My '04 MCS (w/ merely 31K miles) recently started to 'shudder' violently when pushed to 3k RPMs or more in 6th gear. By shudder, I mean a continuous and powerful full-body shake, vibrate or rattle. This has never happened before, doesn't happen in other gears and is directly linked to the RPMs. As soon as the RPMs are over 3k the shudder kicks in and continues until I fall bellow 3k RPMs. While above 3k RPMs, the shudder gets more aggressive if I accelerate hard and is less bad if I hold an even speed. I haven't noticed anything else strange nor made any changes or mods recently. I've seen two mechanics who weren't able to diagnose it; my ECU apparently thinks everything is peachy. One of the mechanics suggested this was an electronic throttle issue that would "go away soon." Of this advice I am suspicious. Any guidance would be much appreciated.

Thank you in advance!

 

This is a tricky one indeed... It can be linked to many symptoms. It could perhaps be your aligment, a bad ball joint, bad control arm, warped rotors, tires not balanced properly and the list goes on. You also stated that no mods have been installed on your car as of late, did you ever hit 6th gear since you did your last install? From 1-5 Gear, anytime you go over 3k RPM do you get any shakes?

I'm curious, let us know. I'm sure somebody in the community has an answer for you.

Regards,

 

3k in 6th gear is xx MPH. I bet if you go to 5th and 5krpm it will shake too. It sounds speed sensitive and not engine related. Get going faster then coast, it should be unchanged.

First thing to check is tire condition. If they are OK, a balance should fix it most of the time.

 

^ +1

 

Thanks for the quick replies!

HRM, you're right it is speed related. After I saw your post, I took a quick jaunt onto the freeway and the shudders are there in 4th, 5th and 6th gear at 70mph or faster. As this means apprx. 3k RPMs in 6th, 3.6k in 5th and 4.7 in 4th it doesn't seem likely RPMs factor in...so my thread name is ill chosen.

However, it seems to me it is engine related as the shudder is only there while accelerating. If I let the Mini coast from 80 back down to 70, no shudder. If I shift into neutral at 75mph, the shudder stops. If I keep a constant speed in excess of 70, very very minimal shudder. It is only when I accelerate (at a speed in excess of 70mph) that the shudder is bad; the harder I accelerate the worse the shudder.

In reply to the couple other questions: I hit 6th (and 70+mph) regularly and the issue just appeared. The most recent mod is more than 15k miles old, so I don't think it should factor in (at that time I put on a Dinan air intake and got a new right rear control arm). The tires are a matched set of factory runflats on 17" rims and appear be wearing evenly and still have some 10-15k miles life left as per the mechanic. I asked the shop mechanic if I needed a balance and he said no.

I hope that clears something up for somebody...to me it looks worse than when I started!

 

Without your mechanic taking your wheels off and balancing them I don't know how he could rule out that issue. That would be your cheapest solution.

Have you checked the inside of your wheels for debris like mud or something stuck to the inside of the rim?

You mentioned it was a whole body shake. Is the vibration more prominent in your steering wheel or do you feel it from your seat more?

Since you're feeling it at high speeds only I seriously doubt it's in your driveline. Personally, I would start ruling out the simplest solutions first like wheel/tire balance.

Chad

 

Without your mechanic taking your wheels off and balancing them I don't know how he could rule out that issue. That would be your cheapest solution.

Have you checked the inside of your wheels for debris like mud or something stuck to the inside of the rim?

You mentioned it was a whole body shake. Is the vibration more prominent in your steering wheel or do you feel it from your seat more?

Since you're feeling it at high speeds only I seriously doubt it's in your driveline. Personally, I would start ruling out the simplest solutions first like wheel/tire balance. Make sure to check for a bent wheel as well.

Chad

 

Check your upper motor mount on passanger side. If it is not tires could be bad mount.

 

Did you ever find the issue? I have the exact same symptoms. I've replaced all 3 engine mounts and I just rotated and balanced the tires and the tires are like new, so it isn't that.