Shortening a Car Coil Spring

[indy4x]

Short history

As some of you may recall from previous posts, I have a 99 Grand Cherokee ZJ that has some modifications

It currently has a suspension lift and while the front coils are proper, the rear has been a bit of a Heath Robinson setup that I threw together just to work out if the ride height was where I needed it to be and to ensure nothing was rubbing

I had the original springs that the PO fitted but they were too tall for my needs but put them back on the Jeep tonight

I sat the Jeep back on a level surface and its loaded up with all my recovery gear etc and I need to reduce the ride height by 55mm to get it to sit level

Marked the springs while loaded and pulled them back off the Jeep so I can cut them down

The springs sit on these mounts



And this is the spring with the potential cut marks




The bottom coil is flattened to sit on the spring seat so do I

A. Cut the spring on the right hand mark and call it good?

Or

B. Cut the spring at the left hand mark, heat up the spring and bend the last coil so it matches the original?

My preference is option B. I have OA so getting it hot quickly isn't an issue but do I then quench the spring in something maybe oil or water or let it air cool?

Thanks

 

[addjunkie]

Heating it hot enough will alter metallurgy and the springs performance

 

[indy4x]

I guessed it would, it was a bit of a long shot and TBH giving it some further thought its a pretty rubbish idea.

I'll put the Heath Robinson setup back on for now and go speak to a spring specialist. I had a custom set made for my Frontera about 12yrs as you couldn't really get decent lift springs in the UK and it wasn't stupid money

If it was a LR or Jimny there would be loads of options in the UK but being a Jeep makes life difficult for custom parts and even harder being a ZJ. My only option is stuff from the US and most of the usual suspects dont ship to the UK

 

[Kram]

Without knowing the grade, any uncontrolled heating past 250c could make it brittle and best avoided on something like this. Most grades of steel have a temper range that should be avoided and so I suggest looking up common spring steel tech documents before you decide to do that.

I suggest you cut it at the left hand mark, B, and see how it goes. Looks like quater turn of the coil and likely wont make that much difference. However its easier to cut again, you cant sensibly weld it back on!

 

[Kram]

Jeep my only option is stuff from the US and most of the usual suspects dont ship to the UK

Tried amazon? I havent looked but theres plenty of US imports available, and generally stress free with easy returns if its a prime item.

 

[Smallfry]

What is the top mount like ? Irrespective of flattening the coils, the mount in the photo cannot be turned, so spring end needs to be in the same place, unless the top mount can compensate.

I can see the spring being spat out sideways

 

[tigdlo]

I've run cut springs in the past it works well for a road/track car as it increases the spring rate too, maybe not the best for offroad if it resists articulation.

The spring seat should match the spring ends, what is the OD and wire diameter? What is the top mount like? There may be another car with suitable spring seat like a 90s mercedes

 

[Screwdriver]

Can you literally pull the suspension system 55mm lower by shortening whatever system it tops out with (presumably a strut)?

That would increase the spring rate a bit but would save faffing about with cutting up springs.

 

[Nomad]

I got a set from Rally Design at a bargain price, plenty of various lengths and spring rates - has to be worth looking to see what they have..

Springs from Rally Design

Car Specific Coil Springs and Universal 2.25

www.rallydesign.co.uk

Mine were to fit a retro Hillman but I managed to match the spring diameter from something else in their catalog then took an educated guess with the spring rate and the free length.

 

[indy4x]

@Smallfry. @Screwdriver

Top mount is fixed



Top coils on the spring are wound tighter like so so no option to trim the top

 

[tom2207]

id just put the grinder through it where you fancy , warm all of the last half of a coil and tap it to shape ,,, leave it to cool and face the fact that the last wee bit wont be springy but it will sit happy . if it goes wrong or wont sit level buy a pair of oem springs then

 

[hotponyshoes]

Just chop it a bit shorter than required and 3d print a new seat that sits over the existing one?

 

[jmp49]

Why not cut it across the horizontal axis of the spring instead of across the wire cross parallel to whats already done lower down, then it will be the length & sit flat on the pocket. The end of it will taper off to a thin section but the stress will be before that thinnest part & I see oem springs finished like this from time to time.

 

[RWD3M]

I'm sure you've thought of it already, but remember that 55mm loaded is different to 55mm unloaded