Severe vibration from rear of car

[mkIIIman089]

Hey everyone, I'm still having trouble figuring out what is causing a pretty violent vibration coming from the rear of my car. I can feel it easily through the seat as well as a slight detectable steering wheel vibration. The part that is most difficult to diagnose it for me is that it is not consistent.

I am using a 4.30 LSD and an Al DSS driveshaft, the car has old square motor mounts, grade 8 bolts and lock washers on the diff/driveshaft flange which have not worked loose, and a Blitz NUR spec. I can shake the half shafts as hard as I can with all my weight and there is no noticeable play, and the same goes for the driveshaft.

It only occours when the drivetrain is neutral or near neutral (no stress accelerating or decelerating) which means while the cruise control is active it does it on nearly every down hill while on the highway.

I discovered also that it seemed to be more pronounced in a certain speed range, and it is in no way related to RPM. This may seem ironic since I calculate my speed via RPM so I can really explain the speed best as revs in 5th gear. Between 3000 and 3500 it does it worst (IIRC 3500 was something like 95MPH) and either above or below that speed it seems to fade away again. I didn't really want to go any faster then that for fear of getting a ticket which could possibly have an effect on my career plan.

Does anyone have any ideas for me? Its really pretty scary when I drive to feel a vibration like this even though every time I check it all looks fine.

 

[jdub]

Have you had your rear tires balanced? Did this start when you replaced the stovk driveshaft with the DSS single piece AL shaft? Could be it's out of balance as well. Wheel and differential bearings come to mind too.

 

[cwapface]

check your driveshaft u-joints, if they are bad then you need to figure out what made them go bad.

 

[IJ.]

Dead or dying Uni Joint would be my guess.

 

[mkIIIman089]

jdub - I don't actually know when it started since I had never even driven on a highway before I switched it, besides when my dad drove it back from when I bought it and he hardly went over 70 that whole time. And I did a flywheel, clutch, DS, and diff all at once. I actually watched my wheels get balanced by my friend's dad, all were 0 in and outside.

cwapface - the shaft only has <7k miles on it right now, but is there a reccomended way other then just applying force in different directions to see if there is any play?

IJ - are you talking about the DS joints like cwapface or the half shaft joints? Also, what's your preferred method of checking?

 

[IJ.]

DS Joints

Pull the E brake on hard then put the car in neutral and see if there's any rotarional play then check for up/down and side to side play.

Also check the bushing in the extension hosing and make sure it's not shagged (try to move the slip yoke up and down)

 

[mkIIIman089]

Alright, I think maybe tomorrow morning before I go to work I'll check it out and post back what I find!

What are the chances that its in the differential itself?

 

[mkIIIman089]

Well, not unexpected, I didn't get a chance to check the uni joints out yet, tomorrow I'm off so I can have plenty of time to spare.

On a bit of a side note, anyone know any good tricks to getting the carpet clean? I was going to just use some Woolite carpet cleaner I had, but any tips would be great. A rouge coke can somehow got in my car under the passenger seat and while doing some hard cornering, exploded, soaking the rear pass carpet.

 

[mkIIIman089]

Alright:

Both joints on the driveshaft are rock solid, as is the differentialas far as up/down or side/side play.

At the transmission though, there is about 1/8th inch of play up/down and side/side indicating that it is the bushing you mentioned IJ. However, I looked through the EPC and TSRM and all there is in the extension housing is an oil seal in that area. Unless I'm missing something (entirely possible) I don't see what your talking about. Please LMK... hopefully it hasn't destroyed the output shaft or something...

kind of takes me back to that question "is the "gap" on DSS driveshafts OK or not?"

 

[IJ.]

Colin: What "gap" are you talking about?

 

[mkIIIman089]

Well, I don't know if you have seen any of the threads on it previously, but on all the DSS driveshafts there has been a length question, wether or not they are too short. When installed they seem like they were made too short (at least that seems to be the common concensus) due to how much erm... splined section sticks out of the transmission. Well, a picture says 100 words so:

 

[IJ.]

Is that your car??

If so that there is your vibration!

That shaft is way too short!

 

[mkIIIman089]

Yea, thats mine. :cry:

Looks like DSS is getting a phone call, and I need to get another $50 in gear oil so I can swap out to the stocker, which is in fine condition AFAIK.

 

[IJ.]

Drain the Oil into a clean bucket and reuse it if it's not oldNfilthy Colin!

Just hope it hasn't shagged the Extension housing bushing!

From those pics it looks like someone has measured from the Tin cover to the Diff flange they then subtract 3/4" and this is the shaft length!

It was meant to be from the Seal to the Diff!

 

[mkIIIman089]

It's practically brand new, a couple months and like 3k miles on it.

I'm sorry, but can you show me where the bushing is in the parts diagram? Or is it part of the housing or something? I'm more worried about the output shaft itself though.

Ah! you ninja edited, lol.

Well, IDK what they are like to deal with but hopefully I can get something done to fix the situation.

 

[IJ.]

Usually it's a pressed in bushing that the Yoke slips into.

I'm not sure on a 154 as I've never been hands on with one sorry!

Contact em and let them know they may not be aware of the Issue!

I ran into this with PWR Radiators their drawings were incorrect for the Mk3 Rad so I worked with them to get it right!

 

[mkIIIman089]

Oh OK, well like I said when I was searching for said bushing all I came up with was that it looked as if the output shaft is by itself and there is only a seal there, which doesn't leak, so hopefully nothing is nuked too bad yet.

What was up with the PWR's? Whatever it was, thanks, mine fit great! Overflow barb leaks like crazy even after they re-threaded it but it fits fine, lol.

 

[IJ.]

The Shroud mounts were wrong making it sit crooked and the lower fan mount was missing!

Just detail stuff but for something that expensive I expect it to be perfect and was really dissapointed when it wasn't!

I ended up taking a bunch of pics did a few drawings and sent em a stock Mk3 Rad to copy.

 

[mkIIIman089]

yea, this DS wasn't what I would call cheap at virtually the same price as my PWR rad cost.

They won't even be open until the 10th so it looks like I'm just going to be waiting until then.

 

[IJ.]

Grab a bucket and swap in the stock one Colin!