billtool

Just started this passed weekend. At about 1500 rpm I get a rumbling sound/feel as if I were driving on pavement grooving during road repair. Hit approx 2000 rpm and it goes away. Original motor mounts. Any thoughts?

IcemanG17

could be wheel balance

Dean_Fuller

feel is in the seat? or the steering wheel?

billtool

Definitely not in the steering wheel. Tires unbalanced would be a stretch. New wheels and tires balanced by a trusted shop.

Dean_Fuller

Did they say anything about the front wheel bearing being loose? See what kind of "play " you get when the front is lifted? Tires wearing okay???

Although this would be felt I think in the steering as well....

Can you tell if its from the front or maybe the rear???

MM would never hurt replacing.

Lizard928

Replace the motor mounts and consider a tune up.

I have that in the 928 that I just got too, and it feels like shot mounts to me.

billtool

I'll get it on the jack stands tomorrow and give the tires a good shaking. I've put about 500 miles on the tires and just now noticed this issue. I'll closely check the wear as well. It's got about 58K on the MM's. I fear that's my issue. I guess while it's up I'll check if the pan is resting on the crossmember.

Dean_Fuller

I just replaced a REAR wheel bearing. It made noise at about 2000 RPM and got worse as speed increased. If I remember correctly not a lot of vibration though.

MM may very well be the problem and would be a lot better than TT bearing. Sorry...I said it.

Lizard928

it will not need to be resting on the cross member to make this grumble....

Mrmerlin

while you have the car up in the air check the exhaust manifolds where they pass the side braces, worn mounts will also drop the manifolds onto the braces and cause vibrations, this can also lead to manifold failure as the bellows will fracture

Landseer

Bill,

I had a very bad low vibration from 2000 to 3500, peaking about in the middle.

This is on the 84 with the Constantine and the 89 S4 auto box. Original 84 exhaust.

Sounded and felt like mounts.

Solved it yesterday, though. I had omitted the center hanger for the exhaust. Lazy.

This caused the entire exhaust to behave like some sort of low frequency tuning fork.

I found it when I switched exhaust systems.

jeff spahn

I would say motor mounts. I replaced mine with some of the defective lot from Roger. When they worked it was glass smooth. As they failed over a period of days/weeks it turned into what you describe. Changing them Saturday at the DFW get together.

Landseer

Interesting Jeff,
I've got one set of solids, out of four sets, that is settling ( its on this particular car / noticed it yesterday also ).
Can almost get my finger into the hook.
Pan is 5/8 inch below crossmember. Still have 1/2 inch before contact, though.
They probably have 2000 miles on them, but been holding the engine up for about a year.

billtool

I eliminated the middle rubber exhaust bracket as well last year when I installed the x-pipe. Completely forgot about it. Taking it for a spin now to get a better feel.

bigmac

Could a balance weight have been thrown?