#21  
Old 05-03-2017, 11:25 PM
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Originally Posted by MD79TA View Post
Guys just want to add flex plate was not with engine builder for rebuild . I took it off old motor and put on the new rebuilt engine following all of Wallace torque specifications . . I'm not sure if this is an issue and could cause the problems I'm having . Thanks Doug
Stock Pontiac flex plates and flywheels have an external balance weight or asymmetrical holes which need to be included when balancing the rotating assembly unless it can be accounted for during the balance operation. If your machinist neutral balanced the rotating assembly you will need to use a neutral balanced flex plate/flywheel.

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  #22  
Old 05-04-2017, 01:34 AM
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Was the engine balanced when it was rebuilt? The flexplate is counterweighted, and if they neutral balanced the engine, you will have a bad vibration when you bolt on the stock flexplate. You should check with the people who built the engine to see what was done. If they didn't balance the engine, but changed the rod or piston weight significantly, that will cause a bad vibration also. Engine out of balance is sometimes hard to notice at an idle, but the faster you run the engine, the worse it gets. I would do as Steve mentioned earlier, unbolt the torque converter, push it back, and start the engine, and slowly rev it up and see if the vibration comes back.

The other thing I've seen is if you are running steel wheels like a Rally II, or Rally I, the taper around the lug holes that centers the wheels, and becomes a seat for the lug nut, gets worn to where the lug nut actually bottoms out on the brake drum instead of the wheel. Then when you get on and off the gas, the wheels shift, and cause vibrations. Seen this on two old GTO's, the first one we discovered this on, took out the transmission, and the main bearings before he figured it out. They vibrated bad when the wheels shifted. At other times it was perfectly smooth. The second GTO, we knew what to check when it happened on it. New wheels fixed both cars.

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  #23  
Old 05-04-2017, 01:58 AM
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Sounds like its skipping. Wires crossed maybe.

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  #24  
Old 05-04-2017, 10:27 AM
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Originally Posted by MD79TA View Post
Guys just want to add flex plate was not with engine builder for rebuild . I took it off old motor and put on the new rebuilt engine following all of Wallace torque specifications . . I'm not sure if this is an issue and could cause the problems I'm having . Thanks Doug
Was it a stock or after market flexplate on it when it was run on the dyno?

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Old 05-04-2017, 10:44 AM
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IF it was the Flex Plate.....the engine doesn't know you put the car in neutral. Plus you could just rev it in park and make it vibrate.

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  #26  
Old 05-04-2017, 11:57 AM
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IF it was the Flex Plate.....the engine doesn't know you put the car in neutral. Plus you could just rev it in park and make it vibrate.
Agreed. He's probably letting the rpms drop to idle speed after going to nuetral. I brought up revving it in nuetral in the driveway in my previous post.

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  #27  
Old 05-04-2017, 06:55 PM
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Test

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Last edited by MD79TA; 05-04-2017 at 06:56 PM. Reason: Wrong
  #28  
Old 05-04-2017, 07:27 PM
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The TH400 has a special 12 point 3/8" bolt that holds the center support. This can be left loose or work loose, and causes a harsh engagement going into reverse or drive. From your description, the vibration is RPM related, not road-speed related. That rules out driveshaft, u-joints, tires, etc. You need to look at the engine and transmission. The advice about unbolting the converter and running the engine up is a good one. If it vibrates with the trans out of the equation, it could be a bad harmonic balancer, fan, or flex plate.....or even internal issues. If it's smooth with the trans disconnected, you next need to look into the converter and the transmission. Good luck.

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Old 05-04-2017, 09:34 PM
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So heres an update:

Took the car for an extended test drive today for about 20 minutes and some of our previous observation were not so accurate.

First, the burning smell is from the front passenger brake. Based on the heat of the wheel after driving and pull while braking the caliper is likely frozen and dragging.

The transmission fluid is at proper level, looks brand new, and smells brand new.

The car definitely shifts hard in to D and R, but the idle is also likely way too high, we are going to adjust it down, but we really need to hook up a tach.

The car is definitely not down on power, I take that back. It will absolutely melt the tire if you lay into it.

The engine has no vibration at all in park. You can rev it up and hold it at a sustained RPM and it is completely smooth. Maybe a little lumpy at idle, but I attribute that to the cam.

The car shifts through the gears perfectly fine while cruising and at WOT.

The vibration is actually still present even in neutral. I thought it was going away last time but today at 40mph I put it in neutral and could still feel it. Perhaps it's not as bad, but still there.

Never got to get over 45mph today, but the vibration seems to be at its worst from 30-40mph.

Transmission tail shaft shows no signs of leaking, someone asked about that earlier I think.

Based on this our next course of action is:

fix the brakes to make the caliper stop dragging. Probably unrelated to the vibration, but should be fixed regardless.

Pull driveshaft and take it to have the U-joint checked out and to check to see if it is in balance.

Front end alignment and wheel balancing.

These are all possible culprits that need to be addressed anyways so that's where we will go next.

Thank you everyone for your input, we will keep you all updated!

  #30  
Old 05-04-2017, 09:40 PM
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I had a bad vibration and it ended up that the crank was not balanced Correctly....it was a process of elimination last resort pulled the engine had the crank checked and rebalanced/repaired vibration was gone ....this was felt in Park slowly revving the engine and
the short drive and I mean short drive down the street, I thought I had a flat tire/tires the vibration was so bad...

I had replaced exchanged everything I could think of that could be changed out, carb,,removed belts, diff flex plate, diff balancer,,spark plugs, wires, dist, checked and rechecked valve adjustment, compression test, etc

Just another thing to check once u have exhausted everything else......

Good luck ..hope u don't end up tearing it down....

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Last edited by cnc; 05-04-2017 at 09:48 PM.
  #31  
Old 05-04-2017, 09:46 PM
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Put the rear axle up on jack stands and spin it up. Report back.

BTW, do you feel the vibration in the steering wheel, the seat, or just so bad it's everywhere? You would be well served to get someone to take it for a ride with a trained azz ( seasoned veteran mechanic), shouldn't be hard to find a taker!


Last edited by STEELCITYFIREBIRD; 05-04-2017 at 09:55 PM.
  #32  
Old 05-04-2017, 09:48 PM
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Quote:
Originally Posted by cnc View Post
I had a bad vibration and it ended up that the crank was not balanced Correctly....it was a process of elimination last resort pulled the engine had the crank checked and rebalanced/repaired vibration was gone ....this was felt in Park slowly revving the engine
When I drove it I thought I had a flat the vibration was so bad

Just another thing to check once u have exasperated everything else......
Starting to think there could be a thousand ways for a vibration to occur!

We will keep it in mind if we continue to strike out.

I really don't want to pull the engine or trans, it took us 4 years to get to where we are now.

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Old 05-05-2017, 06:26 AM
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You do not need a Tack to adjust the idle, for now just get the motor fully warmed up, check that the choke is open and set the idle as low as you can with a soid stable idle with the car in gear .

Then check that you get no off idle stumble and your good for now.

With the Cam it sounds like you have a 750 rpm idle speed should be had in gear no sweat as long as the Carb if functioning normal.

Also if your running a Holley Carb any readjustment of the idle speed will call for a readjustment of the pump arm, and this assumes it was adjusted right in the first place of course!

My money's on a shot U joint in regards to your vibration issue.

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Last edited by steve25; 05-05-2017 at 06:32 AM.
  #34  
Old 05-05-2017, 08:46 AM
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Yup, sounds like U-joint.

  #35  
Old 05-05-2017, 08:56 AM
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"First, the burning smell is from the front passenger brake. Based on the heat of the wheel after driving and pull while braking the caliper is likely frozen and dragging"

Check the rubber brake line going to the caliper too, These can delaminate internally and create a check valve effect such that the caliper doesn't release after braking. Had this happen to me. Good luck with the vibration problem, hope you get it figured out.

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Old 05-05-2017, 09:07 AM
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Quote:
Originally Posted by MarkS57 View Post
"First, the burning smell is from the front passenger brake. Based on the heat of the wheel after driving and pull while braking the caliper is likely frozen and dragging"

Check the rubber brake line going to the caliper too, These can delaminate internally and create a check valve effect such that the caliper doesn't release after braking. Had this happen to me. Good luck with the vibration problem, hope you get it figured out.
That actually sounds exactly like what it is doing, thanks for the heads up!

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Old 05-05-2017, 09:08 AM
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Quote:
Originally Posted by steve25 View Post
You do not need a Tack to adjust the idle, for now just get the motor fully warmed up, check that the choke is open and set the idle as low as you can with a soid stable idle with the car in gear .

Then check that you get no off idle stumble and your good for now.

With the Cam it sounds like you have a 750 rpm idle speed should be had in gear no sweat as long as the Carb if functioning normal.

Also if your running a Holley Carb any readjustment of the idle speed will call for a readjustment of the pump arm, and this assumes it was adjusted right in the first place of course!

My money's on a shot U joint in regards to your vibration issue.
Quote:
Originally Posted by tpssonic View Post
Yup, sounds like U-joint.
Thanks, I hope that is the issue!

  #38  
Old 05-05-2017, 11:29 AM
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I had pretty much the same problem and it was the U-joints. My vibration was around 60-70 mph and worse when decelerating. $100 for new U-Joints and balanced.

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  #39  
Old 05-05-2017, 12:33 PM
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As for the caliper. Get wheel off. Get someone to pump up the brake pedal, then release pedal. Now try to turn rotor, rotor is stiff? loosen bleeder, if rotor spins, hose is bad, if rotor is still stiff, caliper is dragging.

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  #40  
Old 05-10-2017, 11:31 PM
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This vibration, could you be feeling something "grounding out" as in a exhaust pipe hitting the floor boards while under a load? Trans case hitting in the tunnel. Like asked before where do you feel it Steering wheel,seat or whole car feels like a big vibration? Also check the rubber insulators on each end of the trans cross member where it bolts to the frame.

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