Could be worn out motor mounts :yes

 

+1 on the motor mounts

 

Already checked the motor mounts and tranny mount. They were fine, both in good shape, but I replaced them anyway about 15k miles ago. The vibration didn't change at all.

I've also done a compression test and all cyl's are within a few percent of each other. A tad lower than spec but that's to be expected on a motor with 150k on it.

-Zach

 

mine vibrate a little more then ushally at 65-75 mph but not anything bad, but not that big of a problum. From 10-70ish and 80-120 Its perfect. Also noticed the same for my brother's S4. Could also be your brakes if it shakes alot when you aply them at higher speeds.

 

I've checked. The brakes are new. I checked the runout on the hub and rotors to cancel out tolerance stacking just for that reason.

The car has IRS. The pinion angles have been set. The runout on the pinion flange and pinion yoke were checked and the driveshaft was balanced and indexed. The wheels were balanced and all suspension rubber in the front is new. Aside from the IRS subframe bushings, there is no rubber left in the rear, only aluminum and Delrin. Every source of vibration that could arise from the drivetrain was checked and checked again, documented and then fixed. The only vibration left in the car is the engine.

I'm almost to the point where I am going to drop the pan and see if the crank is fully bobweighted. If it is, then my shortblock is internally balanced and has the wrong HB and flexplate. I'm probably going to do that regardless unless someone knows for certain that there are some mismatched engines out there in the 2000 mustangs.

I only have to make the motor last for about 6 more months and then it's replacement will be ready. But until then I have to drive it every day. Given that I have tracked down every other vibration in the car, it just makes the engine vibe that much more annoying.

-Zach

 

my 96 3.8 has 233K miles and massive vibration at times and certain rpms. it started to around 180K and its getting worse. feels decent under WOT at temp. i think it started with a massive rear wheel hop on a 2nd gear WOT pull at 50mph. seems like the rain or high moisture lowers the vibration. when i pull the accessory belt the damn thing feels like brand new engine. wish i could drive it without that belt... it is externally balanced and this has to be the harmonic balancer causing this, even if it appears to be fine. ford dealer had no idea, said the harmonic balancer is fine and told me to use higher rpms. possibly the autozone power steering pump? try pulling the belt and starting it briefly. any more than a minute without the water pump might be trouble.
i found a forum with a guy that had this same issues replacing everything but the HB and that turned out to be his issue. even if it has not turned or moved or changed in anyway it can be too far gone?
what you guys think?

 

Could be your balancer is coming apart. Or is lose on rubber.Or it could be a tuning problem.Have you ever put plug wires on it.Has it been this way since you bought it .My 99 is external.

 

If you find out PLEASE let me know my 99 does the same thing around 1000 to 1500 rpms and it drives me nuts i cant figure it out

 

I'm almost positive that's just your exhaust resonating in such a way that it vibrated the cabin similar to a subwoofer or speaker. My car does the same thing and I can tell its just the exhaust, could be wrong but I think ur good.

 

My car vibrates all of the time. but then again my exhaust is welded to the chassis with no rubber in between anyway, i would check the balancer and if you have a manual get the flywheel resurfaced.

 

35Mpg? What do you do, 10MPH everywhere? ._.;

 

I have the same issue, I wouldn't call it a problem.
I have an 01 V6 with 113,000 miles.

Under 60mph, no shaking.
Accelerating from 60 to 70, shaking
Driving at 70, no shaking
Accelerating from 70 to 80, not sure...
Driving at 80, no shaking
Accelerating from 80 to 90, no shaking
Driving at 90, no shaking.

That's my experience, may not be exact, it's been a while since I went on the highway in my Mustang. It's not a big deal to me. I thought it was something in the AC that was loose or shaking, because it sounded like it was coming from really, really close to me, like closer than the engine is.

 

Check the balancer, mine would vibrate upon start up to about 1500-2000 or so. And it was aweful! The 90-00 are external and 01-04 are internal. I would check that balancer though

 

99-early 00 is external

late 00 -04 is internal

I do believe

 

i have a 2000 with 135,000 on it and it was doing the same thing a horrible shake from 1500 - 1800 rpm change the HB and its pretty much all the way gone. sometimes ill still get a little bit of a shake at 1600 but not nearly what is was before. changing the balancer is pretty easy to do also just get the rite puller from your parts people. oh and youll probably have to go to ford to get the HB no body else can get them

 

Figured it out and i was right, well sort of. MAF sensor partial failure. replaced it with a used one from a tbird 4.6, replugged the ect/act connectors and engines like new with no vibration and mpg is wayyy up. dont doubt this engine/car can do 32+mpg. i have seen this. obviously not city running. city is about 22-23 max.