Tech Tip: Motor Mounts - Supporting the Engine and Transmission

Tech Tip: Motor Mounts – Supporting the Engine and Transmission

Motor mounts are not a very glamorous product, but they do have an important function: They support the engine and transmission, and dampen noise and vibration. The mounts isolate the engine and transmission from the chassis so vibrations and noise are not transmitted to the rest of the vehicle.

Motor mounts are not a very glamorous product, but they do have an important function: They support the engine and transmission, and dampen noise and vibration. The mounts isolate the engine and transmission from the chassis so vibrations and noise are not transmitted to the rest of the vehicle. On some front-wheel drive cars, upper mounts (torque struts) also control the fore and aft movements of the engine during acceleration.

Most motor mounts are relatively simple in design and consist only of metal attachment plates and large rubber insulator blocks. But some vehicles have “hydraulic” or “hydro-mounts” with hollow chambers filled with glycol or hydraulic fluid. Hydro-mounts act like a jelly-filled donut to absorb vibrations that would otherwise be transmitted to the chassis. Hydro-mounts are often used with four-cylinder and V6 engines that don’t idle as smoothly as a V8, and in luxury vehicles where motorists expect less noise and vibration. Some hydro-mounts even have internal valving and/or a solenoid to change the dampening characteristics at different RPM to better tune out unwanted vibrations. These are called “switchable” hydraulic mounts or “electronic” mounts.

WHEN MOUNTS GO BAD
When a motor or transmission mount fails, one of several things can happen. If the rubber separates or delaminates from the steel, the mount can break. The design of the mount usually prevents the engine from falling out of the car, but it can’t keep the engine from twisting or rocking when the vehicle accelerates or is under load. This can produce thumping and rattling noises, as well as overstressing components such as radiator and heater hoses, wiring connectors and the exhaust system. In rear-wheel drive applications that have an engine-driven fan, a broken mount may allow the fan to hit the radiator or shroud. Drive belts or pulleys may also be forced to rub against other components if clearances are tight.

A broken or loose motor mount in a front-wheel drive application can be even more serious because it may allow engine movements that interfere with the throttle or shift linkage. Excessive fore and aft rocking of a transverse-mounted engine can also lead to exhaust leaks where the head pipe joins the manifold or cause the head pipe itself to fail. If the broken mount is an end mount, it may also contribute to a torque steer condition and cause accelerated wear or separation of the inner CV joints on one or both halfshafts.

The motor mounts are seldom checked unless there is an obvious problem, and they may even be overlooked if the engine or transmission is being replaced. You should remind customers to check their motor mounts if the engines seem noisier than usual or they can feel engine vibrations inside their vehicles. The condition of the mounts should also be inspected when any major engine or transmission work is done, or when replacing a clutch, halfshafts or a driveshaft.

Mounts can be visually inspected for cracked, loose or broken brackets, loose or missing bolts, collapsed rubber or fluid leaks (hydro-mounts). A pry bar can be used to check for separated or broken mounts.

Another way to check mounts is to put the transmission into drive and lightly load the engine while keeping the other foot on the brake. Excessive engine movement may indicate loose or broken mounts that need to be replaced.

Replacement mounts may or may not have the same construction as the original. Fluid-filled hydro-mounts are expensive, so a more affordable alternative may be a solid replacement mount. But a solid mount obviously can’t provide the same level of dampening as the original hydro-mount. Consequently, the vehicle owner may not be happy with the way his car feels if a less-expensive solid mount is substituted for a fluid-filled mount.

Replacing a motor mount always requires supporting the engine and/or transmission. The weight must be taken off the mount before it can be unbolted and replaced. This can be done with a floor jack from underneath, or with an engine hoist overhead. Mount access can also be a challenge on some transverse-mounted engines in front-wheel drive cars.

Other items that may be needed when replacing motor mounts include new fasteners, new mounts for a steering rack (these should also be inspected periodically or if the steering feels loose), a new mount for the center support bearing on a rear-wheel drive vehicle with a two-piece driveshaft, new upper strut mounts (if the steering feels stiff or makes noise when turning or driving over bumps), or even new body mounts if a vehicle has a subframe and the original mounts are in bad shape.

You May Also Like

GM Tech Tip: Clunk Or Thump Noise From Front Suspension

Some customers may comment on a clunk or thump noise coming from the front suspension while driving over rough road surfaces. This noise will typically occur when the front suspension is returning to the upward position after a hard downward stroke, such as after driving through a large rut or pothole.

gm-suspension-noise-featured

Models:
2008-2011 Buick Enclave, LaCrosse, Lucerne
2011-2012 Buick Regal
2005-2010 Chevrolet Cobalt (Including SS)
2006-2011 Chevrolet HHR (Including SS)
2008-2009 Chevrolet Uplander
2008-2011 Chevrolet Aveo
2008-2012 Chevrolet Equinox, Impala, Malibu
2009-2012 Chevrolet Traverse
2010-2012 Chevrolet Camaro
2011-2012 Chevrolet Cruze, Volt
2008-2012 GMC Acadia
2010-2012 GMC Terrain
2007-2010 Pontiac G5
2008 Pontiac Grand Prix
2008-2009 Pontiac Montana SV6, Torrent
2008-2010 Pontiac G3, G6, Vibe, Wave

GM: Intermittent Check Engine Light, DTC P2138 With Reduced Engine Power

Some customers may comment on an intermittent malfunction indicator lamp (MIL) being illuminated with a message or an indicator that displays Reduced Engine Power. The technician may observe on a scan tool DTC P2138 – Accelerator Pedal Position (APP) Sensor 1-2 Correlation set as Current or in History.

gm-check-engine-light
Lost And Found: When Good Tools Go Missing

There are those occasions when a phone call or a complete search of the shop doesn’t yield any sign of a lost tool. For the most part, you can mark that tool down as “gone for good,” lost to that place where wayward nuts, bolts and tools always end up.

wrench-on-engine
Tech Tip: Ford/Lincoln/Mercury Transmission Fluid Leak

Follow these tips to diagnose and fix a transmission fluid leak on several Ford, Lincoln and Mercury models. The first step is to remove the LH halfshaft and inspect the halfshaft journal surface finish.

Transmission leak
Automotive Automatic Transmission Filter O-Rings And Lip Seals

Many transmission filters require a seal at the point where they assemble into the transmission. Most of these seals are called “lip seals,” although some filters may use an O-ring. Before filter installation, it is important to make sure that there is no O-ring or lip seal in the case or pump bore left over from the old filter.

Other Posts

VIDEO: What Else Should Be Replaced With The Strut?

Complete a thorough inspection to increase profitability. This video is sponsored by Auto Value and Bumper to Bumper.

Autel Introduces A New ADAS Product

The MA600 Mounting Plate Package consists of a mounting bracket, mounting plate, mounting adapter and laser adapter plate.

WATCH: What Is The Fluid Inside A Bushing Or Motor Mount?

In this Tech Minute, Andrew Markel discusses suspension bushings and motor mounts, and the nature of the non-oil fluid that aids their function. Brought to you by Auto Value and Bumper to Bumper.

BRAKELIGHT: The Car Cradle (March 1986)

Some ideas just never catch on… Related Articles – Welcome To The Future: Are Your Networks Protected? – BRAKELIGHT: BFE Sponsors Soapbox Derby – BRAKELIGHT: Spiffs from the 1970s (1976) I wonder if the Car Cradle paid for itself by shaking out the coins that were trapped in the seats? The ad claims that there