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A different torsion bar question


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I have a 2000 Suburban 1500 4X4. There are sevral other Suburbans, Tahoes, Yukons of the same vintage in our parking lot at work. We've noticed that there is quite a lot of variation in ride height (an inch or two) in the front ends of our trucks.

 

I've read a lot of posts here about cranking up torsion bars and I hear these results:

1) Ride stayed about the same and I'm happy.

2) Ride got stiffer but I'm happy.

3) Rides too rough, went back to stock.

4) Rode ruff, wore out front end components.

 

I would say that an alignment is a must after any adjustment, but there must be a normal or "factory acceptable" range that a person can adjust the torsion bars through without moving the front end geometry out of it's design range.

 

I'm looking for some other peoples thoughts on this before I start cranking mine up.

My Suburban sits lower than theirs :) , and I just can't live like that for too long.

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Slight comment that isn't particularly popular here. The torsion bars are not for cosmetic adjustments, but for geometry. Age might have them sag the front end, though. Their purpose is to adjust the front end height due to the weight of added equipment on the nose, such as a snow plow.

 

The ride will roughen up. Some folks notice this, others do not. Much of it is determined by the kind of roads that are locally predominant. Crossing rough railroad track crossings can often tell the tale on this.

 

Anyway, that's my take on it...

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As far as ride quality is concerned, one important thing to remember on these trucks is that the rubber bump stops are part of the suspension. There are variences in the ride height of these vehicles even when new, but these differences should be slight. The majority of the vehicles that I have seen sit at about 1/4" to 1/2" between the bump stop and the A arm when on level ground. My truck has 90K on it now and I have had to adjust the ride height once. I drive on rough dirt roads fairly often so maybe that is why I have had to adjust. Back to the bump stop issue, if you raise the truck above the factory setting without lowering the bumpstop back to the proper location you will get a "spongy" ride, and of course when "crankin" the bars you get a higher spring rate (stiffer ride). Most of the time if you don't get carried away, there is not much of a difference. Now as to front end wear, always get a front end alignment after making any changes to ride height. Also, the CV axles and Unit bearings don't perform very well at a much higher that stock height. I have friends that crank the bars to maximum height and end up replacing bearings and axles every 30K or so.

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There is a factory spec for adjusting torsionbar height, it's called trim height. It's measured by the center of the a-arm pivot point (the bolt) to the ground and at the bottom of the knuckle at the ball joint. The difference between the 2 measurements is your trim height. GM has a minimum, a maximum, and a recomended.

 

Here's a very good post from lrymal on the actual procedure GM uses:

http://www.gm-trucks.com/forums/index.php?...&hl=trim+height'>http://www.gm-trucks.com/forums/index.php?...&hl=trim+height'>http://www.gm-trucks.com/forums/index.php?...&hl=trim+height'>http://www.gm-trucks.com/forums/index.php?...&hl=trim+height

 

Here's a post with the trim height numbers:

http://www.gm-trucks.com/forums/index.php?...&hl=trim+height

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I played with my adjuster bolts yesterday, I was curious. Before I touched anything, I measured my trim height and it was at 3.75" on the left side with the right side at 3.5". I put 4 full turns on the left side and 5 full on the right. That put me level at 5" of trim height. I took it for a ride and it rode like crap, IMO. A lot stiffer then what I'm used to or what I'd like. The truck sat almost level though and it looked good. The CV angles weren't bad and I was only .2" over maximum trim setting.

 

I ended up setting them back down to 4.5"(GM Spec) and I was amazed at the ride difference a 1/2" makes. I have an alignment scheduled for Friday.

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No, I was just using that as an example of what trim height was. The pivot point of the a-arm is the same as the s-10, but the outer measurement is the flat part at the bottom of the steering knuckle. GM recomended for a 1500 4x4 is 4.5" with 4.8" being their standard for maximum.

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I want to know how the ride is affected. The springs aren't getting any stiffer. your just changing the installed height. The same amount of weight is still on the spring. The key is "higher" so the truck sits higher. I can't see how your changing the damperning affect.......

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I want to know how the ride is affected.   The springs aren't getting any stiffer.  your just changing the installed height.   The same amount of weight is still on the spring.  The key is "higher" so the truck sits higher.   I can't see how your changing the damperning affect.......

 

 

 

 

Your right, the torsion bar doesn't have anymore tension on it. The two biggest factors attacking ride quality when you re-index the torsion bars are less downtravel on the front suspension and less leverage on the torsion bar. Less downtravel is pretty much self explainitory but the second is a little harder to explain.

 

With a stock trim height, your lower a-arm is just about parallel with the ground. So when you hit a bump, the tire is driven up and you have the whole length of the a-arm giving you leverage to overcome the resistance of the torsion bar. Now with the torsionbar "Cranked", your arm is no longer parallel to the ground and the tire is closer to it's pivot point. This reduces the leverage you have on the torsion bar.

 

I don't know if that's a good explanation or not. It would be much easier to explain if I could draw a picture.

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