around as normal. This is especially so if the motorway ends with those raised painted lines that get closer together to get you to slow down.

3 It only happens on acceleration.

4 If I press the brakes slightly while accelerating (tricky to do!) the noise is just the same.

5 It used to only happen when lightly cornering during acceleration, but is happening in straight-line acceleration too now.

6 It's a kind of rat-a-tat grinding noise...

7 ...the frequency of which is dependent on road speed, not which gear I am in.

8 I can feel it slightly through the steering wheel.

9 My front brake pads and discs were recently changed and this made no difference to this noise.

 

I reckon this is a wheel bearing failing. My mileage is very high (192k) and I have no idea when these were last done (if ever). My rear bearings are new and were replaced when I replaced the rear discs and pads. This made no difference to the noise.

 

Any other suggestions?

 

I was thinking of just getting both front wheel bearings replaced. Should I replace the CV joints too? I also have got new balljoints and track rod ends waiting to be fitted. Should I get these fitted at the same time as the bearings?

 

Thanks.

[dr_mat 0]

Could be wheel bearing, could also be CV joint - particularly if the noise came on earlier when cornering.

[Trig 0]

Hard to tell without hearing the noise. Could be the CAT heashield's come loose & reverberating. Does it happen at a specific rev range/speed..?

[aclwalker 3]

Thanks for the replies.

 

The noise does come on early on in cornering but now has also started doing it even when going straight. If I wobble the steering wheel slightly while it's doing it (while driving straight) it can make it subside then get worse then subside again.

 

It's definately not a heatshield noise. All heatshields are secure and the CAT heatshield was removed due to a buzzing noise I was getting and the fact that most of the welds have broken off.

 

I frequency of the noise is directly proportional to the wheel speed and I estimate that I get one 'grind' per wheel revolution. This itself points to something in the drivetrain.

 

I reckon my wheel bearings could do with getting done. It's a very high mileage with unknown front wheel bearing history (rears are new).

 

I just wonder if I should also get the CV joints done too. I don't get any clicking on full lock, but I suppose you don't always get that. The CV boots look intact.

 

I've never heard of inner CV joints needing replaced. Has anyone had this done before?

 

Can CV joints be replaced without having to dismantle the same bits need dismantled for wheel bearing replacement?

[Trig 0]

Sounds like wheel bearings in that case, I had an kind 'scratching' noise that occured once for every wheel revolution, it was a bearing.

[aclwalker 3]

One more point I've just remembered....

 

Sometimes, when not accelerating as such but simply cruising on the motorway, I can hear a sort of rumbling vibration. I sometimes feels like driving over marbles or something. It's hard to hear the noise in these circumstances though, since it's drowned out by the road noise and engine noise at motorway speeds.

 

When I slow down though to local road speeds and then accelerate, that's when I really hear it. Due to the slower speeds, it's also much easier to count the grinds and link them to approximate wheel revolutions.

 

I guess I'll get the wheel bearings done first and then if that doesn't sort it I'll look at the CV joints.

 

Thanks.

[bix 0]

Sounds like a CV joint, check to see if any of the gaitors are split.

[aclwalker 3]

The other day, I had an horrific metalic screeching/scraping noise driving off from cold which lasted about half a mile and then suddenly went. When the noise stopped, I distinctly felt the car freeing up a bit. The noise was loud enough to turn heads!

 

It hasn't done this again (but has done the usual stuff described further up the thread).

 

I jacked up both sides at the front yesterday. There was no play in either wheel bearing. There was free play in the driveshafts, however, when rotating the wheels back and forwards. Probably about half an inch of free play at the circumference of the tyre, before the driveshaft would then start to rotate too. There was a clicky, rattley sort of noise too when doing this rotating back and forwards (no clicking on the usual full lock CV joint tests though).

 

On the driver's side, however, there was a bit of resistance at points in the rotation. This resistance was not like brake pad resistance and in fact actually caused the wheel to rotate backwards a short distance once I let go at the point of resistance. A brake pad wouldn't do this. It was as if the mechanics had jammed slightly and pushed the wheel back round in the opposite direction.

 

I guess this could be the bearing or a CV joint.

 

I'm going to try again this weekend but will remove the brake pads and try to listen to where the noise is coming from.

 

The scraping and screeching was deeply worrying though.

 

Any other comments are appreciated.

[khurrado 0]

The other day, I had an horrific metalic screeching/scraping noise driving off from cold which lasted about half a mile and then suddenly went.

 

I have a similar problem on the driver side, tbh i havent heard it for a a while now, its comes intermittently, but is a very worrying sound. I thought it was the pads worn out, but they're fine. Im sure ive read past threads on this topic b4.

[catch_twotwo 0]

Just a thought... but if it's a "orrific metalic screeching/scraping noise" how did you get half a mile :?: I'd have been out of the car looking it over within about 15 feet....

[Kevin Bacon 5]

The clacking noise when rotating the wheel back and forth is normal, that's diff backlash. The amount of free slack is normal too. 0.5mm slack in the CVs/shaft/diff equates to nearly an inch at the outside of the tyre.

 

This driver's side issue where the wheel 'springs' back when you let go at the point of resistance is classic wheel bearing. You can't detect 'slack' in the front bearings by jogging the wheel about like you can with the rear ones. At 192K, I'd do the bearings regardless of history!!

[DEL VR6 0]

My first impression from reading this thread and replies was also bearings. Go with that first like kevHaywire, has suggested mate.

[aclwalker 3]

Cheers Kev and everyone else who's commented.

 

I was just worried that if I get the wheel bearings done (and the balljoints and tie-rod ends fitted that I've had waiting to go on for ages) that I might have to dismantle it all again for the CV joints.

 

Thanks for putting my mind at rest regarding the differential "backlash". Any more details about what is meant by this term?

 

Maybe you could answer another question that's been bugging me too regarding driveshafts? I hear that the long shaft is supposed to have a rubber donut to balance the shaft. Is this really important? I don't seem to have one and there doesn't seem to be any evidence of one being there at all (no band of different coloured rust, lol).

 

Cheers. Now I just need to investigate my coolant leak that's appeared in the last few weeks...

[Kevin Bacon 5]

Get the lot done at once mate, good peace of mind....if a little pricey, but it's done for another X amount of years.

 

Diff backlash is the tiny gap between the diff ring gear and the pinion gear. Although helical gears mesh tightly, when the pinion and ring gear preloads are setup correctly, there should be a little play. If it were solid the gears would wear out extremely quickly. The noise it makes can be alarming when you first hear it, but it's normal.

 

I've never seen a Rado VR6 with a balance weight on the driveshaft. I know some 16V and G60s had them, or were supposed to, but again I've not seen one on those either. They are prone to falling off though. Generally speaking VW shafts are OK and rarely induce any harsh vibrations.