Loud knocking noise

[djavery87]

Hi all.

New to this but here goes. Drove home from Dawlish yesterday and noticed when I hit 40mph a loud knocking noise. The noise continued if I accelerated but if I kept the speed below 40mph it didn't happen. Anyone have any clues to what this could be? I have a 2.5 diesel.

[g8dhe]

Welcome aboard!
Probably worth taking a good look around the wheels especially the back side and prop shafts, you don't say if its related to road speed or engine speed, but most probably road speed I guess. There have been several reports of late of the prop shaft fittings and supports breaking.

[djavery87]

Thanks for replying. It's road speed. When you say take a look around the wheels and prop shaft. What exactly am I looking for.

[g8dhe]

The wheels your looking for bulges on the inside normally unseen side.
The propshaft has various universal junctions and supports that can break, if you search on propshaft there have been a couple of recent reports which have included pictures of the problems one here viewtopic.php?p=724898#p724898

[djavery87]

I've had a look under the van. No signs of bulges on the wheels. The propshaft looks ok. Can't seem to see any parts broken or warn? Would there be any other signs that it's the propshaft or is there anything else that could cause the knocking.?

[djavery87]

Just seen a mechanic and hes advised to change the tyres first and see if that makes any difference as he's noticed the different sizes between front and back. Could be causing problems with the diff as it's 4wd?

Does this make any sense. If so what size tyres should I be looking for?

[Bob]

Original tyre sizes are 195/70/15 front, 215/65/15 rear.

This gives the same rolling circumference.

Many people fit 215s all round, which is fine.

If yours are different to this you can check the circumference with an on line 'tyre size calculator'.

This is really important on a 4wd.

[djavery87]

Thanks for the reply.

So would you recommend getting for 215s? Also any recommendations.

Thanks

[g8dhe]

Yes most people fit the rear size of tyre all the way round that way your spare should also fit any wheel!
The different smaller width tyre used on the front reduces stress on the steering system, but no one has ever reported problems when using the same size all around, makes life a lot simpler as well when it comes to moving tyres around to spread wear as well.

[Bob]

Agree with Geoff.

As for which tyres, depends on how you use Bongy.

Frequent long motorway trips, buy premium. Short local hops, cheaper ones will do. All seasons if you live up north and need to get to work in winter.

[djavery87]

Been busy with things. But got hold of some 17inch alloys with tyres all the same size. Fitted them and that's sorted the knocking noise. .
A new problem has started. The front alloys are getting very hit to the point I had to pullover as the smell was strong. Anyone have any ideas to what this could be?

[Bob]

I can only think they are fouling on something, different offset, perhaps?

[Doone]

I wonder if the heat is from sticking front brake calipers?

[djavery87]

Thanks for the replies. I've checked and I can't see them fouling on anything. Just took it for another drive and after the drive the caliper had a slight but of smoke coming from it? Do you think it could be sticking like suggested. If so is it a trip to the mechanic?

[Doone]

It is, if you don't want to fix it yourself. This search will show you what might be needed: search.php?st=0&sk=t&sd=d&sr=posts&keywords=Caliper