Hey guys, I just did a turbo swap in my 88 NA. The motor is a fresh built s5 turbo engine/flywheel and s4 turbo trans-back. After the swap, I had a bad vibration in the drivetrain. It's when I am accelerating in gear, worst from 2-3k, and doesn't do it as much when I clutch in. I put competition mounts from Mazda on the motor, trans, and front of diff. I had the turbo drivetrain on my NA, but with an s5 turbo trans, and it did not vibrate at all. Last night I replaced the trans crossmember and driveshaft. The new driveshaft still wasn't perfect, but it wasn't as notchy as my old one. I am beginning to think it is the trans, it looks like it is sitting crooked against the bell housing. It fell when the car was sitting with no engine and the front was held up on a jack stand. Someone pushed my car out of the way and the trans fell down. I also think it could be the competition mounts on the engine. Anyway, I appreciate any help in advance.

 

Check the u-joints on the driveshaft.

 

do you have more info on when it vibrates?
High speed?
idle?
in gear accelerating hard?

 

It does not really get worse the faster I go. It is just really bad around 2-3k rpm and only when driving, in gear, not at an idle.

As for the driveshaft, would the tiniest little notch in the u joint really cause that much vibration?

 

Tiny little notch's tend to become great big notch's sometimes quicker than you would expect.

 

In my experience, for a driveshaft to cause vibration, it has to be basically locked up at one end or the other. A little 'notch" in the joint is fairly normal for these.

If it is rpm dependent, it is in the engine, an engine accessory, clutch or input shaft of the trans. If it is speed dependent, it is in the back half of the trans or driveshaft/rearend/tires.

 

I agree completely, I do not see how so small of a notch could cause that vibration. If it is the engine do you think if I switched back to stock mounts it would help dampen it?

 

From FSM Chapter 8, "Propeller Shaft":

"After replacing the propeller shaft with a new one, drive the vehicle and if noise or vibration occurs, adjust with balance weight washers, trying them at various locations on the flange."

As a quick check whether driveshaft balance is the problem, add a regular washer to one of the four bolts at the differential flange. If the vibration changes, you can suspect driveshaft balance.

If the input shaft was not connected to anything at the time, the tranny falling is unlikely to damage any rotating parts housing since the output shaft is recessed in the tail housing unless...the cross member was on it and got bent or it hit on the input shaft and bent that.

 

The crossmember was on it and the bushing failed, so I got a new crossmember. It didn't do much though. I will try the washers on the flange as a sort of last resort for thinking it's the driveshaft.

 

I should have read more thoroughly before posting

So if it's engine speed vibration, not wheel speed related, then I completely agree with what the others have said. It's not the driveshaft. So what does that leave you? Well, mounts could do it, but you said they're new. The transmission falling is highly suspect. Especially if it was on a jack stand. And the input shaft is not entirely recessed in the bell housing. It does protrude some. So if it was pushed backwards, the input shaft could have caught it on the way down, damaging the input shaft.

 

wondering if you have fitted the auto tailshaft,, twice.. its 50mm shorter .. looks like it fits.. and vibrates like hell when you mix them up

PS.. rockford?? in the US do a replacement Ujoint for the staked one .. and works ok if you are carefull pressing out the olds

 

AGreen is right on. If the vibration is worst at 2-3k rpm regardless of gear, it's not the driveshaft. I should have read more thoroughly, too.

 

I built the engine, I know all parts on the rotating assembly are S5 turbo. It has a resurfaced flywheel and fresh pilot bearing. Only thing I can think is clutch/ pressure plate, it is being replaced shortly. I will inspect the pilot bearing and input shaft on the trans when it is apart.

Strange thing is slight vibration reving engine in neutral clutch in, heavier vibration when accelerating in the 2-3k range but is happy and vibration free at 4500.

If the clutch and pp don't do It I will disassemble and inspect the engine. This is my first time experiencing this. Thanks for the help.

 

I have a similsr issue at first it would only vibrate at just before 60mph. So I changed the the cross member and mounts and now it vibrates at 20 to 30 mph.
Is their a way to replace the ujoints.

 

For the guys talking about the driveshaft yoke showing, that is normal. It needs a little room to slide forward and back

 

If it still vibrates when you have the clutch depressed, then you just eliminated a lot of things.

I had a water pump pulley once that was pressed on every so slightly crooked, it took a dial indicator to notice, but it caused a shitload of vibration at 4k rpm. Not saying that is it in your case, just pointing out that little **** like that can cause issues.

 

Thanks jjwalker, I'll take a peek at this.

 

Could it be my exhaust? I am just running a rb 3" downpipe with the presilencer on it, and it ends there since I havent gotten the parts to finish it yet. I have it mounted with a rubber hanger on the trans exhaust mount. It is not rubbing against the chassis. Could the tone of the exhaust cause a vibration? I was thinking it's possible cause it gets worse once its warmed up. And is only bad at certain rpm, and gets worse the harder you hit the gas.

 

I don't think that could be it since it is held on by a rubber hanger. If it was hard mounted to something then yes. I have a couple of stock motor mounts we could try? Have you changed the clutch and PP yet?

 

I haven't. I am planning on doing that tomorrow. I think I would like to try stock mounts as a test.

 

were positive he put the right year flywheel on it? n370?

 

Most Likly you bent an alignment pin on the trans. The input shaft being slightly off center will cause vibration. If this is the case the shifter will start to vibrate at 3k&up.

Was the trans unusually hard to line up and push into the engine?

 

Ryan, I did double check it was n370, and it is a resurfaced flywheel from Atkins.

The trans was not unusually hard to press into the engine. As far as I remember..

 

Trans and clutch removed, noticed something pretty weird about the clutch disc. The splined "sleeve" is not solid mounted to the rest of the disc. You can turn an alignment key in the splines, without it moving the disc. It will spin about 20 degrees back and forth. I am confident this is the problem, and have a spare disc to install for testing. We will be putting it back together tomorrow evening.

 

that does sound very unusual! let us know your results!