Vibration at 60mph

[philly029]

I have an 83 GT, 5 speed. The car is nice and smooth until I hit about 60-65 mph no matter what gear I'm in, then I start feeling a vibration. It still does it if I push in the clutch and put it in nuetral. I indexed my driveshaft 180 degrees and it still does it but it seems to have smoothed it out a little. I had new front tires put on hoping that might be the cause because they were shot anyway. I can feel it in my shifter and can hear a slight hum also. Any ideas anyone?

Thanks

 

[fordman54935]

Maybe its possible it is the rear wheels that are causing the problem?

If the steering wheel shakes, it almost always means an out of balance front wheel/tire.

If you can feel the vibration more in the seat, floor, or shifter, it is possible that the rear tires are causing it.

Hope this helps!

 

[philly029]

I'm not really feeling it in the steering wheel but I do feel it in the shifter. Should I have my rear tires rebalanced? What if it still does it?

 

[Legendary]

I had the same problem on the freeway. Shaking through the shifter even in nuetral. I put in an aluminum driveshaft and the problem went away. But I think it was my 373 gears causing the extra shaking.

 

[Stump1000]

Check your exhaust from your h pipe all the way back. I've seen them real close to the car or the cross member and when your driving it hits, makes an awful noise and feels like a vibration

 

[Mavrick]

I'd get all your wheels balanced...

 

[cjman15]

Check your exhaust from your h pipe all the way back. I've seen them real close to the car or the cross member and when your driving it hits, makes an awful noise and feels like a vibration

^^ I think that's how mine is too... my car will get very loud and shaky when I hit freeway speeds of 65+... i know it's not my tires tho, i just got new ones and they were balanced and aligned properly...

I'd say make sure all your tires are aligned and balanced, then if it's still real bad, check the exhaust

 

[philly029]

Ok, I'll try to get the rear tires balanced first, If that doesn't do it I'll try the driveshaft.
Thanks for the quick replies. If any one else has any ideas, please let me hear them.
Thanks again.

 

[cb18201]

bad u-joints cause that, also with different gears that can cause your u-joints to die on you and cause that bad shaking. ide check that out.

 

[shinysideup]

just go faster ! who lives @ 60? cruise @ 80! and BALANCE THE TIRES! DOH!!!!

 

[MrKwik]

I can prety much guarantee its the 4.10 gears causing the vibration if you are using the stock driveshaft. Put in the FMS aluminum shaft and the problem will go away. Every mustang I have had with deep gears has had this issue and that fixed it every time. The shaft will come with the yokes and new ujoints all assembled and ready to bolt in for about $160.

 

[gt90stang]

Hi,

First read this:

http://home.hiwaay.net/~ctfrench/Driveline Vibration.htm

You can index the driveshaft rear each 45* and the front can be indexed as well. Try this before buying a new shaft as it might get worse with a perfectly balanced DS.

Good Luck, Don

 

[v8only]

Another vote for the alum driveshaft/

FYI, prices went up guys, the alum ones are now $250 across the board. Summit may have some left at the older price, but I don't think so.

 

[philly029]

Ok, I indexed the driveshaft 180 degrees, it didn't stop the vibration but it made the vibration start at like 65 mph and it seemed to be slightly diminished. Am I on the right track? Should I try indexing it at 45 or 90 degree steps?

I'll keep everyone up to date.

 

[85GTlover]

Ok, I indexed the driveshaft 180 degrees, it didn't stop the vibration but it made the vibration start at like 65 mph and it seemed to be slightly diminished. Am I on the right track? Should I try indexing it at 45 or 90 degree steps?

I'll keep everyone up to date.

Can you tell me the size and what you call the socket that takes those driveshaft bolts out? Is it 12 point 12mm?

 

[gt90stang]

Yes, it is 12mm 12 pt. I could only get a socket on mine when the axle was lowered and the body was supported on jack stands. Also, if you have to try 45* increments then you'll probably need a tap to clean out the normally unused holes it is a 12mm x 1.75 tap.

For testing for vibs it is easier to make an extension bar that fits a 12mm box end wrench. Then just tighten the bolts enough for a short test, but not full torque.

My SOP testing got to where it was hard to tell what was best. So I got a K&K Music Big Shot musical instrument pickup ($40) and mounted it on my console inside the car. Then I connected my 1/3rd Octave Real Time Audio Analyzer to it and could easily see the effects changes made. This was a poor mans version of a driveline vibration analyzer. I would start the car and get into 3rd gear and then hit peak hold on the RTA. Then slowly accelerate up to 70 MPH, then I would lock the data for analysis.

I found that I had two issues, one at 47 MPH and one at 57 MPH. I was able to minimize the vib at 47 MPH one with a hose clamp on the flange. This pretty much cancelled my 0.002" flange runout. I think the 57 MPH vib which isn't too bad is due to the flange runouts effect on the driveshaft and I don't know how to fix it to make it perfect, but it is way better than the initial install.

Good Luck, Don

 

[carphreak2356]

Im going with the croud and going to have to tell you to ballance your tires, tell whomever does it to do a road force ballance, if they dont have the proper equipment to do that, leave. The road force balance will tell you if your tires are not balancable, it can also tell you rim runoff and if it is your rims setting your wheels out of balance. 2 new tires would never hurt, but a road force ballance of your tires would be my suggestion. if not, have your driveshaft ballanced at a machine shop somewhere near you, they can do it fairly cheap. if your driveshaft is out of balance you can go right ahead and buy an alluminum drive shaft, OR just have your old one balanced. this should all be a little easier than keep indexing your driveshaft.