Noisy Jaguar Diffs

[Wag]

I'm a proud new owner of kit based on a 1977 Jaguar V12 Saloon. Great in all respects apart from a very noisy diff. This maybe because I virtually sit on it but I just wondered if anyone had words of wisdom as to why it is so noisy. (other than worn out please!)

[kitcarman]

Let me guess.

It’s a Cobra with the diff bolted direct to the chassis?

It feels like a dentists drill is being forced up your.

Den

[Wag]

Thanks for the quick response. Close, it's a Daytona but I guess it has been build the same way, I've not actually crawled underneath yet. If your right am I stuck with the noise?

[kitcarman]

Wag said:

If your right am I stuck with the noise?

Yes and No.

Is it an SR V12?

There are things that can be done to quiten it down, but it’s a design problem that you won’t eradicate completely. Just like me really, you’ll suppress it but never stop it.

Den

[Wag]

Kitcarman, I'm impressed, yes it is a SRV12 and this forum could prevent me from ever getting any work done again!
I would appreciate any tips you have. I'm not about to rebuild the car as its fundamentally ok but as I intend to use it fairly often it would be worth knowing what can be done. Depending on the complexity I'll plan to do when it's convenient.
I appreciate your help.

[gdr]

Don't worry, Kitcarman is correct, the Jag diff bolted to chassis makes a racket even if diff in perfect nick. My GD427 was the same except the single roll hoop acted like a nice big amplifier. Only solution is to drown it out with engine and wind noise.

[chris_n]

For what it's worth my Dax Tojeiro is the same too, even down to hearing a slight whine through the roll bar next to my ear!

I had been thinking it was only a matter of time until the diff needed looking at, but based on this thread might not be too urgent!

[Wag]

Looks like I'm discussing a well known kitcar "feature". A whine is a good description but the resonance is harsh. On a reasonable road at 60 or 70 I can find a clear zone when everything appears calm but once you slow down or accelerate you get the whine, as the diff appears to take the strain and spin-up. If I understand it I can live with it, I just thought there might be a trick to improving the situation.
Thanks for everyones comments.

[kitcarman]

Wag,
Did anyone welcome you on board. If not WELCOME!

The simplest, most economic and most effective solution is. . . .
. . . .sorry I can’t go there .

The next thing is to squirt the chassis and roll bar tubes with expanding foam. It stops the sound reverberating.

To stop the up your arse, you need to remove the diff and place a rubber gasket between it and the chassis. You also have to sleeve the mounting bolts and ENSURE they’re anti-vibration ‘wired’ ‘cos the rubber will encourage them to work loose.

It must be much worse in a saloon as it’s noticeably louder in a convertible with the roof up. I’d therefore ensure you’ve got oodles of internal sound deadening felt every where you can put it.

Finally, you need a damn good music system. Never mind the tone, what you want is 400 watts and 18” speakers.

Good luck.

Den

[Wag]

......and ear plugs.
Thanks Den, and everyone who joined in. I'll do exactly that and post the results in due course. I'm pleased to have discovered such a great pool of knowledge from fellow enthusiasts. Do your wife’s, girlfriends, family and friends all think your mad. Mine do!
Cheers.

[kitcarman]

Wag said:

......and ear plugs. Do your wife’s, girlfriends, family and friends all think your mad. Mine do! Cheers.

Wag,
The place I wouldn’t go. . .well I’ve relented. Sawdust in the oil works wonders.

Ear plugs. . . Emmm. . . For the diff noise or that from Mrs Wag?

Yes, they all think we’re mad. Look at the problems some lads have got – just to get to Exeter.

Den

[gdr]

I'd avoid any rubber between diff and chassis though, since the Jag diff carries all the rear suspension loads and any flex could alter handling especially if your kit does not use the Jag trailing arms.
On the XJ & XJS the subframe provides the isolation of diff from body.

[kitcarman]

gdr said:

I'd avoid any rubber between diff and chassis though, since the Jag diff carries all the rear suspension loads and any flex could alter handling especially if your kit does not use the Jag trailing arms. On the XJ & XJS the subframe provides the isolation of diff from body.

The rubber that Roadcraft used was quite hard, and the SR V12 does employ trailing arms, but not those from Jag (awful looking things anyway).

Den.

[chris_n]

kitcarman said:

Finally, you need a damn good music system. Never mind the tone, what you want is 400 watts and 18” speakers.

All that heavy audio stuff just slows you down! The best music is what comes out of the exhaust pipes when my foot's flat on the floor.

[wag]

I agree, the (engine) noise is half the fun. The other half is owning a great looking car that's not your average, depreciating, computerised family box. We've already got one of those!