Vibration Problem

Sir Hacksalot · Apr 18, 2004

I recently upgraded to 4.10:1 gears, and that went smoothly, no gear whine, no problems, except this vibration I now get in 4th gear when the car hits 4500 rpms, and it stays all the way to about 5500 rpms. It does nothing of the sort in 1, 2, or 3 gears...in fact, it pulls nicely all the way to my 5500 rpm shift point, and when it had the old 2.73:1 gears, it never did it. I jumped on it a few times on the interstate, and the same thing...4500 rpms in 4th starts vibrating, and when I shift to 5th, it continues to vibrate until the rpms drop down below 4500.

I have put the car in neutral, and revved it up to 5500, and I get no vibration, so I am guessing that rules out the engine.

The car has a Ford Motorsports aluminum driveshaft. Could this be the culprit? Do they 'get out of balance', and can it be re-balanced by the appropriate shop?

Also, with 108K miles on the ticker, could this possibly be simply a sign that the transmission mount needs to be replaced?

I also have the following mods:

Eibach lowering springs
Tokico shocks and struts
Hotchkiss upper and lower control arms
Caster and camber plates
Catted X pipe
Cat back/Turbo mufflers
Under drive pulleys
Black Magic Electric Fan

Any advice on where to hunt down the source of the vibration would be welcome.

Thanks
Sir Hacksalot

HISSIN50 · Apr 18, 2004

your problem is quite common with gears, especially steep ones like you have. the driveshaft vibs are exacerbated. however you already have the normal fix (alum DS)..........i might call around for quotes to get the rotating assembly balanced (better to dynamically balance it on the car so the whole rotating mass can be taken into account and balanced, not just the DS).

i just got an alum DS, and it has some huge weights on each end. does yours have those (or is mine messed up from the factory?).

good luck.

87'GTstang · Apr 18, 2004

HISSIN50 said:
your problem is quite common with gears, especially steep ones like you have. the driveshaft vibs are exacerbated. however you already have the normal fix (alum DS)..........i might call around for quotes to get the rotating assembly balanced (better to dynamically balance it on the car so the whole rotating mass can be taken into account and balanced, not just the DS).

i just got an alum DS, and it has some huge weights on each end. does yours have those (or is mine messed up from the factory?).

good luck.

ditto!

Since you say it only happens at about 4th gear, think about the speed you're traveling to get in that gear, it's not RPM related but speed-related rather if you think about it (speed-related problem vibrations are 9/10 times unbalanced driveshaft or dirveshaft-related).

HISSIN50 · Apr 18, 2004

87GTstang, was the ditto remark aimed at you also having weights on the Alum DS, or that you agree with the sentiments i posted?
i just got this alum DS (before prices got too out of hand) and am trying to figure out if i should send it back. many thanks.

(Sir Hacksalot, sorry for the slight thread jack, but it keeps your thread fresh for new eyes to see).

87'GTstang · Apr 18, 2004

Ditto both ways. The problem with the driveshaft and the weights you are referring to. I have either 6 or 8 weights total on my driveshaft. Most are about 1/8" x 1" in size. Just because it's aluminum doesn't mean it's invisible to counter-weight problems. Although I got mine from the junkyard (the aerostar one).

HISSIN50 · Apr 19, 2004

87'GTstang said:
Ditto both ways. The problem with the driveshaft and the weights you are referring to. I have either 6 or 8 weights total on my driveshaft. Most are about 1/8" x 1" in size. Just because it's aluminum doesn't mean it's invisible to counter-weight problems. Although I got mine from the junkyard (the aerostar one).

thanks so much for the info!

Sir Hacksalot · Apr 20, 2004

HISSIN50 said:
your problem is quite common with gears, especially steep ones like you have. the driveshaft vibs are exacerbated. however you already have the normal fix (alum DS)..........i might call around for quotes to get the rotating assembly balanced (better to dynamically balance it on the car so the whole rotating mass can be taken into account and balanced, not just the DS).

There is a shop in Ankeny, IA that builds custom drive shafts, should they be able to balance this on my car if I go there? If so, any idea on what this should cost me.

i just got an alum DS, and it has some huge weights on each end. does yours have those (or is mine messed up from the factory?).

I did not see any weights on it.

I will make darn sure I pay a visit to this company to see about getting things balanced out.

Thanks for the info,
Hax

gt90stang · Apr 20, 2004

You need to read this:

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

Good Luck, Don

Sir Hacksalot · Apr 20, 2004

Thanks for the link, that was actually very very informative.

There is a shop not far from my house that specializes in driveshafts and gears, and may go pay them a visit.

Hax

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