The mighty Silverado is a fantastic workhorse; for many, it’s their ride for sure but also their livelihood. No truck means no work. So paying attention to little telltale signs of trouble is smart; solving truck problems early is always cheaper. I’m a GM mechanic, and very shortly, we’ll get this figured out.
A Silverado commonly shakes at 45 mph because a road wheel is out of balance. However, there are several other possibilities; they include:
- Tire issue
- Incorrectly torqued wheel
- Damaged wheel rim
- Drive shaft issue
- Brake rotor issue
- Transmission issue
- Engine issue
In this post, you’ll learn why your Silverado shakes at 45 mph, and you’ll learn what you can do to fix it.
Wheel Out Of Balance
As you know, vehicle wheels must be balanced; even new wheel rims and tires aren’t perfect. Any excess material causes an unbalanced weight on one side of the wheel and will feel horrible on the road. And so, all wheels must be checked and balanced by adding a small amount of weight on the opposing side of the wheel.
Typically lead is used to balance the two halves of the wheel. If the wheel rim is steel, the lead weight is fixed to the outer rim with a clamp, and if the rim is alloy, the weights are stuck on using double-sided sticky tape.
Problem is, especially in off-road vehicles, the weights come loose and fall off.
How to diagnose – Visually check the rim for missing weights. A steel rim that’s missing a weight will offer a witness mark around the rim’s edge. Note wheels may have more than one weight, so seeing a weight in place doesn’t mean there isn’t one missing. Note also, weights are placed on the inside and outside as needed.
How to fix – Take your Silverado to a tire shop and have them balance the wheel, or better, have all the wheels rebalanced but insist they remove all the old weights first.
Missing wheel weights is by far the most common cause of a wheel imbalance. But not the only reason a wheel may be imbalanced
Here are a couple of other possibilities:
- Mud inside the wheel rim
- Damaged wheel rim
Mud inside wheel rim – Mud on the inner wheel is a common cause of an unexplained sudden vibration. It may coincide with a recent off-road excursion in wet, muddy conditions.
Mud simply sticks to the inner side of the wheel and causes an imbalance.
How to diagnose – Go ahead and run a visual inspection of the wheel on both sides.
How to fix – Scrape the mud off with a plastic or wooden scraper or power wash both sides of the wheel rim.
Damaged wheel rim – We’ll cover a damaged wheel rim a little later.
Improper Wheel Torque Spec or Tightening Sequence
All manufacturers offer a spec their wheel fasteners must be set to. Overtightening risks deforming the wheel rim to the hub interface resulting in improper mating of the surfaces.
How to diagnose – If the imbalance is a recent development after, say, a wheel replacement or tire fitting. And if a torque wrench wasn’t used to tighten the wheels, then this increasingly points to incorrect torque spec.
How to fix – Loosen all wheel fasteners and torque to specification.
Incorrect tightening sequence – Incorrect tightening sequence can cause an imbalance also. Wheel fasteners must be tightened in a start sequence, i.e.
A tire issue is always high on the list of possibilities. Tires are, after all, the component most likely to be damaged since they are in constant contact with the road surface.
Tires require special care when examined. First off, best to check some basics, and the basics are:
- Is tire pressure set correctly?
- Are the tires directional, and are they fitted to the correct side of the vehicle?
- Are the tires free from damage? – Bulges, cuts or flat spots, cupping, etc. will all create a horrible on-road experience, both feel and noise.
If the tires look okay, then we’ll need to run a complete wheel swap test.
Before assuming you have a more serious problem, it is important to eliminate the tires as a possible vibration source.
In the GM garage, we had a new known good set of wheels (rims & tires), especially for eliminating driveline issues.
How to diagnose – Borrow a set of known good wheels from another Silverado and test drive the vehicle. Narrow down your search for a possible bad tire by adding two of your own wheels to either the front or rear axle and test driving again.
This is the fastest way to eliminate faulty tires as the root cause of your vibration.
How to fix – Fix is obvious, too; replace the offending tires. I say tires because it’s best to replace tires in pairs on the same axle, i.e., replace both rear or front tires together.
Damaged Wheel Rim
A damaged rim is, you guessed it, very common. A gouge, flat spot, or buckle will feel horrible on the road. It’s easy to damage a rim, especially after-market wheels. Only top-end aftermarket wheels and OEM wheels are strong enough to withstand potholes.
How to diagnose – A visual of the wheel rim will usually give you the heads-up. A gouge or recent impact will be obvious. A buckle, however, may require the assistance of a tire shop.
If you suspect wheel damage, have a tire shop take a look at the wheel and have them attempt to balance the rim; that will quickly reveal a buckle.
How to fix – A buckled wheel can’t be fixed; it must be replaced. A gouge may be repaired, but it will depend on how bad it is and where it’s damaged. Your local tire shop has a ton of experience in this area.
Drive Shaft Issue
A damaged driveshaft isn’t a common issue, but it is still possible. A dry or worn U joint on the prop shaft is common and worth checking to eliminate as a possible root cause.
How to diagnose – Climb under the truck and check the rear U joint is OK. A heavily rusted U joint is a sign we could have found the root cause. Prop shafts are balanced, so while you are down there, check for missing weights or recent impact witness marks.
If the U joint looks crusty, go ahead and remove the Prop to Diff bolts to release the prop shaft. Now rotate both sides of the prop shaft with your hand; it should be silky smooth; if not, go ahead and replace the U joint.
How to fix – Remove the prop shaft and bring it to a vice.
The U joint removal process is as follows:
- Mark the Prop shaft to Diff with paint so we can pair them later
- Using a suitable socket, hammer the caps to release pressure on C clips
- Using a suitable set of internal circlip pliers, remove the C clips. If they break, no problem, you’ll get replacements with the new U joint. A very crusty U joint may require heat to shift the clips and the caps.
- Remove the caps from the old U joint (diff side)
- Place the shoulders of the U joint on an open vice and, using a suitable soft hammer, strike the Yoke sharply to push one of the caps out (either side, you pick)
- Now spin the shaft over 180° and repeat the process to remove the opposite cap.
- Remove the old U joint
The U joint fitting process is as follows:
- Using grit paper and a file, remove any burrs and clean the Yoke to cap surfaces. The file may be required to repair damage to the C clip walls also.
- Lube the cap mating surfaces with oil
- Remove the new U joint caps and grease fitting and set aside carefully
- Fit one new cap to the Yoke and squeeze in a vice so the cap is flush
- Position the new U joint in the Yoke with the grease point facing the Diff (not prop shaft)
- Use a socket and vice to push the cap below the C clip groove
- Now fit the new C clip (machined (square edge) side facing out)
- Position the opposite cap on the Yoke and squeeze the assembly in the vice, be careful it doesn’t bind. Close the vice gently, making sure the needle bearings stay in place
- Use a suitable socket to push the caps home below the C clip groove
- Fit the new C clips
- Rotate the U joint by hand (if stiff, strike the U joint with a hammer gently to seat the needle bearings)
- Fit the two remaining caps and the grease nipple
- Refit the prop shaft careful to align the paint marks, and remember to grease the new U joint
Brake Rotor Issue
A warped brake rotor can cause a vibration; that said, this is usually accompanied by a pulsing brake pedal sensation under braking. Damage should be eliminated as a root cause of the vibration.
How to diagnose – Remove the wheel and check for signs of damage. Turn the wheel and check runout using a dial gauge.
How to fix – Replace the rotors or have them turned.
A transmission issue is notoriously difficult to diagnose and less likely to be the root cause of the vibration; that’s why it’s towards the bottom of our list. That said, it is possible.
How to diagnose – When attempting to diagnose tranny issues begin by checking the basics first to eliminate the basics is the usual starting place.
The basics include:
- Check transmission oil level
- Check for transmission leaks
- Check for tranny fault codes
- Check tranny oil maintenance record and oil condition
- Check for rear tranny mount fault
A faulty torque converter could cause vibration, as could the torque converter lock-up clutch.
Your GM dealer is worth a visit if you suspect it’s a tranny issue. In many cases, a TCM software update will fix irritating tranny issues.
While an engine issue is a possible source of the vibration, it would likely be accompanied by a check engine light which is pretty difficult to ignore.
What is more likely is a loose or faulty motor mount. The motor mount, as you know, is a block of rubber that supports and fixes your engine in the engine bay. There’s one on either side of your engine, and on some models, they are what’s known as active.
Active means the ECU controls the mount stiffness.
How to diagnose – Pry on the mount to assess how loose it is when compared to the opposite side mount. The mounts should roughly offer a similar amount of movement.
How to fix – Replace the mount.