Vibration from driveshaft
 

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?

Re: Vibration from driveshaft
 

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

Re: Vibration from driveshaft
 

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...

Re: Vibration from driveshaft
 

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?

Re: Vibration from driveshaft
 

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

Re: Vibration from driveshaft
 

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

Re: Vibration from driveshaft
 

Maybe the bolts are still there in the center but it is so rusted out it isn't truly attached. If you are able to see it doing it I would look at the part that is coming down the most it should give you the most indication that if it drops down far enough to see it is going up far enough to hit? How are you differential bushings? It may be rockin' if it isn't in there tight. May as well check you rear trans mount too.

Re: Vibration from driveshaft
 

So I checked the rear cross member mounts and found that the 'rubber stopper' was a little worn. Also the rear differential bushings are shot, but they always kinda were... This drive shaft vibration seems to have pretty much destroyed what was left of them. So I guess I'll replace these parts, but I a couple worn bushings doesn't seem to be enough to warrant such a violent vibration... I guess we'll see.

Re: Vibration from driveshaft
 

There doesn't seem to be any rust in the center attachment point. I'll have to check where the driveshaft is deflecting the most tomorrow. Thanks for the recommendations :)

Re: Vibration from driveshaft
 

Congratulations on your 4.44, definitely a lot of fun:D

Maybe it's the delay that is the problem. That would make more sense. Does anyone know if an svx on 4 jack stands is supposed to start with all wheels or do the front wheels start first, followed by the rears at a higher rpm?

Re: Vibration from driveshaft
 

does the power light flash? If I understand correctly the rear wheels kick in harsh and after moderate throttle application? your duty "C" solenoid might be sticking....if im way off its because I had too much vodka.

Re: Vibration from driveshaft
 

I think at lower gears and lower rpms all the wheels spin and as you go up in gears the fronts more so

Re: Vibration from driveshaft
 

So, I took off the rear transmission cross member and checked things out. I didn't find anything unusual, so I put it back together. I was going to bring it in to a shop (my very, very last resort), but I started it up and the vibration disappeared:D:D:D:D. No idea how, but whatever. There does seem to be a slight vibration driving, but that's probably because the rear differential bushings are completely gone now. Anyway, thanks guys for the help, I really appreciate it:)

Re: Vibration from driveshaft
 

My power light does flash, but it pulls the code for the dropping resistor. I haven't gotten around to getting one yet... Oh, and thanks for the cylinder heads a while back. That was awesome

Re: Vibration from driveshaft
 

the trans cross member can have some play where it connects to the transmission mount at the back end of the transmission. Especially the center stud it has a rubber bushing that can get loose and if all three aren't tight it will have plenty of play. You probably tighted it all up so thats good. There are a couple of options for the diff bushings depending on how worn out they are.