Sectioning struts for Koni 8610-1437race insert

[74_5.0L_Z]

johnc put together a great write-up about sectioning struts about three years ago in the following thread:

http://forums.hybridz.org/showthread.php?t=85960&highlight=section

 

I followed his directions to the letter for the front struts, and everything worked perfectly. I am in the process of sectioning my rear struts for Koni 8610-1437race inserts, and I have a question regarding his write-up concerning the rear struts. Here are the instructions for the rear from the original write-up:

 

For Koni 8610 Inserts, other inserts (Tokico, etc.) require different lengths.

 

REAR

 

From the dished bottom center of the strut to the top lip the overall length should be between 14.938†and 15â€. The perch height measured from the top of the hub casting (opposite hub) is 7.250†assuming a .250†thick spring perch. The strut tube is cut at 7†measured the same way as above. Approximately 2.250†is cut from the bottom of the top half of the strut tube but measure first to be sure of the exact length.

 

(content deleted for clarity)

 

When you can easily slide the insert into the strut all the way to the bottom, make two spacers for the rear struts that are 2.250" tall and 1.5" in diameter out of .125 wall steel or aluminum (6061 T6) tube. Drop in and center these in the bottom of the rear strut tubes and install the inserts. Measure to make sure the inserts site at the correct height. You'll probably have to shave a bit off the spacers. Once the spacers are correct, pour a little synthetic oil into the tube, install the spacers and the inserts, tighten the gland nut down, and torque to spec.

 

The problem that I am having is this:

The write-up suggests shortening the rear housing by 2.25" and then using a spacer below the insert of 2.25". The unmodified length of my housing is 16.75". If I remove 2.25", the inside length will be 14.5". From the Koni catalog the length of the 8610-1437race housing (Dimension A) is 13.07 inches. Also they suggest that the housing length is 0.04 to 0.16" shorter than Dimension A. Using 13" for the desired inside length (13.07 - 0.07). If I section my strut housing 2.25" and subtract 13", I get (14.5 - 13)= 1.5.

 

So, here are my choices.

 

1. I can section the rear housing by 2.25" and use a 1.5" spacer below the strut.

2. I can section the rear strut housing 1.5" and use a 2.25" spacer below the insert.

3. I can section the housing some dimension in the middle and make up the difference with an appropriate spacer.

 

johnc (and others), What is your suggestion? Have I made an error in my math?

[EMWHYR0HEN]

I would go with your first choice. If your sectioning the struts to re-gain some suspension travel your going to want to take off as much strut as you can.

[heavy85]

I personally would buy the struts first and measure before you weld them together. My '72 struts are SO tight that I had to grind the paint and the raised stamped part number off the strut and grind the inside of the strut housing. This was just to get them installed even before sectioning so my point is you have to be REAL straight when you weld them back together or you'll be fighting to get them in. I installed a strut to align the pieces then clamped two pieces of angle iron around the housing. Pulled the strut out, tacked, reinserted strut, make any adjustments. It's just such a tight fit you have to be real precise. I know the later struts are bigger but I dont know if the '74 (assuming from your screen name) uses the smaller or bigger tubes.

 

I ended up taking ~2" out of both the front and the rear. Then measured the length of the required spacer and cut to fit.

 

Cameron

[blueovalz]

I personally would buy the struts first and measure before you weld them together. My '72 struts are SO tight that I had to grind the paint and the raised stamped part number off the strut and grind the inside of the strut housing. This was just to get them installed even before sectioning so my point is you have to be REAL straight when you weld them back together or you'll be fighting to get them in. I installed a strut to align the pieces then clamped two pieces of angle iron around the housing. Pulled the strut out, tacked, reinserted strut, make any adjustments. It's just such a tight fit you have to be real precise. I know the later struts are bigger but I dont know if the '74 (assuming from your screen name) uses the smaller or bigger tubes.

 

I ended up taking ~2" out of both the front and the rear. Then measured the length of the required spacer and cut to fit.

 

Cameron

 

This is almost verbatim in what I had to do as well in order to get these "tight" inserts inserted. The only difference was that I tacked them without the angle. The higher up you cut, the easier it will be to avoid a misfit due to warping when welding.

[74_5.0L_Z]

Thanks for the replies.

 

I had to deal with the alignment issue when I did the front struts. For that I did as John suggested and made a mandrel to assure squareness and concentricity. I still have the mandrel and will use it for the rear.

 

I guess my real concern was with losing too much droop travel in the rear. I have read somewhere on here that insufficient rear droop travel can create a snap oversteer situation. I obviously want to avoid that.

 

Ideally what I'm hoping for is a very light preload of the spring at full droop. With my current set-up, The springs are unseated at full droop, and I have to guide them onto their upper perch when I lower the car off the stands.

 

If all else fails, I'll come up with some droop limiters that are set at the point where the spring uncouples.

[johnc]

The length of the strut is the important part (14.938 to 15"). How much is cut out of the strut tube and the length of the spacers below the shock are tailored to meet that measurement. I'm going to edit my strut sectioning instructions to remove any reference to how much to remove and how long to make the spacers. This has caused people trouble in the past.

[JMortensen]

I guess my real concern was with losing too much droop travel in the rear. I have read somewhere on here that insufficient rear droop travel can create a snap oversteer situation. I obviously want to avoid that.

I think the warning against snap oversteer is an old one and it comes from people sectioning the rear struts to fit the front insert. If you take out 3.5" out of the rear and don't have the car sufficiently low you may very well be riding at the top of the strut's travel. Couple that with a lightly sprung and damped car and you have a situation where you could really smack the top of the adjustment range in a bumpy turn and cause a problem. On a stiffer sprung car with more rebound damping that runs lower in the travel I just don't see this being an issue. Nowadays you also see guys like Cary running closer to zero droop, but they are running seriously stiff springs and the damping to match, and I think that is the difference between the days when that warning was more applicable and today.

 

That's my take anyway...

[74_5.0L_Z]

OK,

 

The new struts arrived today, and I have some more questions:

 

First, I think I need to acquire some gland nuts. The struts that I removed from the rear were the old Koni sports (8641-1032). The gland nuts from those sat around the top of the strut insert and acted to center the insert in the housing. I assumed that koni would use the same gland nut for the 8610-1437, but it appears that I am wrong.

 

Second, the box had a bag of parts. Some I recognize and some I do not. The ones that I recognize are the four nuts and rod end spacers. The ones that I do not recognize are two large OD steel rings, and two slotted plastic discs. The purpose of these last items is not immediately obvious. They were not included with my 8610-1149 struts that I put in the front a few years ago.

 

Any help will be appreciated.

[johnc]

The two large OD steel rings fit inside the Koni gland nut and you use them in case the strut is a bit low in the strut tube. The large plastic rings fit around the shaft and sit on top of the gland nut. The bumpstops bottom on them. All of these parts are optional.

 

The Koni 240Z gland nuts are part number: 73.25.01.003.1 and Koni is very proud of these little things.

[74_5.0L_Z]

Thanks John,

 

I ordered the gland nuts from Truechoice today ($19.95 each).

[speeder]

Dan, I need to come see you - I'm doing a set of struts shortened with the same Johnc's stuff on a 240Z.

[TONY C]

the 2 stotted plastic discs might be for turning the shaft to make adjustments to the shock.

[74_5.0L_Z]

I have completed sectioning my rear struts and installing the Koni 8610-1437race inserts. I ended up taking 2.25" out of the housing and installing a 1.5" spacer below the insert. At the same time, I got rid of the stock upper spring isolators and installed Ground Control camber plates.

 

I finished putting the car back together on Saturday and discovered that I had virtually no droop travel with the back of the car at 6.5" (measured at horizontal portion at the back of the rocker panel and a 245/45/16 tire). So, to gain some droop travel, I lowered the car so that the back of the rocker panel is at 5.625" an the front is at 5.25". I now have 1" of droop travel without me in the car. The control arms are almost level with the ground and the front angle upward to the wheel.

 

I was a little concerned that this would not be enough, but not so concerned that it prevented me from running in an autocross on Sunday;). I was a bit afraid that I might experience a snap oversteer situation, but much to my surprise that was far from the case. The car performed very well. In fact, it went pretty much anywhere that I pointed it.

 

While I am very happy with how the car performed in an autocross, I have lingering concerns that the limited droop travel might be insufficient for a track event.

 

How much droop travel are you track gurus running?

[johnc]

I've always run about 2 to 2.5" of droop travel from static ride height. A lot of this droop was done to work with the Quaife diff I had in back.

[tube80z]

How much droop travel are you track gurus running?

 

I'm not a track guru but at hillclimbs, which are higher speeds and rougher courses I haven't had a problem with one inch of droop in the 400 to 500 pound spring range. I run less than that in the front.

 

Cary

[74_5.0L_Z]

Thanks for the replies.

 

I think I am going to do two things:

 

First, I think I'll lower the car an additional 1/2" to gain some more rear droop travel.

 

Second, I'm going to install some stiffer springs. I've been wanting to do this for a while, but I needed to wait until I had some decent rear struts. Currently, I have 250 lb/in springs in the rear and 200 lb/in in the front with a 1" front sway bar and no rear sway bar. I now have 8610-1149 front struts and 8610-1437race rear struts.

 

I just need to decide which springs to get. I plan to go through all the math and pick the springs as suggested in chapter 16 of Milliken's RCVD.

[tube80z]

I just need to decide which springs to get. I plan to go through all the math and pick the springs as suggested in chapter 16 of Milliken's RCVD.

 

I have a simplified spreadsheet I use. You can pick a target frequency and if you know your weights, sprung, unsprung, and all the weight transfer parameters you can work this out. Measuring the car is usually the most time consuming piece. With slicks we're currently very close to 3 Hz.

 

With the radial atlantic tires we've found 550 springs work for a car in the 2200 pound range.

 

Cary

[74_5.0L_Z]

I worked through Cary's spreadsheet and also though all of the calculations in chapter 16 of RCVD and worked out my new spring rates to go with the new struts. I ordered my new springs yesterday.

 

In the rear, I plan to run 8" 450 lb/in springs and no sway bar. In the front, I plan to run 8" 425 lb/in springs and a 7/8" sway bar. This set-up combined with the weight distrubution, roll centers, unsprung weight, motion ratios, and such should result in a front load transfer that is about 5% higher than my front weight distribution.

 

My resulting undamped natural frequencies will be 2.39 Hz for the front suspension and 2.44 Hz for the rear. Looking at the koni 8610 graphs, the 8610-1149 shocks will work well with these spring rates in the mid range of their adjustment, and the 8610-1437race struts will work well with these spring rates on the low end of their range of adjustment. I am working on the assumption that a damping ratio of ~0.7 is desirable in the 0 to 4 in/sec range of damper shaft velocity.

 

In addition, I discovered an interesting thing while comparing the 8610-1437 to the 8610-1149: The 1437 has a longer stroke than the 1149, but the 1149 has a longer overall extended length. I discovered this because I was trying to regain some droop travel in the rear. By moving the 1437 from the rear to the front and the 1149 to the rear, I was able to regain 3/4" of droop travel in the rear.

 

Moral of the story: I would only section the rear struts by 1.5" if you are using the 8610-1437race strut. The strut housing can be sectioned more for the 1149 insert.