Pasky

Driveshaft is balanced (ls1 driveshaft), tires are balanced, and the flywheel is balanced. I can't figure why it vibrates like it wants to come apart. This isn't the engine bogging, thats a different feeling this is happening at anywhere from 1200-1700 rpm at 60-85mph. If I start to give it gas in sixth, my car feels like its coming in for a landing from the atmosphere. I never replaced the transmission mount on my T-56, its still stock, could this be it?

LPEdave

It sounds like a burned or loose plug wire. Check them all, it's typically pretty easy to spot if you run the car in the dark looking for sparks.

Dave

Pasky

So this would normally only happen in sixth? I just bought some wires and im going to be doing that tonight, I havn't done it because I was busy the last two days putting the center console back in. I suspect you are correct because my headers burned a few. Thanks, but why wouldn't it vibrate at low gears?

Pasky

BTW, it never happens in in 4th. Slight vibration in 5th, barely noticable, but sixth is like, "HOLY **** hold on to your pants, she is coming apart!"

jbird

The reason the vibration could be more noticable in 5th and 6th is because the engine is under quite a bit more load in the overdrive gears. Think of it like pedaling a bicycle. In a really high gear, if your muscles were shot you'd have a pretty rough time, but in a lower gear you might manage ok.

LPEdave

You could drive around all day on 7 cylinders in 1st thru 4th gear, and never know you were missing one. As jbird mentions, there's more load on the engine in 6th than 1st, especially at those low RPM's.

Dave

Pasky

Thanks guys! That has to be it! I have noticed a loss in power lately. Good thing I bought some wires. How can I check for fouled plugs? I plan on pulling all of them tomorrow and re-check the gaps and run the wires and twisty tie them in place. Thanks a lot guys.

turbo_Z

First thing that came to mind was a burnt wire a bad plug since the same happened to me before. IMO if you pull the plugs to check the gap you may as well buy new ones to replace them with.

Hyperspeed97z28

I got a nasty viberation in 6th as well... feels like the rear end, but i'm on my 3rd rear so I know it isnt the rear.... (3.42-3.73-4.10's)

I should change my wires as well .... BLAH

Pasky

I agree, but the plugs have less than 200 miles on them and were replaced 2-3 months ago. The car has been in the paint shop for about a month and a half and i've been doing suspension work on them.

Pasky

just replaced the wires, feels better now, but still shakes. I looked underneath and to my horror I saw the passenger side motor mount bolt fell out . Ok so now I got that to worry about, could that have been the cause? Also I hear a thud when its shaking, I feel the transmission mount is playing a part in this. One more thing, I let the car run and it was pitch dark so I popped the hood and I see a few sparks coming from the coil. I've never noticed this before. My idle was a bit eratic, it would move between 100 rpm quickly of idle, like jump from 800 to 900 very fast and then back to 800. Bad coil?

Pasky

Anyone know?

1racerdude

Narrow up your plug gap to .035 and wipe off the porcelain with brake clean.Give it a try, to much resistance will cause things to arc and a lot of gap is maybe to much.Been running .035 for 40 years and the only thing a wide gap does is smooth the idle.I go to .015 on a NOS engine,just to make sure it fires.

kmook

Nice I think I'll try that next time around myself.
Damn!

1racerdude

Kmook,
You have heard guys with blowers say they are blowing the spark out under boost--Same principal with a NOS engine or any built engine that has upped the compression.
Wide gap is for "stock engines" to smooth the idle and sell tune up's.(opti's too).
IMO if you can start a fire with one match,why use the whole box.