rumble from my rear end (forgive the description)

[tfbrown]

My 73 240Z has a pronounced rumble from somewhere aft of the transmission...all 6 u-joints are tight, the tires are balanced and the exhaust is not touching the frame. The amplitude increases as roadspeed increases, the frequecy does too but not very much. I put the car on jacks and ran it in 4th to about 80 mph and the rumble gets quite annoying..... (my best quess is that something somewhere is a little loose allowing just a few thou movement) any ideas where this is coming from..I haven't looked at the rear bearings yet??...also after my run on the jacks stands I noticed a puddle of gear oil under the transmission but couldn't see how it got out...it was about a cup full.

Thanks in advance

[Phacade]

I dunno. All I can tell you is my '73 240z is doing something VERY similair. Its just down right uncanny, in fact. When I drive down the road I get a 'whoomp-whoomp-whoomp' sound from the rear end. The faster, the more pronounced. Of couse the rear end of my Z operated on only one gear ratio, therefore it would make more noise the faster it goes. Now from talking to Z mechanics, friends, etc, I believe the problem is the rear end itself. Its tired. I have the original R180 but am getting ready to drop in my R200 [insert full belly grunt from Tim Allen from Home Improvement here]. It has a 3:90 gear ratio and should be a definate improvement.

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"Go into emptiness, strike voids, bypass his defences; hit him where he does not expect you" -Lao Tzu

[auxilary]

checked the front differential mount? It's a common thing to wear out and tear, but I'd assume it only makes noises when shifting gears or letting off the gas - any time there's difference in movement in the diff.

[dhayes5]

Originally posted by tfbrown

My 73 240Z has a pronounced rumble from somewhere aft of the transmission...all 6 u-joints are tight, the tires are balanced and the exhaust is not touching the frame. The amplitude increases as roadspeed increases, the frequecy does too but not very much. I put the car on jacks and ran it in 4th to about 80 mph and the rumble gets quite annoying..... (my best quess is that something somewhere is a little loose allowing just a few thou movement) any ideas where this is coming from..I haven't looked at the rear bearings yet??...also after my run on the jacks stands I noticed a puddle of gear oil under the transmission but couldn't see how it got out...it was about a cup full.

Thanks in advance

I have a '72 and I have rebuilt the entire suspension -- new poly bushings, shocks, bearings, wheel cylinders, Toyota 4 piston calipers etc. and I still have noise from the rear end. It is similar to yours -- it is a zzzzzzzzz (mid to high pitched) that increases with speed but stops when I let go of the accelerator pedal. I also still get a little klunk even though my differential, tranny and motor mounts are new. The gears in the differential did not "look" worn but I did not investigate further. I too may be going to an R200/280ZX 5-speed setup. Not much help but misery loves company.

[speedyz]

I am having the same problem with my '75 280. I have replaced the halfshaft U-joints ($200.00). That didn't help. The problem seemed to get worse after I flushed the diff with fresh heavy weight oil. I just ordered a new diff mount. I will try that as well as replacing the diff with one I got off of some race buddies from a later model Z. My fear is that the problem lies in the driveshaft. Those U-joints can't be replaced. A new one with replaceable U-joints is $230.00. My family car, '92 Ford Crown Vic, had a similar problem with the loud whirrrr coming from the rear end and it was just frozen up drive shaft U-joints. The Z, however, has so much more back there that can go bad. I will let you know how all these changes work once I get them completed in the next few weeks.

[Daniel]

Lets call this rumor or fact,you make the call.There is a rear tranny mount .It is a rubber sandwich.They go bad from normal stop and go as well as the leaking fluid decreases the life of the rubber.I have heard that if replaced with the solid "racing part' it rides real rough.The snap sound when starting out is normal Z.I replaced everything in the rearend and still have it.I was told it was wear in the axle splines.When removing any of the drive/axle shaft mark how they came out.They are balanced at the factory to minimise vibration.Never reuse the nuts,bolts,washers that secure the shafts.The bolts stretch,thewashers don't lock.Make sure the bolts are all the same.You want uniform weight /balancewhen they spin.The leak may have been the rear tranny seal.Easy to fix.Drop the driveshaft pop out the old,in with the new.Make sure the driveshaft piece that goes into that seal is smooth.Any rust or roughness will eat the seal as it slides in/out during normal use.