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K5 shaking

rhinoblzr

rhinoblzr

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My blazer is shaking like crazy at idle. I put the th400 and doubler in, and in doing so i broke the distributer cap.

So i put in a new hei distributer, harmonic balancer, spark plugs, and wires to freshen her up.

I thought my timing might be off so i used a piston stop this morning in the #1 spark plug hole and put a new mark on the harmonic balancer the stock mark was off.

Im wondering if the Craigslist th400 is vibrating for some reason. I reused my th350 tc on it. She ran fine before the trans ,doubler install and broken hei cap

I made a quick vid. Let me know what you guys think? Timing? Tranny? Sorry its sideways.

 
I reused the one on the engine. Are they specific to trans? I unbolted the flex plate from the tc today and fired her up and the flexplate wobbles and the shakes didnt go away. I redid my whole ignition system last night just to make sure it wasnt the engine. Guess i'll get a new flex plate and see what happens. Dropping the doubler and trans takes me about 4 days since i can only work at night solo.theres a lot of tc free play between the trans and flexplate so I was thinking of putting washers inbetween the tc and flex plate but then the tc pilot wouldn't sit all the way into the crank.
 
The TH350 and TH400 use the same "stock" torque converters--if you have issues with the flex plate having too much clearance between the trans and flex plate you may have put the flex plate on facing the wrong way,that'll do it..(there are videos on youtube and threads on google about that)..

Also if the flex plate came off a 400 small block or 454 (probably unlikely)--it'll have external balance weights on it (they also use a different harmonic balancer with a half moon shaped counterweight)--a 350 engine is internally balanced..so using a flex plate with balance weights will throw it way off..if both of yours have no balance weights they are interchangeable..

Two more possibilities--the torque converter didn't "click in" 3 times when you installed it into the transmission..this will damage the front pump as well as cause issues with the clearance at the flex plate..

Or,maybe since you had to change the distributor cap,you put the plug wires on "one hole off" or crossed a few of them,its easy to mix up #5 and #7.--if you did them one at a time, then that isn't likely..
 
Thanks, a lot of good knowledge. Everything was good before the trans and doubler install. I never took the flexplate off so it cant be backyards. I really think somehow i bent the flexplate during install.

You pointed out some good stuff that now i feel i may have messed up on. I installed a new balancer for a 350. It didnt have the moon.(old one did) I noticed weights on my flexplate. I almost ordered one for a 350 and it said it was internally balanced. Does that mean no weights? So do i order a balancer and flexplate for a 400? since i have a 400 crank. I know these questions sound remedial but im new to all the gasser stuff and appreciate the help.
 
I would try to identify just what engine you have first--if the engine code is still there (it is located in front of the passenger side head where the block sticks out a bit,the alternator might be in the way)--see if it has a 3 digit code, like "CDE" as an example ,there may be other numbers there that were a partial VIN of the vehicle it was installed in originally..

You can google the engine code to find out what engine it is--or by the casting number on the rear next to where the bellhousing bolts up on the drivers side (pretty tough to read with it installed in the truck)..

If it turns out to be a 400 small block (and it sounds like it is, going by your description of the original harmonic balancer,if it has the half moon shape missing on part of it instead of a full solid circle ),then you'll need the right balancer and a flex plate with balance weight(s) welded to it for a 400 small block..that is how GM did it originally..mix the wrong parts together, and your engine shakes itself apart in short order..

Now,that balance weight you posted the link too,I have never used or seen one in person,and its been awhile since I had a 400 SB or 454,I hear now they sell a "universal" flex plate that comes with weights you install if you need an externally balanced one (the 454 uses a different weight than a 400 SB)..I have only fooled with stock parts and engines...

Now,to add to the confusion,if you have a "383" stroker engine that uses a 400 crank in a 350 block or some other custom hybrid,I "think" you'll need to go with the externally balanced harmonic balancer and flex plate with the balance weight--but sometimes the engine builder will drill the crankshaft counterweights and add metal to internally balance it,and then you'll need a harmonic balancer off a 350 and a flex plate with no weights..you may have to consult a engine builder to figure out just what to use in that case..
Hate to see you order the wrong parts and have to do the job twice !..

Also it is possible to bend the flex plate,but they aren't that wimpy,you'd have to put some force to it to tweak it enough to bend..
 
Only thing u changed really was the Dampner on the engine.
U said it was different from the original.
U said 400 crank, well that requires a 400 balancer and flex plate so if u put a 350 balancer thats not going to work .
Make sure u have the correct balancer.
 
So as of now this what i think happened could be wrong.With the stock dampner and flex plate on it was shaking after the distributer install. So i changed out the dampner with the wrong one. It was still shaking. So then i redid the whole distributer and found i was off bye one. Ignition is all good now. Then i looked at the flex plate and saw it wobbling.

I think im going to replace the dampner with the correct one and see if that fixes it now that the ignition is good.

A flexplate is so light. Would it make the whole truck shake your teeth out?
 
The wrong balancer would make it shake more I would think ,being heavier,but even a small amount of imbalance can cause some pretty intense vibrations,like if the weight came off a factory flex plate..you need both working together to cancel out the imbalance..

Think of a tire being an ounce out of balance--get it spinning at 60 mph and it'll produce a pound of imbalance,it gets amplified with higher rpms..

I'd make sure the flex plate actually IS wobbling or bent--if you look at it spinning with the engine running with the dust cover off,and it has a weight welded to it (or that aftermarket bolt on thing you linked),it is easy to mistake seeing the weight spinning by for a "warp" in the flex plate..

I thought my 6.2 diesel had a warped flex plate,but closer inspection revealed it has a balance weight and that is what I saw --I don't have the dust cover on my tranny,I have not used one on many vehicles and had no issues..but I do fear someday on of the feral "barn cats" that hang around will be under my truck when I start it,and it might get mangled up in the flex plate..:eek:..
 
Changed to a 400 sbc balancer and she runs sweet again:D. With all the new ignition goodies and a new balancer she runs better than ever. At least a 100hp on the butt dyno lol. . Finally i can get back to fabricating on her:grind:. Thanks so much for helping everyone i can't thank you guys enough. It was a fun troubleshoot and i learned a lot. took some quick vid.


 
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