Huge vibration with RPM

[econti]

Today I swapped in my old diff to try eliminate another problem.
Now the swap is done, I suddenly have a huge vibration through the whole car that is related to engine RPM. Feels like someone fitted solid steel engine mounts and didn't tell me.
I checked all the obvious places, the engine and box mounts are fine, strut brace is not contacting the manifold, etc etc.
Has anyone else had this problem?

[Gunner_1886]

As in, the vibration is there through the whole RPM range?

[roguetoaster]

Perhaps you damaged your driveshaft or center bearing when you were removing/installing the diffs? Did either diff get hung up on the DS?

You should also check bolt torque again for everything you had on/off.

What were you trying to solve with the swap anyway?

[econti]

As in, the vibration is there through the whole RPM range?

Yes. It's pretty bad at idle, and gets worse with higher RPM.
Oddly enough it was less bad once the car was warmed up.

Perhaps you damaged your driveshaft or center bearing when you were removing/installing the diffs? Did either diff get hung up on the DS?

You should also check bolt torque again for everything you had on/off.

What were you trying to solve with the swap anyway?

Nope, didn't get hung up. Had it sitting on the jack the whole time.

I was trying to solve the problem of the car not holding sideways... No seriously the unis/CSB had so much play that you wouldn't believe it. The inner and outer parts of the old CSB just separated completely when I put slight pressure, and the unis were binding something shocking. Lots of clunks from them, it was just bad all round

[roguetoaster]

Yes. It's pretty bad at idle, and gets worse with higher RPM.
Oddly enough it was less bad once the car was warmed up.

Nope, didn't get hung up. Had it sitting on the jack the whole time.

I was trying to solve the problem of the car not holding sideways... No seriously the unis/CSB had so much play that you wouldn't believe it. The inner and outer parts of the old CSB just separated completely when I put slight pressure, and the unis were binding something shocking. Lots of clunks from them, it was just bad all round

If the vibration is there at idle it isn't the diff or CSB. Better when warm almost always means engine.

Any chance of a video?

[DER E30]

You're sure the motor didn't break the motor mounts off the subframe? Mine did something similar, it was the oil pan sitting on the steering rack...

[econti]

Solved!
Let me explain....

It turns out that medium and small case diffs have very slightly different snout lengths, somewhere around 5mm I would estimate.
When I swapped back to the small case, I did not know this, and so didn't adjust the driveshaft length to suit.

I don't know what trickery it caused, but extra length was provided by the flex disc flexing.
I took the 4 nuts that join diff snout to d/s, and let it sit how it wanted, and no more vibration.
2ez

[varg]

That's a concern I have with my eventual medium case diff upgrade, my drive drive shaft will not collapse at the splines at all. Even tried persuading it with a dead blow mallet, wouldn't budge. Rear u-joint is a little notchy too.

[econti]

That's a concern I have with my eventual medium case diff upgrade, my drive drive shaft will not collapse at the splines at all. Even tried persuading it with a dead blow mallet, wouldn't budge. Rear u-joint is a little notchy too.

Replace it all, don't fuck around. The spline lock thing is cheap.
Mine was really stuck on too, so I stuck the end of the shaft in a vice, used lots of penitrating fluid and some vice grips as I didn't have a spanner big enough.

[roguetoaster]

I still don't see how that slip joint not being adjusted down caused a vibration at idle.

In any case, if you need to remove the sleeve for the slip joint I sometimes use these:

[pandaboo911]

Huge vibration with RPM

My driveshaft doesn't even have the slip joint nut. Don't need it cause the driveshaft is fully compressed.

My car is swapped but still no vibration.

Vibration will be axles, diff mount, diff flange, csb, or the driveshaft itself.


Sent from my iPhone using Tapatalk

[econti]

I still don't see how that slip joint not being adjusted down caused a vibration at idle.

Neither do I. Maybe it pulled the engine and box back far enough that it was contacting something?
Mystery. At least it's gone.