Rear clunk after installing new struts

[JohnnyO]

I replaced my rear struts and refreshed my rear suspension in March and since the first test drive I have had a rear clunk. I did not have this clunk prior to replacing the rear struts. I replaced the struts with the rear diff installed but mustache bar removed. Not sure if that matters or not.

Since then I have loosened and re-torqued all rear suspension bolts both jacked up and under load, front and rear differential supports and checked the U-Joints on the drive shaft and half-shafts.

When I reinstalled everything I did not install a rear anti-sway bar that the PO had installed. I do not think that this could cause the clunk. Please correct me if I am wrong and I will order stabilizer end links for it and install it.

Another thing I noticed when removing the mustache bar was that I only had a top stopper. They look like this only $34/pair cheaper through Courtesyparts.com. In place of the bottom stopper was a 3" washer without the ribbed rubber. I don't think that is the problem because it would have existed prior to installing the new struts.

Could I have damaged the front diff mount by holding the diff up with a jack for 2 weeks while I blasted and painted the suspension?

Could the old Mulhollands have been riding so low that no matter how hard I got on it she would never create enough torque to slam?

Grasping at straws here. Any help appreciated.

John

P.S. Found a great old post with part numbers for replacing Mustache Bar bushings at zcar.com from 2002.

http://www.zcar.com/70-83_tech_discussion_forum/datsun_240z_early_series_mustache_bar_bushing_644441.0.html

[Arne]

When does it clunk? On bumps? On torque changes?

One thing that happens now and again is one or both of the new inserts are not completely cinched solid in the strut housing. Occasionally I've heard about cases where the gland nut will bottom out on the strut housing, when it is supposed to bottom on the strut insert instead. That will allow the insert to move in the strut tube and clunk.

[JohnnyO]

It clunks under heavy acceleration and when I let off the gas after heavy acceleration. It sounds like it is coming from the rear center of the car. I went with the KYBs and the gland nuts were on there pretty tight when I was done. I have checked the strut mount insulator nuts and the actual strut top nut.

I would have to remove the springs to check the gland nuts. Not really looking forward to that.

[Zs-ondabrain]

Sounds like the diff mount fianlly gave under the pressure of holding up the car for a while.

Courtesy carries them. You may wanna look into an R/T mount with the Bump stop options. Brian at http://www.technoversions.com/DiffMountHome.html has them for $72 Shipped. It will sandwich your diff and stop it from moving up and down (causing the thump)

"The differential on Z-cars is subject to a tremendous amount of torque when accelerating. The stock differential mount is from the bottom, so the rubber pulls, rather than compresses, as the front of the differential moves up during acceleration. Even with a stock engine, Datsun realized that the movement needed to be limited, so installed a strap to prevent the differential from moving too far up. With added power, the differential mount in the stock car is overstressed. Also, when changing to a stronger differential (such as an R200), the factory limiting strap will no longer fit."

Both me and Arne have one with great results.

Dave

Edited June 6, 2011 by Zs-ondabrain

[steve91tt]

I agree with Arne. It's not the tightness of the gland nuts you have to look for it's whether or not they are bottomed out on the strut tube. You should be able to see a thread or two when tightened. If not the strut may be moving in the tube. This happened to me last year. I had to put a couple of washers at the bottom of the inside of the strut tube to make the clunk stop.

[JohnnyO]

Dave, I have read great things about the r/t mount but am trying to stay stock. I will drop the front diff mount and check to see if it is separated. This is easier than dropping the struts.

Arne/Steve,

I remember when I filled the strut mounts with oil and tightened the gland nuts that there were a couple threads showing and oil didn't leak out of the top so I assumed the cartridges were snug. But, you never know so I will check them after I check the insulator.

[tlorber]

Johnny, just so you know, I have the R/T mount AND the original mount in place and still get a clunk. The R/T mount is definitely a more secure configuration but it may not solve the problem. Once I get my car back underway I will be checking the struts, and may need to shim them as Steve911 mentioned.

[Arne]

There are about a half dozen potential clunk sources back there. The RT mount (much as I am pleased with mine) should not be considered as a total cure. Diff mounts, halfshaft u-joint, struts, even transmission problems can cause clunks - all of which pretty much sound like they are coming from the rear center of the car...

Back to the OP's issue - Since this clunk is new after the strut and rear suspension rebuild, I would suspect either the strut inserts moving in the tube, or a now-tired front diff mount. The diff mount can be bad enough to clunk w/o being visibly separated. That's where a good diff strap or the RT mount can help.

But I'd still suspect the strut inserts. If either of the gland nuts are bottomed out on the tubes (no threads visible), I'd look there.

[JohnnyO]

Thanks for the tips guys. I will try to find time this weekend to check out the gland nuts and the front mount.

[JohnnyO]

So it was the rear diff insulator. I replaced it Saturday and inspected the old one and could see it gave way. I suspect that it gave way when I lifted the rear of the car by the drear diff. I read somewhere on here that that was ok but I would not recommend it.

I ordered the part from Nissan of Chesapeake along with some other parts I needed and paid $20 less than the theives on ebay.

Thanks for the help guys.

[LeonV]

The differential housing is the rear jacking point as specified by the FSM; page GI-11, figure GI-9 (in '72 FSM). That's where I always jack the rear up and never had a problem.

FYI...

[Zs-ondabrain]

It is IF you place the jack near the rear of the diff, so the weight is held more by the Mustache bar than the front diff mount.

it's all in the position of the jack,

Dave