Bad engine or transmission mounts let the drivetrain move more than it should. The most common symptoms are a clunk or bang when shifting into drive or reverse or when accelerating, more vibration at idle, and the engine visibly rocking when you rev it. Mounts are rubber or fluid-filled blocks between the engine, transmission and frame, and they wear out with age, heat and oil contamination.
Engine mount symptoms
- Clunk when shifting into drive or reverse, or on and off the throttle.
- Excess vibration felt through the seats, steering wheel or pedals, especially at idle in gear.
- Engine movement: with the hood open and the parking brake set, a helper shifting between drive and reverse shows the engine lifting or rocking.
- Visible damage: cracked or separated rubber, or fluid leaking from a hydraulic mount.
Transmission mount symptoms
A worn transmission mount produces similar clunks and vibration, and on rear-wheel-drive trucks it can change driveline angles enough to cause a vibration at speed. It can be mistaken for transmission trouble, so check it before suspecting the transmission; see car jerks or shakes when accelerating.
How to check your mounts
- With the engine off, look at each mount for cracked, split or separated rubber and for fluid leaking from hydraulic mounts.
- With the engine cold, use a pry bar gently between the engine and frame near each mount; excessive movement or a separated mount shows up quickly.
- With the parking brake set, your foot firmly on the brake and a helper watching from a safe distance, shift between drive and reverse at idle. A healthy engine barely moves; a bad mount lets it lift or rock.
Rubber vs hydraulic mounts
Many trucks use solid rubber mounts, while many cars use fluid-filled hydraulic mounts that damp vibration better and can leak when they fail. Performance mounts made from stiffer materials reduce movement but pass more vibration into the cabin.
Can you drive with a bad mount?
For a short time, but a completely broken mount lets the engine move far enough to damage hoses, wiring, the exhaust and other mounts, so replace it soon.
What wears out mounts
- Age and heat hardening the rubber
- Oil or coolant leaks soaking the rubber; see oil leaks
- Added power and hard launches
- A misfire or rough-running engine shaking the mounts
Why replace worn mounts
Besides comfort, a broken mount lets the engine move enough to strain hoses, wiring, exhaust parts and the shifter linkage, and to make the drivetrain clunk. Mounts are commonly replaced when an engine or transmission is out of the vehicle, because access is easy then.
Replacing an engine or transmission?
If you are fitting a replacement engine or transmission, plan on new mounts as part of the job; see engine replacement cost and transmission replacement cost, and browse engines and transmissions by code.
More guides: hard shifts or mounts? · car shakes when accelerating · car jerks when shifting · car rolls in park · transmission mount symptoms.
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