Driveshaft Basics

A driveshaft, also called a propeller shaft, connects a vehicle’s transmission to the differential. As far as propulsion systems go, the driveshaft has a pretty simple purpose: transmit torque between the engine/transmission system and the wheels. Drive shaft rotation energy is transferred to the wheels through a gear system housed in the differential. Barring a catastrophic mechanical failure or excessive vibration, drive shafts require little maintenance or repair.


Driveshaft Standards

A vehicle’s driving shaft has to be designed to meet high standards for the following performance metrics:

  • Durability
  • Shear Stress and Vibration
  • Warping when Exposed to Temperature Extremes
  • Torque Transmission Efficiency

Usually, joints connect several propeller shaft components when the shaft has to be relatively long.

Driveshaft Joints

There are several prominent joint designs for propeller shafts. The most common are universal and constant-velocity joints. Universal joints have the advantage of allowing two components of a propeller shaft to pivot through a wide angle. This is advantageous in complicated machinery where the line between an engine/transmission and the differential is blocked by other components. Constant-velocity joints are specially designed to maintain constant rotation speed between two components of the driving shaft, even at significant angles. Universal joints generate vibration and angular momentum discrepancies if deviation angle becomes large enough. Joint design can be as important as the driveshaft itself.


As with everything, cost/performance tradeoffs are inevitable in drive shaft selection and repair. Constant-velocity joints are more expensive than universal joints but are usually worth the price in efficiency and durability. Drive shafts can be severely degraded by vibrations and improper joint alignment. Sudden braking/acceleration can also reduce driveshaft lifetime since doing so puts stress on the shaft, joint components and differential gears.

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The Transfer Case

This is a vital component commonly found in all wheel drive and four wheel drive vehicles. It is connected to the rear and front axles and the vehicle’s transmission through a drive shaft. Two wheel drive vehicles do not require a transfer case. This is due to the fact that they are equipped with a driveshaft that goes directly from the transmission into the drive wheels.

Types of Transfer Cases

Drive Type

Chain driven

Chain driven cases utilize a chain that usually drives only one axle. However, this type of vehicle component can also drive both axles. These cases are lighter and quieter than gear driven ones. They are commonly used in vehicles such as full size trucks, compact trucks, sports utility vehicles, and Jeeps.

Gear driven

Gear driven transfer cases can utilize sets of gears in order to drive both the rear and front driveshafts, or only the front driveshaft. These are generally heavy and strong units that are commonly used in large trucks. However, there are several gear drive cases that are manufactured for passenger cars.

Shift Types


These cases are equipped with dash mounted buttons or switches that have front sealed automatic locking drive flanges or an axle hub. In order to engage a four wheel system, a car must be moving at very low speeds. The speed that a 4×4 can be engaged at also depends on the vehicle. This is only found with a four wheel drive high option. Additionally, a car must be stopped in order to engage a four wheel drive low option. The transmission should be shifted to neutral. After doing this, the four wheel drive low option can be used.


These cases are equipped with a selector lever. This lever is found on the driver’s side floor transmission projection. It also has either a two manual front axle center selection or two sealed auto front axle locking hubs. In order to engage a four wheel drive system, a vehicle must be running at low speeds. To engage a four wheel drive low option, the car must be completely stopped. At the same time, the transmission must be put into neutral. After this, the four wheel drive low option can be selected.

Housing Type

Independent or Divorced

Independent cases are completely separated from a vehicle’s transmission. They are commonly bolted to the car’s gear box output shaft. The very short driveshaft connects the transfer gearbox to the rear and front differential. These transfer gearboxes are commonly utilized on long wheelbase vehicles that include military or commercial trucks.


A married transfer gearbox is bolted directly to a vehicle’s gear box. This transfer gearbox is an integral component of a gearbox. These two components also share the same housing. This transfer gear-case is commonly found in some four wheel drive cars and recent Subaru products.

Rebuilt Cases

Sometimes, these cases can bog down due to excessive use or old age. Buying a brand new case can be financially burdensome. This is the reason why many car owners consider rebuilt cases. Rebuilt cases can be similar or much better than brand new transfer cases. At the same time, only broken parts of a transfer gearbox are replaced.

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Transmission Rebuilds: When & How

Automatic transmissions are delicate mechanisms designed with precise clearances between the moving parts. Rebuilt TransmissionParts that move, of course, wear down. And when the wear gets so bad the gears no longer mesh correctly, the vehicle will no longer shift as it should. Well before this point the transmission should be rebuilt or replaced.

Signs of Trouble

Some initial transmission symptoms may not indicate the need for major work. Replenishing low fluid solves some problems. If topping off does not help; draining the unit, changing the filter and replacing seals and gaskets may coax a tranny back from the edge of failure if it has only minor symptoms like these:

  • Leaks
  • Fluid is dark or smells burnt
  • “Check Engine” light is on

A few more serious trouble indicators almost always indicate the tranny should be replaced or rebuilt:

  • Slow or no response to change in engine speed
  • Resistance to shifting into park or drive
  • Hesitation when gears change on the road
  • Shimmy during gear changes
  • Metal shavings in fluid
  • Tranny-related noise

Rebuilding Procedure

A rebuild begins with jacking up the vehicle or raising it on a rack. The mechanic then drains the transmission, takes it apart and lays it out on a bench. Each part in turn is cleaned and inspected for wear. Professionals will use new replacements for worn parts, but home mechanics may wish to consider carefully selected used parts from local sources, especially for the more expensive components.

Some parts should always be replaced during a rebuild. The clutches and bands, for instance, work by friction and so undergo tremendous wear. Seals and gaskets should also always be changed out. The torque converter, the fluid coupler that transfers rotational energy from the engine to an automatic transmission, is subject to large amounts of stress in operation and is quite susceptible to damage during the removal process. Many mechanics replace the torque converter as a matter of course.

Cautions for Do-It-Yourself-rs

A rebuild can be a challenging proposition. It involves removing several hundred pounds of dead weight containing nasty liquid from a vehicle over the mechanic’s head, and there often is no plug to facilitate drainage. After, all the delicate parts covered in toxic goo must be disassembled in an environment free dust…and the whole put back together with replacement parts as appropriate. Then the rebuilt tranny is put back on the vehicle and filled with fluid. At this point the used fluid must be disposed of properly.


Do-It-Yourself mechanics, particularly those with the proper tools and a good deal of experience, can and do rebuild automatic transmissions with entirely satisfactory results, and many do enjoy the process. An owner at a lower skill level, however, or someone who does not have the time or the tools to do the job right, should consider having it done professionally. This usually involves purchasing a new or rebuild transmission built from a reputable specialist like Rocky Mountain Driveline who performs exhaustive test to ensure perfection. You may still do a self-install, though this still means dealing with the weight and proper disposal of the old fluid. As an alternative, the installation can be handled by just about any local shop.

Transmission failure can make a vehicle unusable or worse, lead to an accident. Investment in a rebuild keeps cars running better and longer. Whether a home mechanic rebuilds the tranny out of the vehicle or a shop replaces it with a purchased rebuild, taking care of tranny problems saves time and trouble in the long run.

Rocky Mountain Driveline is your local leader for rebuilt transmissions. Stop by or call today!

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Flywheel Resurfacing, What & How?

The flywheel in a car has several purposes. Its main purpose is to store energy to provide momentum and keep the crankshaft turning. It also helps balance the rotating assemblies and smooth vibrations transmitted to the drivetrain. It transmits energy smoothly to the transmission, providing power to perform its work.

The transmission receives power from the engine through the clutch assembly. The clutch disk is covered in friction material similar to that found on brake shoes. When the disk is pressed against the flywheel by the pressure plate, a high amount of friction allows it to grip the surface, and rotating energy is applied to the transmission to make your car move down the road. When the disk lining begins to wear, it loses this ability to grip.Flywheel Resurface

As a result, it will begin to slip, and over time, it will polish the mating surface, making the slipping worse. The friction from this slippage causes a great deal of heat. There is so much heat produced, in fact, that it will effectively “heat treat” the metal surface. This can damage the surface, causing it to become too hard. In some cases, cracks and blisters can develop in the surface of the flywheel due to this increased hardness. This condition is often referred to as “hot spots” on the surface. Hot spots occur because the heat is applied unevenly. Consequently, the hardened places are not evenly distributed across the surface.

For these reasons, whenever the throwout bearing, pressure plate or disk is replaced, manufacturers also recommend the flywheel undergo a “resurface”. During a resurface, the part is fixed to a machine that cuts a very thin layer of metal off the surface. This process exposes fresh metal to the disk, and provides a slight roughening of the surface. This will improve grip over the previously polished surface. The amount of metal removed during a resurface depends on the depth of the hot spots.

It is a good idea to stop using the vehicle when the clutch starts to slip, and have it repaired immediately. If too much metal has to be removed during the resurface, the part will be too thin, and it will no longer meet manufacturer’s specifications for proper operation, weight and safety.

Some symptoms of problems in the clutch assembly include:

  • A great deal of force is required to engage the clutch pedal.
  • The car is difficult to shift into gear from neutral.
  • A squealing noise is heard while shifting.
  • The engine races when leaving a stop or climbing a hill.
  • The car has sluggish acceleration accompanied by the engine racing.

    Since the flywheel is attached to the engine’s crankshaft, the engine and transmission must be separated to remove the flywheel for a resurface. In many vehicles, this will mean the engine must be removed and reinstalled to perform this work.

    Rocky Mountain Driveline has the machinery and expertise onsite to resurface flywheels. A resurface will help to restore like-new operation to your clutch assembly.

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    A Guide Towards Great Handling

    Installing a new or rebuilt Rack & Pinion system in your car can easily breath new life back into the vehicle. Precise and smooth control of the wheel can be the central part of the driving experience which determines comfort and handling. It may sound like a complicated procedure, but this repair job is one that is actually within the reach of anyone with even minor automotive experience. The process is virtually the same with most vehicles. The only variable may be the method for removing the system from the frame.

    The first replacement step is to remove the old Rack & Pinion system. You will need to adjust the wheel so that the tires are in the forward position, and lock them in place. Once complete, disconnect the positive and negative cables from the car battery. Using a jack, lift the car so that the front wheels can be removed. Continue the repair by draining the power steering fluid and detaching the lower joint of the wheel column.

    Rack & Pinion

    The next step involves the tie rods and engine mounts. Remove all nuts from the inner and outer tie rods. Once free, disconnect the tie rod ends from the steering knuckles. The front exhaust tube must then be detached before removing the center member and all the nuts attached to the engine mounts. Next, you will remove the bulkhead hole cover by, again, removing all nuts.

    Now, to the Rack & Pinion itself. Remove the lower joint and mark the neutral position of the steering for later reference. Also be sure to mark the central housing and the shaft. You then remove the entire system by detaching the power fluid pipes and the mounting bracket bolts.

    Installing the new system is essentially the above process in reverse. The new system should be put in place…the mounting brackets, too. Verify all replaced nuts are properly tightened using a torque wrench. The hoses which supply the system with power steering fluid must now be put back into place. Reconnect both the high-pressure line and the low-pressure line, ensuring they are well secured to prevent future leakage.

    The pinion shaft must be properly aligned when it’s reinstalled. This step takes advantage of the neutral position of the wheel marked earlier. The mark indicates where the component should be attached to the steering joint. Once these items are in place, the bulkhead can be properly put back into place. The front stabilizer is next on our checklist. Gather the nuts and mounting gear for the engine mounting center. Put the component back into its original position. Tighten it securely into place. As the replacement nears an end, tighten the nuts on the tie rod ends, and secure the new cotter pin. All other securing nuts should then be put in place for tightening. The last step in the process is to refill the power steering fluid reservoir. You must then bleed the system to achieve optimal performance. In some cases, the repair process may also call for aligning all of the wheels.

    Rocky Mountain Driveline is your local leader for rebuilt rack & pinion units. Call or stop by today!

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    Differentials…What Are They?

    The term differential refers to a mechanical device that receives energy from a power source and converts the direction of that energy at right angles, left and right, with limited loss of power. While the term, these days, is generally considered a key automotive part, mechanical differentials can be used in any situation where such directional conversion of power is desirable. In automotive uses, wheels are attached at the end of the left and right driven arms extending out of the directional power converter mechanism.


    In addition to converting the application of power, this directional power converter has the ability to operate with the left and right converted power arms, called axles, rotating at different speeds. In automotive applications this allows a transference of power even while the two converted power arms, and the attached wheels, rotate at different speeds. Meaning the vehicle is turning. This is accomplished by the use of slip gears that mechanically ensure, even though only one physical power force enters the power conversion mechanism, the operation of the various sized gears results in a mechanical equivalent of two power inputs and two powered outputs. This arrangement of gears is therefore a mechanical equivalent of the mathematical equation that is a proof of this direction of power conversion system.

    In early automotive differentials this caused a loss of traction at the point where the wheels met the road. This, depending on the vehicle weight and amount of applied power, could be a problem. The result was development of a differential that had a limited amount of slip or loss of power to the left and right angle powered arms exiting from the case containing the differential mechanism. In automotive applications the left and right arms are called axles. Since the use of this mechanical principle for automotive purposes the term axle is used for the left and right power converted arms to even non-automotive mechanisms.

    Early Forms of Mechanical Differentials
    The ability to covert the direction of applied power is actually not a modern invention. Ancient devices have been found that also used this manner of converting applied power from one direction and applied that power in one or more different directions.

    In the first quarter of the eighteenth century this mechanical principle was applied to clocks. By the first half of the twentieth century analog computers were using this principle to do simple arithmetic calculations.

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    Driveshafts 101: What You Need To Know


    All automobiles have a driveshaft. This is the piece of equipment that transfers the energy created by the energy into the force that drives the wheels. It’s actually a very simple device.

    The driveshaft looks like a simple cylinder. What it actually is is an outer tube that protects the shaft itself, which is a spinning cylinder. The frequency of the spin depends on the engine. In addition to automobiles, boats and motorcycles also have driveshafts. Some vehicles may, in fact, have more than one. It is important that the driveshaft balance be maintained.

    If your car is rear wheel drive, it will have a long drive shaft that runs the length of the car and then a differential to transfer torque to the wheels, which are connected by short half-shafts. You may sometimes hear a mechanic talk about an automobile’s ‘diff’, shortening the word to something easier to say. A front-wheel drive vehicle has two short shafts, one to each front wheel or, more commonly, a device called a ‘transaxle’, which serves the purpose of the drive shaft, transmission and differential. Obviously, this is reversed in rear-engined vehicles. There are various different arrangements, dependent on the exact configuration. Four wheel drive vehicles have a slightly different configuration again, with front and rear shafts and differentials.

    So, what do you need to know about your driveshaft? It’s a moving part and, as such, can fail. Being relatively simple, it is less likely to fail than your transmission (transaxles, of course, are as vulnerable to failure as standard transmission). The most common problem is with the balance of the shaft. An unbalanced driveshaft causes vibration and a loss of power. Race car drivers spend a lot of time worrying about balance because it can make the difference between winning and losing. For the ordinary person, making sure your driveshaft is balanced can help with both power and fuel efficiency. In some cases the universal joints attached to the shaft have to be repaired or replaced.

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    Rocky Mountain Driveline Profiled in Parts & People

    Rocky Mountian Driveline is profiled in the pages of Parts & People. Owner, Scott Farley, discusses their growth and continued success in the CV axle and driveshaft industry. Get to know the Farleys and take a closer look inside Denver’s premier driveline business!

    Rocky Mountain Driveline Balances OE Replacement and Performance Segments
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    CV Joints: What Are They And How Do They Work?


    Every car in America has only one engine, but four wheels. This creates a problem: how do you deliver power to both axles and all four wheels with only one source of power? The answer is through the use of a complex series of joints to properly transfer the power. Originally this was done by using universal joints, since they allowed the rotational force of the engine to be transferred to any angle. You will still see such connections used to drive the rear wheels on delivery trucks and some off road cars. But it has been noticed since the 17th century that these universal joints do not maintain constant velocity throughout the rotation, which puts stress on the axle and causes it to receive power unevenly. The solution is to develop a constant velocity or “CV” joint, which can deliver power from one shaft to another more exactly.

    There are many types of CV joints, but they all do effectively the same thing: they cushion the rotational force of one shaft against another by putting ball bearings or additional connections between the two. This enables the receiving shaft to, ultimately, rotate at the same speed as the powering shaft as it is driven forward by the bearings instead of a direct connection. The bearings transmit the force directly and over time instead of in the indirect and angular method used in older universal connections. This enables a CV connection to deliver more power, more efficiently, and with less wear than traditional connections.

    CV-Joint2The CV connection has been used in front wheel drive cars since the 1960s, and it is also used on all four-wheel drive cars. It is necessary to have at least two of these connections in order to deliver power to the front axle, and the use of such adapters allows the axle to “bend” around the passenger compartment. They are also essential in rock crawlers, off road vehicles and trucks which have been modified for mudding. The high ground clearance of these cars necessitates that the drive shaft be “stretched,” and the use of a CV in the right spot can ensure that the drive shaft is properly angled and able to maintain a proper angle and connection as the truck moves over rough terrain.

    At Rocky Mountain Driveline, we offer the best constant velocity connections and products for your vehicle. We can help you pick out what is best for the sort of drive line arrangement you want to have, and help you plan out how your drive line may change if you have your vehicle lifted or lowered. We also offer reconstructed constant velocity connections of all sorts, so you can get the best prices on the best products.

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    Signs Your Driveshaft Is Failing

    Jeep-Front-DriveshaftThe driveshaft is an important element of your vehicle that rotates and delivers power to the engine and gears that turns the wheels of the automobile. In addition, it creates torque that makes the car go. It also stops the vehicle. A car cannot function without its driveshaft.

    Generally, they do not break down all at one time. It’ll begin to wear and tear over time. Fortunately, there are signs that indicate there is trouble. One of the most common symptoms is vibration. The entire car or parts of the car may begin to shake. The floorboard is one of the common areas where trembling or vibrations may be felt.

    Another common sign of trouble are squeaking sounds that get louder when the speed is increased. The sound may go away when the vehicle is going fast and may come back when the car slows down or comes to a stop. If this occurs, it could mean that the U-joint, which is connected to the drive shaft, is damaged.

    Turning issues can also be an indication of a problem. If the car’s wheels are not turning properly or resist when the car is turning the corner, most likely it is a sign that the drive shaft needs repair. DriveshaftAnother sign of possible trouble is difficulty turning the wheels when parking in tight or close spaces.

    Driving an automobile with a defective or damaged driveshaft is potentially dangerous. If there is any sign of trouble, the car should be taken in to a certified mechanic for immediate inspection for repair or replacement. Replacing or repairing a drive shaft can be very expensive. If the problems are detected early and dealt with in a timely matter, however, the cost for repair or replacement may be significantly lower.

    It is highly advised to be on the lookout for any of these and other signs of trouble to keep your vehicle in top running condition. For those in the Denver area, visit Rocky Mountain Driveline for the best service in town!

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