Hi Guys

Having got my 1989 XJS V12 running after an 8 year lay up, I've been giving the chassis a thorough clean and undersealing with black waxoil, starting from the front end and then slowly working back.

Doing it in one section at a time and leaving the rear suspension and axle until last but then got a bit of a shock when I looked at the inboard rear disc brakes.

These are a little unusual to others I have seen, as they have a round steel hoop welded around the outer edge of the discs, where the ones on my other car don't.

But the very first XJS I owned also had these hoops around the discs.

And as I was driving along one day I suddenly heard a 'tinkling' sound coming from the rear axle, so I stopped to look underneath as best as I could by the side of the road.

As I looked I was amazed to see a steel hoop was dangling on one of the drive shafts and at the time didn't know what it was or how it had got there, so when I got home I jacked her up and had a proper look.

What happened was one of the discs (probably both) had worn so thin, that this steel hoop had become dislodged and had fallen off the rim of the disc and had found its way onto the drive shaft.

So when the drive shaft was spinning with this hoop around it, that is what was the cause of the tinkling sound, so I had to cut the hoop off with an angle grinder.

Which brings me to my present car, as the rear discs also have these hoops and the discs look so thin, it won't be long before I get the same problem with one of these hoops falling off and finding its way onto the drive shaft.

I need to replace the inboard rear discs and that doesn't look like the easiest job in the World.

So what is the best way to go about it?

Should I drop the rear suspension unit or would it be easier to leave the unit in place and then replace the discs in situ?

This is one job I have never done, so any advice on how to do it would be appreciated.

I have heard that it is possible to buy a completely reconditioned rear suspension unit, so you can just swap it over.

In case I decide to go that route, does anyone know where I can get one in the UK and how much they would be.

In the event it costs megabucks, then I will just fit new discs.

 

Removing the entire rear 'cage' is the most popular way. And it isn't all that hard, actually. And it sure beats spending hours working on your back.

Besides, removing the discs requires that the lower arms be allowed to swing wayyyyy down to get the discs out. Not too bad if you have a hoist but if you're working on jackstands the car will have to be higher than most people woud be comfortable with.

Replace or overhaul the calipers while you're at it, and tend to other needed repairs. New brake hose, too.

I've not heard of nyone selling totally refurbished assemblies, personally. They'd have to be awfully expensive, though, I reckon

Cheers
DD

 

Ward Engineering (Colchester) or Grublogger will sell you a complete 100% renewed rear axle, around £2,000 I seem to remember from their websites (nice work if you can afford it). As Doug says renewing the rear by taking out the entire cage is the best way - if you have the car under cover in a garage to do so. Then you can do the calipers, discs and anything else you need to do, like shocks, springs and handbrake, brake flexible connection.

And apart from a rich sense of satisfaction, you will have £1,500 left in the Kitty for the ensuing string of expense the XJS Godesses have lined up for you in recompense for the many driving miles of bliss they will also, to the dedicated acolyte, eventually provide.

Greg

ps: and forget about those daft OE discs with the rings, fit solid normal aftermarket replacements and they will last indefintiely. Apparently the rings were sound/vibration dampeners, I was told no idea if true!

 

+1 on removing whole IRS. I have done it twice and the second time was a breeze. First time was just the difficulty of the unknown.

The discs are sandwiched between the half shafts and the diff outputs.
Ensure you retain the shims on the outer side of the discs as they will influence the camber (I am slightly out of my depth here, I'm sure i'll be corrected if I'm wrong). Which makes me wonder that if the new discs have a slightly different thickness in the centre then reshimming may be necessary. You may have to measure this with calipers and make the adjustment if required.

By the way, take care when freeing the IRS as it will be suspended by 4 rubber to steel mounts prior to their removal. Two of mine were separated due to age. I recommend supporting the IRS with a trolley jack (or better, a transmission jack for balance) from the start. Have a friend help to balance and guide it during the lowering. I lower it onto two small furniture dolleys about 2 feet apart joined by a 3x2 to stop them squirreling around which allows it to be wheeled sideways out of a wheel well.

 

I just completed this job. The parts were less than 400US, but the time it took me to do, easily justifies shops charging a lot to do this. Just wrench turning, not really rocket science.

 

Hi Doug

That does sound the best way to go but a mate of mine seems pretty convinced that the discs are not as worn as I think and that it would pass an MOT no problem.

So unless you (or anyone else) can think of a reason why not, I am going to cut the IRS out of one of my V12 scrappers that I bought some time ago for spares and recondition that one then do a swap after the Summer.

Many Thanks for your help

 

Hi Greg

I checked out the recon IRS and its quite an expensive piece of kit to buy! so I think I will pass on that one and get the spanners out (again!)

As I said to Doug, I've got a V12 scrapper, so may recondition that one ready to swap over after the summer, with Aftermarket discs as you suggest, as a mate of mine thinks my discs are not as bad as I think.

My other Car has aftermarket type discs and they seem a lot thicker, so I think this 'ring thing' round the outside, gives the impression the discs are more worn than they actually are.

They are all nice and smooth and show no signs of any grooving or cutting like you might get with worn brake pads. (the present pads are all good)

Thanks for your help

 

Hi Texasscot

Great advice many thanks!

I've had a good look round the IRS and it looks a lot more daunting, than it probably is, the worst part seems to be taking the rear silencers off, which is always a bit of a pain to have to do.

As for the shims, that bit is right out of my comfort zone but I do know a Jag expert who can do that for me, as otherwise the IRS will be up and down like a 'YoYo'

 

Hi Superchargedtr6

You are bang on with that one, they certainly know how to charge! and I like the satisfaction of doing stuff myself.

Its just a bit frustrating, when you want to get back on the road, after an 8 year layup, when a potentially big job rears its ugly head at the wrong time.