new grinding noise

[flyboy]

On my short commute to work (5 mi) a new noise just arose and arose quickly. The car was not making this noise prior. While at rest, there is no noise whether the clutch is in or out. While I accelerate, there is no noise (maybe because the transmission and drive train are under load?). However, if I am rolling there is a grinding noise coming from somewhere near the gearbox or drive train. The noise is very evident whether the clutch is depressed or not and whether the vehicle is in gear or not - I just have to be rolling. As soon as I come to a stop, the noise stops.

I had been meaning to change out the gearbox oil and just did that. I haven't driven much since the change out (only around the block), but the noise is still there.

Possible thoughts were a bad U-joint (I didn't see anything that looked troubling) or perhaps a main shaft bearing?

Any assistance would be appreciated!

[mbouse]

the source of a noise can be very frustrating to locate. any chance a passenger can be pressed to service to assist?

at this point, it could be nearly anything, until you begin the process of elimination. might even be a wheel bearing.

between the transmission and the rear end, you have several wear items:
guibo
center support bearing
and two u-joints
any of which could be the source. when were these items last replaced?

and the last time the drivetrain was visually inspected? you could have picked up some debris and it is wrapped around the drive shaft.

[So Cal Mark]

if you had the wheels off, you might have a splash shield rubbing on a wheel or brake rotor

[flyboy]

Mark and Mike,
Good suggestions, but most of them would be sounds that would be continuous. This sound only occurs when the transmission is not under load. If I am accelerating, no noise. If I shift, the noise appears, then disappears when I am in the next gear and accelerating again. I can drive in 3rd gear at about 2500 - 3000 rpm continuously with no noise but as soon as I back off, with or without the clutch in, the noise starts up again and persists until I come to a stop or until there is load again (i.e. I put the car in gear and accelerate).

This is not a pleasant noise. It is a loud, squeaking/ grinding noise. I recorded it and I am trying to figure out how to attach it to the forum...

[engineerted]

What happens if you pull up on the E-brake? Look under the car and see if can see any spots that may be rubbing on the drive shaft.

Ted

[So Cal Mark]

a failed center support can let the driveshaft contact the ebrake mechinism as Ted suggested. It would be nice to know exactly what work you did on the car. Other than that you need to raise it up and do some inspection

[ventura ace]

Can you put the back axle on jack stands, block the front wheels, then crank up the car and put it in gear to listen for the noise? If it is there, you can carefully move around the car and listen for where the noise seems to be coming from. Be careful that you don't get caught in the spinning wheel!

Alvon

[flyboy]

Wouldn't something rubbing the driveshaft externally be a noise I could expect all the time? Or, if the center support has issues, could that cause the driveshaft to sag when not under load and not sag when under load thus causing an intermittent grinding/scraping/squealing noise?

When the problem first arose, I hadn't done any work in the recent past. I was just driving down the road and the new sound arose all of a sudden. I went home and changed out the gearbox oil but that didn't make any difference. While I had the front of the car on stands to do the gearbox oil, I inspected the u-joints and didn't see anything that looked off. I didn't specifically look for anything rubbing on the driveshaft but nothing caught my eye.

I will check what happens if I pull the e-brake up a bit while driving. And I like the idea of putting the back of the car on stands and engaging the drivetrain with the wheels off the ground to see what happens.

If anyone is interested in hearing the noise, I can send a recording over email.

I probably won't be able to get under the car until the weekend but I will report out at that time.
Thanks for the input everyone!

[ventura ace]

Please send me the recording. I'm curious!

Alvon
ventura_ace@juno.com

[adrians]

Flyboy,

Does your car have the lower flywheel inpection plate, or is it open to the road, there may be something jammed in there and only touchs when the load it off the drivetrain.

[wmpwilson]

Did you ever find out the source of this noise? I am having a similar noise---

Mine is making a terrible grinding noise under heavy de-celeration. If I down shift, especially while driving downhill, or in a right hand turn, I get a grinding noise. I can push in clutch and it will still be present at times. To clarify, the noise is not always present during downshifting, but at higher speeds and heavy de-celeration it is present.

[baltobernie]

A worn rear diff will often "whine" while decelerating or coasting. As it gets worse, the sound becomes a growl. Any pressure at all on the gas pedal makes the noise go away instantly. Does this describe your situation?

[wmpwilson]

It seems to be coming from the front right area. Last night on my way home from work I tried to isolate noise and conditions which cause the noise---It is not speed related, but rather conditions, i.e., while turning right, going down hill, downshifting....I am going to try and get an assistant to help me pinpoint it down.

Any suggestions as to where to focus would be great.

Thanks,

[wmpwilson]

I know it has been awhile since this post has had any activity. I am just recently getting back to working on my 77 after a couple years hiatus...drove it around the block today, and was reminded again that it has an existing grinding noise when de-celerating. It sounds like something from the exhaust system rubbing against the ground or driveline, but I can't see how this is happening. Maybe carrier bearing? Any comments?

Thanks....

[flyboy]

Ah, it has been a long time! Looks like wmpwilson and I took the same approach - park car for years!

I recently got the car up and running again to sell (sad). First guy that called in response to my ad said maybe it is a brake dragging. I sure didn't think so and certainly didn't want to believe I parked a car over a break for which I already had the parts. But, when he came by and we took it out for a spin around the block, the rear brake locked up when I stopped at a stop sign. Put it in reverse to get it unstuck and that seemed to take care of the grinding noise with load on or off. I haven't driven it enough to confirm or done the rear brakes (or sold the car) but, as others suggested, grinding can come from anywhere and even the brakes might be worth a look. I suppose that the attitude of the car, slightly leaned back while under load and slightly forward while coasting, was enough to cause the sound to come on and off.