Z-Car

Datsun 240Z Rear-End Clunks

pretty girl in front of a datsun 240z

There are four main causes :

U-Joints

Check all six U-Joints. Two on main propellor shaft, two on each half-shaft. Grip both ends in hand,
and twist. If there is ANY play or excessive stiffness, replace. If a U-Joint is bad, you will usually
get a loud clink when slowly going forward after going in reverse (or vice-versa). Nissan U-joints
really are much better than most aftermarket U-joints. Spicer brand joints are also good. Avoid
joints that are drilled for grease fittings, especially in high torque applications (ie V8 conversions)
because the holes for the fittings reduce the strength of the “cross”.

Rebuilt Driveshafts are available from

Z CAR DRIVESHAFTS FROM “Pro Am” the Drivers Warehouse..

6125 Richmond Ave.

Houston, Texas 77057

Call Tom:

1-800-847-5712

1-713-781-7755

 


Bad Diff Mounts

Take a floor jack and place it under the differential. Slowly raise it up. If the diff moves at all
before the car rises, then your mounts are probably bad. The front mount uses a rubber block that
will often come apart. The rubber strap going across the top of the diff should prevent this, but often
does not. You have three choices : Replace with new front rubber mount, which will again
eventually fail. Replace with a solid mount. Stops problem, but introduces a little more road
vibration into the car. Lastly, add a strap buffer which will help save the front mount. Available
from Marc Sayer’s Performance Engineering. This is his description :

Z Car Differential Snubber – Due to the design of the front differential mount and retaining strap on
the Z cars, the mount is easily damaged. It is an expensive and fragile part, as well as being a pain
to replace. The mount works in tension as well as compression, which means that the rubber to
metal bond is stressed. The strap is supposed to limit this to prevent damage to the mount, but it
does not do an adequate job. Solid mounts are too hard and transmit too much noise. I have come up
with a poly snubber that bolts to the strap itself. This maintains the rubber mount and the “soft”
action of the stock rubber strap. It can be adjusted for pre-load (against the diff housing). Since it
acts as the limit of upward motion of the diff, it can even be used with torn diff mounts, saving you
the cost of a new mount. Z car————————–Z700-1050.

The Rear Mustache Bar Mounts also can lead to excessive clunks. If the rear of the diff lifts before
the car, check the tightness of the bolts that attach the mustache bar to the diff. Also check the bolts
that attach the mustache bar to body. If there is any play at the mustache bar ends, replace the
bushings. Polyurethane will hold up better, but will transmit slightly more noise and vibration.

Another area of possible slop in the rear end comes from the rubber control arm bushings If you
have this problem, you’ll feel the rear end of the car jump (slight fishtail to one side) as you let out
on the clutch and accellerate hard.


Worn Hub Splines

Another source of clunks in the rear is worn rear hub splines. You can lock the wheel with the
brakes and turn the stub axle on the back side of the hub (turn the flange that the half-shaft bolts to).
The bearings are not loose and the retaining nut is tight, but there is still play between the input stub
axle and the output axle. The fix is to replace the stub axles, or replace with a used rear strut
assembly (much cheaper).

 


Excessive Play in Differential

Lastly, you could just have a differential with a lot of play in it. The R160, R180, and R200
differentials seem to have a lot of play, even when new. Many of the original 240Z road reports
mentioned that they felt a clunk when taking off in first gear. These reports were on new cars, not 25
year old Z’s! If your differential is not making any other strange noises, and you have checked
everything else mentioned on this page, then you may just have a differential that is a little playful.


Tagged on: , ,

One thought on “Datsun 240Z Rear-End Clunks

  1. Jorge M.

    Well I have to say it is spot on. My series 1 240z’s rear end was/is all mess up. Taking off and driving down the road. clunk (shift) clunk (decel then accel) clunk. Then going down the freeway 60mph+ you hear and feel something rattling hard. So I replaced the rear diff mount with a solid billet aluminum mount and in the process of replacing a shot original rear diff mount I noticed both my wheel hub stubs had play in them and u-joints on the driveshaft being stiff at certain movements. So not having enough time to replace the u joints and exploring the play happy stubs i have to put everything back together with a new shiney solid mount.

    Feels more solid than it did before but still the clunk is there (stubs) and the freeway rattle is still there (u driveshaft joints). So looking here confirmed what I suspected about the axle hubs. Great post! Definitely helps us Z owners that are new to the Z game.

Leave a Reply and Let me know what you think...