Can someone explain to me.., what it means to index torsion bars? Options

[mike_the_man]

I've heard this mentioned when lowering the front end, but I'm not real sure what it means. Do the torsion bar adjusting end caps have to be in the same spot (same number of splines) on each torsion bar? If not, and you start cranking on the adjuster till the ride height is even, would one bar be more pretensioned than the other? Does any of this make sense???

What's happening is that I lowered the front of the car, not a whole lot, and added the bump steer kit, but when I go over a bump, the front end feels light. It feels like I'm still getting some bump steer, or something. I'm not quite sure how best to describe it. I haven't had it aligned yet, so that could be part of the problem, but I want to make sure I have everything else set up right first, then get it aligned.

Sorry for the long post, and thanks,

[Joe Bob]

Indexing torsion bars is where you get the splines on each end adjusted.....

The 914 front end is adjusted by the hex head bolts....some have interior allen adjusters. Once they are "indexed", the front end cranks up and down with the adjusters.

The rears on the 914 are adjusted via spring perch height.

Now on a 911...indexing the rears is REAL pain in the ass.....they don't have coil overs like the 914 does.

[mike_the_man]

So how do you index them? (IMG:style_emoticons/default/confused24.gif)

I'm not sure why this is so confusing for me, I'm usually quite smart. (IMG:style_emoticons/default/huh.gif)

[Joe Bob]

Trial and error mostly.....if you are talking about putting in new ones on the front of the 914.....you lift the front end....install and then put in the adjusters....hopefully they will be close. Then lower the car...run in back and forward and then use the adjusters.

You may need a front end alignment afterwards.

[mike_the_man]

So as long as I get them close, I can use the adjusters to even it out? If I have to adjust one a whole bunch, it doesn't pre-tension the bar, does it?

[Mueller]

rough description:

car up in air, looking at the drivers side from the front of the car, the a-arm should be pointing to the 4-5 o'clock position. Put the adjuster in the middle range...

when you put the car back down on the ground, see if you like the ride hieght, if not, you can turn the bolt. If you run out of adjustment before obtaining the perfect ride height, you'll have to raise the car back up, pop off the adjusment cap and move it clockwise or counter-clockwise a few splines......it's a trail and error thing, unless there is documention that I do not know about (highly likely, LOL)

[SLITS]

Indexing - interesting situation. Make a couple of assumptions here:

1.) The splined are broached parallel to each other

2.) The spring rate of each bar is exactly the same.

Indexing would be that both bars are installed the the housing in the exact same position.

1. If you place a reference mark on the adjuster end of the bar, say using the R & L stamps, you could install the bar in the front housing so that the R & L are vertical to the ground plane (assuming your car is exactly level).

2. Then place a reference mark on the adjuster.

3. Pull the suspension down on one side with a bar and install the adjuster and note the position of the reference mark on the end of the torsion bar in relation to the refererence mark on the adjuster.

4. Going to the other side and preforming the same operation, but making sure the distances between the reference marks is equal to the side you've already finished would be "indexing"

This is probably more trouble than it is worth, but it's your car.

We used this method on spark plugs where the high compression piston crown could feasibly hit the spark plug electrode at TDC - we "indexed" the plug so that we would know the position of the electrode in relation to the piston crown.

Twitchy Steering:

Bump steer is the result of angularity of the tie rods in realtion to the ground plane. The tie rod end moves in an arc. If the postion of the tie rod is at 90 degrees and is deflected upwards in a bump the degree of change effectively shortens the bar and pulls the front of the tire inward. The slowest rate of change would be, say 85 to 95 degrees in realtion to the ground plane.

If you have lowered the car and the tie rod is further up the arc, say at 75 degrees in realtion to the ground plane, the rate of "shortening" is increased for the same deflection of the suspension. Hence, the front of the tire is pulled inward at a greater rate resulting in "twitchy" steering on bumps.

If this doesn't make sense to you - draw it out on graph paper and swing the arc formed by the tie rod end when deflected by a bump.

Ok, that's my thesis for the day! <_<

[mike_the_man]

Bump steer is one thing that I more or less understand (probably about as well as I understand anything, anyway), but I installed spacers on the rack, and the steering rack arms are more or less parallel, so there shouldn't be much bump steer, correct? I'm thinking an alignment should clear up most of it.

[SLITS]

More or less doesnt' really work - it is or isn't does. I believe you had this thread going before about how low you can go and it was explained that the "avaiable" spacers were a compromise.

Also, when tracing the problem, what is the condition of the ball joints, tie rod ends, the rack and pinion, suspension bushings, wheel bearings, shock absorbers, torsion bars - these are all things that can lead to "twitchy" steering.

And alignment - toe out is twitchy, but fast toe in is stable but scrubs speed. If the car is out of alignment - you can't predict the consequences.

[mike_the_man]

Ya, lots of variables to look at. I'm going to check the ride height one more time, and make sure everything is ok, then get an alignment. I'll see where I sit after that. So, the next question is what specs should I use for an alignment? The car will be mostly street driven with the occasional autox.

[SLITS]

That would be a question for the "racers" in the crowd. I know it has been answered on the PP site, not sure about here - you might want to search.

Me - I would prolly go with 1/2 degree negative front with 1/16" toe-in and 3/4 to 1 degree in rear with a minimal toe in. Not a race setup, but...........,

[Eric_Shea]

Too much worry'n goin here. Perform the factory procedure (which is basically what Mike Mueller replied with).

Jack up the car.
Take the wheels off.
Take the adjustment caps off.
Use a pry bar or similar device to make certain the a-arm is down all the way.
Slide the adjusting cap on "leaving as little adjustment room as possible at the top."
Coat the threads of the adjusting screw with Moly-Lube and insert them tight into the adjusters.
Drop the car and see how you like it. Crank it up. Crank it down. Bounce the fender after each attempt and measure at the top of the fender lip.

Done.

Use factory alignment specs as well. You may want a tad more negative camber but tire wear will probably start to become an issue.

[Dave_Darling]

Back to the first part of the original question--

When we say "index the t-bars", what we usually mean is to take the adjuster off the aft end of the torsion bar, and put it on in a different orientation. Sometimes called "re-clocking". The idea is that if you run out of adjustment with the adjusting screw, you can move the whole part a fair amount by putting it back on the torsion bar's splines in a different orientation. That lets you start working the adjusting screws again.

The pre-load determines the ride height, so don't worry about it getting off without you knowing it--if you change the pre-load on the torsion bar, the ride height will change. That's what you're doing when you fiddle with the adjustment bolt, and also what you're doing when you "re-index" the torsion bar.

Not sure on your bump-steer-like issue. Could be something as simple as loose universal joints in the steering column...

--DD

[mike_the_man]

Hmmm, a loose U joint. You may be on to something there. With the front of the car up in the air, when I crank the steering wheel from lock to lock I hear a clunking sound, regularly, maybe every half turn or so. A loose U joint could be the cause. I'll investigate tonight.

[Eric_Shea]

Make sure your rack is bolted on tight as well. If anyone has been down there monkey'n around you might have issues with the two 17mm's holding the rack to the crossbar.

Could be the rack itself. I've got one if you need it. In the Classifieds

[jporsche914]

is it hard to lower the front end and put the rack spacer in??

[Jeffs9146]

is it hard to lower the front end and put the rack spacer in??

That depends on the weather! (IMG:style_emoticons/default/lol2.gif)

It is easy, but as stated earlier, you will need an alignment after you make the adjustments.

Jeff

[Eric_Shea]

is it hard to lower the front end and put the rack spacer in??

(2) 17mm and (2) 13mm bolts get the suspension pan off.

(2) 17mm bolt hold the rack to the crossbar.

You should also have a 13mm and a 14mm open end wrench to loosen the u-joints under the dash.

Loosen the u-joints.
Take the pan off.
Remove the 17mm bolts holding the steering rack.
Insert bump steer spacers.
Install new (supplied, longer) 17mm bolts holding the rack to the crossbar. Torque to spec.
Install the pan.
Torque the u-joints to spec.

Lowering the car requires an 11mm socket on a ratchet or an 11mm open end wrench. The socket is obviously faster. Loosen the adjustment screws on the end of your torsion bars as discussed here. Bounce the car and take measurements to the top of the wheel arch. There is a factory procedure for setting the ride heigth which basically requests that the tie-rods be parallel with the ground.

Get an alignment.

Hope that answers your question.