Author Topic: Violent shaking under load  (Read 5801 times)

Offline OfficialTull

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Violent shaking under load
« on: August 11, 2015, 07:37:53 PM »
I have a 1986 GMC c1500. I've swapped out the engine, tranny, and driveshaft from my old 1979 c10 so I have a 350, th350, and a one piece driveshaft that was cut and balanced for the truck by a professional shop. The motor is practically brand new and the transfer was rebuilt less than a month ago.

Now on to the issue at hand. The truck is shaking horribly in the low to mid rpm range. Today I decided to try putting a load on her in the driveway to see what would happen so a put on the parking break held down my break pedal and gave her some gas. She shook pretty horribly to say the least.

Needless to say I'm here because I'm at a loss. Anyone have any ideas? I'm kinda grasping at air here but is my converter?

Thanks in advance for any help you guys can give!

Offline frotosride

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Re: Violent shaking under load
« Reply #1 on: August 11, 2015, 07:49:10 PM »
It then issue only while in gear? If so is is worse when cruising at mid rpm?
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Offline bd

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Re: Violent shaking under load
« Reply #2 on: August 11, 2015, 08:05:58 PM »
Is it possibly a misfire?  Have you verified the ignition firing order?  Will it shake in neutral?  If you think the converter is bad, remove the three bolts that retain the converter to the flexplate and slide it back toward the transmission.  Run the engine to see whether the vibration goes away.  With the converter unbolted and slid back, check the flexplate for cracks around the crankshaft flange.
Rich
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In other words... if people learn by making mistakes, by now I should know just about everything!!!
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Offline OfficialTull

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Re: Violent shaking under load
« Reply #3 on: August 11, 2015, 08:06:52 PM »
honestly it felt worse while putting the load on in the driveway but that could just be because I wasn't moving.

Offline OfficialTull

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Re: Violent shaking under load
« Reply #4 on: August 11, 2015, 08:07:45 PM »
Nope. No shaking while in neutral, just when under a load.
Edit: firing order is correct, that much I am absolutely certain of.
Edit 2: another tis bit of info, while driving she only shakes while accelerating in the low to mid range, and again its a violent and noticeable shake.
When flooring it the vibration seems to be gone and I'm just feeling the engine as it only shakes a tad and feels like almost nothing.
When at cruise rpm after getting to speed it feels like riding on glass.
« Last Edit: August 11, 2015, 08:14:55 PM by OfficialTull »

Offline OfficialTull

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Re: Violent shaking under load
« Reply #5 on: August 12, 2015, 12:25:09 AM »
Ok got another update. Called my old man and had him come out. Repeated the load test in the driveway again as described above and achieved the same results but this time the engine stalled after about 10 seconds or so of constant rpm. No sputtering no warning literally just died right there. Not sure if this helps determine anything but its new so I figured I should add it in.

Offline OfficialTull

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Re: Violent shaking under load
« Reply #6 on: August 12, 2015, 11:03:55 AM »
Well just got off the phone with the transmission shop that rebuilt my trans and not only did they replace the converter when they rebuilt the tranny but it would seem that if the truck is fine when in neutral then its not the torque converter. Kinda feel a bit silly thinking about it now since the converter should spin in neutral anyway.

Offline zieg85

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Re: Violent shaking under load
« Reply #7 on: August 12, 2015, 12:25:47 PM »
My 92 C1500 would shudder more than a shake from take off.  Took it real easy it wouldn't do it.  Pulling a load it would do it more.  Sounds to me the transmission is the cause of it.
Carl 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
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Offline OfficialTull

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Re: Violent shaking under load
« Reply #8 on: August 12, 2015, 01:07:21 PM »
Trans was just rebuilt and it shakes under load when the brake is held. that and with the engine stalling the way it did last night I'm wondering if maybe it is ignition related after all. Going to till the cap off the distributor when I get home and take a look at her.

Offline OfficialTull

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Re: Violent shaking under load
« Reply #9 on: August 13, 2015, 08:20:47 AM »
Well everybody, meant to post last night but I began celebrating before I did. Anyway the wires were exactly where they were supposed to be. But here's what I discovered when I removed the cap...

Guess there's a reason Accel discontinued the corrected distributor caps after all. dang rotor stripped one of the wires to the core and that was my shake. Seems you were right BD, it was a misfire. Can't seem to post an image though. Might try uploading to Imgur and posting a link to it since the size it too big. Anyway changed the cap and problem solved.

Took a year but this was the last issue i had left to fix. The truck runs amazingly now guys! Thanks for the help!

Offline zieg85

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Re: Violent shaking under load
« Reply #10 on: August 13, 2015, 08:45:46 AM »
Great news thanks for sharing
Carl 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
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Offline Manswame

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Re: Violent shaking under load
« Reply #11 on: July 06, 2019, 08:15:19 PM »
I'm having this same issue. I'm more commenting now to book ark this post. Gunna try looking at my wires/plugs.
1982 K10 with 305 STOCK

Offline JohnnyPopper

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Re: Violent shaking under load
« Reply #12 on: July 07, 2019, 05:10:25 PM »
Sound like you had 'wild fire' under the cap, not good to zap plugs when they're not 'officially' ready.

Nice thing is when a poster comes back with what they found and what fixed it!

Thanks OfficialTull mangster, you are great example of team work!
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