Chopping springs?

Chopping springs?

Author
Discussion

sheepy

Original Poster:

3,164 posts

219 months

Monday 13th June 2005
quotequote all
Evening All,

I've been trying to sort out a problem with the front of my XJS. Basically after adding new springs (bought about two years ago) to my car (about a year ago), I've found that the car is sitting about an inch too high at the front.

I've removed the springs and checked that there are no packing rings (which can adjust the height). I've also checked that I've got the right springs too.

Now on investigation, it turns out that Jaguar rationalised the spring choices for early XJ cars. Basically there seem to be two choices now: ones suitable for V-12 and ones suitable for six-cylinder cars (of which mine is one).

So if I have the "right" springs, and the car sits too high, I'm wondering what my options are. My parts supplier has sugested upgrading to the DB7 front-end (at cost of ), but I'm wondering if it is feasible to cut the springs down slightly.

Anyone done this? How much should I cut off of a 12" spring (uncompressed) to get a 1" less compressed height? What should I cut with (hacksaw or grinder)?

All hints and suggestions welcome.

Sheepy.

GreenV8S

29,023 posts

254 months

Monday 13th June 2005
quotequote all
If they're a standard ish size, I would have thought you could get springs off the shelf. They're certainly available in all lengths and lengths for coilover dampers, and I expect you'd get a good range for strut springs too. Otherwise, I know people have shortened springs by cutting through a coil at an angle and having a blacksmith square the end off. It isn't pretty or elegant, but it would get the job done if you can't find a spring the right spec. Certainly wouldn't do major suspension mods just to change the spring length.

saxo-stew

7,913 posts

208 months

Tuesday 14th June 2005
quotequote all
i really really cant recommend chopping springs. its dangerous for a start.
if you cant get the right springs, get some custom made to the specs you want. for a pair of springs, you're looking at about 90 delivered.
try D.faulkner springs.

>> Edited by saxo-stew on Tuesday 14th June 10:32

sheepy

Original Poster:

3,164 posts

219 months

Wednesday 15th June 2005
quotequote all
Thanks for the suggestions. Not sure why cutting the spring is dangerous. Granted, the heat generated will alter the spring rate, but I'm not sure about dangerous.

Problem with finding the "right" springs is that no-one seems to have any idea a) why mine are wrong, b) what I coudl buy off the shelf to solve the problem or c) what the spring rates etc are so I can get some custom ones made.

My original Jaguar parts supplier (who I no longer use and would recommend people to avoid) suggested that "your car must be wrong" Oh yes, silly me I'd not noticed that my XJS was a special light version made just for me by BL And they had the cheek to ask why I'd stopped buying parts from them!

Sheepy

denisb

509 posts

225 months

Wednesday 15th June 2005
quotequote all
I have done a few spring chops and recommend the following -

- Cut the spring in small increments, that way less heat goes into the metal.

- Put some thought into where you cut. You want the spring abutment to be as identical as possible to the original.

- Test fit the reduced spring to make sure to fits the seats OK

- Let the suspension drop FULLY and make sure the spring can't easily dislodge.

- If in doubt throw it away and either try again or contact a spring manufacturer.

If you follow the above rules you'll be as safe as you can be.

I have not had a problem YET!

GreenV8S

29,023 posts

254 months

Wednesday 15th June 2005
quotequote all
I still think you should chop the spring only as a last resort. I assume you can get the existing springs off the car.

With a spring in your hand you can easily measure the internal diameter and free length. You also need to know the spring rate. There are a few ways you can find this out:

Measure the length of the spring when the spring is on the car with the normal weight on the wheels. Knowing the weight on that wheel, and the mechanical leverage between the spring and the wheel, the load on the spring can be calculated. From the loaded and free lengths you can work out the deflection and hence the rate.

Put a known load on the spring and measure how much the length changes. For example I've roughly measured springs in the past by putting a plank across the top, having somebody of known weight sit on it and measuring the deflection.

If you scrape the paint off the spring at one point and measure the thickness of the wire very accurately with a micrometer, count the number of complete coils and the internal and external diameters you can calculate the spring rate.

Any company that supplies springs will measure a spring for you if you take/send a sample spring to them.

You can buy a spring gauge to measure the spring yourself.

Basically if your spring is a reasonably conventional size and shape I would be optimistic that you can get a replacement made the correct length.

>> Edited by GreenV8S on Wednesday 15th June 21:18

lanciachris

3,357 posts

211 months

Thursday 16th June 2005
quotequote all
More likely the shocks and springs at the rear are knackered.

sheepy

Original Poster:

3,164 posts

219 months

Friday 17th June 2005
quotequote all
lanciachris said:
More likely the shocks and springs at the rear are knackered.
Hi Chris,

Nope, they are brand-new and the back is sitting at almost the perfect height as per the original Jaguar specs.

There does not seem to be a logical explaination (other than possibly a bad batch of springs which the supplier denies).

Sheepy