Drive train vibration

I have a new vibration coming from the drive train of my 88GT. Symptoms
a Vibration occurs at speeds over 45mph, gets louder as the vehicle is
placed under load, doesn't seem to change with engine rpm, stops when
vehicle is coasting clutch engaged, comes back when clutch is depressed at
speed.
Out of balance tires would vibrate regardless of the clutch being in or out,
so I'm looking for something in the drivetrain. It could be the U joints I
suppose but I've never had any fail like this before. It could be an out of
phase (miss aligned) drive shaft but what would cause it to shift after
almost 300,000 miles of operation? The rear axle bearings have never been
replaced, but then wouldn't the vibration be present at all speeds? Right
now I'm just looking for a good starting point.

Ironrod wrote:
> I have a new vibration coming from the drive train of my 88GT. Symptoms
> a Vibration occurs at speeds over 45mph, gets louder as the vehicle is
> placed under load, doesn't seem to change with engine rpm, stops when
> vehicle is coasting clutch engaged, comes back when clutch is depressed at
> speed.
> Out of balance tires would vibrate regardless of the clutch being in or out,
> so I'm looking for something in the drivetrain. It could be the U joints I
> suppose but I've never had any fail like this before. It could be an out of
> phase (miss aligned) drive shaft but what would cause it to shift after
> almost 300,000 miles of operation? The rear axle bearings have never been
> replaced, but then wouldn't the vibration be present at all speeds? Right
> now I'm just looking for a good starting point.

With 300K miles on the odometer it could be anything. If it has the
original U-joints in it then that is the first place I would check.

"Michael Johnson" > wrote in message
...
> Ironrod wrote:
>> I have a new vibration coming from the drive train of my 88GT. Symptoms
>> a Vibration occurs at speeds over 45mph, gets louder as the vehicle
>> is
>> placed under load, doesn't seem to change with engine rpm, stops when
>> vehicle is coasting clutch engaged, comes back when clutch is depressed
>> at
>> speed.
>> Out of balance tires would vibrate regardless of the clutch being in or
>> out,
>> so I'm looking for something in the drivetrain. It could be the U joints
>> I
>> suppose but I've never had any fail like this before. It could be an out
>> of
>> phase (miss aligned) drive shaft but what would cause it to shift after
>> almost 300,000 miles of operation? The rear axle bearings have never
>> been
>> replaced, but then wouldn't the vibration be present at all speeds?
>> Right
>> now I'm just looking for a good starting point.
>
> With 300K miles on the odometer it could be anything. If it has the
> original U-joints in it then that is the first place I would check.

And the slip yoke at the rear of the transmission. Explain this: >>stops
when
>> vehicle is coasting clutch engaged, comes back when clutch is depressed
>> at
>> speed.

If you're driving at the speed it vibrates and you press the clutch or put
the transmission in neutral, and let the engine idle, does the vibration go
away?

Al

"Big Al" > wrote in message
...
>
> "Michael Johnson" > wrote in message
> ...
>> Ironrod wrote:
>>> I have a new vibration coming from the drive train of my 88GT. Symptoms
>>> a Vibration occurs at speeds over 45mph, gets louder as the vehicle
>>> is
>>> placed under load, doesn't seem to change with engine rpm, stops when
>>> vehicle is coasting clutch engaged, comes back when clutch is depressed
>>> at
>>> speed.
>>> Out of balance tires would vibrate regardless of the clutch being in or
>>> out,
>>> so I'm looking for something in the drivetrain. It could be the U
>>> joints
>>> I
>>> suppose but I've never had any fail like this before. It could be an
>>> out
>>> of
>>> phase (miss aligned) drive shaft but what would cause it to shift after
>>> almost 300,000 miles of operation? The rear axle bearings have never
>>> been
>>> replaced, but then wouldn't the vibration be present at all speeds?
>>> Right
>>> now I'm just looking for a good starting point.
>>
>> With 300K miles on the odometer it could be anything. If it has the
>> original U-joints in it then that is the first place I would check.
>
> And the slip yoke at the rear of the transmission. Explain this: >>stops
> when
>>> vehicle is coasting clutch engaged, comes back when clutch is depressed
>>> at
>>> speed.
>
> If you're driving at the speed it vibrates and you press the clutch or put
> the transmission in neutral, and let the engine idle, does the vibration
> go
> away?
>
> Al

I have a 93 that driveshaft(?) vibes at about 70 and goes way with clutch
disengaged, engine idle.
Does it in 4th and 5th gear at about 65 to 75
Where is the slip yoke ?

"Big Al" > wrote in message
...
>
> "Michael Johnson" > wrote in message
> ...
> > Ironrod wrote:
> >> I have a new vibration coming from the drive train of my 88GT.
Symptoms
> >> a Vibration occurs at speeds over 45mph, gets louder as the vehicle
> >> is
> >> placed under load, doesn't seem to change with engine rpm, stops when
> >> vehicle is coasting clutch engaged, comes back when clutch is depressed
> >> at
> >> speed.
> >> Out of balance tires would vibrate regardless of the clutch being in or
> >> out,
> >> so I'm looking for something in the drivetrain. It could be the U
joints
> >> I
> >> suppose but I've never had any fail like this before. It could be an
out
> >> of
> >> phase (miss aligned) drive shaft but what would cause it to shift after
> >> almost 300,000 miles of operation? The rear axle bearings have never
> >> been
> >> replaced, but then wouldn't the vibration be present at all speeds?
> >> Right
> >> now I'm just looking for a good starting point.
> >
> > With 300K miles on the odometer it could be anything. If it has the
> > original U-joints in it then that is the first place I would check.
>
> And the slip yoke at the rear of the transmission. Explain this: >>stops
> when
> >> vehicle is coasting clutch engaged, comes back when clutch is depressed
> >> at
> >> speed.
>
> If you're driving at the speed it vibrates and you press the clutch or put
> the transmission in neutral, and let the engine idle, does the vibration
go
> away?
>
> Al
>
>
>
Yes that is exactly what happens, foot on gas car vibrates, foot off gas
(car still moving) vibration clears, foot on clutch car starts to vibrate
again. I'm starting to think it might be the motor mounts.

"biggus" > wrote in message ...
>
> "Big Al" > wrote in message
> ...
> >
> > "Michael Johnson" > wrote in message
> > ...
> >> Ironrod wrote:
> >>> I have a new vibration coming from the drive train of my 88GT.
Symptoms
> >>> a Vibration occurs at speeds over 45mph, gets louder as the
vehicle
> >>> is
> >>> placed under load, doesn't seem to change with engine rpm, stops when
> >>> vehicle is coasting clutch engaged, comes back when clutch is
depressed
> >>> at
> >>> speed.
> >>> Out of balance tires would vibrate regardless of the clutch being in
or
> >>> out,
> >>> so I'm looking for something in the drivetrain. It could be the U
> >>> joints
> >>> I
> >>> suppose but I've never had any fail like this before. It could be an
> >>> out
> >>> of
> >>> phase (miss aligned) drive shaft but what would cause it to shift
after
> >>> almost 300,000 miles of operation? The rear axle bearings have never
> >>> been
> >>> replaced, but then wouldn't the vibration be present at all speeds?
> >>> Right
> >>> now I'm just looking for a good starting point.
> >>
> >> With 300K miles on the odometer it could be anything. If it has the
> >> original U-joints in it then that is the first place I would check.
> >
> > And the slip yoke at the rear of the transmission. Explain this: >>stops
> > when
> >>> vehicle is coasting clutch engaged, comes back when clutch is
depressed
> >>> at
> >>> speed.
> >
> > If you're driving at the speed it vibrates and you press the clutch or
put
> > the transmission in neutral, and let the engine idle, does the vibration
> > go
> > away?
> >
> > Al
>
> I have a 93 that driveshaft(?) vibes at about 70 and goes way with clutch
> disengaged, engine idle.
> Does it in 4th and 5th gear at about 65 to 75
> Where is the slip yoke ?
>
>
It's the part of the drive shaft assembly between the front U joint and the
rear of the transmission. As the rear suspension moves throughout its range
of motion the distance between the differential and the trans changes, the
slip yoke accommodates the changes by sliding in and out of the transmission
on splines.

"Ironrod" > wrote in message
...
>
> "Big Al" > wrote in message
> ...
>>
>> "Michael Johnson" > wrote in message
>> ...
>> > Ironrod wrote:
>> >> I have a new vibration coming from the drive train of my 88GT.
> Symptoms
>> >> a Vibration occurs at speeds over 45mph, gets louder as the
>> >> vehicle
>> >> is
>> >> placed under load, doesn't seem to change with engine rpm, stops when
>> >> vehicle is coasting clutch engaged, comes back when clutch is
>> >> depressed
>> >> at
>> >> speed.
>> >> Out of balance tires would vibrate regardless of the clutch being in
>> >> or
>> >> out,
>> >> so I'm looking for something in the drivetrain. It could be the U
> joints
>> >> I
>> >> suppose but I've never had any fail like this before. It could be an
> out
>> >> of
>> >> phase (miss aligned) drive shaft but what would cause it to shift
>> >> after
>> >> almost 300,000 miles of operation? The rear axle bearings have never
>> >> been
>> >> replaced, but then wouldn't the vibration be present at all speeds?
>> >> Right
>> >> now I'm just looking for a good starting point.
>> >
>> > With 300K miles on the odometer it could be anything. If it has the
>> > original U-joints in it then that is the first place I would check.
>>
>> And the slip yoke at the rear of the transmission. Explain this: >>stops
>> when
>> >> vehicle is coasting clutch engaged, comes back when clutch is
>> >> depressed
>> >> at
>> >> speed.
>>
>> If you're driving at the speed it vibrates and you press the clutch or
>> put
>> the transmission in neutral, and let the engine idle, does the vibration
> go
>> away?
>>
>> Al
>>
>>
>>
> Yes that is exactly what happens, foot on gas car vibrates, foot off gas
> (car still moving) vibration clears, foot on clutch car starts to vibrate
> again. I'm starting to think it might be the motor mounts.
>
>

Next time shut the engine off. That will end anything connected to the
engine. Be careful, you will not have power steering, and if you use the
brake, power braking will go away too. Just push in the clutch and shut the
key off. Don't lock the wheel Let the clutch out to start he engine.

Al