Correct rear springs

[Tintin]

Hi

I feel I am gong round in circles with my rear springing and hope someone may be able to put me out of my misery!

I have replaced the rear springs and shocks on my 4 litre 1996 2+2 celebration and it is now looking low at the back. The sub-frame plate to ground dimension is 165/170mm against the spec distance of 190mm. I am on 225x60x16 inch tyres. The new shocks are standard Boge and the new springs are CBC2793.

An early SNG Barrett parts catalogue lists about 5 different springs for the XJS rear end of which I think only three are still available. The springs listed for the convertible (non sport-pack) are JLM10995 (no longer available). The springs newly fitted are CBC2793 (listed for some 3.6 4.0 and 5.3 coupes). The convertible rear axle weight is, I think, greater than the coupes at 1155 Kg and therefore I suspect the CBC2793s are not stiff enough to carry the convertibles rear end weight correctly.

The new shocks are CBC5742 but the early parts catalogue specifies MHD3540BA. I have no idea whether these are the same units with new parts numbers or if shocks could account for a 20-25mm ride height difference.

Visually, the new and old components look the same - coil diameter, spring diameter, number of coils, length of shock between mounting eyes etc.

Is there a different spring/shock combination that will restore a 190mm ride height?

Robbie

[davidr]

Robbie - I always find the Jaguar Classic Parts website useful as it has the original exploded parts diagrams and lists all of the variants.
As you say, the correct springs are NLA for our cars.
But I notice that they do a packer (15 on the diagram part no CBC5435). If you're happy with the ride and handling of the setup you have then maybe spacers to raise the ride height may be the way to go?

[Tintin]

Thanks David - I wasn't aware of the packer option - certainly there were none on the old units. I will do some further research into the packer sizes and maximum number that can be fitted - a height increase of 20mm - 25mm is a fair distance for packing!

Robbie

[davidr]

Another thought - the car is I think designed to have gas shock absorbers of the type that naturally extend. This gives the car a bit more ride height. Could that be it?

[ptjs1]

Robbie,

The issue of available original springs and shocks for XJSs has been an issue for us owners for some time.

To clarify:

- CBC 2793 is a Sportspack spring for an early facelift 4.0 or 5.3 Coupe. There are some slight inconsistencies in even the genuine Jaguar parts system!

- CBC5742 is a Non-sportspack shock for an early facelift 4.0 Coupe

As you've realised, some of the original shocks and springs are not available now. However shock MHD3540BA (late convertible non-sportspack) is available from Jaguar. In addition, a lot of the non-Jaguar springs have an extremely poor quality reputation with many owners seeing ride height problems or sagging after only a few months. Are the springs and shocks that you've bought genuine Jaguar or after-market?

As David has said, there are packing rings fitted and still available. However, I don't know if that would take up 2+ cm of ride height?

When I changed my springs and shocks, I decided that I wanted a slightly firmer setup but still wanted the original ride height. In the end, the only way that I could get what I wanted was to fit Eibach springs (developed by Ray Ingham as a sports spring) + Gaz adjustable height-platform shocks. This then enabled me to dial in the rebound characteristic that I wanted but also set my ride height exactly where I wanted.

My guess (and it is a guess!) is that the ride height is predominantly being set by your springs and packing washers. I appreciate that if all of this is newly fitted parts, then you don't necessarily want to have buy replacement springs and / or shocks. However, whether the problem lies with the springs or the lack of packing pieces, you're going to have to remove and strip the springs anyway.

If I were you, I would ring Keith Parrington and have a chat. He may be able to advise you on the unladen height of the springs, the potential impact of the packing washers + options on how to resolve the problem.

Good luck

Paul

[Tintin]

Thanks both for your helpful advice. A post on Jag lovers from Chris Knowles of KWE suggests a maximum advisable packing of three rings and that 3 x 4.8mm packers will raise the body by 25.3mm (due to the fulcrum arm effect). I would like to keep the car as original as possible and therefore subject to any feed back from Keith Parrington (and because its an inexpensive option) I will go with that. If the result is not right I will look again at adjustable shocks and alternative springs.

Annoyingly my brake parts have not arrived so the car will not be ready for Gaydon tomorrow, but I will e mail you separately David, for a possible meet up next week.

Robbie

[davidr]

Robbie - PM me if you want a lift up tomorrow. I intend to leave around 8am (ish!)

[greeban]

I am in the process of replacing my rear springs - mine is a late 4.0 Celebration coupe and I have measured the old spring height which is 260mm. Berkshire Jag have measured their sports spring CBC2793 which are 250mm in height, so the original springs on my XJS cannot be these unless they have somehow grown in length with use!

Berkshire Jag suggest the v12 5.3 spring C39692 which is the softer spring but is 270mm in height. My shocks are the sports shocks CCC7466 (they are stamped CCC7467 but I assume as Paul says there have been slight inconsistencies in Jaguar's own numbering).
This suggests to me the last few XJS Celebrations sold were given the slightly softer spring set up with the sports shocks rather than the harder spring setup.

Has anyone else fitted the C39692 springs to the rear as I would like to raise the back a little as mine sat low, likely due to the springs sagging. If Robbie found his car sat low using new CBC2793 then this kind of answers my question but just wondering if anyone else has similar rear setup of soft springs and sports shocks?

Regards
Graeme

[Tintin]

Hi Graeme

There are two issues with these springs - one is getting the correct spring part number for the car and the second is the quality of the after market parts. An after market CBC2793 may have different properties (and ride height) to an original CBC2793.

Berkshire Jag were the suppliers of my "too low" springs, and did offer to replace them with alternatives but the work in getting the assemblies out and refitting them with packers on a trial and error basis was too boring and in the end I kept the CBC2793 springs and swapped the standard Boge dampers with AVOs. I could then modify the ride height at will by adjusting the threaded spring seats with the assemblies in situ; the damping rate is also adjustable. I am well pleased with the result.

Robbie

[greeban]

Thanks for the reply Robbie.

I have decided to go for the taller, softer springs as I love the soft ride and this will serve as some useful data for anyone else that is looking to replace their rear suspension. When done, I will measure the height from the floor to the diff plate and report back.

[greeban]

Have fitted Berkshire Jag's C39692 springs and unfortunately the ride height is 176mm versus the spec height of 190mm - this is better than before with the tired original springs but only marginal so am going to leave for now and perhaps this winter may fit some spacers to bring it up to spec.

Ride wise I have not noticed any change - still the lovely cosseted ride; I have pushed it around a few familiar bends and cannot notice any major change in the way the car handles so am happy with it at the moment.