strange vibration after manifold swap

[68jimmy]

Well I finally completed my manifold swap this past weekend. I had a factory aluminum q-jet manifold that I replaced with a new performer 2104. I went thru my 1406 edelbrock, adjusted the floats, installed some leaner jets, and replaced the gaskets. Figured while it was apart I'd replace the hei cap, rotor. Once that was all done I fired it up, set the timing, tweaked the carb and took it for a spin.
First thing I noticed that the new manifold really woke up this motor. the second was now a vibration that starts at about 30mph. It doesn't feel like it 's coming from the engine, although when I let off the gas it seems to go away and starts again when I press the accelerator. After getting back home I re-checked my ignition wires to be sure I had the firing order correct. I discovered that my #4 plug wire to the hei cap was *%^# which kept it from snapping onto the cap. I figured that must be it and that I was getting a miss on one or more cylinders. I ran and picked up a new set of wires, installed them and took off again. Same vibration is still there.
What's weird is that this vibration was not there last week prior to all this work. A couple of months ago I did replace the carrier bearing, but I did not have time to get under the truck and check it yesterday...
Anyone have a similar experience after some engine work? The engine is a 350 with a th350 behind it.

Thanks in advance!

donovan

[Huck]

Possible vacuum leak --as it might not show in the low rpm range. Got a gauge you can throw on there quick? Should be 16-19 at idle. Is your primary wire to your HEI the proper gauge of wire?? Needs to be about 3 gauges thicker then the original stock. Got a missing plug?? Is your dist cap and rotor good. Sometimes you can get that white powerey crap build up in on of the plug wires holes on the cap so look down into them holes.

[68jimmy]

Originally Posted by Huck

Possible vacuum leak --as it might not show in the low rpm range. Got a gauge you can throw on there quick? Should be 16-19 at idle. Is your primary wire to your HEI the proper gauge of wire?? Needs to be about 3 gauges thicker then the original stock. Got a missing plug?? Is your dist cap and rotor good. Sometimes you can get that white powerey crap build up in on of the plug wires holes on the cap so look down into them holes.

I'll get a vacuum gauge on there and check... As for the HEI it's been working great prior to the maniold swap. Now I did change the cap, rotor and plug wires with this swap as well... If I sit in the truck and rev the engine there is no vibration, it's only seems to occur when I'm driving. Thanks for the input...

[jbon64]

you may want to re-check your new carrier bearing . when you accelerate the rear pinion moves up a bit and when you de-accelerate it moves back down , so if somethings not correct at the carrier bearing it could be out of whack just enough to cause a vibration. if you have a 2-piece drive shaft make sure it's phased correctly , also , when you replaced your carrier bearing did you also replace your u-joints ?? i taught the neighbor kid some new words trying to track down a vibration that turned out to be a needle bearing that had dropped into the cap when i installed new u-joints. the width of that one tiny needle bearing made life hell for me for a couple weeks

[68jimmy]

Originally Posted by jbon64

you may want to re-check your new carrier bearing . when you accelerate the rear pinion moves up a bit and when you de-accelerate it moves back down , so if somethings not correct at the carrier bearing it could be out of whack just enough to cause a vibration. if you have a 2-piece drive shaft make sure it's phased correctly , also , when you replaced your carrier bearing did you also replace your u-joints ?? i taught the neighbor kid some new words trying to track down a vibration that turned out to be a needle bearing that had dropped into the cap when i installed new u-joints. the width of that one tiny needle bearing made life hell for me for a couple weeks

Agreed. That is the first place I'm going to check. I did replace the rear u-joints when I did the carrier bearing but not the others... The carrier bearing was purchased from napa and was the original type, rubber donut around the actual bearing. Thanks.

[Green Machine]

Any chance you could have a too long intake bolt in one of the center holes ? There is one exhaust pushrod on each side that lines up with an intake bolt. If it is to long it can hang up and/or bend a pushrod and will hold a valve open causing a miss, just a thought.

[68jimmy]

Not sure if this pertains or not, the motor is an '88 which has the two canted center bolts for the manifold... All of the bolts are the same length and were all used with the previous manifold as well... Like I indicated earlier there is no vibration when I'm parked and revving the engine, it only occurs when I'm moving. Coincidence I guess with some other part going belly up... Thanks anyway!

[GREASEMONKEY72]

i would say its the cairrier bearing because im having the same problem, i can grab the drive shaft and move it up and down in the bearing so im gona take it to the shop that rebuilt my trans and installed it and see from there but goodluck with yours and i hope you get it figured out

-steven