Hi guys,

I am chasing a rear clunk noise which happens when going over the road cracks and potholes. Pushing the rear of the car with hands in an up/down motion doesn't reproduce it.

I replaced all the bushings in the rear 10 years ago. I probably put about 1000 miles on the car.

First, I thought the noise was due to my read speaker deck, I removed it. Another thought was the deck lid, there is small play in the deck struts due to the loose bushing/pin attaching the struts to the mounting location.

I jacked up the car, removed the strut assemblies and checked the rear strut insulators. They are solidly attached, no play. However, I saw a hairline crack on the LH side.

I checked all the rear sway bar bolts, nuts, plus the R200 hardware, rear half-shafts bolts/nuts, fuel tank/pump, mustache bar hardware. 10 years ago I installed an aftermarket RT mount, there is a 1/8 in gap between the R200 and the RT poly bushing when the car is rested on the jack stands.

What are your thoughts? I went through a lot of posts about the rear end clunking (hundreds of hits lol), and I think I checked all of them on my car with the exception of that hairline crack in the insulator.

I am planning to order a pair of strut insulators to begin with (240z ones with an adapter, unless someone has a pair of later 280z ones in a good condition?).

Thanks!

I doubt that hairline crack is the source of your problem, That crack probably doesn't go very deep. Hopefully it's just a surface feature.

So, the first thing I would check are the nuts on the top of the strut insert (down in the recess in the top center of the strut insulators). If one of them has worked their way loose (or were never tight to begin with), you would get a noise like what you describe. And you can't just "check for play" with the strut assembly off the car. That spring will extend to take up any available play. There would only be play with a load on the strut that has partially compressed the strut insert.

So was this noise always there, or is it something that has developed over time?

Did you replace the factory diff mount? When you use a bumper with the RT mount it essentially just replaces the strap. It reduces upward movement but the diff can also move downward if the stock mount is worn.

Also, the bushings and bumpers on the ends of the mustache bar look worn. If you crawl under the car and grab the mustache bar end with your hand you'll be surprised at how easily it can be moved up and down.

New bushings might help, although sometimes they can bring some diff whine in to the cabin.

Z Car Depot Inc

Mustache Bar Bushings Poly Differential 240Z 260Z 280Z

Mustache Bar Bushings Poly Rear Diff Mount S30 - 800-172 (). New Energy Suspension black polyurethane bushings for 1970-78 Datsun 240Z 260Z 280Z mustache bar.

Edited 13 hours ago13 hr by Zed Head

11 hours ago, Captain Obvious said:

I doubt that hairline crack is the source of your problem, That crack probably doesn't go very deep. Hopefully it's just a surface feature.

So, the first thing I would check are the nuts on the top of the strut insert (down in the recess in the top center of the strut insulators).

So was this noise always there, or is it something that has developed over time?

1. I will check the insulator nut on both sides, will compress the springs to do it. The noise has developed over the past year. There is no clunking when shifting gears, it is the annoying noise going over small/large cracks on the roads. The roads here in WI are not as good as in CA.

   11 hours ago, Zed Head said:

   Did you replace the factory diff mount? When you use a bumper with the RT mount it essentially just replaces the strap. It reduces upward movement but the diff can also move downward if the stock mount is worn.

   The factory diff mount was replaced with a brand new (then, 10+ years ago) Nissan diff mount. I just checked it - the rubber is solid, there is no play.

2. I am ordering the poly bushing kit for the mustache bar. The diff whine will probably get droned out by my MSD-2225 fuel pump :-) anyway. I insulated the FP with some nice rubber padding, and it is still loud.

Appreciate your guys' ideas!

It is summer here, time to enjoy our toys. Last winter I upgraded my stock Bosch L-Jetronic to the microsquirt ECU with the inj/spark control, need to start driving the car to properly tune it.