Knocking noise that increases with road speed (take 2)

[Northern Lad]

Afternoon All

Ref: 1998 1700 xflow, 150 bhp, lightened flywheel, type 9 gearbox and De Dion 

A few days ago I tried posting on here only to discover that there's an issue with android on this forum.

My missive went into great length about what had happened and asked for any thoughts on potential problems. However, things have moved on somewhat.

The last blat of 2021 left me with a knocking noise that increased with road speed but wasn't apparent below 10mph. The car was put up on axle stands and started, put into gear and listened to....the loudest knocking seemed to be coming from the gearbox. That's me done for the season passed through my mind with me tucking the car up for winter and looking forwards to a spring engine and box out session in warmer times. Subsequent purchase of an engine crane (available to borrow if you're in the same boat and can fetch it), enabled swift extraction of engine and box with the offending item being taken to a renowned gear chap the next day. He gave it the once over and to my surprise stated that "there's nowt wrong with this, Lad". Now, I trust his judgement as he's a very clever chap who could have said the type 9 box is made of cheese but i can upgrade it for you at great cost...he didn't. He did, however, make various suggestions that included all of the drive train and associated mounts. 

I have experienced similar noises in other cars, mostly front wheel drive, that turned out to be cv joints. So, I have a few questions to throw out there:-

1. Has anybody had a similar experience and if so what was the solution?
2. Can a worn out driveshaft / cv cause an apparent noise at the gearbox?
3. The nearside cv joint was significantly warmer - not hot - than the offside. Is this significant?

I have bought new driveshafts from Caterham that seem to be a little longer than the ones I took off (is this normal?), new engine and gearbox mounts and once I've got the diff off for my gearbox chap to give the once over I will fit new uj's to the prop. Have I missed anything obvious as i don't want to put it all back together for it to knock again.

Your opinions would be gratefully received.

Cheers, Steve 

     

[Beagler]

Check the propshaft u/js whilst gearbox or diff is out. If its highish mileage have them replaced to save future diff removal

[Jonathan Kay]

My previous post:

Is it new and has any work been done it recently?

Does it go away if you declutch?

Is it affected by cornering?

...

Then I'd feel by hand for play in the prop shaft and drive shafts.

And check the engine and gearbox mounts.

And the wheel bearings and discs.

And look for clearance and witness marks on the de Dion ears.

Jonathan

[Jonathan Kay]

"Subsequent purchase of an engine crane (available to borrow if you're in the same boat and can fetch it)... "

Thanks. That's very generous, and please consider adding it to the Equipment for Loan Register.

Jonathan

[aerobod - near CYYC]

Worn CV joints where the spring has lost much of the tension could be knocking due to not putting enough preload on the diff side gears. With the new shafts being longer, ensure they compress to the previous shaft dimensions when putting a reasonable axial load on them.

[bstark]

You may not be so lucky, but I had a knocking sound that increased with road speed that was eventually traced to one of the centre caps of the alloy wheels...

Just took a bit of sealant to sort it. I was imagining all sorts of things so was delighted when it turned out to be something so simple. Fingers crossed you have the same luck!

[David Brown]

If you do a search you will see the issue I had last winter with the propshaft on my CSR. Very easy to get refurbed but afraid you've stripped the wrong end (like I did). You need to drop the diff and remove from that end. 

[David Brown]

Perhaps because this exercise resulting in me removing the engine/gearbox three times and diff twice persuaded me to swap it for an Elise.