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Replacing engine mounts. Need insight.

18K views 11 replies 5 participants last post by  VetteAholic  
#1 ·
I've gotten this shake to my motor that has gotten worse within the month. I suspect a bad engine mount of mounts.

I've got a question, to do this job will I be able to put my 1992 on jack stands(2 on the front) and then with a jack and a piece of wood, jack it up to raise the motor a bit by the oil pan(after removing the bolts to the mounts)??


This shake happens at idle, then when doing about 70 my front end seems to start shaking again.
 
#2 · (Edited)
Your shaking at 70 mph doesn't sound like a bad mount to me. If a mount has gone bad it's almost always the left one because engine torque pulls on it; eventually tearing it in two. Then under hard 1st gear acceleration the left side of the engine can lift up. You can see if the mount is bad by opening your hood and pushing hard on the brake pedal at the same time you give it full throttle. If it's bad the left side of your engine will lift up several inches. I'd check the balance of the tires as that is usually the cause of vibration at high vehicle speeds. When I replace motor mounts I always drill and tap them for a 3/8" flat head bolt; joining the two halves together. Then they can never pull apart.
 
#3 ·
Thanks for the insight TB.
 
#5 · (Edited)
When you say at idle, do you mean at a dead stop? or when doing about 70, does your car shake in neutral only?

I lean more towards engine mounts. If you can drive normally & hit 70, then put the car in neutral and the car starts shaking, this is not an alignment issue. If as soon as you get to 70, with the car still in gear it starts shaking, then its probably not the motor mounts. If it shakes at idle and at 70, it could be both among other things.

I don't know how many miles are on your car, but if you've got a fair amount I'd say inspect them and change them if needed. They could be just loose and need tightening--they could also be dry rotted and in need of replacement. When you're satisfied the motor mounts are no longer a variable and you've still got that vibration, then I'd get an alignment.
 
#8 ·
Both, park and in gear while stopped. My engine is pushing around 165k(M). I know one thing is for sure, my ball joints(I think that's the correct name) on the control arms, where they store the grease. Well those gave out on me, both sides. I've tightened down the engine mount bolts but with no luck. I'll have to really start digging in and checking all suspension/distributor possibilities.
 
#6 ·
Bad Motor Mounts?

As your engine weighs around 600-650 pounds there is a lot of downwards pressure on your mounts. About 300 pounds per mount. When a motor mount fails it tears apart. You can easily check a mount by putting your car in gear then give it about 1/2 throttle. If the mount is bad the left side of your engine will lift up an inch or two. In the past Chrysler used a short piece of 1/4" cable that was attached to the frame and engine block to prevent the engine from lifting when a mount failed. I drill thru the center of my left-side mount with a 5/16" drill bit then tap the frame side of the mount with a 3/8-16 NC tap. Then I countersink the engine side of the mount and screw a 3/8-16 NC flat head bolt into it. The bolt will prevent the mount from ever tearing apart.

There's no way a bad engine mount will cause a vibration at 70 mph. But you may have a bad transmission mount as when they fail the rear of the transmission will often shift over to one side and cause an increased loading on the front u-joint. Which causes a lot of vibration. To check for a bad transmission mount I usually put a 2 X 4 under the oil pan then jack it up. It only takes a couple of hundred pounds of upward force to pick up the rear of the transmission.
 
#7 ·
To check for a bad transmission mount I usually put a 2 X 4 under the oil pan then jack it up. It only takes a couple of hundred pounds of upward force to pick up the rear of the transmission.
Thank you for the tip TB, I will check that out. I'll run a scanner as well and see if I get any codes(I also think I'm getting a misfire, at idle)
 
#9 ·
Vibration

You may have a bad spark plug wire if your wires are the original wires. They should have around 25,000 ohms resistance each (plus or minus a couple of thousand). An "open" will indicate the carbon core is burned out.

But check out your rear transmission mount as it has very likely broken after 165,000 miles. When a transmission mount breaks the rear of the transmission will hop up and down and it'll also shift over to one side..........increasing the loading on the front u-joint and causing a LOT of vibration. They only cost about $10 and they're easy to change.
 
#10 ·
You may have a bad spark plug wire if your wires are the original wires. They should have around 25,000 ohms resistance each (plus or minus a couple of thousand). An "open" will indicate the carbon core is burned out.

But check out your rear transmission mount as it has very likely broken after 165,000 miles. When a transmission mount breaks the rear of the transmission will hop up and down and it'll also shift over to one side..........increasing the loading on the front u-joint and causing a LOT of vibration. They only cost about $10 and they're easy to change.
I'll get it on jack stands and have a picnic down there looking for things. Thanks again for the info TB. Also could you please give me some insight on my question I asked:

"I've got a question, to do this job will I be able to put my 1992 on jack stands(2 on the front) and then with a jack and a piece of wood, jack it up to raise the motor a bit by the oil pan(after removing the bolts to the mounts)??"