Zerocyde

Hello all! I'm having a strange oscillating vibration that is probably my rear or th350 giving up the ghost from this new LS swap but hell, maybe it's just a tire balance issue. I was looking for some thoughts from yall on tracking it down.

It's not constant, it oscillates like MMMmmMMMmmmMMMmmmMMMmm. Sometimes it's barely noticeable, sometimes it's extreme. It's not tied to speed, but the gas pedal. Cruising at 30 or 80 it pulses the same but if I'm accelerating the oscillations speed up faster and faster. Also, it seems to stop completely when letting off the gas completely or popping it in neutral. My limited knowledge tells me that sounds like a rear end issue but I'm no expert. I vaguely remember it from before the LS with my 383 (but I could be wrong) so I doubt it's the brand new motor.

Details if needed: 88 camaro, had a world class t5 (383 took are of that!) now has a mildly built th350 with around 2600ish stall. 4.11 rear. 416 stroker LS swap built by a big performance shop.

Thanks for any help!

ratfink6923

iTrader: (2)

It would probably be helpful to get the car on a lift and have someone accelerate while you listen to the pinion bearing. I've also heard of driveshafts doing this at the slip yoke if the transmission isn't properly grounded.

ShiftyCapone

iTrader: (7)

Is this a new observation or has it always been present with your new combo? These cars become a megaphone for drone and vibratory noises when the power goes up.

Zerocyde

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I was actually thinking doing that on jackstands this weekend. What do you mean by "properly grounded" transmission? I did buy the big UMI adjustable torque arm because I thought it might be the LS not angled the same as a SBC and I feel like I set it properly but it didn't do anything to the vibration.

ratfink6923

iTrader: (2)

I meant the lack of a ground strap between the engine and body creating a static charge.

Did you set pinion angle with the diff off the ground or loaded at ride height?

Zerocyde

I put the front on jackstands and the back tires on ramps. I'll probably do it again this weekend while im workin on it and double check the measurement.

wlink14

Raise the rear of the trans, try 3/4". That's how I got rid of my humming/weird noise. Just chuck a thick block of steel/alum under your trans mount and get longer bolts.
Trans should be tucked way up tight in the tunnel.

jmd

iTrader: (4)

Oscilloscope app on phone can tell you the freq. which can translate to either wheel / driveline speeds.

Wireless chassis ears (Steelman) can narrow it down.

//<86TA>\\

iTrader: (14)

I had a very similar vibration and it was driveshaft/driveline angle issues. I needed to raise the back of the transmission or lower the engine, which in my case was the issue since I had poly motor mounts. Also verify pinion angle.