Diagnosing and identifying the cause of drive shaft vibrations and noises can be quite frustrating. This page will help you to follow the clues and hopefully find the source of those aggravating and worrisome drive shaft noises, vibrations, and shudders.
There are different types of drive shaft vibrations. There are angle related vibrations and there are dynamic vibrations.Angle related vibrations are caused by a u-joint running through improper angles. Dynamic vibrations are things like a bad balance, vibrations that are a product of weight and speed. I’ll go over the symptoms of each below.
- Angle related. These are typically felt at lower speeds, from 0 to about 40 mph. These are also worse on heavy throttle and load, when accelerating or going uphill. Angle related vibrations are often described as a shudder and usually get better or go away when you let off the gas or shift into neutral. Another sure way to know it is angle related is if the vibration started immediately after installing a lift.
- Dynamic vibrations. These are worse at high speeds, usually 50 mph and up. The faster you go the worst they get. Letting off the gas either makes no difference or it makes it worse. If letting off the gas makes it worse it usually means that there is a loose part which is rattling around when unloaded. Another good indicator of loose parts is a vibration that gets worse and worse over time. This means that whatever is worn and loose is wearing more and becoming more loose whereas an angle issue does not change over time. Lastly, if your drive shaft is several years old or older it is almost certainly a bit worn which could be causing the vibrations.
If your symptoms seem angle related you may want to measure your angles and adjust if necessary.
This page shows you how to measure angles.You can also watch a video explaining what the angles should be and why here.
Check and make sure your shaft is installed correctly, if you have a double cardan (cv) shaft the double cardan should be at the transfer case. It sounds crazy but I've heard of "professionals" installing them backwards. This is usually only even possible if you have flanges at each end like on a Toyota or a Land Rover.
If it seems more like a dynamic vibration it could be any of the following.
- A poorly balanced shaft. Most reputable drive shaft shops will get this right but It is possible, even we sometimes get it wrong.
- A loose part.This could be on the front or rear, both should be checked. on some vehicles, even in 2WD the front shaft is spinning passively. A good test for loose parts is to set your park brake and/or chock the wheels, put the vehicle in neutral (not running though), then scoot underneath your vehicle. Give each drive shaft a good hard shake up and down. If you can feel anything moving and/or hear a knocking sound then there is something loose that needs to be replaced or tightened.
- A bad transfer case yoke or pinion yoke. This is not common but it does happen. The yoke on the transfer case could be machined a little off center which would cause the entire drive shaft to run off center. This in turn causes the entire drive shaft to run off center and vibrate. Another fairly common and similar thing is a bent output shaft on a transfer case or transmission. This is especially common in vehicles that use a slide-in slip yoke style attachment at the transfer case and that have had a drive shaft failure while moving. If the shaft comes loose at the axle and spins around a couple times while still connected to the transfer case it can bend the output shaft.
- Something else entirely. There are a lot of moving parts on a Jeep or truck and a lot of things that could be making noises and vibrating. Many times it is not a single source but a vibration will actually be a combined result of several factors.
Drive shaft RPMs are often an important thing to know and consider when diagnosing drive shaft vibrations. For example, if a shaft is only spinning a few hundred RPMs it is very unlikely that the vibration is a dynamic vibration. Also, sometimes people will gear their ring and pinion very low (higher number means "lower" gearing) which will cause their shaft to spin abnormally fast an normal driving speeds. The target for highway driving for most vehicles is to have the drive shaft spinning at around 2,500 to 2,800 rpm at 60 mph. If it is over 3,000 rpm you might have a situation in which your drive shaft basically thinks it is going 100 mph while the rest of the vehicle is only going 80. You can use the calculator below to figure out your drive shaft rpm at different driving speeds.
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Hopefully that helps. If you have other questions, please give us a call.
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