Sc400 Bucking Between 30-45mph

[seanst2005]

Hi all. I just got a White 95 SC400, 95k miles. Very nice inside and out. However, there are a couple of issues. The most pressing in my view is, when I am going between 30-45 mph it seems to buck or jerk. Turning off O/D doesn't help too much. Any ideas as to the cause? Is it fuel/air/spark system, or should I be looking at the transmission. I have heard that the center driveshaft bearing (?) has issues on these vehicles and need to be replaced on occasion, or maybe it was the driveshaft going out of balance and needing to be replaced (Sorry, I can't quite remember what the mechanic said.) Please help! Thanks in advance.

[SPRUCE SC300]

It could be that rubber dampener between the two drive shafts. If there is any play in the drive shaft, it will be felt in the form of high-speed vibration as with any other centrifugal force application. You are right, that part does go bad however mainly on the V8 models. I would check that first since the transmissions in these cars tend to be extremely reliable.

Good luck.

[seanst2005]

Thanks, Spruce. And just for clarification, this is happening when I am driving at a steady pace, no acceleration or deceleration occuring, so there should be no change in load on the shaft. Thus, the out of balance issue??

I found another thread, that addressed this issue, and the advice was change the spark plugs(?). There was no conclusion as to whether this resolved the problem or not.

Bottom line, I will try the driveshaft bushing solution and let you know if it fixes it or not.

[SPORTcoupe300]

I'd have to say I'm leaning towards the sparkplugs being the problem.

What's the last time the car had a tune-up?

I used to have an old minivan back in the day and it had the same problem.

I went to a mechanic and he diagnosed a bad transmission.

Since the car was worthless, I decided to ride it out till the transmission dies, but then after a while I stated to hear small missfires.

I then realized that this had nothing to do with the tranny.

Turns out one of my wires hadn't been working for months (5 cylinders) and one went out recently (4 cylinders).

After the tune-up the car purred for another 40,000 miles.

If you don't know for sure when a tune-up's been done last, check your wires.

If they're factory wires they'll have the year on them.

That should give you a good idea whether it is time.

Good luck.

[Lextreme]

Had the same problem with my LS400. I changed the torque converter and everything is cool now.