Front coil spring - unsprung length

[ibnct]

I am preparing to replace the front lower wishbone bushes on my 1979 Series 2 Daimler VDP. Can anyone tell me what the unsprung length of the coil springs are on this car please?

[mike020150]

Hi,

I have never seen an 'unsprung' figure quoted presumably because there are significant variations between new springs before fitting and used springs still suitable for refitting. Hence, Jaguar specified the ride height (24 5/8" to the centre of each outer headlight with full fuel tanks and correct tyre pressures) and made adjustments with packing rings (max 3 in the pan and 2 on the crossmember). The 1/8" thick rings each adjust the ride height by 5/16". I set my ride height with new springs too close to the spec and only a few thousand miles later, I need to reset it by adding several more rings so don't be afraid of aiming high if you don't want to repeat the task! Mike.

[ibnct]

Mike, thanks for responding. I'm hoping to keep my existing springs. The reason for my query was because I am making my own spring compressor using 20mm studding and wanted to get an idea of how long the studding needs to be to fully decompress the spring. I don't want to make it longer than necessary to minimise the height I have to jack the car up.
I accept that older springs will likely be shorter in their free state, but if someone can advise what the free length of a new spring is It would be appreciated.

[greenlane]

Hi
I bought some new springs for my XJ12 series 2 some time ago and have had them stored away.
They are in a Boge box which I believe was the original equipment supplier. They were supplied as being for a V12 without aircon, as there are various springs depending on the engine etc.
I don't know if the lengths are different or just the stiffness.
My car had noticeably sagged when it was on the road, so it might be interesting to compare the length with the originals.
The new ones are 13.25 inches long.
Regards,
Simon.

[ibnct]

My car is a 4.2litre with air con but the information you have given me is a good starter for ten and much appreciated. Thank you for taking the time to respond.

[PaulGover]

...
The reason for my query was because I am making my own spring compressor using 20mm studding and wanted to get an idea of how long the studding needs to be to fully decompress the spring.
...

I'd very strongly advise the use of a professional tool, not a bit of studding. From my personal experience, the front springs can bend 15mm studding to a terrifying extent. Also, the threads on studding nuts are usually pathetic - neither enough turns nor a decent profile. I've also read a reliable source who had a home-made compressor fly off and do real damage to him. Don't forget that studding is usually mild steel, not the high-tensile stuff used for the suspension system, and the screws in commercial spring compressors. And don't forget that if the compressor gives way, you're dropping around half a ton of iron about a foot; that does one heck of a lot of harm.

The club hires out an admittedly very expensive compressor; there may be alternatives from other suppliers, or perhaps ask a garage to drive out and remove the spring for you.

If you insist on going the DIY route, take great care to make proper top and bottom attachments to the spring pans - there are a couple of V grooves at the top to centre a compressor; at the bottom you need some sort of ball and socket affair. Anything substandard risks sliding to a point that can provide damaging sideways forces (hence my bending experiments).

[piman]

Hello Paul,

that is a valid point, but studding is available in high tensile grade also, this is what I used for my MK 2, using double length nuts. It's also worth using long guide studs and nuts on the lower arms to guide the bottom pan down and provide a reserve of safety.

The commercial compressors are hugely expensive for what they are.

Alec

[ibnct]

Hi Paul, thanks for your advise and concern regarding the use of a home made spring compressor.

The reason for going down this route is due to the high cost of buying/hiring the proper tool. The problem with hiring is that I don't want to be time restricted over when I can use it, or have to worry about getting it back by a certain date.

I intend to lay a bolt across the vee grooves you refer to which passes through the studding to provide a pivot. I haven't finalised the bottom arrangement as yet but am considering a circular plywood block fitting inside the bottom pan cup backed up by a 100mm diam. 6mm thick steel washer through which the studding passes. I will also be doing some back of fag packet stress calculations to support my contraptions design.

As Alec said, I do intend fitting long studs & nuts to the lower wishbone to guide the pan and provide a measure of backup safety.

Of course if anyone has, or knows of the real thing going cheap, I'd like to know.

[richardpierce]

Out of the car my front springs are 314mm long as I've just taken them out using the last nut and run method

Regards
Richard


PS: The car is an XJ12 S1 no A/C

[ibnct]

Richard, thanks for helping me narrow it down further. Not sure I'm familiar with "the last nut and run method", but if it's anything like what I imagine, then Usain Bolt could have some serious competition!!