I need some dimensions or pic moustache bar area

[Mikes Z car]

madkaw,

Here are pictures of the moustache bar spacing from a newer car, one made in 1/1972. Down in the pictures is towards the front of the car.

Edited June 3, 2014 by Mikes Z car
grammar, my english teacher would be proud

[madkaw]

Okay guys-thanks for the replies. So I get under there and my moustache bar looks like mike's pic in that there is a gap between the bar and the downlinks , but the curvature of the bar causes that gap to diminish closer to the center of the diff.

Zed might have nailed this. I can take a pry bar between the bar and the frame and get quite a bit of up/down movement at the bushing. Zed, I went back to stock bushings, but they seem loose. My memory fails me and I will have to search but isn't there limited threads on the stud for the bushing? It seems that even though the nuts are torqued down the rubber washers aren't hardly touching the moustache bushing. Maybe I am missing some washers to make this tighter?

[madkaw]

So I dropped one side of the bar to look at hardware. I am definetly bottoming out on the steel inner bushing . There's no getting it any tighter against those rubber washers without spacers or something. I have no idea what amount of play is okay. It seems the pressed in rubber bushing is there to dampen twisting motion but it seems too much give for up and down

[Zed Head]

Your bushing rubber looks in better shape than many I've seen. The washers are supposed to bottom out on that inner sleeve. It leaves the bar kind of hanging in between, with the web of rubber of the bar bushing supporting the weight. The scalloped layer of rubber on the washers is more of a final damper for any movement. That's my take on the design. I think that the idea is to minimize pathways for the high frequency vibration. The diff howl.

But the rubber gets weak over time. If you've compared a new rubber transmission or diff mount to an old one you can really see the difference in rubber stiffness.

I've had good luck with the urethane mounts, with 2-3 washers added to the inner sleeve to leave a small air gap between the urethane and the washers. Basically, extending the sleeve length. The same general concept of the Nissan design. A little bit of float. My diff noise is less than when I got the car and had old worn clunky stock mounts. I had clunk and howl, pretty bad for both. I also have a an RT-style front mount now.

I think that most of the urethane mustache bar bushings are designed to clamp the bar tightly, race-car mentality, and transmit a lot of vibration to the body. That's why they tend to be noisy. Another opinion.

Maybe try some new mounts or get a another bar for experiments.

Forgot to say also, that the bar can move side to side on the mounting posts. The bushing rubber in the mustache bar ends is not solid, it's a web.

Edited June 3, 2014 by Zed Head

[zKars]

The moustache bar bushing rubber is likely old and soft or beginning to break down. Tightening down the nut just locks the bushing's center steel tube and the steel face of the washers to the frame, you rely on the hardness of the "eye" bushing rubber and the hardness of those "nubs" on the upper and lower washer to prevent the rotation/twisting of the M-bar that might allow it to touch those up-rights or anything else. Squishy bushings will let it twist all over the place. I'd love to have a go-pro and a light back there and take your car for a good spirited drive to see just how much that m-bar twists around.

I am also facinated by your earlier comment about diff whine increasing when you put the front diff mount back on. I think you've just increased and/or created a better/new vibration path from the diff to the body rather than a change in driveshaft angle being the source of the increased noise.

I just experienced something similar. I installed a new transmission insulator/mount and put poly bushings on the trans mount cross member ends. I did this to see if it would raise the trans tail to correct the driveshaft angularity, thus eliminating some driveline vibration I have. Well the end result was both good and bad. My driveline vibration is drastically improved (new trans mount insulator was a good 3/4" taller/thicker than the squished worn old original mount), BUT I now have much louder diff whine AND transmission noise! Did the drive shaft angle change this or is it the new poly bushings in the cross member that transmit more noise to the body?

BTW, to stay on topic a bit more, I also have a few clunks in the rear, and have very close M-bar/upright clearance with R200/Z31CLSD finned cover/brace etc, and when I put a pry bar between body and M-bar near the ends, I can move/twist the bar pretty darn easy. My M-bar bushings are really soft and the nubs on the washers are half worn out and soft too. New ones are on order. Had to come from Japan, all out of stock in Canada. Used to have the poly bushings, but then again, the diff whine transmitted was un-bearable. I'll have to experiment with some thin materials at the Diff/Mbar contact and Mbar/body mount points to see if we can't reduce this transmission.

Edited June 3, 2014 by zKars

[madkaw]

The moustache bar bushings are new or close to new. I went from a r200 to this STI-180 diff and went back to the r-180 bar. In hast I cut out the inner sleeve on the bar and had to go stock bushings. I believe it helps cut noise a lot.

I have a buddy with a lift and I am planning on putting it up there and taking a movie as I load the driveline to see whats going on.

The stock front diff mount on my car raises the pinion angle enough to change the angle. Whether thats the reason for the noise I am not sure, but there is a LOT with the stock mount.

I run the 83 trans BWT-5 so my angles are not stock either.

[bpilati]

I think using poly in the differential mounts is a huge mistake, because it allows the vibration to be transmitted much easier into the cabin. Stiffening these mounts adds nothing beneficial to the cars handling quality. I have poly as well, but wasn't thinking at the time. It is clear to me know that it was a huge mistake. Using poly in your suspension is a good idea, but not so much in the drive train.

[madkaw]

You might be right about the poly, but this thudk that i am getting seems to tie into reinstalling my r-180 and going back stock bushings.

I think the rubber washers need more preload then what they have. I found some huge washers that will cut down the the spacing and preload better. We will see how it goes!

[zKars]

I'm assuming you're thinking of putting your spacer/preload washers between the MBar and the two stock nub washers to get the nubs to touch/compress against the MBar eye. You must be sure the ID of those new washers is LARGER than the OD of the central sleeve in the MBAR bushing, ie does not touch it, or you will create a metal to metal sound pathway between the outer Mbar eye that the new washer now rests on, and the central sleeve, which is in tight contact with the frame above. However there is nothing to keep this washer from migrating off of center eventually, and coming in contact with the central sleeve again.

Think carefully what tightens against what and how rubber isolation is kept when this is all assembled or it may result in things getting worse, not better, or changing over time, confusing this more. You really need nub washers with bigger tougher nubs to increase preload.

The stock rubber bushing system was designed to contrain a stock torque level drive line with a non-LSD diffs etc. I'm not sure you/us/we can get the balance of stiffness and sound isolation we crave with our "improvements". I hope I'm wrong...

Edited June 3, 2014 by zKars

[madkaw]

I understand your point . It's an easy thing to try and takes about 5 minutes to remove.

It will be quick to determine if this effects anything. I really need to get this thing on the lift .

[Zed Head]

I think the rubber washers need more preload then what they have. I found some huge washers that will cut down the the spacing and preload better. We will see how it goes!

This is exactly what I did when I was dealing with loose diff problems. It helped with the thud/clunk. but did add a little high frequency noise from the diff, the more wahers, the worse the noise transfer. But it did give me the idea to find some washers that effectively added length to the sleeve that comes with the poly bushing. My current setup has the poly bushings in the mustache bar but the lengthened center sleeve, using washers that fit inside the urethane bushing hole, but are the same outer diameter as the sleeve material, and fit pretty tightly on the post. I think that they are called AN washers. ACE Hardware. So there's a fraction of an inch of wiggle room for the bar, but under load it gets taken up. I never had the fully compressed urethane bushings, or new stock rubber, so don't know what they sound like. But mine is much quieter than the old worn out parts.

[grannyknot]

Steve, I installed new rubber bushings to the M-bar when I switched to the R200 diff but the THUNK every time I changed gear got to be too much.

I burned out the new rubber, put in the poly replacements and the thunk is gone and I guess there is a little more driveline noise but not much.

I'm very happy with it. I also have the R/T mount with a poly plug just touching the top of the diff nose and a new stock rubber mount underneath.

Chris