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Old 05-20-2007, 01:59 PM
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Bucking in gear at idle

Okay,
This has been buggin me since I first started driving the car.
At first, I thought I had a u-joint angle issue that was causing this.
(and I still might) vibration @ about 70mph. Put in an adjustable upper control arm to change the pinion angle a bit, but vibration is still there.
At 70 in 5th gear (vibration @ speed --not RPM) I grab the shifter at the bottom, near the boot----no vibes at all . Now I'm thinking tires.

So something else is buggin me as well. I have not been able to get even 10" of vacuum at idle, since day one of installing this engine. (GMPP 454 HO). And I have read from other people that they are getting up to 20" on this same motor. I cannot find any leaks on the engine on the outside---perhaps there is one on the inside??

Would this make the car "buck" at idle in gear??? This thing has a violent lurching at idle. Once power is applied it goes away. None of my other manual trannys have ever done this to this extreme. Even the 79 chev with a 454 moves pretty smooth even in granny at idle.

Initial timing is at about 8*, the engine idles smoothly enough when just hangin' out, but as soon as the clutch is engaged, it is just like your 10 yr old is trying to get your attention by jerking the rocking chair.

Could a bad joint angle cause this???? Or is there something else a bit skewed somewhere. The car drives okay, and is not high strung at all in traffic----except when I want to idle in gear.

Bryan

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Old 05-20-2007, 03:20 PM
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About the vibration, ever think of having the tires rebalanced? My car did the same thing until I got the tires rebalanced. Could be a slightly shifted weight. Or all your weights might be on the inside only to make you rims look better etc. You cant do this I tryed and the guy at my local garage said that you have to put weight on the outside or they will always shake some. Compremise looks for no shake?

As for the bucking, my old car did that lol. I found out later it was a crack in the vaccum hose on the bottom side {barely noticeable}. Hope this helps!

Steve
PS: Thanks for trying to help with my balencer issue, still not solved penetrating oil is doing its thing as we speak.
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Old 05-20-2007, 04:11 PM
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As for the low vacuum and the bucking idle it does sound like a vacuum leak.
If the leak is on the bottom side of the intake it sometimes doesn`t give much clues, I used to have a 350 that had a severly warped intake that leaked like rip and it never smoked, it`s only clue was a off idle stumble. Pull your carb and look in the intake plenum, if you see oil it has a leak. The vortec engine I put together last had a intake leak and it smoked like no tomorrow, but it still had good vacuum, no throttle stumbles, and no idle issues so it threw me off, it pulled 18 in vacuum, but the gauge did fluctuate at idle but not severly, it was pulling in the oil to the extent that it was acting as a seal so it didn`t show many signs, when I pulled the carb and looked in the plenum oil was everywhere.
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Old 05-20-2007, 04:41 PM
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Re-adjust the valves, they may be a little tight.
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Old 05-20-2007, 06:10 PM
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Non-adjustable valves
new GM Crate.
Next week-end I guess I will pull some plugs for a looksee and inspect the inside of the manifold.
Only 2500 miles on this thing----been happening from day one

Elelbrock 1411 carb--------6lb pressure

And come to think of it-------idle mixture screws don't do too much untill screwed all the way in.--------tail pipes are black too.

There is like ZERO hesitation when I romp on it.

Bryan
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Old 05-20-2007, 08:34 PM
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Doc here,

If you run out of Simple checks..

Pull the inspection Cover from the clutch, and if you can get any sight on them, inspect the pressure plate springs for a cracked spring.

Had a similar problem on a 56 Vette with a Close Ratio 3 Speed and highway gears years ago..used to eat up springs and disc's like crazy..did the same thing just before the disc let go.

Doc
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Old 05-20-2007, 09:00 PM
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How about a carrier bearing or out of balance driveshaft causing the vibration?
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Old 05-21-2007, 06:43 AM
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Doc---with the inspection cover off---all that is visible is the engine side of the flywheel----diaphram clutch anyway

Blazin---the shaft has been balanced twice----carrier was replaced at the second balancing due to a faulty bearing (bearing and rubber fell out of carrier) The new bearing is noisless now.

Bryan
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