enigma94

iTrader: (1)

Hi all, Its been a couple of years since I sold my last LS400 and have just recently purchased another one for a daily driver. Its a 98 with 152k. Prior to purchasing it I had my mechanic look over the car, along with myself. The only real issue the car had was a vibration between 45-55 and then off and on as you go faster. Having experience with vibration issues with my old LS i knew this had to of been wheel balancing, motor/tranny mounts.

We had the car on the lift and everything looked good under the car, newer strut rods, trans mount looked good as well. The only thing that looked dire was the Differential mount bushings. The car looked well maintained and even had new struts/shocks, so i went ahead and purchased the car thinking the vibration was either due to balancing or those diff bushings.

I had the tired re-balanced and it seemed to take a very slight bit of the vibration away but it was still pretty severe at 45-55. Thinking it had to be the diff bushings as it was visible that the diff was sagging a bit I had my mechanic change them out over the weekend.

Well he calls me this morning and says that the bushings did not solve the vibration and that he believed it to be the actual drive shaft. Specifically the U-Joint between the front drive shaft and the rear, or there is play in the splines where the 2 connect. Being that the car only has 152k on it and that ive never seen or herd of this being a common source for vibration issues makes me question weather thats really the issue. He says there is definitely play between the 2 shafts but could this be the cause or is there suppose to be some play?

I made sure to look at the coupler bushings between the drive shaft and the diff, and the shaft and the tranny when we were inspecting the car and they were in good shape so I know this is not the issue. The vibration is definitely in the rear of the car/seat not in the wheel. Has anybody herd of the U joints or the splines wearing out and causing this sort of vibration??

I am inclined to have him look closely at the motor mounts and have him just replace the tranny mount since its only $40 as these were the sources of my vibration in my old LS, but if there is play in the drive shaft it would seem that this could be the issue and motor mounts are not cheap to replace. So im wondering if the play in the shaft is something that needs to be addressed or if this play is normal and not the source of the issue...

enigma94

iTrader: (1)

Did some more looking and found that both motor mounts were pretty bad and had 1'' of flex when power braking on the lift. The tranny mount was also pretty bad and was sagging close to and inch as well. We replaced both motor mounts and the tranny mount and it rides like a dream! So it appears that the movement in the shaft is normal, just for anybody running into this issue in the future.

RA40

iTrader: (6)

Glad that was easily solved. I cannot recollect discussions with problems regarding the LS400 drive shaft. We have plenty of discussions on vibrations so this is good info to have on a checklist when hunting them down.

YoshiMan

Now what about those rubber coupling things on the drive shaft? Anyone know anything about those going bad?




I have new engine and transmission mounts, but have a rumbling sensation at first when it's really cold out that comes on around 35 MPH. It goes away once the car has been driving for a bit... and doesnt exist if its 45ish degrees or warmer. I'm wondering if the shaft couplers have hardened with age and don't respond well to cold weather sometimes....

enigma94

iTrader: (1)

Exactly. The lack of discussion about the driveshaft going bad and being a cause of vibration led me to believe that it wasn't the issue we were hunting.

These are the driveshaft couplers I was referring too in my original post. I believe they are also sometimes called guido/flex bushings/couplers. From the problems you're descibing these could very well be the issue. They are very easy to visibly check with the car in the air so I would look them over to make sure they aren't deteriorated. Is the vibration felt more in the seat/rear of the car or the steering wheel/front of the car??

peterls

I also have intermittent vibration issue, and have not resolved it yet, even though I replaced engine mounts and the transmission mount; the vibration that was caused by the engine is gone with new mounts.

However, just like Yoshi, I too feel vague vibration in steering wheel, my seat and generally in the entire car, but only sporadically, and only when its cold.

Since the problem is not consistent and hardly noticeable, I am leaning towards one of these possibilities:

1. The rubber coupler that is in the pictures above (we have only one on our cars, right?)
2. The drive shaft center support bearing
3. Transmission (doubtful)
4. Differential (it does make a bit of a howling sound around 65-70mph even with new diff oil)

The car makes no noises and vibration does not change when turning, so I am excluding wheel bearings from this equation.

YoshiMan

I think we are on to something!

Yeah, mine feels like its under the car, and probably in the rear as well.

If i am not mistaken, I THINK there are two of those couplers on the driveshaft.

In the summer, the car doesn't do it at all, and it goes away after the cars been driving for a bit.

I might bite the bullet and replace them both to see if it gets better. Not sure if i have seen anyone else do those yet and report the results, Everything else i've checked seems to be in good order

peterls

I remember reading a loooong thread about someone who was chasing similar vibration issue... spent some serious $$$ replacing everything, and finally figured that it was the driveshaft support bearing. Someone else though reported pretty bad vibrations, and finally figured it was the rubber coupler(s) - he even posted a picture of the bad coupler, and the rubber was shredded to pieces.

Tip: it seems that European Ford Transit 2000-2006 driveshaft coupler fits our LS400 (at last the 1st gen). Read it somewhere posted by a guy who lives in N.Zealand... The point is that Ford's coupler is 10x cheaper.

Whoever replaces these things first should post results.

enigma94

iTrader: (1)

There are 2 couplers one on each end of the drive shaft. Like I stated before they are pretty easy to do a visual check on if the car is in the air. If they seem to be in good working order you can check the guide bearing(center support bearing) I believe you need to remove a heat shield to gain access to it. It should be pretty obvious if the bearing is going bad by leaking fluid or a appearance of lack of fluid(rusty ect). There are also 2 bushings that hold the diff to the rear cross member that will go out and allow the diff to sag which could cause vibration. These are also very easily inspected with the car in the air.

I would look over all 3 options and find the one that looks the worst and go from there. I do know the rear diff bushings are a PITA to replace as I believe the whole diff has to be removed so keep that in mind.

kornpeef

double check the upper and lower control arm bushings. check to see if there are any witness marks of the arms rubbing into frame.