Vibration from driveshaft

ScottyB · #1 05-08-2010, 11:53 PM

So I replaced my transmission with ond from an outback with the 4.44 final drive. There was some problems with tranny fluid leaking due to old hoses, but now that's all fixed and the tranny seems to be running smoothly.

So this is what happens. The car's in the air on 4 jacks and when I put the car in drive and give it some gas the front tires start, then at some rpm the rear wheels engage the driveshaft jerks violently and bangs into the bottom of the car. After the initial jerk dampens out a little, the vibrations still continue. Everything I've looked up talks about the staked u-joints so I checked them. There didn't seem to be anything obvious but LAN said in some thread that you can't always tell until you take it out, so i did. There seemed to be an uneven spot on the u-joint closest to the rear diff. All the other rotations seemed fine, but I figured this uneven spot was causing the problem. I went to get another svx drive shaft, but the mechanic said mine seemed fine. He said it's normal for driveshafts get a flat spot like that and that the svx driveshaft he has looks and feels just like mine. So I put my drive shaft back in and the vibration's still there.

So what could it be? (And it wasn't doing this before I switched trannys)

Should I get the driveshaft tested by a driveline shop?

svxpert · #2 05-09-2010, 08:50 AM

Quote:

Originally Posted by ScottyB

then at some rpm the rear wheels engage the driveshaft jerks violently and bangs into the bottom of the car.

did you bolt the center carrier bearing to the correct position under the car?

ScottyB · #3 05-09-2010, 10:09 AM

Quote:

Originally Posted by svxpert

did you bolt the center carrier bearing to the correct position under the car?

Yeah, it's in there right with the bulk of the carrier in the groove along the underside. I guess you could put it in two different ways, but the other way wouldn't let the exhaust fit...

svxpert · #4 05-09-2010, 06:36 PM

which part of the driveshaft slams into the underside of the car? if its bolted up in the center and the 4 bolts are connected to the rear i dont see how it can be hitting the underside? any pics?

ScottyB · #5 05-09-2010, 09:47 PM

I'll put up a video when I get a chance... it's finals week=). It's splined on the tranny, carrier bearing is bolted in, and the 4 bolts are attaching the shaft to the rear diff... It shouldn't move, but it does. I looked at the underside from a distance as my brother applied the gas and I could see the whole driveshaft buck and the diff jump a little... Hopefully tomorrow I'll get that video up

Quote:

Originally Posted by svxpert

which part of the driveshaft slams into the underside of the car? if its bolted up in the center and the 4 bolts are connected to the rear i dont see how it can be hitting the underside? any pics?

gbianchi · #6 05-10-2010, 10:50 AM

Is the rear end also 4.44, sorry if it is but I know just enough to get into trouble. I swapped trannys and rear ends and all is well, don't know what would cause the rear wheels to be delayed from spinning right away in 1st gear as mine did, good luck ....G