magnificen

Hello all! Just a question and concern about some late experiences with my 1996 LS400. Every time i get to 40mph on the speedometer, i get this suttle but rough rumble on the pedal and a little grinding noise can be heard around the engine bay. I hope its not the t word (transmission) Is this a sign that something horribly wrong is going bad or just a quick and easy fix? I checked the ats fluid and everything looked okay. Thanks all.

Moarpower

Try to replicate it by increasing the revs in N. If you can feel it in the floor it's not too good. Beat case is a pulley bearing

magnificen

I must add that after and before 40mph this rattle subsides and goes away and its smooth surfing from there. Usually when I'm around 40mph the rpm on the engine is around 2000-3000 revolutions per minute. What is the function of the pulley bearing if i may ask?

Moarpower

So in the engine there are many pulley which guide or turn rotate the belts and the parts they are connected to. IE aircon, alternator, water pump etc. The bearings are what allow the pulleys top turn smoothly without grinding and wearing out the parts. However, all bearings fail eventually.

It could maybe be a mount, but if it is a grinding that increases or decreases with rpm, it is a pulley. These are the 2 best cases. Hopefully its not anything internal or transmission related.

Do a full transmission service and see whats in the pan. Look for metal flakes. It is unlikely that a transmission problem would be louder in the engine bay.

magnificen

Ah ok. Yea that does sound reassuring. I will stop by my mechanic tomorrow and have them take a look. I don't know if this is related but at the same time this started, I began to here a ticking noise almost like a mosquito, right behind the dash indicator display. This noise would pick up as my speed does around 60mph, it is farily noticeable with the radio at a moderate setting but i can drown it out by just turning it up a bit. Around interstate speed (70-80) is when it gets irritably noisy.

Moarpower

I would say that there is a chance it is related

Banshee365

Check the rear transmission mount. It may look fine upon visual inspect but place a floor jack under the trans and lightly lift to see if it’s seperated.

Superfast1

Check the flex discs on your driveshaft, 1 at the tranny & the other at the rear axle. If they're cracked, you'll get vibration at a certain speed, however it shouldn't make any grinding noise in the engine bay. Noises do travel so you may thought it's in the engine bay but it could be further behind it.

magnificen

Update: Yes it was the flex discs. Thank you so much. It happened to be the one in the front near the transmission. The one near the rear axle was fine. I had just replaced this a year ago so I was wondering as to why it went bad after a short period of time. Any thoughts?

YODAONE

What brand flex disc used in first replacement?

How many miles before failure?

magnificen

Sorry i am just seeing this. I am not sure of the brand used in the first replacement but it was on 311,xxx miles.

jaaa

Yeah, sounds like a non OEM.