new driveshaft didn't help - bummer

My 77B is smooth and quiet on acceleration all the way up to 70MPH, but upon deceleration a rumble is heard. Under hard deceleration a vibration accompanies the rumble. It sounds like an exhaust rumble, but the exhaust is tight and rattle-free when I pound on it when under the car. Here is what I have done thus far...

1. Removed the clamped-in forward muffler and replaced it with a solidly welded straight pipe
no change

2. Replaced the rear exhaust hanger assembly with a new, correct, original style one
no change

3. Found worn u-joints and slip, so I replaced the driveshaft with a new a$$embly
no change

4. Drained the rear differential and re-lubed with fresh 75-90wt gear oil w/ lucas oil additive
no change

Also, when I shift under hard acceleration at 4500rpm there is a definite momentary grind/rumble/protest just as I depress the clutch.

This one is starting to make me nutty, guys...I'm open to any ideas that the brain trust can offer.

Have you checked the transmission mounts for cracking..?

The grind/rumble/protest thing is something else, but for the rumble/vibration I would certainly be looking at the power unit mounts, both front engine and the dreaded transmission rubbers.

You could also look at the clearances of the exhaust piping. If the measurements are small, any shifting of the power unit could be causing the exhaust to bow just enough to make contact with the body structure somewhere.

Come to think of it, the grind/rumble thing could be related too.

Jack

I didn't check these mounts, but that sounds like a good idea!

thanks

Here's another thought...

The FIRST thing I did was replace the rear sway bar bushings, #8 in the image below, because they were worn (I could clunk the bar up and down), thinking this surely was the cause of the rumble. The bar feels nice and tight now, but the rumble remains

The rumble is MOST pronounced when the vehicle is going 45mph on flat, level ground and I am neither accelerating nor decelerating, ie, the drive train is spinning fast with no load on it.

So, is there any chance that the source of the rumble could be a bad end fitting (#2 on the picture)? I cannot feel any play, and the fittings LOOK ok, but if the axle were free to torque (under no strain) back and forth it seems that this might cause the symptoms.

What are your thoughts?

Anything that is lose can cause a noise, If you have play at the sway bar links remove them drive around and see if the noise is gone. Only makes the noise when on a load...? still sounds like mounts to me. Or in worst cases something internal...

Quote "there is a definite momentary grind/rumble/protest just as I depress the clutch."; Worn TO bearing?

worn pinion was the noise i heard. sorry

Did you line the prop shaft up?

Mostly "B" Ren.

I am getting mixed signals here.

Let's go through this again.

Noise = any noise

Rumble = heavy.low frequency sound/vibration

Either of the above / which one ?

At idle with car stationary ?

Under load when accelerating from rest?

Free running ( at normal ? road speed not accelerating or decelerating ) ?

Coming from? Front of car - rear of car - middle of car ?

Road speed related. Eg. gets more and less discernable with changes in road speed ?

Load in car - more with two passengers than with just the driver ?

Different with side loading ? More or less when in the middle of a turn ? Noise from one side of the car or the other ? Which one, inside or outside of curve?

Have you checked the drive shaft joints CLOSELY? Most often a worn joint will be loose, but not always. Use two hands, one to turn the shaft back and forth while gripping the joint area all around with your other hand. Alternative. Twist the shaft back anfd forth while sticking you finger in between the two yokes. Check with finger in at least two openings per joint. ANY play is too much. The hidden typw failure is when one or more needle bearing sets become dried out and actually sometimes rust. Their resistance to the correct flexing will give a vibration and sometimes a deep noise.

Yes, the transmission mounts are a PITA to change, especially if OD is fitted. Difficult and messy, no matter how you slice it.

As per my earlier comment, suspending the power unit correctly is critical. If any of the rubbers fail things become misaligned and can allow stuff to rest against other stuff and transmit natural vibrations. Look EVERYWHERE for signs of something going wrong here.

Drive shaft: If the joints are not in phase it will make the rumble, but probably not the noise. Also make sure that the last guy who changed a joint did not distort the face of the adjacent companion flange. It is common for morons to smash the edges of the companion flanges when using the hammer-and-vise method. That is the way I do it, but at least I look at tings when I am done. This bulges out the face of the flange and when you go to bolt up the flange to the transmission out-put or axle pinion flanges the shaft is cocked off to one side a little. Not a difficult fix using a flat file for a couple of minutes.

Please report back here at 0700 Sargent with a full report of casualties and successes. ;-)

Jack

If you still have the air pump check your gulp valve.

What condition are your tires in? If the car has sat for a long period, they could be flat spotted some.

Also, worth checking the tightness of all your lug nuts, then possibly having the tire balance checked if you find nothing else.

Could be wheel bearing noise, but let's don't get too worried about that until other things are checked off.

I did see the NEW driveshaft fitted, but some people may slip it apart to have a look down inside to see how things fit and work then put it back in without realisation.

Curiosity as it is with a new part.

I just changed out a overdrive that was giving me fits and put in a standard 4 speed trans. I have the same issue you are having. A rumble and vibration under no load conditions. Just bring it up to speed and back off the throttle ever so slightly. The ONLY thing i changed before the noise/vibration/rumble was the transmission. My next step will be to repair the overdrive trans or install a Datsun box. It will probably be a few weeks before i get to this project. I want to tear into that regular trans to see whats up. I would think its your trans or diff. I think the exhaust torques away from the chassis under load and gets closer to the divot in the frame rail when decelerating. If its a no load noise then it should be there when idling at rest....Maybe? Good luck with this one! Bob

Let the car cool down, jack up the rear end and bash the rear muffler with the heel of your hand or a big rubber hammer. Listen closely for rattle noises emanating from said can.

It is sounding to me like something vibrating in sympathy with either the engine or something else in the drive line all the way out to the tires. My first guess is the muffler, my second is something in the trunk. Remove everything from it and go for a ride.

Make sure that the battery is being held firmly in position and that someone hasn't replaced one of the cables with one that is outrageously long and flopping against somehting.

I would still look at the exhaust first though.

Jack

Check the manafold to exhaust pipe for donut seals are tight of missing.