Lowering

Tiny
PEANUTG13
  • MEMBER
  • 2002 GMC SONOMA
  • 124,000 MILES
I just got a used truck which was lowered before I bought it. When I went to look at it, the dealer raised it to stock. I was okay with that since I thought I would be able to lower it myself. I don't see any springs under the truck but it does have shocks which I believe that makes it look high. It also has leaf springs. My question is, how will I be able to lower the truck? Can I make those shocks shorter? I would appreciate the help. Also does the truck need shocks without springs?
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Friday, April 26th, 2013 AT 10:08 PM

8 Replies

Tiny
CARADIODOC
  • EXPERT
Altering the ride height is a real bad idea. That's why the dealer's suspension and alignment specialist put it back to stock before they put it out for sale. Depending on how the truck was lowered previously it will usually cause greatly accelerated tire wear, and it will reduce your braking ability and handling. Lawyers and insurance investigators love to find modifications that change "scrub radius" and other parts of the suspension geometry. They will convince a jury that you were partly at fault for the crash when the other guy ran the red light because you were less able to avoid it, and they will be right.

Alignment specialists know how much incorrect ride height affects tire wear. Even when the numbers are perfect on the alignment computer, the geometry between the upper and lower control arms makes the wheels go through the wrong motions. The only system that will not be affected as far as tire wear is the solid front axle. That was only used years ago on some full-size trucks.

No mechanic will lower your truck. They know they can end up sitting in a courtroom explaining their actions. If you still want to pursue this there's two ways to change the height. Shorter coil springs, or in your case adjusting the torsion bars is the wrong way to do it. That is what changes the suspension geometry. "Drop spindles" raise the wheels on the spindles without affecting the upper and lower control arms but it still changes scrub radius. There will still be accelerated tire wear but it won't be as bad because while the truck body is lower to the ground, the ride height of the suspension system will not be changed.
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Friday, April 26th, 2013 AT 11:11 PM
Tiny
PEANUTG13
  • MEMBER
Okay. So are you saying that the truck shouldn't or not safe to be lowered? Is it because it was lowered before? I don't understand how my truck can't be lowered. Thanks for your time. Please help me understand
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Friday, April 26th, 2013 AT 11:22 PM
Tiny
CARADIODOC
  • EXPERT
It's not that it can't be done. The problem is most owners do not understand the ramifications of making modifications to what the engineers designed in. If a vehicle could be raised or lowered without compromising safety, the manufacturer would offer that as an option. In fact, you will find some trucks sit quite a bit higher than similar versions based on optional equipment but that is an entire package that was developed by the experts to work properly as part of a system.

You can also find trucks that appear to be lowered but that is an illusion created by adding moldings along the bottom of the body.

All cars and trucks have height specs that are published. Alignment specialists have small books that show each model, where to take those measurements, and what they should be. As an alignment mechanic there were three parts to my job. The first was to inspect the steering and suspension systems to identify and replace loose or worn parts. That included "reading" the tire wear patterns and determining what was needed to improve that wear. Next was measuring and correcting ride height. When I worked for a mass merchandiser that commonly meant installing new coil springs on the rear of GM cars, (which was real easy and inexpensive), and on Chryslers it involved adding helper springs around the rear shock absorbers and simply adjusting the front torsion bars. The final step was to perform the alignment. Years later when I worked for a very nice Chrysler dealership I saw mostly newer vehicles and very few with sagged springs. The exception was the Dakotas that still were using torsion bars. In almost every case of tire wear complaints, the "before" readings on the alignment computer could easily be shown to be the cause of the tire wear, and the "after" readings, which were after I made the adjustments, were right at factory specs. The funny thing is though I rarely had to adjust the "camber", "caster", or "toe" with the factory-provided adjustments. All I did was raise the front end by adjusting the torsion bars. As the suspension approached the proper ride height the alignment numbers and suspension geometry fell right into place. We often ended up charging the customers for an "alignment check" instead of the full alignment.

To add a few tidbits of information, your truck has what is referred to as the "short arm / long arm (SLA) front suspension. The lower control arm is the long one and from the frame it goes straight out to the lower ball joint. That arm should be nearly parallel to the ground. The upper control arm is considerably shorter and it usually angles down from the bushings to the upper ball joint. The different lengths makes them go through different arcs as they travel up and down. That causes the wheel to tip in and out on top as the truck goes up and down over bumps in the road. A long time ago a few vehicles had equal length upper and lower control arms. They found that design made the tires slide left and right across the road as the vehicle went up and down, and tires would scrub off in about 10,000 miles. With your SLA suspension the tires don't slide sideways as much, and they tip in and out on top to reduce the effect of that sliding. The system is strong and one of the best for tire wear and comfort as long as the geometry is correct, meaning ride height. The only disadvantages are it's a heavy system and it takes up room needed for the drive train on lightweight front-wheel-drive cars. That's why those use a strut suspension system.

The "scrub radius" I mentioned earlier is a designed-in angle that can not be adjusted, but it can be wrong if ride height is wrong. Imagine standing in front of the truck and looking back at the upper and lower ball joint. Draw an imaginary line through them. That line should intersect the road surface exactly in the middle of the tire tread. That will not be the case if tires with a larger circumference or wheels with a deeper offset are installed. Due to friction and rolling resistance the left half of the tire tread wants to pull to the left, and the right half of the tread wants to pull to the right. Lowering the ride height by replacing or adjusting the springs will not change that relationship but it does seriously affect the other geometry as I mentioned. Using drop spindles raises the wheel and tire so in effect it lowers the two ball joints along with the rest of the truck. Now that imaginary line intersects the road surface closer to the inside of the tire. A lot more of the tread wants to pull toward the outside and little of it wants to pull toward the center of the truck. When the left tire strikes a bump it will want to pull that way instead of staying straight. That can be very tiring to maintain directional stability on longer drives.

Where braking comes into play is when one tire momentarily loses traction from going over bumps, potholes, and even sand on the road. The two halves of each tire tread balance each other to maintain straight braking. With altered scrub radius, in the case of a lowered vehicle, if the right tire slides over some sand while braking, the left tire will pull the steering linkages to the left and you will have to counter-steer to the right. THAT is what a good lawyer will explain to a jury when he is trying to shift the blame from the guy who caused a crash. You don't want to give him that option, and no mechanic wants to get you involved in that possibility.

You also have to consider drive line angles. If your truck is a four-wheel-drive it will have cv joints on the two front half shafts. Those are designed to go through specific angles as they rotate. The inner joints have three large rollers that move back and forth about a half inch each revolution. Rear universal joints go through the same angle changes on purpose. Their needle bearings in the cups can't be allowed to stay in one location because they will wear indentations into the cross and cups, then when you bounce up and down on bumpy roads or load the truck, that angle will change and cause the needle bearing to roll across those indentations. That will set up a howl and vibration. Similar wear takes place in the front inner cv joint housing but it is minimized by those rollers moving back and forth a lot. When the angle between the shaft and joint is reduced those rollers go through a smaller change so all the wear is concentrated in a smaller area. You will likely never notice that on your truck since you don't drive in four-wheel-drive often, but when that occurs on front-wheel-drive cars it sets up a horrendous steering wheel shimmy during acceleration. Due to the engine torque the rollers bind when trying to run over the raised parts of the worn spots. That prevents the shaft from smoothly changing length as it rotates. Instead, it pushes and pulls on the spindle. Those are attached by the ball joints to the control arms which are mounted on rubber bushings that can easily flex so the moving spindle tugs on the steering linkage.

That wear can set up a severe steering wheel shimmy but it can be way too small to feel, (the wear, not the shimmy). Those rolling surfaces are polished, and the only way to identify that wear is to clean the housing, then shine a light in it and look for the slightest irregularity in the reflection. People have also run into that shimmy on front-wheel-drive cars when putting the ride height back to where it should be. Since the wear was concentrated on a smaller-than-normal area, once raised back up the rollers go through their normal range of travel and they run over those raised spots.

One last comment that most do-it-yourselfers aren't aware of is when any suspension parts are replaced that are mounted with rubber bushings, mainly the upper and lower control arms, the pivot bolts must not be tightened while the vehicle is jacked up. Those parts will be hanging down and if the bolts are tightened that way the bushings will be clamped in that position. When the vehicle is set on the ground the control arms will pivot up and those bushings will be in a permanent twist. That will greatly reduce their life. The vehicle must be lowered from the jacks so it's sitting at normal height, then the bolts can be tightened.

The smaller GM trucks eat upper ball joints like crazy. At the correct ride height there will be reduced movement through the pivoting of the ball in the socket, and reduced wear. Also, If you watch the visual "camber" graph on the alignment computer, you will see very little change as the truck is bounced up and down when it starts out at the correct height. When the height is not correct the camber will change a lot as the truck is bounced. Camber is the inward or outward tilt of the wheel as viewed from in front and has the biggest affect on tire wear. Camber can be corrected on most vehicles except many Fords, so it will look good and "in specs." On the alignment printout, but it's that exaggerated tilting while driving that causes accelerated wear to both edges of the tire tread. It will look the same as under-inflation wear and is often mistaken for that. That's why if ride height is not correct you will still have poor tire wear even though the alignment computer says the adjustments are perfect. Some of the newer computers now even make the mechanic use a special gauge to check ride height before allowing him to make any adjustments.

This whole ride height story took up about ten hours in my 180-hour-long Suspension and Alignment class. Some of my kids wanted to alter the ride height on their cars and trucks but once they learned what would be affected no one wanted to pursue the project. We wouldn't have let them do it anyway because of liability reasons, and that is not something legitimate to be teaching.
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Saturday, April 27th, 2013 AT 1:11 AM
Tiny
PEANUTG13
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Thank you for all that but there were many words I didn't understand. All I want to know is, if my truck needs springs because I only have shocks that I know of. And how I can lower the truck, the simplest and easiest way. Do I need to change to shorter shock? Do I replace shocks with springs? Do I change leaf springs? Thank you for your time
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Saturday, April 27th, 2013 AT 11:33 AM
Tiny
CARADIODOC
  • EXPERT
I was an suspension and alignment specialist for over 25 years but I never altered ride height, even on my own muscle cars.

You're confusing shock absorbers and springs. All vehicles have both. Shock absorbers stop the truck from bouncing. Springs support the weight of the truck and set the ride height. If you don't see a coil spring just inside each front wheel, then you have torsion bars. Those attach to the lower control arm near its pivot point, and the frame under the seats. The shock absorbers can become short enough to handle whatever the suspension does so if the truck is lowered, the shocks should still work. You can verify that by looking at them to see if the dealer had to install new ones. If they are shiny and clean, they are likely new. If the paint is flaked off or they're dirty, they are not new and were working okay when the truck was lowered.

Torsion bars are always adjustable. You would have to find the adjusting bolts and turn them counter-clockwise to lower the front end. That is going to mess up the alignment but no conscientious mechanic will realign it at the wrong ride height.

There is usually some type of spacer block between the rear axle housing and leaf spring. You install different size spacers and u-bolts to change where the axle sits.
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Saturday, April 27th, 2013 AT 4:09 PM
Tiny
PEANUTG13
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Yes. The shock are new and shiny. So in order to lower it there are torsion bars to adjust. So the shocks do not have any " say " on the height of the truck. I will try to get good pictures to help with my problem. I did see the springs in the front but the back is higher
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Saturday, April 27th, 2013 AT 6:13 PM
Tiny
CARADIODOC
  • EXPERT
Yup. You have coil springs in front, not adjustable torsion bars. It looks like the dealer did a good job of correcting the ride height.

Shock absorbers have nothing at all to do with ride height. You can stretch them out and shrink them by hand and they will stay at whatever length you put them. It takes a lot of effort to do that though. That's what stops the truck from continuing to bounce up and down as you go down the road. Oil inside the unit has to pass back and forth through a tiny restriction. That's what provides the resistance to changing length.

There are two things that can confuse this issue. Most replacement shock absorbers are much higher quality than what came on the truck when it was new. The lowest grade of replacement shock absorbers is equal to the originals. Almost all better shock absorbers since the mid 1980s are "gas charged". That gas is under a slight pressure and its purpose is to prevent the hydraulic oil from foaming or becoming aerated on long trips. The confusing part is that gas charge causes them to expand fully on their own and that's why people think they hold the vehicle up. In reality you can collapse them back down by hand very easily. It takes perhaps ten pounds of hand pressure to collapse them. That is hardly enough gas pressure to hold up a 4000 pound truck.

Another point of confusion is that you can buy rear shock absorbers with helper coil springs around them. Those are meant for vehicles that have sagged springs but that aren't bad enough yet to warrant replacement. They will raise the back end about 1/2" to get the ride height back into specs. The important thing is the shock absorber still does the same job of reducing the bouncing and that's all. The spring just happens to have a convenient spot to mount around the shock absorber. It's still the helper spring and the main spring together that keep the vehicle at the correct height.
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Saturday, April 27th, 2013 AT 7:40 PM
Tiny
PEANUTG13
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So with those pics I showed you, how would I lower my truck?
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Sunday, April 28th, 2013 AT 9:52 PM

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