88 GT hatch 5.0 manual Vibration

boatjunkie · Oct 11, 2011

Hi all, been lurking for a while and have not found answers so here goes.

88 GT hatch 5 speed manual all STOCK 125K miles, all original never in accident, cherry!. I am 2nd owner.

I have a vibration that is related to speed. Kicks in about 65 MPH then really takes off at 75 MPH and up. its not in the steering wheel or the brake and brakes dont make a difference. the car just shakes like mad. following symtoms.

Vibrates when cruising at 75 MPH plus
When in the gas or off. Even with tranny in nuetral and engine idling when doing 75 MPH or higher.
Can reproduce at same speed in 4th or 5th gear.
Following has been done to the car in the last 2 weeks to stop the vibration...
complete tune up
New tires, balanced 2x's
New Aluminum DS and ujoints from Summit
New front Struts
New rear shocks and quad shocks
New Axle bearings
New Pinion bearings
Straight edged Axles they are not bent
very little play in tranny at shaft
Rotors cut
Front bearings good

I have a 92 LX 5.0 auto Vert with 40K miles that i swapped the following with
Tires and rims
Rear Drums

Still vibrates.. Balancer is in good condition and no vibration at idle or at same RPMS as 75 MPH.. besides I would think that if it was the balancer it would stop when i put in nutral and idle at 75 MPH.

Today the seal on the pinion shaft came out. It had about 200 miles on it since i did the bearings... SO my guess is this vibration knocked it loose??? I put it back in and when i turn the Drive shaft the seal turns with it...

So any ideas? I also do not have a dampner on the Tranny or the Axle (dog bone)

Help? I am ready to crush this car. use it as a daily driver on the highyway... After an hour on the road my but is numb from the vibration.

hoopty5.0 · Oct 11, 2011

My car did that once, it turned out to be the 4 bolts on the rear of the driveshaft were loose.

foxbodymike87 · Oct 11, 2011

ever try an alignment?

MAC'n89Blckstng · Oct 11, 2011

try the bushing thats in the tailshaft housing. I had a vibration and it was from that. does it still do it at speed when the clutch is pressed? that sometimes takes the load off the drivetrain and lessons a vibration.

boatjunkie · Oct 11, 2011

Yes, with cluth in or in nuetral still there no difference.

No i have not done alignment but will consider it.

boatjunkie · Oct 12, 2011

Ok put in the new pinion seal and borrowed the dog bone from the 92 LX vert and put on the 88. No difference, vibration is still there

. Stock 2.73 gears....

wythors · Oct 12, 2011

Points to ponder:

Since the vibration is constant when you put in the clutch, the engine/balancer can be ruled out.

Can you tell if the vibration is coming from the front or the back?

Do you feel it more in the steering wheel or your butt?

Can you feel it more in the shifter than anyplace else?

Does it do it in both 4th and 5th in that speed range, or is it rpm-related in those two gears?

boatjunkie · Oct 12, 2011

hard to tell if front or back, the whole car kinda vibrates, dashboard all the way back to the retractable cover under the hatch.

Nothing in the wheel
Nothing in the shifter handle (stock)
mostly in the but. it does not seem to be side to side, more up and down. and have swapped tires and rims..

4th and 5th gear, same speed range. when put in nuetral and rpm at idle 800 to 1000 when coasting at 75 mph its still there, not a difference at all until she slows down under 65 mph then goes away. could probably duplicate in 3rd..

I have also checked the ground effects to make sure none were loose and flapping around.

car tracks straight as an arrow. was going to check ball joint this weekend. its driving me nuts. i am a former certified ford mechanic from back in the mid 80s... I also had a 1987 GT hacht manual and never had this issue.
Thanks for trying to help out

wythors · Oct 12, 2011

If you don't feel it in the shifter and it does it in both 4th and 5th, I think you can rule out anything transmission related.

You'd feel a major balljoint problem very distinctly through the steering wheel, rather than an all over vibration. I would guess that it is rear end related. Try finding a friendly shop with a drive on lift and run it with the rear axle supported in the on the ground position. You should be able to see if it's coming from the rear that way.

S&B · Oct 12, 2011

why dont you jack the car up and get it up to speed that will rule out the front and let you see what is making the vibration. Now it will not be under load like driving on the street but when I had a vibration we did this and it ended up being a back tire that was balanced but must have had a slipped belt or something

black87ttop · Oct 12, 2011

I'm gonna say it's a bad pinion bearing...thus causing the piniob seal to pop...that's a common trait on 8.8' s , when pinion bearing hoes it causes seal to be wore inccorrectly and they pop...just my guess...i def put all my chips on s rear problem tho..

black87ttop · Oct 12, 2011

Scratch that I missed that you replaced the pinion bearings..hmmm... Did it do this before you touched rear? If you did this to remedy the problem than fine, but if you had the rear work done at Dj earlier time for maintenance than I would bet that the bearing was the culprit..

boatjunkie · Oct 12, 2011

Yes, the vibration was there before the rear was touched. repalced axle bearings 1st, then heard the wine in the pinion and replaced that also. Will jack it up and put the rear on stands and bring her up to speed and take a look. need to get another person to give me a hand. stay tuned.

in the mean time, keep the ideas comming i promise when i find it i will post so others can resolve this issue in the future.

91TwighlightGT · Oct 13, 2011

Maybe you have a bent wheel?

boatjunkie · Oct 13, 2011

91TwighlightGT said:
Maybe you have a bent wheel?

Swapped all 4 wheels from my 92 LX 5.0 vert. did 2 at a time, then did all 4 still no difference. Tires were remounted and balanced 2 x's.

oldfox · Oct 14, 2011

pinion angle will do this. The angle of the drive shaft coming out of the transmission must match the angle of the drive shaft entering the rear end
or they will bind. The worse the misalignment the the worse the vibration
at lower speeds. Check the rear transmission mount and see if it looks
squashed down. Even if it looks good try and raise the rear of the transmission (few washers) and see if the vibration changes.
In 30 years of messing with hot rods I have only seen this twice.
But it might be worth a shot.

I had a car that drove me nuts trying to find a vibration something like your
car. I had eliminated the engine and rear end and drive shaft.
Out of desperation we pushed the car down the expressway with a tow truck
with no drive shaft at about 75 the vibration was gone but I had already
replaced the drive shaft with a new one. I tried a different drive shaft and had the same problem. At the time I worked at a AMC dealership an old guy there (Bill) told me and showed me how to set it correctly

If you look at the trucks that are jacked up real high you will see that they
rotate the the rear end to match the transmission.
Hope this helps.
If all else fails pushing the car with no drive shaft and the engine not running
will at least let you know which end the problem is in
I hope this helps
the washer trick will let you know quick and easy.

foxbodymike87 · Oct 14, 2011

If this helps any, tells you how to measure your pinion angle.

Pinion Angle - Wolfe Race Craft

boatjunkie · Oct 14, 2011

oldfox, i will give it a try. So is the trick to get the drive shaft as straight as possible in a line with the diff and output at the tranny flange? the link below says 0 angle if possible. Or do i need to get the same angle to match at both ends.

Thanks for the washer idea. i will give i a try tomorrow and let you know how i make out.

i did put the axle on jack stands and had the wife hold here steady at 75 mph and there was no visible or feeling of vibration. I also sat in the car at 75 mph on the stands and nada... hope it just needs a load on it to get the vibe.

oldfox · Oct 14, 2011

boatjunkie said:
oldfox, i will give it a try. So is the trick to get the drive shaft as straight as possible in a line with the diff and output at the tranny flange? the link below says 0 angle if possible. Or do i need to get the same angle to match at both ends.

Thanks for the washer idea. i will give i a try tomorrow and let you know how i make out.

i did put the axle on jack stands and had the wife hold here steady at 75 mph and there was no visible or feeling of vibration. I also sat in the car at 75 mph on the stands and nada... hope it just needs a load on it to get the vibe.

I think it was same angle on both
Let us know what you find

S&B · Oct 14, 2011

maybe its something on the front ???

88 GT hatch 5.0 manual Vibration

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