Tracking Down The Clunk - Worn Lower Diff Mount?

[EuroDat]

48 minutes ago, Zed Head said:

There was a thread on a different forum about using two part urethane to pour your own engine mounts.  I commented that sufficient adhesion might be difficult to achieve, considering the shearing forces at the interface of "rubber" and steel, but this application seems about right for it.  If the material fails everything is captured so that no parts come loose, unlike the motor mounts.  Remove the rubber from the bar end, build a mold, and pour.

The inside of a mustache bar end will give the dimensions needed to find a replacement from another car.  I have one with the old sleeve still inside.  There are really two dimensions that you could consider, old sleeve in, or bare bar.

I don't think two part pu would hold up to the stresses on an engine mount. The pu bushes you see in kits is a blended nanoclay-modified PU blend. Can't remember exactly, but it's a little different to what we home hobbiest use, me included.

The engine/diff mount insulators are originally HNBR. Nissan uses HNBR and noted in the price. The NBR aftermarket units are a lot cheaper, but will sage much quicker.

Edited July 15, 2017 by EuroDat

[Zed Head]

45 minutes ago, EuroDat said:

I don't think two part pu would hold up to the stresses on an engine mount.

The pu bushes you see in kits is a blended nanoclay-modified PU blend.

That was my point on the other forum, but based on adhesion to the metal base.  

Wasn't aware that "nano clay" was used in the PU material.  Where did you get that information?

An aside, and no offense intended, but "nano" is one of the most over-hyped, and incorrectly used terms in the materials world, in my opinion.  Anything can be described in "nano" terms.  It's just a unit of measurement.  A personal peeve.  I think that it got its popularity from Mork and Mindy.

[Captain Obvious]

That was nanu, not nano.   

[Captain Obvious]

4 hours ago, Patcon said:

@Captain Obvious

Can you post up the dims from the NOS replacements?

Will do. Later tonight.

[Captain Obvious]

Here's a dimensioned sketch of the OEM bushing. For those of you who don't want to deal with my chicken scratch, the bottom line is:

OD ~ 1.977
OAL of bushing outer wall ~ 1.575 after installation (1.985 reference before installation)
length of center bolt cylinder ~ 2.565
ID of bolt hole through ~ .677 (clearance hole for 17mm dia bolt shank)

Note that the 40mm after install dimension should be on the inside edges of the bent over flanges instead the outside as it's drawn. I'm no draftsman.

[Patcon]

Perfect

[Namerow]

from Wikipedia...

Hydrogenated nitrile butadiene rubber (HNBR) is widely known for its physical strength and retention of properties after long-term exposure to heat, oil and chemicals. Trade names include Zhanber (Lianda Corporation), Therban (Arlanxeo ^[5]) and Zetpol (Zeon Chemical).

Depending on filler selection and loading, HNBR compounds typically have tensile strengths of 20–31 MPa when measured at 23 °C. Compounding techniques allow for HNBR to be used over a broad temperature range, -40 °C to 165 °C, with minimal degradation over long periods of time. As a group, HNBR elastomers have excellent resistance to common automotive fluids (e.g., engine oil, coolant, fuel, etc.) and many industrial chemicals.

The unique properties and higher temperature rating attributed to HNBR when compared to NBR has resulted in wide adoption of HNBR in automotive, industrial, and assorted, performance-demanding applications. On a volume basis, the automotive market is the largest consumer, using HNBR for a host of dynamic and static seals, hoses, and belts. HNBR has also been widely employed in industrial sealing for oil field exploration and processing, as well as rolls for steel and paper mills.

[Hardway]

Wow!  This thread has really taken off.  Once again the Z community is out in force.  Well GOOD NEWS!  I solved MY rear diff clunk (yours may be different).  I went back to my original "diff sandwich" setup but with a small update.  First, using another member's suggestion I cut a piece of heater hose and inserted it in between the two plates of the lower diff mount.  This took some real effort as I used a large flat head screw driver to pry open the mount enough to get the piece of heater hose in.  As I talked about it later with Mike W, it probably would have been easier to put it on the diff so it was held in place while I worked on it.  Either way, its in and you can see it in the pictures below.  Next I had ordered a new snubber bushing for my RT mount a few weeks ago.  If anyone is wondering they are made by Prothane and are part number 19-1318-BL.  Got 'em on Amazon for $17.61 shipped for two as they are sold in pairs.  Just like I did with my old '72 240z, I only cut off one layer of the bushing.  I also cut the threaded stud down to clear the parking brake mechanism.  Using my adjustable safety stand I was able to push up on the cross member to get all four bolts in over half way, then working from side to side I tightened in equal steps and torqued anything down.  With everything buttoned up I did a once over on all the other suspension fasteners to make sure they nice and tight and they were.  Down came the car for a test drive, success!  Just cruising around and doing some spirited driver revealed no clunks or noises.  The only time I heard anything was when I drove it really hard, almost approaching abuse I could hear and feel the rear drive line make a thump/thud sound but not quite a clunk. I think it was just from drive train shock from hard driving.  I never drive the car like this so in my opinion I think everything is good as the drive line now feels rock solid.  I do not get any noise or vibration from this setup either.  If you have any questions please post them and I will do my best to address them.

[Captain Obvious]

Glad you got rid of the clunk!!

Just one comment/question. The rubber portion of those inboard control arm bushings are clamped into place by the brace you removed. With the brace removed, the rubber can rotate.

Point is... If you had the wheels hanging when you took that brace off and put it back on, I believe there's a risk that those inner bushings rotated changed position. Did you do the final tightening of the hardware with the car on the ground (or the wheels suitably loaded)?

[Hardway]

Good call CO!  I do need to double check everything with it on the ground.  I will do that this evening.  A good reminder for all of us!

[Captain Obvious]

Glad to help.       Only reason I even thought of it was because I had removed the same brace not long ago. I took the cheaters way out and put blocks under the tires to keep the suspension loaded while I had the back end up high enough to get under there. 

[Zedyone_kenobi]

Hardware... I am going to be cutting up a heater hose this weekend!! 

 

That was brilliant... Now I wonder if their s a way to inject some hard curing silicone to accomplish the same thing. Some type of rubber epoxy maybe.  Very nice!!