Bigsyke

So we all know there is a 2,200-2,800 rpm vibration. It seems harmonic based and happens even worse on deceleration. When my exhaust was misaligned, the sound was deafening. My exhaust lasted 3 months before cracking and the flex pipes breaking in half. (solid tranny mount and engine damper didn't fix the vibrations, and I have no harmfull engine movement).

Because this seems simply rotational, has anyone seen an improvement apon installing a fluidampr? I think the goal here is to save flex/test pipes.

travlee

iTrader: (8)

i never had any vibration in that range

KornerCarver

iTrader: (2)

I've never had any vibrations like that.

woody03

iTrader: (5)

^^^

iideadeyeii

iTrader: (6)

^^^

350z006

iTrader: (79)

^^^

Classy

iTrader: (7)

^^^

Syner

^^^

StuLax18

iTrader: (4)

That's when I ***.

Eff your combo ***** *** pods!

Syner

fk u stulax18.

e30cabrio

iTrader: (30)

I'll take any excuse to **** talk the vq35 & can't use this one bummer.

MicVelo

Never heard of that and I've heard a fair amount...

What is this fluid damper you speak of? What are you trying to dampen? It sounds like you're talking specifically about your exhaust system. If so, when you look at any well engineered dual system, a good install will include pipe bracing and rubber/neoprene isolators fore to aft.

Solid transmission mount? Bad idea for a street driven car. I like my teeth.

Bigsyke

If you search for things like heatsheild rattle, exhaust vibration/rattle, you will see it's around that rpm range. That alone is enough to tell you there is some vibrations happening throughout this range.

It's an out of sight-out of mind sort of thing. It's there, but heavily masked with OE cats or a supported exhaust system.

A solid tranny mount is no different than an OE mount. There are no vibrations.

travlee

iTrader: (8)

there are a ton of vibrations with a solid tranny mount....

StuLax18

iTrader: (4)

On the FX I get a rattle at about 3000, like a loose washer is just going in.

Bigsyke

I have the Z1 mount installed. I feel 0 vibrations in the cabin. There was no difference when I installed it.

travlee

iTrader: (8)

the z1 is not solid, it still has poly bushings

http://www.z1motorsports.com/350_g35...oducts_id=6527

MicVelo

OK, now the problem is more specific - rattle and vibration from exhaust system between 2k-3k rpm. Severe enough to sheer exhaust piping. Yes?

You mention it was most severe on decel. How about acceleration?

At this point I'm guessing that it's related to torque effect from the engine on accel/decel, and NOT steady state cruising (where torquing over of the engine is minimal).

I know you said they were OK but have you verified that there's no sheering of the motor mount bushings? I ask because this really sounds like a mount issue. This requires disassembly. Revving the engine at standstill won't reveal a broken mount as there's no real torque load on the engine that would be revealed (visible motor torque over or twisting) as it is during hard acceleration or under compression loaded deceleration.

You may have a broken mount on the one side opposite the engine torque motion as stock engine mounts work on retention through tension which, over time, can cause the rubber isolators to pull out or sheer inside the mounts (starting partially then leading to total failure). High performance mounts, OTOH, typically work under compression loading so the mount in the direction of the engine torque is resisted. It's generally a smarter arrangement - particularly on big V8 applications.

Secondly, if indeed you ARE running a solid transmission mount with stock rubber or urethane bushings, that could also cause the type of damage you describe. Think about what the engine and transmission are doing..... the engine moves but the tail shaft of the trans and any braced exhaust components don't (or resist mightily). That creates excessive sheer points on the brittle componentry.

Worst yet, a solid mount puts a HUGE load and strain on the transmission CASE, which could also fracture due to insufficient "give" or flex. It has been known to happen.

But as Trav points out, the Z1 mount is a urethane lined aluminum mount, NOT solid. Your point of there being no difference kind of tells me that you've never actually run a solid unit before. Trust me, if you did go solid on your car, you WOULD feel it, particularly on the street.

I used to run a high durometer (rubber pad insert) trans mount (Datsun Comp) on my race roadster that was WORLDS apart from the street version that I switched out when I built the car. And that wasn't solid, obviously. Again, think about it, a solid mount transfers all of the engine and transmission vibration directly into the cross member, hence into the entire chassis and body structure.

This is why I said a solid mount on the street is a bad idea. BUT, that all said, if you can stand a solid rear mount then at least go to a solid or very high durometer rated engine mount set... maybe a 75A+ rated setup.

Let us know what you find out.

timeltel

"There is a 2,200-2,800 rpm vibration".
"It seems harmonic based and happens even worse on deceleration".
"This seems simply rotational."

Suggest a search of the forum, "Shifter vibration" and (hint) "Flywheel vibration".

MicVelo

Dayam, timeltel to the rescue again. Coulda saved me a boatload of speculative troubleshooting.

Never even thought of that.