Rhythmic thunking slowing to a stop from right rear

[sboy79]

Still sorting out my 280z after manual trans swap and r200 diff install. Transmission was rebuilt and diff was resealed after inspection (everything looked good). Upon first test drive when coming to a stop I can hear a rhythmic thunk/thump coming from the right rear of the car. The only thing that wasn’t touched in the swap was the donor half shafts so I rebuilt them with Japanese u-joints. Reinstalled them and still have the same thunk. The driveline is original but u joints seem fine (nice and tight). This *sounds* like a half shaft or driveline u joint problem but I can’t find any slop in any of them. 
 

Next step might be swapping the half shafts side to side to see if it moves but before doing that I thought I’d post here and get some opinions. 
 

All bushings in the rear end have been replaced with rubber except for mustache and diff mount which are poly (couldn’t locate rubber replacements). Brake drums and shoes are new. 
 

What else should I be looking at?

Thanks in advance for the help!

[dutchzcarguy]

5 hours ago, sboy79 said:

when coming to a stop

So you only hear it while braking light? It must be IN the brake drums.. Maybe you didn't install the springs the right way in them? check the service manual!

Is the noise always there and not loud or only louder while braking?  If not found put some locking pliers on the rubber brakelines and test again.. watch OUT !! test on a save road as your rear brakes are not working now.. but if the sound is still there you KNOW  that it's not the brakes! 

Edited July 26, 2024 by dutchzcarguy

[Patcon]

I like the idea of swapping axle shafts side to side.

[sboy79]

2 hours ago, dutchzcarguy said:

So you only hear it while braking light?

I can hear it when coasting to a stop (no brake) but that’s a good point. I could just adjust the brakes super loose and try it again to make sure it’s not a brake thing. Locking pliers are probably easier though and I’d still have front brakes immediately. Clamping the lines like that won’t damage them?

Edited July 26, 2024 by sboy79

[Patcon]

I like the idea of swapping axle shafts side to side.

[Patcon]

I'm not a huge fan of clamping brake lines but it shouldn't hurt them

[Zed Head]

I'd swap the wheels first.  Easiest and a possibility.

2 hours ago, sboy79 said:

I can hear it when coasting to a stop (no brake)

 

[sboy79]

Ok. Swapped wheels. No change. Swapped half shafts. No change. 
 

My other observation is that it isn’t present at first and then comes back when the car is warm. I’m thinking diff. It’s the only thing (other than driveline) that hasn’t been rebuilt. 

[dutchzcarguy]

19 hours ago, sboy79 said:

Clamping the lines like that won’t damage them?

If the rubber lines are in good condition, no problem, if they are damaged by the plyers they were already not save to use anyway.. Maybe use a bit of cardboard between the line and the clamping plyers.  (Also attach those plyers on a rope or something that they not interfere with driving and if they fall off you wont have to go look for them or buy new ones!)  And as you said you will always have the front brakes.. and the front is used for braking about 60-80%!  you barely notice the difference!

[dutchzcarguy]

On 7/26/2024 at 5:45 AM, sboy79 said:

All bushings in the rear end have been replaced with rubber except for mustache and diff mount which are poly (couldn’t locate rubber replacements).

Mustache bar .. i don't know but the diff mount you can order a new one at nissan for as far i know.. (For a 240z i don't know if the 280z is the same.) I do have a new diff mount rubber for my car laying around. could look for a number on it if you need it.

(Personally i HATE poly in places where rubbers where.. especially a diff can give strange noises through the mount to the body..)

Maybe untightening the diff mount just for a test is a easy thing to test.. don't forget to tighten it up again!

Edited July 27, 2024 by dutchzcarguy

[jonbill]

I'd lift the rear end, take the wheels off turn the wheels and check if you can see or hear it.

[Zed Head]

19 hours ago, sboy79 said:

Ok. Swapped wheels. No change. Swapped half shafts. No change. 
 

My other observation is that it isn’t present at first and then comes back when the car is warm. I’m thinking diff. It’s the only thing (other than driveline) that hasn’t been rebuilt. 

 

On 7/26/2024 at 5:02 AM, sboy79 said:

I can hear it when coasting to a stop (no brake)

 

On 7/25/2024 at 8:45 PM, sboy79 said:

when coming to a stop I can hear a rhythmic thunk/thump coming from the right rear of the car.

 Not super clear what's happening.  How about a softball in the cargo box behind the passemger seat?

You mentioned the diff, you could swap stub axles.  You didn't mention the hub flanges.  Might have a bent hub axle.

Or, maybe it just sounds like the rear but is actually from the front.