Vibration on Overrun

[Troutman]

I get a slight vibration/rumble sometimes on the overrun. It's not harsh, more like when you drive over a rough road surface. Except it's happening a super smooth tarmac.
Could this be engine/gearbox mounts starting to fail?

[BYprodriver]

I don't know what you are driving but if it's a 986 & the front engine mount has never been replaced with the improved 987 version, it needs to be. Look for fluid leaks from the trans mounts & replace if fluid is leaking.

[Nimbus117]

As above. Mine vibrates between 3200-3000 on deceleration every time. Will get mine done when I have the clutch replaced.

[Troutman]

Originally Posted by BYprodriver

I don't know what you are driving but if it's a 986 & the front engine mount has never been replaced with the improved 987 version, it needs to be. Look for fluid leaks from the trans mounts & replace if fluid is leaking.

No fluid leaks but it sounds like that might be the problem.
It's a 99, 986 2.7. 65k miles

I didn't realise the trans mount had fluid in it though.

[papasmurf]

mine did the same thing right around 3k rpms....never could really feel it accelerating but could feel it through the bottom seat cushion from time to time when coasting or when shifting gears around that rpm range....my mileage was probably around 60k when I replaced it.

[litespeedp]

Had same vibration at around 3000 RPM just like everyone here on my 60,000 mile 2000 S with manual transmission and replacing the front engine mount was the fix!

[nieuwhzn]

Yup, have fun with replacing the engine mount.
Btw, the Boxster flat 6 engine does have and eigenfrequency at about 3000rpm and you will feel some more vibration at those rpms when the engine is unloaded, even with a perfect engine mount.

[smygolf]

A couple of Days ago i noticed a strange rattle from what i thought was coming from the top assembly. But i couldn't locate it exactly and its like a rattle a loose washer but not metallic rattle.

so i mounted the hardtop and the rattle is still there, And its around 3000 rpm it start!
But i have no vibration in the seat or anything like that.


Sometimes it sounds as its coming from rear near the motor mount.
Any one else have had the same thing with a faulty motor mount?

*edit*
Its Box S from 00
75K miles

[Nimbus117]

Have a look at this thread, I may not bother with the front engine mount now:

Boxster 986 vibration @ 3000/3200 rpm (fix?) - 986 Series (Boxster, Boxster S) - RennTech.org Forums

[southernstar]

Thanks for this Nimbus. I do not have any vibration problems, but am replacing my front engine mount anyway as the rubber looks a little ragged (and the new mounts are apparently an upgrade over the original ones installed on the 986).

Brad

[teleski]

Long Island, eigenfrequency... perhaps you work at Brookhaven (or Stony Brook)?

[sb01box]

Originally Posted by Troutman

I get a slight vibration/rumble sometimes on the overrun. It's not harsh, more like when you drive over a rough road surface. Except it's happening a super smooth tarmac.
Could this be engine/gearbox mounts starting to fail?

Been reading this thread and trying get the definition of "overrun" can you educate me?
Thanks in advance

[nieuwhzn]

Originally Posted by teleski

Long Island, eigenfrequency... perhaps you work at Brookhaven (or Stony Brook)?

Ugh, should choose my words more carefully...you found me out.
Working for MIT actually, stationed at Brookhaven since 1999.

[nieuwhzn]

Originally Posted by Nimbus117

Have a look at this thread, I may not bother with the front engine mount now:

Boxster 986 vibration @ 3000/3200 rpm (fix?) - 986 Series (Boxster, Boxster S) - RennTech.org Forums

Well, you should bother with the front engine mount anyway. The rubber in these things deteriorates pretty rapidly. I decided that the 3000rpm vibration was getting a bit too much and replaced the mount, the rubber was actually ripped in a couple of places. With the new mount there is only some vibration left when sitting around 3000rpm with an unloaded engine, like when decelerating.
Interesting article on RenTech, pity that the 'final solution' was never handed to us. Could be that the exhaust system is the culprit or at least amplifies the vibration. A good check would be to see if people that replaced the stock exhaust still have the same 3000rpm vibration with an unloaded engine.

[teleski]

Originally Posted by nieuwhzn

Ugh, should choose my words more carefully...you found me out.
Working for MIT actually, stationed at Brookhaven since 1999.

;-) I spent a summer at Brookhaven in the mid 80s while in college. Spent half the time sweeping the pit while they constructed BNL-787, the rest writing Fortran code on a VAX teletype terminal. Great times.