Torsion Bar Question

[Starrman]

I'm getting new tires and an alignment later today and I was checking the front ride height. The passenger side was an inch higher than the drivers, so I got under to adjust the torsion bars. I was able to get the drivers side a half inch higher before the bolt bottomed out and the passenger side bolt was only halfway used. I loosened it a couple turns to get that side down a half inch so both sides are even now.

 

I also noticed the rubber bumpstop is just above, barely touching the pad on the lower control arms on each side. My Yukon just hit 100k and has never been in an accident or had any suspension components replaced except for shocks. Do the torsion bars wear out and loose their stiffness? Could my drivers side be wearing out?

[Matt_]

first answer... yes torsion bars do wear out, just like any other spring will.

 

is yours worn? probably not... an inch difference per side is normal. you can walk around a dealership all day with a tape measure and you'll be hardpressed to find a truck thats even side-to-side. was the ground perfectly level? how much gas was in the tank? stuff like that will throw it off too.

 

also, dont be concerned if one adjustment bolt is turned in further than the other.... this is also normal.

[nickvrebel]

as stated above, it's possible, but unlikely.

 

I know of one case where torsion bars were "wore out"... it was a 1500 Suburban that was converted to a stretch limo - the additional weight over time took it's toll.

[deerchooper]

had a gmc awd mini van. the wife drove it local on short trips. i walked out one morning and the passanger side was on the ground. t-bar broke, gm did a t-bar change and i had to buy both t bars and adjusters to the new gm change. 9 bills for that.

[Zembonez]

The truck will be worn out LONG before the bars. The torsion bars on my Explorer are adjusted quite a bit different from right to left but it sits level and has been fine right up to its current 184,000 miles.

[sc4808]

I would add that at normal ride height the bump stop should be either touching the control arm or no more that an 1/8" inch or so from it.

 

The bump stops on these trucks is actually designed to be part of the suspension and is calculated into the front spring (torsion bar) rates.

[Starrman]

Thanks for the info everyone. I had the new tires installed and an alignment done after adjusting the torsion bars. The ride height is just about even on both sides....passenger side is about 1/8-1/4" higher than drivers but that is a lot closer than the 1" it was.

 

The bump stop actually touches the control arm on the inner side and is slightly above (can't quite stick my fingertip under it) towards the outer side (control arm angles down). I just wasn't sure if this was normal.

 

I like the new tires. I went from a 265/70/16 Bridgestone Dueler AT to a 265/75/16 Firestone Destination AT (I have a Predator so I can adjust for different sizes). I've had the Duelers for about 4 years and 50k miles and they had hardly any tread left. The Destinations seem to ride quieter and smoother than the Duelers, but that could be due to the fact that the old tires were so worn. The truck does sit up a bit higher now though, both the wife and I can tell when getting in and out of it, especially getting out, it's a farther step down and we almost need to use the running boards...lol.

[05silvycrew]

here's a really really good article about GM's torsion bar setup. It explains everything you need to konw about keys, adjustments, and the torsion bars.

 

http://www.gmfullsize.com/tech/torsion401.html

[Matt_]

here's a really really good article about GM's torsion bar setup. It explains everything you need to konw about keys, adjustments, and the torsion bars.

 

http://www.gmfullsize.com/tech/torsion401.html

 

Be careful about some of the stuff you read here since it is not all completely accurate.

 

I'm not sure which sentence is worse... this one, "A linear spring requires the same amount of force all the way through its range of compression." or this one, "The twisting action does not change the pre-load on the bar directly, so cranking your bars is just like adding a block in the rear or a coil spacer."

 

Whoever wrote that article does not have a good understanding of how springs work. And not for nothing, understanding of "linear springs" is high school physics.... you don't need to be an engineer to realize that the first sentence I quoted above is false. Linear springs follow Hooke's law.. F=kx <--- this says the force is NOT constant, it changes linearly with deflection. Understanding how torsion bars work is a little less intuitive so I can see the confusion that some have. But torsion bars are indeed linear springs just like coil springs that follow Hooke's law... except instead of being compressed, they're twisted and therefore the "x" for displacement is replaced with "theta" for degrees (or radians) of rotation.

 

So i digress: be careful what you read on the internet.... (and that article needs to be re-written..)