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REAR SUSPENSION BUSHINGS AND MOUNTS


JTO

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I am new to this site. I have a 1972 240Z. I am replacing some rear suspension/drive train bushings. I removed the transmission mount cross member, the differential front mount cross

member and the mustache bar and I am replacing bushings and mounts in these components. I have a couple of questions:

I installed new bushings, sleeves and large washers on the mustache bar. What is the torque setting for the mustache bar bolts. I suspect you tighten the nuts until the large washers are fully seated against the bushing sleeves. Is this correct or is there a specific torque?

There is an "arrester belt" that straps over the differential housing near the front of the differential. The existing belt showed signs of wear so I replaced the belt. Is the belt meant to fit tight/snug against the top of the diff or is it there more as a guard against the diff coming loose and flying around. The new belt I installed does not fit snug against the top of the diff. I am not sure if the old one did.

I ordered new bushings and sleeves (from Energy Suspension) for the small "mustache" bar that mounts in the transmission mount cross member. The bushings and sleeves provided do not fit. Energy Suspension confirmed they are the right parts. I purchased the car new and as the sole owner, I know The transmission cross member is OEM. I purchased the car in Canada and I am wondering if the cross member is different than on a car purchased in the US. So far I have been unable to locate bushings that will fit, or a new bar c/w bushings.

Any comments would be appreciated. Thanks.

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Welcome to the forum, an original owner that's wonderful!

I'll just comment on the arrester belt, no it was never snug over the top of the nose of the diff so your new belt is working as designed however that doesn't mean it is a good design in the first place.  Many owners have gone to the R/T mount to help eliminate some of the thumps and clunks that happen back there, I have some old rubber conveyor belt that is about a 1/4" thick, in the past I have cut 2 pieces of that belt 2"x 4" and slipped them between the top of the nose of the diff and the bottom of the arrestor strap so that the strap is snug, I've found it to be quieter when I'm driving the car hard.

Edited by grannyknot
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Hey JTO. Zkars here from Calgary too!  Send me a PM and we can chat or meet up.

Replacing the bushings on the mustache bar and trans mount are fraught with issues. If your stock mustache bar bushing are badly worn, you may not have much choice but to use poly replacements, but doing so will result in more vibration and noise from the diff. These do not affect suspension or handling, so don’t do them unless you have to. 

Pretty much the same goes for the trans mount. Are the bushings too small? If so you have to remove the outer shell of the old bushings to make room. But again, unless the stock bushings are shot there is no point to changing them other them to increase noise. I know others have expressed concern over fitment. IF you want to go back to a stock mount, I have more than a few. I’m the local parts hoarder....

The belt over the diff is a last resort to prevent the diff nose from hitting the tunnel if the isolator mount fails. It fits a bit loose. I’ve added a rubber spacer in there to take up slop, no sense letting the diff lift at all. 

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grannyknot, zKars...Thanks for your response. Much appreciated.

I had a clunk in the rear and what felt like slack in the drivetrain so this is why I am inspecting/changing mounts and bushings. I had previously inspected and replaced bearing cups and spiders for all six UJ's, and replaced all control arm bushings (with rubber). They all still seem good. I cannot detect any issues with the hubs (no noise, no play) or the struts so I am now looking at transmission and differential mounts. The transmission rubber mount and bushings as well as the mustache bar bushings all appear worn (all now 50 years old). The front diff mount looks good as I had changed that in 1997 (21,000 miles ago). I had no problem procuring transmission and diff rubber mounts but the only bushings I was able to locate were urethane so I guess I will go with them (and see how noisy they are).

I like the idea of the rubber spacers between the diff and the arrester belt so I will give that a try as well. Thanks for the suggestion.

I am still trying to determine how tight the nuts should be for the mustache bar mounting bolts so if you hear of anything, please pass it on.

Thanks...Tim

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I would never redo these parts without upgrading to the RT Mount.  While you are in there, it's the best solution going forward.  The OE mount was a bad design and the RT Mount corrects the bad design.  With the diff removed, it's a very simple install.  I learned the hard way that trying to do it with the diff in place is very difficult and frustrating, but can be done.  Start with a new OE diff mount and the RT Mount and then you can remove and discard the strap and strap mounting parts.  If you back to OE, the front mount will fail again at some point.  The OE mounts will be NLA someday, so a future failure of the mount due to the strap design could get costly.

If you have a street-only Z, I'd cut the upper RT snubber a bit shorter than normal.  In my race car, I kept a bit of preload, but I'd give a street car a bit of a gap to cut NVH.

https://www.technoversions.com/DiffMount.html

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zKars...Maybe you could send me an email at tim.ogle@shaw.ca. I would be interested in hearing about what 72 240Z parts you have.

Jeff G....Thanks for the RT Mount info.  I took prints of the photos from the link you sent so now I will get back under the car so I can visualize how it would go in. 

Ernesto....I agree the torque shouldn't be much different. I will go with the 54 - 69 lbs. Seems like a pretty large range of torque but we will see, Thanks.

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10 hours ago, JTO said:

zKars...Maybe you could send me an email at tim.ogle@shaw.ca. I would be interested in hearing about what 72 240Z parts you have.

Jeff G....Thanks for the RT Mount info.  I took prints of the photos from the link you sent so now I will get back under the car so I can visualize how it would go in. 

Ernesto....I agree the torque shouldn't be much different. I will go with the 54 - 69 lbs. Seems like a pretty large range of torque but we will see, Thanks.

I usually go about 75% of the torque range, so for the mustache bar I'd torque the nuts to 65 ft-lbs.

The RT mount is super easy to install with the diff out.  It slips right into place once you remove the strap hardware.  You will need to do some trial and error on how much of the snubber to cut off.  If you go with a RT mount or not, start with a new front diff mount.  Your is most likely shot.

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You can get a fair idea of diff looseness just by lifting with your hands on the mustache bar ends, and using a jack under the diff nose.  The clunk at the diff nose seems to come from the diff nose dropping back down after it lifts up under load.  Lift-clunk-lift-clunk, as you shift gears and accelerate.

The torque specs are in the FSM.

https://www.classiczcars.com/files/category/11-240z/

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To all that responded, thanks for the info. Much appreciated.

On another matter, I had noted in a previous post above that I had purchased the PU bushing kit for the transmission cross member mount from Performance Suspension but the bushing kit they sent doesn't fit. The bushings and sleeves are too long and the bushing diameter is too big. I have attached a photo of my cross member. The distance between the brackets that carry the bar is 2.135". If anyone happens to have a spare cross member sitting around or a cross member out of their car, could you take a measurement between the two brackets and let me know if you get the same or different measurement. I know my cross member is OE but for some reason may be different than most.

Thanks...Tim

DSC01452.JPG

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I am 99% sure that I have seen the problem with that type of mount before.  There's a thread where somebody removed their old bushings then found that the new ones wouldn't fit.  I'll see if I can find it, but you might search around in the meantime.  Short answer is "I don't think replacement bushings exist".

For whatever reason, Nissan doubled up on rubber back there.  You've got a rubber mount on a rubber mount.  Never really understood why.  And the mount doesn't see much twist because the motor mounts stop the engine from twisting.  It's not like the mustache bar mount.  Nissan actually calls it an "engine mount".

Anyway, don't tear it apart assuming that you'll find a fix.

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