Car rumbles at speed, when I let off the gas slightly it goes away. What is it?
 

Ok guys here is my problem. At above 80 miles an hour the car makes a low rumbling sound that is quite audible. It even makes it at less speed but increases as I go faster. I was thinking this might be something engine related but if I put the car in neutral or let off of the clutch it is still there as I roll. So I started thinking it might be in the tranny as I have had fluid leaking from the speedo gear o-ring. I changed the transmission and clutch and it is still there. Funny thing is though is when I let off of the gas while the car is in gear just a LITTLE bit, there is a very definable sweet spot where there is no noise. It totally goes away, no matter the speed. I can't let off all the way, but about 80 percent off of the throttle and it stops. U guys think this could be in my U-joint or something? And why the sweet spot when I let off of the gas just a little?

You say if you let it off slowly, nothing? You may want to check the clutch components to see if all is well. 80 mph and greater might be having the clutch spin fast enough to slip with the lightest bit of drag..

Universal joint? Rear end?

i would grease your u-joint or replace your u joint and see if that helps

ok so how do I grease this U-joint? Or is it easier to replace it? I heard it was a pain in the ass. I do have a spare driveshaft laying around. Would that be easier.

I also know what it is like having a bad diff and this isnt it. sounds like the u-joint.

Trippy; I'm experiencing similar symptoms in my '91. I had a similar problem with my '89 and it was indeed the driveshaft universals. Unfortunately, the driveshaft came with no zerks on the u-joints, and the shaft itself was not (yet) rebuildable...
A trip to a driveline fab shop left my wallet $400 lighter and my 'shaft was rebuildable, and in new condition with upgraded u-joints (zerks for grease and h/d). I've renewed my search for someone who offers rebuilt 'shafts...

fc driveshafts are one piece. you can't just replace the u-joints, the whole driveshaft has to be replaced. if you have a spare one then put it in and see if it fixes it.

don't worry, even 240 guys got screwed w/ the one piece driveshaft w/o the replaceable u-joints.

actually there is a place that makes u-joints for our driveshafts now. I can't remeber the name of the place right off the top off my head, but if you search you will find links to them.

to the OP. I would think that sounds like it is a bad u-joint.

for now just pop your spare one in to see if it cures your problem

hell yeah. This will be my weekend project.

...takes like an hour to swap one out...

yeah, took 45 minutes, problem solved. Fuck. I replaced the whole damned transmission with a fucked up transmission over this---

EwWwWww. But good job. I guess time to replace the tranny again :P

240sx has two piece.............................