Lowering Bottom Spring Perch

[Captain Obvious]

I'm not a suspension guy, and I got a stupid question... What would happen if I were to remove the lower spring perches from the strut tubes and reattach them an inch lower than they were originally? Make that change and nothing else... Put it back together with everything else the same as when it came apart. No adjustable threaded collars. Stock springs with a lowered bottom perch.

The whole sprung weight of the car sits in equilibrium on the springs, so with a lower perch, the same weight should compress the same springs to the same length and that would lower the car by an inch, right?

And the only down side would be that I would be at greater risk of bottoming out the strut on compression, right?

[EuroDat]

Wow. I am considering doing the same thing since removing the bumpers.

My plan was to lower it 3/4" to get back to its original height with the bumpers. I don't think it will be a problem witn bottoming out because I will be going back to "normal height".

I don't like cutting the springs because that will make the ride hasher. Cutting springs reduces the spring length and its flexability.

Aftermarket springs wil lower it, but how much?

The procedure I wss thinking of using is this:

1. Make a jig. A ring that fits snug over the tube and three rods from the ring tack welded to the spring perch.

2. Measure ring distance from top of tower.

3. Carefully grind the spring perch weld away until perch is free.

4. Lower the perch X mm and check it doesn't retate on the tube.

5. Reweld perch.

6. Grind tack welds free from perch and remove jig.

7. Repeat.

 

[EuroDat]

I have done this on a Ford Escort mk1 years back and it worked well. Never had any problems with it and I drove it 85k km.

[cbuczesk]

Another option is to remove the strut tops, heat them to remove the rubber insert, cut 1" (or whatever) off the rubber, insert into the metal cup and then fold the metal sides over to hold it in place. You'll want to cut 4 slices in the metal side to fold it over in 4 sections. Does that make sense?

Chuck

 

[EuroDat]

If you want to lower the car 1". You don't need to do any mods to the rear strut perches. You can simply change the insulator to the 240Z type which is the same height as the front. That will lower it 25mm.

http://www.thezstore.com/page/TZS/PROD/classic20m01a/23-4370

The only real strut mod would be the front strut towers.

Edited June 8, 2018 by EuroDat

[LeonV]

Not recommended, your springs will need to be stiffer to make up for the lost travel and avoid harsh bottoming-out of the suspension. Sounds like a lot of work for little gain, just buy some lowering springs or shorter top mounts as mentioned.

[Captain Obvious]

Leon, Thanks for the input and I understand about the loss of travel and the increased risk of bottoming-out.

I'm running KYB inserts, with stock springs and rubber bushings. In other words, pretty much stock 280Z with KYB's.  I've been driving with this setup for a number of years now and I don't believe I have ever bottomed out the stock suspension. Ever.

So how close to the limit do you think I am now with the stock set-up? Any guesses? If it weren't for the rubber bellows being in the way, I could put a marker line on the strut shaft and go for a spirited drive and see how much of it was worn off.

And Chas, Yes, you're absolutely right. One inch drop on the rears is easy. The idea was just for the front.

[Zed Head]

Never mind.  Had a comment about preload but it was off.  Should work fine.

I've noticed that the travel of aftermarket shocks seems to vary.  So you might find that certain shocks bottom out sooner than others.  Seems like a good reason to go through all of the parts and see what's what.

Edited June 9, 2018 by Zed Head

[LeonV]

15 hours ago, Captain Obvious said:

Leon, Thanks for the input and I understand about the loss of travel and the increased risk of bottoming-out.

I'm running KYB inserts, with stock springs and rubber bushings. In other words, pretty much stock 280Z with KYB's.  I've been driving with this setup for a number of years now and I don't believe I have ever bottomed out the stock suspension. Ever.

So how close to the limit do you think I am now with the stock set-up? Any guesses? If it weren't for the rubber bellows being in the way, I could put a marker line on the strut shaft and go for a spirited drive and see how much of it was worn off.

And Chas, Yes, you're absolutely right. One inch drop on the rears is easy. The idea was just for the front.

That's a good question. If you can gain access to the damper shaft, put a zip tie on it and see how high it goes.

A spirited drive should definitely not bottom-out the suspension. that's not the design case for max suspension travel. Instead, find a road(s) in your area that has potholes, expansion joints, dips, etc. to test  travel on.

[Captain Obvious]

Thanks Leon. A plastic zip tie is a much better idea than using a marker.

I might even be able to get that around the shaft even with the bellows installed. Might be impossible to see it once it gets pushed up though. Maybe I'll give it a try and see what happens. Thanks for the great idea regardless.

[LeonV]

[Captain Obvious]

Leon,

Other recent suspension discussions reminded me of this thread and I wanted to circle back around a little.

First, I took a look at putting a zip tie on the strut shaft, and with the bellows in the way I don't think it's possible. Just not enough room in there to lift the bellows out of the way. You might be able to get in there and do that if the bellows were not installed, but with the bellows (stock style with the bottom retainer clip) installed, I don't think it's possible.

In another thread, there was discussion that they changed the spring perch location between the 240 and the 260. Lowered it about an inch for the 260:
https://www.classiczcars.com/forums/topic/38373-240z-eibach-springs-in-260z/

Have you ever seen a similar comparison between the 260 and the 280? In other words, do you (or anyone else) know if the front perch location is the same from that point on to the end of the 280 run, or did they move it around again for one of the years?