factory Viscous LSD going bad?

[Brettt]

So after trying a multitude of things to stop our vibration, it is still hanging around. We have replaced both axles, hub bearings, played with ride height and even checked to make sure the frame and strut towers were good and square. The vibration isn't as bad as it was at its worst, but it is still there. The Nissan mechanic across town said to take a look at the lsd. I guess it makes sense considering we've replaced everything else drivetrain-related.

The question I pose to you guys is this: have you ever heard of a factory viscous unit causing a vibration only when you turn one way? Ours happens when we turn right and only when we turn right. Not sure really what else to do. We've got some diff-quieting stuff to put in the transmission for this weekend, but I don't understand enough about the viscous unit to really know if it will make a difference. After I get done with classes tomorrow its down to the shop to drain the fluid and try out some redline heavy shockproof gear oil. Past that, I suppose we start pulling the transmission...

Thanks guys

 

[Greg Amy]

...have you ever heard of a factory viscous unit causing a vibration only when you turn one way?

Nope. But they don't last long as "LSD" in racing conditions.

We've got some diff-quieting stuff to put in the transmission for this weekend

Won't do anything. The diff is a sealed unit, with the viscous fluid completely contained inside another internal container. Save your money.

Does the frequency of the vibration correlate to speed? Are you absolutely sure it's not a wheel/tire? When you replaced all those parts, were they with new stuff?

GA

 

[Brettt]

Both of the axles are new units. We had tried remans in the past, but got new ones this time in an attempt to rule things out. The only part we haven't put on the car is new outer hubs, but the hubs on the car don't really look bad. The bearings didn't look bad themselves, but I plan on replacing them tomorrow since we have 2 sitting in my tool box.

The frequency of the vibration seems to correlate with speed, but the intensity seems to remain more or less constant with angle on the steering. If you give the car more steering input, the intensity of vibration ramps up quite a bit with the left side loaded in a corner.

Same as before, however, it's smooth turning left. Even with the ride height just shy of 7" we still have only maybe 1/4" of lee-way in our left half-shaft when I take the nut loose before it bottoms out. Like I said before, we measured the lower control arm mounting points and they're within a silly millimeter of factory specs.

The only thing that I can think of is Topeka only has 5 right hand corners... so we can take some camber out of that wheel and hopefully give us a little more room there. We're running out of ideas...

Another racer here told me "Just run it until something breaks. Then you'll know what was wrong." As much as I hate that idea, it is starting to sound pretty good...

 

[Greg Amy]

I'm not clear: did you, or did you not, replace front wheel bearings with new? Sounds like a bad LF wheel bearing.

 

[Brettt]

As far as the wheel/tire situation, I've had two different kinds of wheels and 3 different types of tires up there. None of it seemed to make a difference regarding the vibration.

 

[Brettt]

We had replaced the wheel bearing towards the end of last season, but not since we have changed the rest of the driveline components. The races looked good when we pulled the hub out and none of the balls were scarred up, so we assumed that wasn't the problem.

-Yes it was a new bearing we put in. Watching the video from the race verified that it was shaking so bad the dash was trying to hop around. Could a wheel bearing cause that violent of a shake? It's much more of a hammering than a buzzing or grinding vibration, if that helps. Almost like you picked up a bunch of snow or something in your wheel to throw it out of whack, but the wheels are all balanced to zeroes- I did it myself.

 

[Matt93SE]

Stupid Q, but you don't have a tire rubbing against the strut or wheel well or something do you?

I would figure with that much interference it should be obvious if you have wheel or tire rubbing, but it's at least work asking.

 

[JLawton]

I hate to say this but I would go with a new hub. It may not look tweaked but it could be enough so things don't line up?

 

[Matt93SE]

Generally with a FWD Nissan, when the first wheel bearing goes, it eats the hub too. Almost all of them I've changed in the past have had hub damage and I wound up replacing them both...

FWIW..

 

[Brettt]

Stupid Q, but you don't have a tire rubbing against the strut or wheel well or something do you?

The tires coming off that side have looked fine and there aren't any indications of wear on the struts or underneath anywhere, so I think we're good there.

I hate to say this but I would go with a new hub. It may not look tweaked but it could be enough so things don't line up?

Good enough for me. I noticed the inner part of the hubs have shown a little wear the last time we put new bearings on there, but I figured a new bearing would be okay. The common response seems to be hub so I'll try to find some in town.

Thank you guys again.

 

[Matt93SE]

Yeah, if there was any visible wear/scarring on the hub, then that's likely your problem. been there done that. ain't cheap.

FWIW, I usually buy a new bearing and a junkyard hub/spindle assy as long as the used bearing seems okay. They're $35-50 at the junkyard. much cheaper than a new OEM hub at $135 ea.

I press the junkyard hub apart and give it a good cleaning and exam. If all looks good, I install it either spindle with the new bearing.

If you use a junkyard spindle, be sure to give it a good cleaning + exam and don't touch anything that's been hit in the front. I've seen a few of them fail rather spectacularly 6 months after a bump on a curb or a front-end fender bender. the cast steel will crack and you don't know it till it's too late.

 

[Brettt]

Yeah, if there was any visible wear/scarring on the hub, then that's likely your problem.

I press the junkyard hub apart and give it a good cleaning and exam. If all looks good, I install it either spindle with the new bearing.

If you use a junkyard spindle, be sure to give it a good cleaning + exam and don't touch anything that's been hit in the front.

Good stuff. Amazingly enough, I managed to find an NX1600 in really good shape in the local yard and snatched the front hubs out of that. They look pretty much brand new and I'm about to get going on the second one so that we have all new bearings and good hubs up front. That should actually make everything that turns except the transmission new.

Hopefully my new-found NX hubs will enable me to channel a little bit of tGA spirit here in Topeka this weekend.

I'll let you guys know how it went after we get back-- Wish me luck!

 

[Matt93SE]

Aaaannnnnd?

 

[CRallo]

isn't there an issue on these cars regarding halfshaft length?

 

[Brettt]

Aaaannnnnd?

Well... got everything put in and tightened down at about 11:30 Friday night. The car doesn't have lights and I couldn't see to drive it around the block, so we just loaded up. Got there at 3:00am and sleep until we can register at 7:00. After all of that is done, the drive over to tech the car shows the problem is still alive.

We go back to the trailer and look at stuff for a while, put the car on stands and have a mechanic that is there look at the thing and ride along. It seems that the vibration is getting worse and it happens under acceleration now, so he mentions that the bearings for the output shafts might be bad.

Along with mentioning that, he says we might look into having a driveline shop look at our axles to make sure they are true. I'm not saying this is a bad idea, but I think that with 3 different ones going in and the problem staying identical, I'm leaning towards the output shaft bearing. We'll pull the transmission apart as soon as we get a chance. I've already looked up the transmission rebuild "How To" on SR20forum, so I think it should go pretty smoothly once we start.

isn't there an issue on these cars regarding halfshaft length?

I haven't really found anything on that topic, but I sure seem to have one. Either my motor is impossibly far over to the driver's side of the engine bay or the shafts we keep getting for that side seem to be too long. Like I said before, there seems to be nothing wrong measurement-wise in the engine bay or underneath and there isn't more than 1" to the frame rail before the pulleys on the side of the motor start rubbing... Even with this being said, there is about 1/8" to 1/4" of play is all before my driver-side shaft bottoms out in the inner CV. The other side has over 1". Ride heights are within 1/8" side to side. Puzzling.

At any rate, I'm going with the bad output shaft bearings for now, since I heard a gear noise on the video from the last race and we've replaced everything starting from outside-to-in.

 

[Brettt]

Buuuuuuuutttttt.... I did still get to drive this weekend! Another awesome racer named Mitch Schwartz let me co-drive his Miata on Saturday and I truly had a blast! It was the first time I've had the opportunity to drive a car other than mine and was a really eye-opening experience. I actually ended up running some respectable times and qualified third in class- only to lose a position during the race and end up fourth. That part was unfortunate but just being out there racing was a huge surprise and really made my weekend.

-Nothing like finding a co-drive an hour after realizing we couldn't run our car- with only about an hour to prepare before qualifying. Needless to say, it made those 4 hours of sleep seem like more than enough!

THANKS MITCH!!

 

[Brettt]

So.... I pulled the transmission and have taken it apart. It looks fine. There isn't a bad bearing on the output shaft like we had hoped and the spider gears in the LSD seem tight. The fluid we drained out of it has little pieces of what appears to be a hard bearing-type material and the drain plug had some larger pieces stuck to it. One of the pieces was even a skinny shaving that looked to be 1/4" long. I'm trying to get some pics of the gear stacks and other internals to show you guys, but I'm not sure how helpful pictures will be when it seems to look good.

Not really sure where to go from here considering we have new hub bearings, new halfshafts, and the transmission doesn't seem to want to show me where the metal pieces came from. And with the new hubs and halfshafts we had the worst vibration ever when we tried to run at Topeka. So to sum it up, everything but the transmission internals are new, the same internals don't show bad wear anywhere, and the vibration is worse than ever.

Please help!

 

[Matt93SE]

Maxima trannies are really bad about eating input shaft bearings. have you looked closely at them?
http://blehmco.com/pics/car/drivetrain/tranny/IM001410.JPG

I don't think that would cause your problems, but you never know...

another thought is to check the play on the diff.
Since you have the case split, drop the diff back in with the bearings and put the case back together. check the axial play on the diff while the case is together.
I wonder if the final drive is rubbing against 1st gear..
http://blehmco.com/pics/car/drivetrain/tranny/IM001408.JPG
(That's my Maxima tranny, but yours probably isn't much different.)

 

[Brettt]

another thought is to check the play on the diff.

After scratching our heads for a while, we decided to put some axle stubs in the VLSDs from both trannies and see how they turned. The unit that came out of the car basically spun like an open diff. with the added benefit of being really notchy... I think we might have stumbled across the problem. The donor transmission had another stock unit that actually worked like an LSD and didn't produce the bumpiness of the other one.

Right now the case is back together and we're going to have it on the car shortly. Hopefully it'll still be light and we can test it out, but if not there is an open track day tomorrow for more testing.

As always with this mystery vibration, going to keep the fingers crossed!

 

[Brettt]

Fixed

Thanks to a donor transmission differential and a deepened inner CV joint the Sentra rides again! That, coupled with the suspension changes I've made gave me some of the fastest laps I've ever run at MAM this weekend. It was a little slick from the rain but still handled great after some suspension tweaks. I swapped the springs around to 560lbs in front and 700lbs in the rear and once i started to get a handle on where the set the dampening, it really started to rotate and fly. I had a ton of fun!
Big thanks to Damian at http://findtheline.com/ for hosting an awesome event!

Thanks for all of the help everyone, it is awesome to have a working car again!