rumbling when driving

[marksawtell]

I am going through slowly getting my 1999 c2 cabrolet 996 in shape. A while ago I noticed a rumbing/shaking when driving. I put up a post and some helpful tips came back but I stil cant get rid of it. the best way to describe it is if you hold one of your hands infront of you loosely whilst driving, you can see it shake (im not on drugs or suffer from alchohol abuse before somebody suggests it... ;-)

The car has done 180,000 miles (which is probably close to a record for a 996 lol)

I have replaced tyres (front and back) and had them all balanced

i have resplaced shocks and springs front and back

i have replaced anti roll bar front and back

I have replaced droplinks (front only)

I have replaced rubber mounts on front shocks

I have replaced wheel bearings (front and back)

I have replaced coffin struts at front.

I have also had a garage have a look at it that check all 4 wheels for camber and toe anf this was corrected and they could not find anything else wrong

the rubling/shaking gets worse with speed and is rythmic . ie spounds like a flat spot on a tyre, but obviously havig replaced all four its not that.

Please somebody put me out of my misery! i am at the point of giving up on this car.....

Any ideas????

As always, thanks for any help in advance :-)

[Dennis C]

My initial guess would have been tires, but it sounds like you've addressed that. Looking at all the things you've replaced, it's hard to imagine what else it could be. Engine mounts maybe?

[logray]

I was also going to suggest engine and transmission mounts.

Is it detectable when the car is stationary in neutral at idle and then again at 3000rpm?

[Karl996]

This might sound stupid, given how much effort you've put in, but have you checked tyre pressure.

When I changed my tyres the shop put the rears to 36. When I checked them they were in the low 30s. Set them at 40psi for now and the rumble is so much better.

Even the wife noticed it.

[marksawtell]

what Dennis C and Logray say makes sense ... i doubt the engine/transmission mounts have ever been changed and after 180k they have to be close to their life expectancy lol

I was stuck in traffic the other day and was convinced i was getting the shaking at idle and t 3000 rpm as logray suggests. I dont know exactly what the tyre pressure should be, im running 275/30 zr19 on the back but had these brand of tyres since i changed to to the aftermarket wheels about 4 years ago and always bought them from the same place and never had an issue until a few months ago, so i dont think its tyre pressure.

Well at 180k, replacing all the above stuff wont of done it any harm, ive got rid of plenty of squeeks and the car drives tightly. I will get some engine mounts today as they look easy to replace and then do the transmission ones after that.

Ill let you know how i get on...

[whall]

Is there a chance that one of your (front) wheels might be slightly bent?

Bill

[JFP in PA]

I would also be one for looking very closely at the engine mounts............

[marksawtell]

Bingo!! Ok got hold of two engine mounts, when I took the old ones off, I noticed one was cracked all the way around the bolt and was leaking oil ( I am assuming there is oil in the engine mounts)

Replaced and voila , no more shaking or rumbling !!!!

Many thanks everyone :-) I think I still shake personally from the continual shaking but the car is now sweet, took it for a drive this morning and fell back in love with my car lol

[logray]

LOL. Nice work... :)

[marksawtell]

yeah thanks again logray :-) I have taken a pic of the old engine mount which its a little hard to see the cracking all around the bolt, but you can hopefully see. Least now my teeth fillings will stop falling out !

[phillipj]

I think Logray should get a raise.... :thumbup:

[Loren]

JFP in PA solved this mystery +1 on his reputation!

[Dennis C]

Glad it worked out for you!

[marksawtell]

yes thank you to everyone :-) had a nice long drive today to essex and back from surrey (in england) and it felt like the day i first picked it up :-) im back to enjoying the car again and counting myself lucky .... until the next thing goes wrong lol

[logray]

Heh, thanks Phillip, but I think the credit goes towards post #2... :)