Vibration at 1500 rpms?????????

[prayers1 153]

I've been doing some driving and noticed that whenever I get between 1500-2000 rpms the entire car vibrates. The motor, 4 spd and rear has been rebuilt, wheels are balanced, front end does not shake and there is NO vibration in the steering wheel.

 

The vibration is so bad that the windows vibrate.

 

Yesterday I drove 30 min each way on the highway, still going through the break-in period. My top speed was 45, taching at 2000. It vibrates when I'm giving it gas at any gear between 1500-2000 rpms.

 

Only thing I can think of is that the motor was not balanced. It had about 100 miles on it after being rebuilt by someone else. The keepers on the valve springs failed, so the motor was pulled out by the PO before I bought. I took it to a machine shop and they suggested to disassemble and install all new bearings and roller tip rocker arms. It does have new oil pump, 28oz harmonic balancer and flywheel.

 

Or, maybe it's coming form the rear. I bought the 3rd member used and had all the bearings replaced, the original posi clutches are still in it.

We did notice that when turning the yoke, at every revolution there was a tight spot that required a good amount of effort to complete the revolution. I was told that it would wear in. Is that true?

 

What can it be and where should I start?

[Kris 90]

Is your drive shafe bent or dented anywhere? My buddy had a similar issue. He had his drive shaft shortened and the shop apparently dropped it before he got it back and put a good dent in it. He took it back and they repaired and rebalanced it and it went away.

[LoneWolf2U 136]

First you need to isolate the problem.

With the trans in gear and the clutch in, run the engine thru the rpm range you had the vibration at 1.5-2k.

Did it still vibrate? yes, there is something wrong with the engine.

It could be as simple as a crossed plug wire or worse as a bad pistion.

No vibrations with engine at rpm range, You need to check the drivetrain further for the balance problem.

[MikeStang 247]

U joints maybe?

Pinion angle could be a bit out of whack possibly?

When I have some weird thing like this happen I try to look at parts that I need to replace anyhow and could poss cause the problem....then I just replace the old parts to see if that fixes the issue.

If not oh well it made me take the time to replace old worn out parts I might have otherwise let go for a while longer haha...it may sound stupid to everyone but hey it's my way.

But I would do like Mach rider says 1st,....go for the easy things right off.

[prayers1 153]

OK I'll try that tomorrow.

 

In regards to the u-joint. When they put the ring & pinion back together and I went to install it in the car, I found that either the yoke was bigger or smaller then the one on the driveshaft. What I did was get the next size u joint and took the caps off and install them on the universal. So in other words the rear universal has 2 different size caps. Do you think that may be the cause of the vibration???

[prayers1 153]

I did as suggested above in neutral and the vibration started at 1400 and ended around 1800 rpms. The cam I have in it is a little radical, 512 lift, so the motor never idles smooth below 1800 rpm's.

 

Do you think the rear yoke universal has any effect as well.

 

Whats the next step??

[1969vert 55]

You might want to make sure you dont have a late model crank in the motor and need a 50oz ballancer and flywheel..if you have a original flywheel it is 28 oz...the crank might need a 50 oz...no way to tell unless you pull the motor and get the casting numbers on the crank....Do you know what year the motor is??? changing the caps on the u-joint are ok done that my self to mix and match..

Edited November 4, 2013 by 1969vert

[LoneWolf2U 136]

Recheck the firing order, you may have a cam that requires the 351w firing order.

I'm running a 587 lift solid lifter cam and it will idle at 750 easy, rocks but idles.

[prayers1 153]

Mach1Rider - Earlier on when I first fired up the motor, it wouldn't start and I doubled checked on the firing order. That's when I discovered the 2 diferent firing orders. It will not run using the other firing order.

 

1969vert - It's a 1968 289 with the M1 289 crank

 

When I put this together, I got a new 28oz harmonic balancer & flywheel.

Edited November 5, 2013 by prayers1

[prayers1 153]

If it matters, heres my cam specs.

 

[MikeStang 247]

That's a pretty good size cam for a 289/302 wow....I have almost the same cam in my 455ci Pontiac and you can hear it lol