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  #1  
Old 05-08-2010, 11:53 PM
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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?
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Old 05-09-2010, 08:50 AM
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Re: Vibration from driveshaft

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Originally Posted by ScottyB View Post
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?
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Old 05-09-2010, 10:09 AM
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Re: Vibration from driveshaft

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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...
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Old 05-09-2010, 06:36 PM
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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?
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Old 05-09-2010, 09:47 PM
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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



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Originally Posted by svxpert View Post
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?
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Last edited by ScottyB; 05-09-2010 at 11:55 PM.
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Old 05-10-2010, 10:50 AM
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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
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Old 05-10-2010, 04:27 PM
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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.
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Old 05-14-2010, 09:10 PM
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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.
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Old 05-14-2010, 09:15 PM
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Re: Vibration from driveshaft

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Originally Posted by sowise View Post
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.

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
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Old 05-14-2010, 09:20 PM
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Re: Vibration from driveshaft

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Originally Posted by gbianchi View Post
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
Congratulations on your 4.44, definitely a lot of fun

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?
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Old 05-14-2010, 11:14 PM
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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.
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  #12  
Old 05-15-2010, 08:14 PM
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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
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Old 05-15-2010, 09:34 PM
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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. 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
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Old 05-15-2010, 09:36 PM
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Re: Vibration from driveshaft

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Originally Posted by SomethingElse View Post
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.
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
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Old 05-16-2010, 07:15 AM
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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.
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