hey all I have an annoying knock in the rear end of my 77 280 Went on to Z garage and it states that this is a common problem with about 15 possible solutions! So far I have replaced struts on all four corners as well as new urethane bushings. I am no mechanic but I can do the small stuff. Anybody had this problem with a obvious simple solution or do I just start at the top of the list. I would appreciate the advise. Greg

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77 280 305 BLUE

Hi Greg ~

Are you able to pinpoint the location of the sound? Left, right, center?
Have you been under there to search for any obvious signs of something hitting something else?

If you have drum brakes, have you done any work on them lately? Shaken the exhaust system and turned the half-shafts while listening to the UJoints? Checked the spare tire well for empty bottles? Checked the wheel arches for rubbing tires? Checked the lugs to ensure they're tight?

Is it an occasional knock, or frequent, or constant? Does it increase frequency as roadspeed increases?

Frank
(NOT a '77 280 specialist ~ just a guy who's had everything go wrong at one point or another, and the entire list above has happened to me over the years)

When does it knock? When you hit a bump, when you hit the brakes, when you accelerate, when you turn suddenly, when there's somebody at the door?

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71 on a rotisserie, two more in pieces in my shed...and a 69 1600 waiting for me to get to it

Knock, knock who's there?

when i accelerate mostly right behind drivers head

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77 280 305 BLUE

This might sound weird ~ try it in reverse. See if you get the same knock by accellerating backwards in an empty parkinglot. Let me know.
Frank

good thought I,ll try that
Thanks frank!

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77 280 305 BLUE

I had some issues with rear end noise both forward and in reverse......turned out to be too much fiber!

Thank you! I'm here all week, please tip your waitresses.

*one more post towards # 4,000

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Keith Hultmark
2009 370Z Touring - Sold (5 years owned)
1993 300ZX - Sold (5 years owned)
1976 Porsche 912E. #163 of 2200 - SOLD (3 years owned)
2018 BMW 330i GT xdrive daily driver
2004 BMW Z4 3.0i ….it is a Z

my first guess for a knock coming from one side under acceleration is a bad U-joint on a half shaft. Usually you can find these just by twisting at the joints by hand. If it's just a single clunk it could also be a bad mustache bar bushing.

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71 on a rotisserie, two more in pieces in my shed...and a 69 1600 waiting for me to get to it

That was my thought, Mark. Sometimes mine only clunked going fwd, but not in reverse. Typical UJoint worn on one side of the ear(z).

My buddy, however, had the same noise with GOOD UJoints. Turned out it was his pinion gear instead. It clunked going fwd, but whined in reverse more than usual. Cost him a bundle.

Mustache bar is a thought, tho ~ what happens? Bushings just wear out?

I have also done rear brake shoe jobs and failed to replace the springs properly ~ it doesn't take much ~ the rotating hub hit them and eventually they sprung back out of the way. But unless I was willing to listen to that racket until they did, I had to jack it back up and pull everything apart again.

Frank

It took me 20 years to get the knock out of the Z.

1-diveshaft flange bolts loose (includes half-shafts)
2-torn rubber in front differential mount (VERY COMMON)
3-Deteriorated mustache bar bushings.
4-loose mustache bar bolts (check all four)
5-excessive backlash in diff gears (uncommon)
6-spider gear pins in differential got loose (uncommon)

Shut off the car let the exhaust cool. Park it on level gorund. Put it in first gear, or park. Lay under the fuel tank with a view of the differential. Rock the car back and forth fairly hard by pushing on a tire, or use a partner to roll the car back and forth. Watch the differential. If it moves, you have problem #2 or #4. If it does not appear to move, listen, and grab the shaft flanges, feeling for play.

Good Luck,
Dave

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-Dave
76Z Turbo'd
72 In Progress---DONE!

If the knock is something like a *THUD* that happens every time you change gears (or especially under hard acceleration) you may be having the same problem I have: a worn diff mount. Mine is the same the car came with from the factory, and its really shot. To add to this, I also removed the large steel plates (factory added weight) from the bottom of the nose end of the differential which are also supposed to alleviate this issue. Mine clunks ALL the time. Check both of those things, and also check the rubber strap that runs over the UPPER side of the diff's nose end.

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-Chris

Greg,
You are in good hands here…. The only other thing to look at is play in the Half Shafts at the sliding portion of the shaft, but this is rather rare unless a boot ripped at one time. I would say I have replaced more half shaft joints than any other car I have worked on.

Z's just click..
there's not alot you can do to stop it..
put new uni's in everything then 6 months later the clicks r back..

if a diff mount is really stuffed it will thud and jump around under wheel spin.
my 2+2 was really bad for diff bounce. get on a dirt road and spin the wheels and it felt like you were driving over corregation..
check front mount and moustache bar..
i have seen a broken moustache bar result from hard driving...
but then again i've known people blowing gearboxes up too... never a Nissan box though...heheheheh
what r these people doing?????????