Engine Vibration Problem-see my fix on last page

mywhite89

Registered User
I am trying to work out an engine vibration problem that occurs between 2100-2400 rpms. The balancer is a bhj and is new, new solid rubber stock height motor mounts. I had every piece except the spec clutch and flywheel checked to ensure a good neutral balance. Those pieces come balanced, at least they should. I can rev the car to 5,000 with no unusual vibration above 2400. Anybody have an idea on what else it could be.

My only other idea besides an engine balance problem is the tranny mount. The guy before me ditched the old mount and put in a solid steel mount which may be putting everything at a slightly different angle. It has poly outer crossmember mounts as well.

The vibration is not horrible, but is definietly noticable and annoying. a 75mph cruise puts me at about 2100 rpm's. I do not see any engine pieces or exhaust touching the frame to cause a vibration either.
 
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Mine has a similar issue but I can't seem to locate if it is the engine or the drive line under torque only.
When it occurs at about 2200 rpm, I can push the clutch in, keeping the rpms stable and the vibration goes away, no free rev vibration at all.

I heard that my 17" Cobra wheels may need some centering inserts but not sure where to get them.
 
is it occurring when you are on or off of the throttle? if its when you let off, check your ujoints, and the bolts attaching them to the diff and trans.. that was my vibration problem.. i took them out (by hand no less, scary, huh?) and put red loctite on tehm and torqued those suckers down. :D my ujoints will snap or my output shaft will split before those bolts come loose again.
 
is it occurring when you are on or off of the throttle? if its when you let off, check your ujoints, and the bolts attaching them to the diff and trans.. that was my vibration problem.. i took them out (by hand no less, scary, huh?) and put red loctite on tehm and torqued those suckers down. :D my ujoints will snap or my output shaft will split before those bolts come loose again.

Mine occurs while stopped in neutral, so that takes a lot of variables out of the equation. I have an aluminum driveshaft, brand new u-joints. I can be on or off the throttle and that vibration occurs. As long as I see the needle come across those rpm increments it vibrates between, if that makes any sense.

I may have a slight run problem that is causing the vibration.
 
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Could the exhaust system be rubbing on something or the rubber isolators are shot?
how about the motor mounts, you sure they are not shot?

After that, you're looking at flywheel/flexplate, if automatic, transmission, if manual, engine.
 
Could the exhaust system be rubbing on something or the rubber isolators are shot?
how about the motor mounts, you sure they are not shot?

After that, you're looking at flywheel/flexplate, if automatic, transmission, if manual, engine.

I've got a manual trans. I've checked all the little dumb things. Motor mounts are 800 miles old. Exhaust hangers 17 years young.(something to check for sure. I'm going to do some testing on it this weekend. I wanted to at least get a thread out their in hopes of solving the problem and posting the fix. keep the ideas coming and I'll check it all out.

It looks like at idle the balancer has a very slight vibration but smooths out with rpm's. Smooth at 2100-2400 for sure. My car has a pretty lopey cam, so keep that in mind in regards to having a vibration at idle.(more like physical front to rear movement if anything) Checked balancer and crank pulley for zero balance. Both were already fine.
 
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btw you shouldnt run a solid tranny mount with rubbe rmotor mounts..Many a cracked transmission have occured from this..May also lead to some of your vibration
 
btw you shouldnt run a solid tranny mount with rubbe rmotor mounts..Many a cracked transmission have occured from this..May also lead to some of your vibration

I am going to replace it. Good point, I can understand why that would be a bad deal. I think I am missing a couple pieces that go with using a normal mount, thats what sucks.
 
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make sure your ujoint are all tight and all the spring clips are in there place










I am trying to work out an engine vibration problem that occurs between 2100-2400 rpms. The balancer is a bhj and is new, new solid rubber stock height motor mounts. I had every piece except the spec clutch and flywheel checked to ensure a good neutral balance. Those pieces come balanced, at least they should. I can rev the car to 5,000 with no unusual vibration above 2400. Anybody have an idea on what else it could be.

My only other idea besides an engine balance problem is the tranny mount. The guy before me ditched the old mount and put in a solid steel mount which may be putting everything at a slightly different angle. It has poly outer crossmember mounts as well.

The vibration is not horrible, but is definietly noticable and annoying. a 75mph cruise puts me at about 2100 rpm's. I do not see any engine pieces or exhaust touching the frame to cause a vibration either.
 
I noticed this on the dyno and meant to talk to you about it. It is definitely engine related. I have serious questions about your engine balance job. :( Start with the peripherals and work you way inward.
 
I noticed this on the dyno and meant to talk to you about it. It is definitely engine related. I have serious questions about your engine balance job. :( Start with the peripherals and work you way inward.

Did you notice it all throughout the rpm band or just at those rpm's also? I might have the rpms high enough above that, that it doesn't quite feel as bad since everything is turning so fast.

I'll pm ya on everything I did.
 
could some of that vibration be caused by the solid tranny mount? I.E. vibration from the motor transferring through the trans to the body of the car. I am running solid mounts for the trans and motor and nothing will vibrate, but when i get to a certain rpm range the whole car shakes like the doors are gonna fall off.
 
can i join ur vibration club

my 94 also does this in neutral from 2100 to 2500 rpm and is only faintly noticeable in light 2nd gear light driving especially when letting off the gas. It does have a strage knock thats random without sync which some mechanics say is the torque convertor as it does sound like the rear of the oil pan to the flywheel/bellhousing of the TC. Also I believe i have a soft lifter as it makes "hot cooling exhaust" noises when cold and I didnt crank it enough to start it. noises seem to fade away as it warms up. My last shuddrer which was real bad on my 89 sc was a bad wrist pin scrapping the cylinder wall and letting gas destroy the bearings. And before that happened i did a rebuild to the engine with new pistons and crank, bearings and used rods which shouls have been new instead of used
 
Just wanted to update this for anyone who has had a engine vibration problem similar to mine. I fixed my problem completely last night by putting my stock tranny mount and all other necessary hardware back on the car. Turns out I was missing the steel bracket that the mount bolts to also.

I didn't realize how bad my car vibrated through ALL rpms until I drove it for the first time last night. DO NOT USE A SOLID STEEL TRANNY MOUNT. My car is smooth as silk, and rides like a thunderbird now. It's a wonderful thing.

Chris
 
btw you shouldnt run a solid tranny mount with rubbe rmotor mounts..Many a cracked transmission have occured from this..May also lead to some of your vibration

I have a solid tranny mount and new regular engine mounts. Is the cracked tranny problem just with higher HP Birds or just in general. I also have a slight vibration at about 75mph
 
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