buzzing

[Robbie693]

Hello,

Driving on the motorway yesterday I had a buzzing/vibration noise briefly as I backed off the throttle abruptly when someone braked up ahead. Does this point to worn diff mounts or torque rod bushes or both/either?

Cheers

Robbie

[billwill]

I get buzzing from the various bits on the crashpad vibrating, especially the plate thing over the radio.

I suspect too that I get buzzing from the radio itself, possibly due to touching the fibreglass or the heater supports, or the wires buzzing against the metal case of the radio.

[Robbie693]

Thanks Bill,

I get plenty of buzzing from the interior trim too but this was definitely from the back end, I could feel it through the seat too. in fact it was more of a feeling than a noise really come to think of it..

Cheers

Robbie

[billwill]

Just remembered the "plate thing over the radio" was once a speaker grille, but I don't have a speaker there now.

Your buzz was on the over-run you say? Could it be the propshaft?

Maybe you need new universal joints in them.

[Robbie693]

I think the propshaft is ok, I got Paul Matty to check it recently while they were doing something else.

It hasn't done it before but I do have some vibration coming in over 80___. I think it was exaggerated by the sudden lift off from these speeds as it stopped as the engine braking reduced so only occurred for a couple of seconds.

I was thinking the torque reaction was perhaps moving the diff about?

Thanks again

Robbie

[billwill]

>I was thinking the torque reaction was perhaps moving the diff about?

Possibly and something touching the transmission when it is hard over that way.

Handbrake rod? The one that goes from the tree thing to the left rear wheel?

[paddy]

The clearances around the diff are small enough that it can touch if there is any appreciable movement. This is especially true if you have the Sprint brace bar which lowers the diff to within a few millimetres of the chassis. (At least it does for me.) Depending on the condition of the mounts and the tie bar bushes I think it's quite possible that you're getting it touching on overrun.

That said, it doesn't do the chassis any good for the diff to be rock hard. The cushioning is there for a reason and if it only happens in extreme conditions (and there is no obvious deterioration of the bushes) I would be inclined to leave it well alone.

Paddy

[oldelanman]

Hi Robbie,
It might also be worth checking the exhaust is not contacting the chassis, particularly the clamp on the silencer input pipe. The exhaust will move with the engine and the high torque reversal when you lift off at speed might be enough to bring it into contact with the chassis at this point. If it is close you can get a bit more clearance by using the stainless steel strap type clamp instead of the U shaped wire type, better than lowering the silencer and risking grounding it. Also worth checking the silencer mounts are OK.

Regards,

[Robbie693]

Thanks guys,

There is plenty of room around the handbrake linkages and the exhaust, or there was last time I looked. I'll check again but, with the exhaust, I have almost too much space as it's a large Peco type therefore bigger, and makes the pipe sit lower than usual. The bobins may be suspect though so will check that.

I'll also check the bushes as Paddy mentioned, what should I look for when checking for wear in the diff mounts? Do they crack or perish in any way that can be seen from underneath?

Cheers

Robbie

[paddy]

I don't think you can see a lot with the bush in situ. If you want to check quickly then I would just use a crow bar to try to move the diff up and down to see if there is anything obviously loose.

Also just check that the bolts themselves are tight.

Paddy

[types26/36]

I think Paddy is probably right about the diff just touching the chassis as there is not a lot of clearance at the best of times, it doesn't always have to be the mountings that are sagging, some diffs just seem to be closer on some cars than others.
If you have the correct washers (with or without brace) then check the chassis has not been jacked up there as it can be slightly bent up below the diff. It can be quite difficult to see if there is clearance between the diff and chassis and I take a piece of wire/string or anything flexible and pass it under the diff from front to back (or vice versa) you can use wire/string etc. of various thickness to find how much clearance you have.

[Robbie693]

Good tip Brian, thankyou.

I'll have a look after the weekend

Thanks all for the help

Cheers

Robbie

[Robbie693]

Well it looks like I have a good 1/2" clearance from the chassis. From what I can see the mounts look ok and the tie rod bushes too. Can't detect any movement in the diff but I didn't shove it much as it was on a trolley jack and one axle stand..

What's the best way to check for movement? I've heard of people using a crow bar but fear about distorting the chassis..

Cheers

Robbie