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Frnt Diff. Mount Counterweight???


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Guys,

I've had this '77 280Z for over six years and never gave this component a second thought until now. I'm fabricating a Ron Tyler front diff mount for my 350 SBC/T-5 installation using the JTR kit, and I know I'll be modifying the original mount to provide clearance for the driveline angle changes.

 

These plates are 3/8" thick each, and the stack is 2 1/4" tall in front of the mount (just clears the 3/4" sway bar) and 3/4" thick behind the bar, all welded together. (see attached pictures)

 

So, is it a factory piece? Or is it aftermarket? Either way, what purpose does it serve? Is it of value to other Z enthusiasts?

 

(I should also tell you that this was originally equipped and sold as a Texas car without catalytic converter, heat shields, or heat sensor and warning light. Otherwise, it's stock, for the moment.)

Thanks,

Steve

IMG_0154.zip

IMG_0155.zip

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That was a weight added on by the factory because the rear diff would clunk sometimes when shifting an auto into gear, by adding the weights (extending outward from the diff towards the front of the car) they were able to dampen the movement of the diff and predominantly eleminate the clunk noise. From the sounds of your application it is certainly not needed and most likely of no value to anyone other than a metal recycler.

 

Dragonfly

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Thanks for the feedback. I see that I can save another 8-10 pounds as part of this conversion :) Curious though that my Z was never an automatic transmission car. I'm the second owner, and it's all very original, except that I pulled the four speed manual and replaced it with a 5 speed from a wrecked '77 2+2 (and that one was original too, until my son wrecked it!). Anyone need a paperweight?

Thanks again,

Steve

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Nissan TSB # TS75-068A, Sept 3, 1975

 

“Countermeasures for S30 R180 Differential Noiseâ€

 

To reduce internal noise in the S30 differential a differential noise damper kit is now available as a service part. Differential noise is caused by the tooth meshing action of the ring and pinion gears, amplified by structural vibration of the vehicle body. The noise damper kit contains a 10 lb mass damper weight which attaches to the differential housing to absorb structural vibration and the necessary attachment hardware.

 

The kit can be also be applied on the 1970-74 S30, R180 differentials only. This kit should not be used on any 2+2 vehicle due to possible interference with the rear seat belt attachment bolts.

 

Kit Part Number: 99991-2000

 

 

Since the only 280Z’s that had a R180 were automatics, one might be inclined to think that only automatics had the differential noise damper kit installed. However, I recall that my four-speed 260Z had the damper weight when I purchased it back in the mid 1980’s.

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My 77 has one too. I bought the car as a V8 conversion and from every thing I can see it was always a stick shift. I did not remove it during the LT1/4L60E automatic swap and I just finished my 300ZX LSD swap and left it in place. I do get a clunk every once in a while shifting from 1st to 2nd and 2nd to 3rd, usually on soft starts only. No clue yet what that clunk is.

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Nissan TSB # TS75-068A, Sept 3, 1975

 

“Countermeasures for S30 R180 Differential Noiseâ€

 

To reduce internal noise in the S30 differential a differential noise damper kit is now available as a service part. Differential noise is caused by the tooth meshing action of the ring and pinion gears, amplified by structural vibration of the vehicle body. The noise damper kit contains a 10 lb mass damper weight which attaches to the differential housing to absorb structural vibration and the necessary attachment hardware.

 

The kit can be also be applied on the 1970-74 S30, R180 differentials only. This kit should not be used on any 2+2 vehicle due to possible interference with the rear seat belt attachment bolts.

 

Kit Part Number: 99991-2000

Hmmm, this might be an effective way to reduce some of the noise from my R180. Anyone have one of these kits that they don't want any more? Please PM me, or email me: daniel at bailin dot org

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That was a weight added on by the factory because the rear diff would clunk sometimes when shifting an auto into gear, by adding the weights (extending outward from the diff towards the front of the car) they were able to dampen the movement of the diff and predominantly eleminate the clunk noise. From the sounds of your application it is certainly not needed and most likely of no value to anyone other than a metal recycler.

 

Dragonfly

 

Ever Z I have crawled under has his hunk of metal in different configurations though. I agree that is a factory item, my 1973 had it even though the other site listed here said it was an upgrade in 1974. It made a great exhaust hanger when I was making custom pipe. Also great for a rub rail on lowered cars.

 

I couldn't tell a clunk from a clump in my old heap, she is a bit of a rattle trap!

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Curiously Ford did the same thing for Fox Bodies...

We called them "Donkey Ball Retrofits"

 

It was two round, lead balls on the end of a length of cable. You put the offending car on the rack, slipped the 'donkey balls' over the driveshaft about midway, and then slid 'em down to the nose of the differential where there was a notch that the cable would catch in... Same thing: NVH (Noise Vibration Harshness) Customer Complaints.

 

Changing the mass of something to stop resonances is the same thing slapping that dynamat in the center of a door panel, or the center of a flat floorpan...

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  • 5 months later...

Hahaha!! I was wondering what that chunk of metal was! I was seriously debating not reinstalling it because I did not see a purpose for it. My Z is a 1978 with an R200 diff, which is also curious seeing this was normally an R180 w/ automatic application. Once I get my car running, I'll have to see if I get the same vibration issues.

 

I can't remember off the top of my head if the VIN on the car indicates that it was once an automatic, I'll have to check. If it was, that might explain why the cover plate for the bottom half of my flywheel is missing. There's so many loose an cut wires that I've found hanging in my chassis, maybe I'll have to look and see if those automatic relays/switches are still there (or look like they once were).

 

Then again, it could just be a factory retrofit.

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