When your semi truck bounces more than it usually does, you obviously are a little concerned and want to know why.
We will give you all the answers you are looking for.
We cover what makes the bounce occur, how to fix it and if it is bad for the truck.
Here’s a quick answer to Why you will Find a Semi Truck Bouncing:
A semi truck will bounce excessively when the dampening of the shock absorber is not effective anymore. Another common cause for the bouncing would be due to a worn-out leaf spring or airbag suspension. The bouncing may occur while the semi truck is breaking or traveling on the road.
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What does it mean when your Semi Truck Bounces?
When a semi truck bounces, the cab or the trailer feels like a ride at an amusement park.
More rocking back and forth in the cab, you will notice the truck moving up and down more freely.
If this happens, take the truck to a workshop and have them check it out at your earliest convenience.
Is it Normal for your Semi Truck to Bounce?
There will be a slight bounce in your truck when on a rough surface or going over a hump in the road and even when breaking. But it shouldn’t be too bouncy.
You will get to know your truck very well. You will more than likely spend more time in it than at home. You will know when the bounce doesn’t feel right, along with anything else in the truck.
Is it Bad if your Semi Truck Bounces?
It depends on how bad the truck is bouncing. If it is bouncing a little more than it did yesterday, then it isn’t going to be too bad. It could get worse, so have it checked as soon as possible.
If the truck is bouncing a lot worse than it usually does, then this could be pretty bad and lead to you losing out on earnings. Excessive bouncing could lead to more damage.
Our advice is to have the truck checked straight away.
Why is my Semi Truck Bouncing?
The most common reason for a semi truck to bounce more than usual is the shock absorbers’ insufficient dampening of the truck’s springs, causing the truck to feel a little lighter.
The airbag suspension could also be a culprit and should not be overlooked when diagnosing the problem.
Semi Truck Front End Bounce
When the front end of your semi truck bounces way more than usual, you naturally want to know why.
It isn’t uncommon for this to happen, and could be many things that cause it.
It is a good idea to take your truck to a mechanic and have them test drive it with you. The bouncing can occur when at high speeds or braking.
Keeping note of when it happens will help to pinpoint the cause.
What could Cause the Front End to Bounce?
The front end of your truck takes as much abuse as the back. It has to deal with pulling a heavy load and then stop that heavy load from rolling down the road.
The cause of the front end bouncing could be the front suspension system. It may need a simple fix or a complete replacement. It could also be the cab’s airbag suspension.
The leaf springs on the front suspension could be out of shape.
How to Diagnose the Cause of Front End Bounce?
Uneven tire wear could mean uneven shocks.
Measure the height from the ground to the wheel arch on both front wheels to see if they are even. If they are not even, it is a clear sign of a shock issue.
Check the shocks for any leaks or damage, check airbag suspension for any continuous hissing sounds.
They usually make a hissing sound for a while after turning the truck off, but not for too long. Spray some soapy water around the whole of the airbags to see any bubbles from escaping air.
How to Fix Semi Truck Front End Bounce?
Once you have diagnosed the problem, you must take the time out to fix it. If it is a leaf spring issue, make sure you use the correct jack and frame lift along with chocks to support the truck.
Remove the front wheel, cut the U-bolts off with a torch, remove the centering pin, and remove the leaf bolts. Fit the new leaf spring in place and the U-bolts.
You may need to replace the shock, as the spring can sometimes damage it and even bend the axle. To replace the airbags, shut off or bleed the air supply.
Disconnect the airlines, be careful not to damage the small steel valve. We advise taking a photo of the airline set up before removing them to make sure you connect them back in the same way.
Remove the top and bottom bolts on the airbag. Take the old airbag off by pushing it down and spinning it. Prepare the new airbag, remove the plug and press the bag down slightly.
Put the bottom bolt in first, but don’t tighten it yet. Pull the airbag back up and in place, then put the top bolt in, tighten all the bolts. Place sealant around the thread of the top airline fitting.
Place and tighten it, then connect airlines, be careful not to over tighten them as you could crack the nuts, and last, build the air pressure back in the airbags.
The shocks are very easy to replace. Turn the wheel fully to allow easy access to them. Remove top and bottom bolts and set aside, place new shock in and tighten bolts.
Semi Truck Rear End Bounce
The rear of a semi truck can bounce for many reasons, usually at speeds of over 40 mph. It can be very difficult to pinpoint the issues, and many truckers spend a lot of money fixing the wrong things.
It is not dangerous if dealt with as soon as possible.
What could Cause the Rear End to Bounce?
Uneven brakes and drums can cause a slight bounce in the rear. This happens from loose nuts.
If the shocks are not working correctly, this can cause the back to not be in line, creating a bounce at certain speeds, and affect the driveline and carrier bearing.
Another cause is the U-joints being loose. This would cause movement in the rear.
Additionally, the suspension ride height could be incorrect. This happens when the air ride valve is not at sufficient pressure.
The cabs cat mount, if damaged, could also cause the truck to bounce.
How to Diagnose the Cause of Rear End Bounce?
You will need to know the height spec of the truck, usually found on a sticker attached to the left frame rail at the rear. Measure between the centerline of the axle and the bottom of the frame ahead of the rear-drive.
If the measurements do not match the spec on the sticker, this may cause bouncing.
Check the U-joints are tight by giving them a shake manually and use a tool to check the bolts. Loose U-joints will cause a bounce when the truck in a high speed.
Check rear brakes are evenly worn. Uneven brake wear will result in bouncing when braking. Check rear airbags for leaks using a bottle of soapy water. Check they’re not cracked or completely deflated.
If they are not all at the correct pressure, the truck could bounce more than usual. Check the shocks are level with each other and not leaking or damaged. Check the cat mount center for wear.
How to Fix Semi Truck Rear End Bounce?
To replace a cat mount is very easy; remove bolts. Usually, two from the bottom and another on the top, place the new cat in and bolt it up.
If you need to replace the brakes or/and drums, chock the wheels and release air tanks. Remove the wheel, remove the drum (you may need to hit the side of the drum with a hammer to loosen it).
Be careful not to damage it. You may need to loosen the slack adjuster if the drum is being stubborn. Remove the brake by taking the springs off.
Clean the area around where the drum and brakes were as much as possible. Place pins on the new brakes and put them in place. Attach the springs on the front and the back.
Place the drum on, put the wheel back on and test the brakes. For the rear leaf spring, secure the truck with wheel chocks and axle stands, and a jack.
Remove the wheel, cut the U-bolt off with a torch, remove bolts to the spring. Use a hammer if needed to work the U-joint out. You can use a mount to support the weight of the leaf spring.
Use a mount and a hammer to place the new spring in place. Place the new bolts in to hold the leaf in place, then place the new U-joint on and tighten all bolts.
To replace the rear shock/s, remove the old one, that is held on by two bolts. Put the old one in and bolt them in place. Make sure they are the correct way around.
If you are unsure, do one at a time and use the other side as a reference. If you are only doing the one side, take a picture.
To adjust the ride height, loosen the mounting studs a little, release the air in the airbags down using the arm on the suspension leveling valve.
Use a pin (golf tee) to hold the linkage in place to know its correct level. Then bring the air back up to the recommended pressure, measuring between the shackle and the mount.
Take the truck around the block a few times, then measure the space again.