I am just starting to sort out my "new" 86 XJS V12. When test driving after various repairs (months to go) I notice that it appears the drive shaft comes in contact with the underbody (tunnel) over fairly mild bumps or relatively mild changes in road surfaces.

I thought it might be the muffler, but have since ruled that out. Could this be a sign of bad motor mounts or, worse, too much body flex?

As always, I would appreciate any insights. I am approaching that stage when I have to decide whether these unknown issues will be too difficult to overcome from a cost benefit standpoint.

Thanks.

 

could be an issue with the transmission mount i guess.

what part of the tunnel? front or back?


is it a cabriolet or coupe?

 

Thanks. I cannot tell which mount as this point. I need to get it up on a lift. It is a coupe.

 

what part of the tunnel is the driveshaft banging on?

if its a coupe, i doubt its any kind of body flex. certainly you wouldve noticed massive amounts of rust by now


could be front subframe bushings.

 

This is by far most likely to be the gearbox tailshaft mounting. The mounting consists of the gearbox sitting on a spring on a bolted-in shelf-type bracket across the tunnel, with a rubber 'cotton reel' preventing the spring from over-compressing and therefore allowing the whole thing to bang about on bumps.

The spring gets weak and the rubber disintegrates. There is a good bit about it in the Great Palm's book, and also on various individuals' sites. The new bits are not expensive, but it is a quite complex bit of maintenance to put them in. Involving removal of the gearbox sump rear bolts, and unbolting of the 'shelf' that the whole spring device sits on from the floorpan/tunnel, and carfully supporting the gearbox while this is done.

Greg

 

Some senior members may give an authoritative answer here, but my take on this, since I had the 'clunk/bump' sound when hitting a certain road bump, I recently had the transmission mount bushing replaced on my '89 XJS, and it cured the problem. -Yes, mine was squashed or compressed. (located in center of tranny mount below transmission).

 

When you say 'drive shaft' I presume that you mean 'prop shaft'?
As gregh says it is more than likely the rear gearbox mounting; the spring loses tension after a while.
Banging from the 'drive shafts' could be a broken exhaust mount letting it drop onto the shaft.

 

alright, i usually dont get too bent out of shape over things like this, but im gonna start arguing.

what exactly does "prop" stand for when you're referring to the drive shaft?

if you Brits have adopted the term prop shaft from nautical origins, then your referring to your propeller shaft.......

if prop is short for propulsion, then i really dont get why you dont just call it a drive shaft.

either way, OP isnt in england, so i wouldnt bother correcting him on the terminology.

 

Propulsion is a means of creating force leading to movement. Nothing to do with a propeller.

 

Funny and, again, thank you all for your help.

 

The propellor shaft is connected to the differential which is connected to the drive shafts (or half shafts). It is just a case of correctly identifying the parts when trying to offer assistance, not being snotty or a smart ****.
Propshaft Assembly-5.3 Litre - Parts for XJS from (V)139052 to (V)179736 | Jaguar Classic Parts UK

 

Heh heh, automotive semantics can be fun and interesting :-)

Jaguar itself isn't entirely sure of which nomenclature to use at times. If you look at X300 service manuals and parts catalogs you'll see that in the *parts catalog* the terms "propellor shaft" and "driveshafts" are used.

However, in the *service manual* these are replaced with "driveshaft" and "axle shafts", respectively.

Elsewhere in the same same manuals/catalogs you'll see that, for example, "boot" and "wing" have been replaced with "trunk" and "fender".....yet "fascia" (dashboard) and "windscreen" (windshield) remain unchanged.

Time and language march on, I guess?

In some 80s-earlier vintage Jaguar service manuals you'll see recomendations that certain tasks be undertaken only by a qualified "engineer" or "engineering shop". In USA-speak this would be a "machinist" or "machine shop"....where you would have your cylinder head resurfaced, cylinders bored, and the like.


Ramble switch "off" for now :-)

Cheers
DD

 

That explains the phrase 'fender bender'; I always thought that the fender was the bumper.
We have a prang over here.

 

I think it was Sam Clemens who said we ".... are two nations divided only by a common language." How true!

Marty..........................

 

My 88 Cabriolet does the same thing, but only when there are 2 people in it. I got a replacement spring for the transmission mount but have not installed it yet. Maybe when it gets warmer!