"bucking"/uneven At 35-50 Mph

[90LS400Lexus]

I have posted this along time ago, with really no replies. My 1991 LS400 (now with 218K) when going between 35-45, sometimes 50 mph and when lightly accelerating, it will have this lurching feeling like there is some major slack somewhere. If the cars engine is not fully warmed, I will also get an occasional "whining" sound at these speeds, but the whining sound does not occur when the car is warmed up fully. Now I know my engine mounts and transmission mount are in bad shape, as they are the originals. I wonder if this could be the cause of this "bucking" at these speeds. I was concerned that it was the transmission, but the car shifts smoothly through all gears, but someone once told me it could be the torque converter causing it. I did not really agree at the time, because its been my understanding that these cars have bullet-proof transmissions and that it should not be failing at only 218K (low for a LS400 as we know). Gosh I hope its not the torque converter, as I CANNOT afford another costly repair on this car. I just had to shell out over $300 to have the fan bracket replaced and still having to fork out over $300 to change engine/tranny mount, which I am hoping is the cause of this. I have never abused the car- I always baby it, so I dont think it could be caused from abuse of the car.

Has anyone else ever experienced this?

Thanks in advance.

[amcdonal86]

I have experienced this with other RWD cars, but not the Lexus. It is usually the motor mounts/transmission mounts allowing the engine to shift positions a lot and causing a lot of play, which results in bucking.

It's usually most noticeable when getting on and off the gas. Maybe not so much when shifting (at least in a car with an automatic transmission) because there is not as much of a cutoff in engine power/drivetrain load.

[Marklouis]

at least start out by replacing your Transmission mount for $35-$50, also the easiest to replace, im posotive it will resolve more than half of the issues you are experiencing..worn mounts can be annoying in your driving experience.

luck!

[jcrome04]

Try this

http://www.lexls.com/tutorials/lighting/bulbout.html

[90LS400Lexus]

Try this

http://www.lexls.com/tutorials/lighting/bulbout.html

Huh?

[90LS400Lexus]

I have experienced this with other RWD cars, but not the Lexus. It is usually the motor mounts/transmission mounts allowing the engine to shift positions a lot and causing a lot of play, which results in bucking.

It's usually most noticeable when getting on and off the gas. Maybe not so much when shifting (at least in a car with an automatic transmission) because there is not as much of a cutoff in engine power/drivetrain load.

at least start out by replacing your Transmission mount for $35-$50, also the easiest to replace, im posotive it will resolve more than half of the issues you are experiencing..worn mounts can be annoying in your driving experience.

luck!

Thanks. I will do this soon. Yeah, when I first accelerate, when I hit about 1200 rpms, there is this hesitation/lurch, then its fine unless its like I said, light acceleration between 35-50 mph especially on slight upgrades/downgrades.... sometimes when downshifting, I can hear a light clunk sound as well.

Try this

http://www.lexls.com/tutorials/lighting/bulbout.html

huh?

[jcrome04]

Didn't hear me the first time?

Try this

http://www.lexls.com/tutorials/lighting/bulbout.html

Wires in the trunk... can get exposed......... some people who have had this VERY common problem on the 1st gen.........have had bucking issues.......... it wouldn't hurt to even check the harness just to be safe.........

Did you check the link even?

[90LS400Lexus]

Yeah, but when I clicked on it, I seen where it said "How to Fix Strange Dash Lighting & Brake Problems 1990-1994 Lexus LS400"... I wondered what in the heck that had to do with this problem. ;) I thought you meant to post that on another thread.

It appears that the wiring harness on the trunk hinge has already been addressed, unless its going crazy again. <_<

I am thinking it could more likely be my transmission/engine mounts since they are the originals @ 220K.

Thanks, I will read up on that link.

Didn't hear me the first time?

Try this

http://www.lexls.com/tutorials/lighting/bulbout.html

Wires in the trunk... can get exposed......... some people who have had this VERY common problem on the 1st gen.........have had bucking issues.......... it wouldn't hurt to even check the harness just to be safe.........

Did you check the link even?

[amcdonal86]

Didn't hear me the first time?

Try this

http://www.lexls.com/tutorials/lighting/bulbout.html

Wires in the trunk... can get exposed......... some people who have had this VERY common problem on the 1st gen.........have had bucking issues.......... it wouldn't hurt to even check the harness just to be safe.........

Did you check the link even?

Come on! Play nice! :P

[jcrome04]

Lol just bustin' your chops :)

The trunk wire harness cause so many different weird issues. I'd say every owner of a 1st gen should just pop it out and take a look just to be safe.

Go with the tranny mount first. It's like a ~$30 part and a 30min job.

(hey look #2,500)

[amcdonal86]

Lol just bustin' your chops :)

The trunk wire harness cause so many different weird issues. I'd say every owner of a 1st gen should just pop it out and take a look just to be safe.

Go with the tranny mount first. It's like a ~$30 part and a 30min job.

(hey look #2,500)

Do you have any instructions for the tranny mount change? I'm thinking of doing mine.

[jcrome04]

I don't personally have any.

I know there is some info around here. just do some searching.

[amcdonal86]

I don't personally have any.

I know there is some info around here. just do some searching.

Thanks for the suggestion. I found it here:

http://us.lexusownersclub.com/forums/index...showtopic=25228