1970 240Z Vibration

[cbfoo82]

I have a 240Z build date 12/70 and I have what I think is the series 1 z-car rear end vibration. To date I have replaced all bushings, struts, and u-joints (including half shaft u-joints).

I have heard that later 240Z's had there rear differentials moved back 2 inches and the driveshaft lengthened or shortened (can't remember) to curb this problem.

Is there a kit or mod that can be done to stop this horrible vibration. Between 65 and 70mph I get a solid rumble in the rear.

Thanks,

Colin

[beandip]

One thing you can look for . Look under your car at the diff mount. Nissan added a metal plate that is about 1/2'' thick and almost 5'' square to help with this problem. Check and see if you still have one there. Over the years someone could have just left it off. Other than that I cannot help you, I haven't experienced the problem my self . With the drive shaft. Someone else I am sure will jump in . Gary

[Diseazd]

If I recall correctly, you'll need a 72 mustache bar, a 72 driveshaft, a 72 front diff mount and a 72 rear diff hanger. www.zbarn.com ask for Roger.....he sells the packages used.

[geezer]

The changes made Guy described. I'll see if I can find the other vibration "fix" Beandip describes.

[240znz]

What about the diff and wheel bearings? Are they OK?

I too had the same noise in the rear on my 70. So far I have.

1. Replaced the half shaft u joints and rebuilt the shaft bearings (horrid plastic things)

2. New diff mount insulator

3. New diff strap

4. New wheel bearings

5. New drive shaft u joints (x2 as I have the early 5 speed)

6. New mustache bar bushes (poly as rubber is NLA)

7. New inner and outer A arm bushes (rubber)

As the car is still not running, I can't prove that any of the above will fix the noise but I strongly suspect that the diff ring gear or pinion is worn. I'm not spending any money on the diff as it will be replaced by a LSD unit at some stage.

So I'm guessing that as the rumble is at normal highway speed only, your ring or pinion gear is worn.

[Arne]

I understood that the differential relocation in '72 and later was primarily to reduce halfshaft u-joint wear. I've had two '71s with the diff in the original location that were drivable, neither has experienced this problem. I'd be looking for something else. Did you have the driveshaft balance checked?

[geezer]

A solid rumble in the rear that occurs between 65 - 70mph. Does it go away after 70 mph or are you just describing the speed range it begins? Two possibilities come to mind. A driveshaft that is out of balance will cause vibrations at varying speeds. A good test to rule this in or out that has worked for me is, using a large gear clamp on the driveshaft that you can rotate in increments to try to achieve a balance. Also if the vibration comes in at between 65-70 mph and is constant and increasingly worse at higher speeds, look for belt separation in one of your rear tires. Use a spare to rule this in or out.

I have found a Nissan publication describing the 240Z Dampener Installation. It was the "fix" for automatic transmission equipt vehicles that had vibration problems arising from body bending frequencies and the bouncing and pitching motion of the differential mounting and also torsional motion of the power train. Is your car an automatic? Apparently the dampner was only fitted at the dealership if there was a customer complaint. That explains why some have them and some don't.

[geezer]

The 240Z Dynamic Dampener used on the cars with automatics, that was provided on request was Part # 55490-E8300. A much more refined piece than the other type. This illustration depicts the parts in the kit that was provided to the dealer and installed, on a customer complaint basis only.

The crude layered steel plate Dampeners that came later were Part # 55418-N33000 (up to 12/74) & Part # 55418-N3701 (after 12/74). Details on the use of these are somewhat sketchy but they look to be a quick fix, used to correct sporatic vibrations and installed by the dealer also.

[d240zx2]

Wish I could help. My 01/70, which I've driven most of it's 68,000 miles, never had the vibration you describe. The U-joint bolts at the differential came loose and caused a ruckus once, but never since.

Frank

[moritz55]

I'll share my 1973 240z w/5spd story, maybe it will help.

I was getting both a "Rattle" when idling in neutral, a "Clunk" when shifting hard and a terrible "Vibration" at 2200 rpm higher. The vibration felt like the car was going to shake apart it wsa so bad.

I had several things done systematically to rule our rootcauses.

1st) Thanks to the knowledge and advice from Arne, the Rattle noise when idling in nutral came from a Clutch spring/coil that was loose. I have an Aluminum (Fidanza) flywheel, and after installing a new clutch (Centerforce Dual Friction) and resurfacing the flywheel - this rattling noise vanished.

2nd) To address the vibration & clunk, I got looking at my rear end. My differential mount was pretty much shot, the rubber between both sets of plates was torn. Also as I got looking at the front of the differential, it was pointing down and toward the passenger side of the car. Almost 5/6inch offcenter in the direction of the passenger side of the car.

.. I bought New Parts from MSA: Differential Mount (~$65), Urathene Bushings for Both the Mustache Bar and the Transverse Linkages, 4 New CV U-Joints and 2 Drivetrain U-Joints (Napa pn: P391) were ordered.

.. During inspection when disassembled, I noticed the Mustache bar was twisted becuase the differential was off-center. Straightened this up and installed the New Urathene bushings. Then installed the Differential Mount and it took 2 attempts becuase I had to remove the twist in the Mustache bar such that the Differential mount screw aligned squarely with the frame bracket - all before tigthening everything up. I also installed the Inner Bushings on the Transverse links. .. Test drove it and the Clunk was gone completely .. most of the vibration (80% or so) was gone up through 3500 rpm.

.. Next dropped the Driveshaft and inspected the U-Joints and did replace both. The Rear one was bad, front was good, but replaced them anyway. The CV U-Joints on the car had been replaced 5000 miles ago and were still in perfect shape, smooth and tight when being turned by hand. Rechecked all the bolts again - no signs of anything loose.

... Took the car out and it was super! No Clunks and No Vibrations up through ~4500 rpm, just pure engine noise. In fact plastic vibrations in my center console/heater control panel are now all gone from 1500rpm and up.

So ... my conclusion was - the Major Vibrations starting at 2200RPM was primarily due to the Differential being mis-aligned with the plane/centerline of the drive shaft(the angle of mis-alignment was about 4-5degrees using a protractor and straight edge). It's easy to check for this as well by looking at the gap between Mustache bar and the frame uprights on either side - they should be equal. The higher RPM vibration (~3500rpm) came from a worn U-Joint on the rear end of my drive shaft. I'm sure it was damaged as the differential shifted so far off-center. These ussually don't wear - but in my case they were stressed a bit.

Anyway - hope this helps some encountering a similar problem.

[moritz55]

I had a typo in the above post....

2nd) To address the vibration & clunk, I got looking at my rear end. My differential mount was pretty much shot, the rubber between both sets of plates was torn. Also as I got looking at the front of the differential, it was pointing down and toward the passenger side of the car. Almost 5/6inch is in error .. should be 5/8inch offcenter in the direction of the passenger side of the car.

[bpilati]

I rebuilt my suspension a couple years ago, new bushings, moved diff, and all that, and still have vibration at high speeds. It's a sports car, it should shake or have a sheetmetal buzz at 80 and up. Sounds like a cheap tin can.