Super hard vibration at 70 when letting off gas


New Member
Mar 31, 2008
Pretty much like the title says. I have a fresh rebuilt T-5 and rear end. This was happining before i did anything to the drivetrain and i figured it wouldnt happen anymore but it still does. What happens is once i get to over 60 if i dont have my foot on the gas the vibrations will surge untill it gets back down to 60 or i give it gas again the higher the speeds the harder the vibrations. I thought i had seen something about this in some fourms i dont know if it was this one or not. it even does it if im over 60 shifting out of 4th into 5th as long as im not giving it gas it will do this clutch in or out. Anyone have any ideas or this happen to them?
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Can you be more specific on rotating the driveshaft i cant do it at my place i live in a APT with no garage so im gonna have to take it to my my dads friends shop and i dont know if hes gonna charge me cause he is the one that put the rearend and new tranny in. It is a stock shaft.
Deffinetly check the bolts, but the DS might also be out of balance. I had this problem at 70mph (very very bad vibration) because my stock shaft threw a weight, so I decided to put an aluminum one on, and the problem is almost gone. It still vibrates some above 90mph, but I only ever went that fast once (I don't drag race), so I don't care. I figure the 3.73's were set-up incorrectly, but I'm not sure.

i have a VERY similar problem. my rearend was just recently gone thru with new ring/pinion, seals bearings, fluid, friction modifier and trak lok. i had my local ford dealership open the cover and check the tolerances. he said everything looked just fine.

i swapped out the transmission summer before last for a supposed 30,000 miles T5. i think it has issues but im not sure if this contributes to my vibration or not. i can run the car up to 60/70mph in 4th and let off and its fine. if i do that in 5th and let off, it vibrates :shrug:

when the ford dealership checked the rear, he noticed the DS was not in the factory correct position. apparently during the trans install and troubleshooting, it had gotten rotated . after he turned it ( rotating the bolt holes ), the vibration did get better but its still there. i asked about the u joints and he said they visually looked good and 'felt' good.

can u joints go bad and still appear to look ok?

mine only vibrates when i let off the gas in 5th gear running 65+. no noises, just vibration
Id recommend going to a dealership that has an electronic vibration analyzer. Theyll be able to go on a road test with you with the EVA going and it will pinpoint exactly where its coming from by the frequency and amplitude of the vibration. Every vibration has its own signature.
what is going on with our cars??? I just had my t-5 replaced and I am now having the same issue, but mine starts above 80-85 mph when I let off the accel. I replaced the u-joints and had a d/s vib and I figured out that I had re-installed the front yolk on the d/s 180* out. I took it out and re-installed the front yolk to line up with the marks I had orig put on and the vib during accel is 90%better but the decel vib concerns me.
i have a 2000 gt and its doing the exact same thing! only quits when i smash the pedal. and it really does it from about 50 mph +. let me know what you figure out, i was thinking that it might be the driveshaft too. all i know is that its a ****** to drive the car like that and is very annoying!