Hey

Well after my t5 swap I noticed a vibration at high speeds well now Im fully aware of it or its gotten worse.

Everything is smooth under 80 mph/2500 rpm

Everything is smooth at any RPM under 75 so 1st at 5,000 is smooth and so it 4th at 3,000+

But as soon as I hit about 80 in 5th it gets bad and continues to get worse
Accelerating to those speeds in 4th also creates a vibration.

I can feel the vibration heavily in the pedals and shifter...also quite noticeable in the seat. I can hear parts of the car vibrate and a scary sound from somewhere near the trans or drive shaft tunnel sounds near the shifter. Im pretty sure the trans isnt touching the car I cleared a large hole in the tunnel for the shifter

OKAY here is the really important part: The vibration gets worse as soon as i back off the gas and then goes away as soon as speeds drops below 2500 rpm 80 indicated. If I accelerate smooth the vibration is not as bad (but gets worse with speed) but as soon as you back off the gas its like....Oh Sh$%

The drive shaft was cut 1" short and he said it balanced okay

Is there anything in the trans that would cause this or is this a drive line issue?

thanks

-Gun

 

I had the exact same thing after an engine/tranny swap....exact same symptoms...started at higher speeds, and got much worse when I let off the gas.

It turned out that I needed to lengthen the driveshaft a bit....it would reach the transmission, but the yoke didn't extend far enough onto the tailshaft. Got the correct driveshaft and the problem went away.

BTW it wasn't driveshaft balance we tried that, and the shop said it was balanced, they measured the length and diagnosed the problem pretty quickly.

 

check pinion angle. that would be my first thought if accellerating feels better than decellerating.

 

good thought.
if car is sitting normal on ground the T5 yoke should show about 3/4". more will cause vibrations and wear out
(info moderndiveline.com)

 

Yeah, he did say something about the pinion angle, too. Whatever the issue we resolved my problem with a different length driveshaft, which changed the angle between the yoke and the shaft allowing the u-joint to turn more smoothly. I know we didn't change the pinion angle of the rear axle, but that could be one way to solve it.

Let us know what you find out.

 

LOL we're posting at same time it seems ...

 

Yeah, except I'm at work.[:@]

 

oh man you gotta be kidding me. [:@]

If the there is more than 3/4" gap between the yoke and trans it vibrates at high speed? WTH I didnt think the gap was that critical I though it was like .5" to 2"

ill get an exact measurement here in a while.

I think pinion angle is good it looks like a straight line to me ill take a pic of that too when im down there.

-Gun

 

Actually, it doesn't matter how much angle the U-joints have on them (as far as vibration is concerned). The angle that matters is the difference between the trans output and the pinion angle on the rearend. They need to be within 2 degrees of each other so that the angles can cancel each other out and eliminate any driveline vibrations. I prefer that the pinion be 1 degree less than the transmission ouput beacuse when you are on the gas (which you are 85% of the time) the angle will be perfect, but when you coast, it will still be within limits. I know my driveshaft is out of balance. I had the trans rebuilt a few years ago (before the 347 was even dreamed about) and at that time, I put in2 new u joints. Ever since then I have had a vibration. It isn't too bad, untill the speedo hits about 115-120 (but in actuallity only going like 95 since my speedo is 20% off from the gear change). When you get moving that fast, the driveshaft is spinning roughly 5000 RPMs, and there is a VERY bad vibration. It's scary. However, It was never this bad before the rearend swap, but due to the higher gear that was in it, the driveshaft never turned that fast and the vibration was never that bad. So... I need to take it and have it balanced, but the only places around here to have it done are expensive and their work is often times crap. I had them build a shaft for me once and the damned thing was crooked. You could clearly see it with plain eyes. They didn't balance it either and then they charged me $190 for the work (they lengthened it by putting in a new tube). So Im not really sure what I am going to do. I thought about taking 4 or 5 hose clamps and putting aroundthe driveshaftand keep turning them little by littleuntill the vibration gets better. Maybe you should try this Gun...

 

Okay well here are some photos .

how do I check to see that pinion angle between output shaft and rear end? Is this horizontal or vertical angle?







-Gun