Kool

I can't wait.

My 30mm hollow torsion bars are on their way here.

As soon as I install my headlight kit I will move on to them.

I plan on using this procedure.

Has anyone used this procedure?

Any pointers?

M758

I have

Take carefull measurements and MAKE SURE you pull the sway bar's off first. Not doing so will cause an error. Also it is nice to have you tires at typical pressure so the amount they compress is normaized.

Make sure you install the spring plates in the center of their travel range. The reason is that this allows you some fine tuning if you did not get splines on the t-bar just perfect. For example you complete it and the car sites 1/4" off on one side. Perfect time to do that 1/4" by using the spring plate rather than doing t-bars again. However if the spring plate is already at it travel limit you are hosed.

Paragon products has write up on the proper use of the splines. The neat thing Porsche did was to have different spline counts outside vs inside. This mean if you are inbetween one set of splines then you can do a 1/2 adjustment by moving the other spline. Ie you are keeping the bar fixed in the housing and moving the end cap to get the position. If you can't get it fine enough move the bar in the housing one spline over and then you can probably get it right on.

Good Luck.

joseph mitro

any tips on reindexing WITH coilover springs. ie, how to set preload equally between torsion bars and springs. i am planning on just readjusting about 1 1/2" of lowering (i want the car lowered anyway). does this sound about right?

none of my searches has turned up any method of calculating how to set preload in both of them equally. all the calculations assume torsion bars only

Kool

Good info thanks Joe.

What size bars did you put on?

If you are careful with the measurements with the torque tube out does it translate good once you put it in the car?

Or will I be tinkering further once everything is back in the car?

M758

Mark,
I went from 23.5 mm to 28 mm and then later to 30 mm.

The poorer your measumement the poorer you result. The system is based on taking measurement of your current spring rate and then mathamaticlly comparing it to the new spring rate. The rate of increase is easy to figure if you know the actually lbs/in rate at the wheel.

For example if your suspension compresses 3" when you have the car sitting on ground and you have 800 lbs of weight on that corner. 800/3 = 266 lbs/in is your rate now goining from 24.5 mm (stock turbo) to 30 mm effecive diameter increased the spring rate greatly (lets say to 400 lbs/in just a guess since I am to lazy to calcualte now, but stiff increases by 4th power of diameter) So if the spring rate does incrase to 400 lbs/in then you need to adjust suspension by 1" since the same 800 lbs at the wheel with cause the suspension to compress only 2" rather than the 3" you had before.

So bottomline is the more accurate you measure the more accurate you final ride height will be. The nice thing about the spring plates is that you do have some fine tuning adjustments you can make without needing to pull the t-bar carrier out again. I know of one guy that used this proceddure and got it wrong because he was not careful with the measurments.

joseph mitro

hey joe - can that spreadsheet be used to calculate the appropriate reindexing amount when using torsion bars AND coilover rear shocks?

jc22

I just completed this project. Halleluja!!! Thank God. Done. Over. Never Again. Three months it took me!!

I used Joe's spreadsheet and it worked well. Thanks again Joe. I ended up a little lower than I wanted but I still have the spring plate adjustments to do. The only problem I had with the calculations was that it was hard to accurately measure the bananna arm-to- hub center because they aren't in line with one another. I really had to estimate. When I put the new tbars in, I just got it close and made sure the two sides had equal measurements which was quite easy.

I shot for 1.5" lower. I ended up getting about 1.125" and 1.375 drop measuring at the tbar end caps and 1.875"-1.25" drop measuring at the wheel well. These numbers are different side to side because the original measurements were not equal side to side. Now they are. Note: on my car this drop stuck my stock wheels and tires about .5"-.75" INTO the wheel well. 12.5" from center of wheel to the fender. Hopefully I can raise it enough using the spring plates which I set in the middle. I don't really care that it's this low except dropping the front down to match would put me well into the "danger zone." If you want to look at all my numbers start-to-finish and compare your own to see what you'll be in for, just let me know.

I used a number of different writups on actually removing everything and they helped but it's all pretty straightforward. The only mistake I made was not taking out the lower shock mount bolts first and ended up stripping them because the weight of the entire rear end was on those bolts when I removed them.

Good luck.

M758

Well... I have never tired to figure them in. It would requre some reworking in the back ground and may not be as clean to produce good results. Honeslty I am not even sure they best way to preload coil-overs. I would assume that you want them set such that for maximum drop the rear coil is still under minor compression. Too much preload will tend to reverse drive the t-bars.

As I think about I bet it could be done, but since I don't run coilovers I could never test it.


I guess the best way to think about coilover is that they add to spring rate.

So I believe most 30 mm t-bar have an effecive wheel rate of 330 lbs/in If you add a 100 lbs coil over assuming 50% effective ness (realy thing is 56% I think) then with the 30 mm t-bar you have 380 lbs in in the rear minus 5-10lbs for preload. Rememeber the preload will tend to unload the t-bar.

So you would need to lower the initial setting of the t-bar be the equvalent of 50lbs/in given the weight of the car. So I I guess I could work it in.

However I don't use the 330 lbs/in estimate of spring rate for the a 30 mm t-bar. If I did then I would need to know the corner weights of the car.

Instead I have the use measure spring compression given what ever the real weight is. Then since I can figure how much stiffer the new bar is simply from it's diameter change I then know as percentage how much stiffer the suspension will be then figure as percent how much different the travel will be. Ie it move 3" now, and new springs are 50% stiffer so it should be set 1.5" different. Thus I never need to know the actuall spring rate or weight of the car.

Adding the coil over given lbs/in rate may require me to calcuate a lbs/in rate for the t-bar which gets messy unless I use the a chart. I have tried to calcuate it properly from geometry of the trailing arms, but it fails to come out cleanly. I think it may be due to not knowing some measurments well or bushing/arm flex that my calcuations do not account for.

The comparitive method I developed assumes all of these are the same (or close it) so then I never need to know what really are.

I hope this post makes sense.

joseph mitro

jc22 - how did you loosen the large bolts? some of these are 22 or 23mm bolts. did you have an impact wrench? i have an impact wrench but i'm afraid it may not have enough torque (260 max) to remove those bolts.

M758

JC22's issue is show in this picture.



Notice the tapmeasure is some distance from the hub.

My solution is to use a square like carpenters square to close the distance.

Imagine and Perfectly square "L"bracket. The bottom part ot the L goes on the hub and closes the gap to the tape measure. Just line it up to the top of hub area.

I piece of card board with two square edges also works.

Kool

Ok so my car has been lowered using the spring plates. They are pretty much all the way down from stock.

I would like to raise the car up .5". Should I center the spring plate and take my measurements from there? Or take it all apart and then center the spring plate? Using the spreadsheet calculation to lower the car to the final height that I want?

Kool

When you disconnect the sway bar. you mean from the trailing arms not from the torsion bar tube completely. I noticed that it is still connected in the picture above.

M758

Center the spring plate when you have everythign all apart.

The initial ride height is un important as all the program cares about is the difference between intial ride height and when the tire's weight is off the ground.

When it comes to the spring plate.. In order to get to the t-bars the spring plate will need to come out of the car. When you are resetting everything (steps 13, 14, 15 on the sheet) that is where you move the spring plate to the center. Remember that moving the spring plate has the same impact as indexing the t-bars. The difference is that the t-bars have much wider adjustment range, but are also much harder to adjust. When they are out of the car it is best to move the spring plate back to the center and effectivly shift that adjusment in to the t-bar setting since you are doing it anyway.

Once you get the "H" measure where it should be with spring plate in the center you will have right ride height. If you like current ride height and enter "0" for the ride height change then getting the H value correct will ensure that the car is exactly at the same ride height you started with irrespetive of where the spring plate is.

M758

Yep.
I the reason is that the sway bar acts as a spring and can throw off the true spring compression measurements. You can leave it attached to the. Just pull the drop links.

jc22

I used an electric impact gun rated at 250 ft./lbs. and didn't have any problems. I'm waiting on a couple of wrenches for the spring plate eccentrics because I don't have anything that will fit up there when installed.