My fresh rebuild has a vibration that starts at around 2k rpm and up. In neutral or park If I hold the rpm it comes and goes. Run it up to say, 2500 and hold it, its shakes pretty good, hold it for 10 or 15 seconds and it goes away, keep holding and it returns comes and goes etc. etc... It did the same thing before for rebuild but was hoping it would be gone now. It is a 72 block, forged crank that was just turned, motor balanced, new motor mounts, trans mount, converter rebuilt and new flex plate, both neutral balanced. Neutral factory balancer. Thanks in advance.
340 vibrates
- Thread starter dgibby
- Start date
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txstang84
Well-Known Member
Not trying to be a doubter, but are you positive you have a forged crank and neutral flex plate balancer and converter?
Did you change anything within the engine? Tell us some more details
Did you change anything within the engine? Tell us some more details
OldmanRick
Well-Known Member
Have you driven the car with the new rebuild? If by chance it "is" in balance, and/or this is just happening in the garage/driveway.......could it be a ignition/timing or very lean carb problem?
My 318 did the same. Vibration before and after rebuild. Weird thing it didn't do it much while driving. Problem stopped after the 904 went out and I rebuilt it. The vibration had a distinct pattern to it. Keep us posted.
340duster
Well-Known Member
Possible ignition misfire?
It started with my reverse servo breaking and I pulled the engine at the same time I pulled the trans. Dropped the engine pan and found badly worn bearings and some grooves in the crank. Had the crank turned and all bearings replaced. Also had the cylinders honed and replaced the rings. Had the rods overhauled and had the rotating assembly balanced. Machine shop assembled the short block. The vibration was there before I had the motor gone through and really hasnt changed since the rebuild. I have driven it since the rebuild and it is the same as before. Thought it could be tire balance or drive line but the drive line is out of it right now and it is still there. Don't think it is a lean carb, had a wide band tester on it last summer while I got the carb dialed in. Same converter as before, just had it re stalled and cleaned since the trans failed. Upgraded the flex plate from the smaller factory one.
txstang84
Well-Known Member
I read your other thread last night...you also said the PO installed a weighted balancer and that was causing the car to vibrate profusely then you installed a "correct" balancer.
Which flexplate did you buy?
Also, I know with internal balance engines, many say you don't need to bring your flexplate and balancer to the machinist for the process, but I figure if I'm paying for it, it's part of the package and I'll let them at least check the balance on those parts...they don't always come out perfect. I know it sounds like I'm beating a dead horse, but you had the shortblock assembled by your machinist and as much as we don't like to believe we'd get hosed, accidents do happen.
OK, enough from me on the imbalance.
Good call 340 Duster...
Are all your plug wires good and is the coil firing up to spec? I had a friend with a later model 4.6 T-bird with one side of one coil pack that went back and it shook and ran like hell...it wasn't firing on 2 cylinders because of the "half" bad coil pack. After changing it, it was a whole different animal.
Which flexplate did you buy?
Also, I know with internal balance engines, many say you don't need to bring your flexplate and balancer to the machinist for the process, but I figure if I'm paying for it, it's part of the package and I'll let them at least check the balance on those parts...they don't always come out perfect. I know it sounds like I'm beating a dead horse, but you had the shortblock assembled by your machinist and as much as we don't like to believe we'd get hosed, accidents do happen.
OK, enough from me on the imbalance.
Good call 340 Duster...
Are all your plug wires good and is the coil firing up to spec? I had a friend with a later model 4.6 T-bird with one side of one coil pack that went back and it shook and ran like hell...it wasn't firing on 2 cylinders because of the "half" bad coil pack. After changing it, it was a whole different animal.
Here is the flex plate that I installed and no, I didn't have it when I had the engine balanced. Plugs and wires are new but I haven't checked the coil. It is a Unilite distributor and Mallory coil. The ignition system and balancer are the only things that were on the old engine that haven't been checked or rebuilt. When I did swap the old external balanced converter it did improve it drastically but not 100%. I did confirm that the converter new converter is a neutral balance. Again, it is the same as before the rebuild for the most part, but was hoping it would have been cured. When driving it is a rhythmic, oscillating kind of feeling, like a drive line or tire balance that comes and goes just like if I am holding the rpm in part and neutral. Seems to start only above 2k rpm.
B&M Flexplate
Flexplate, Internal Engine Balance, 2-Piece Rear Main Seal, SFI 29.1, 6-Bolt, Mopar, 727, V8, Each
B&M flexplates are ideal for 6,000+ rpm usage. They have precision-stamped centers and a rust-resistant, gold iridited finish. Some units are SFI-approved and are NHRA/IHRA-legal for all classes.
B&M Flexplate
Flexplate, Internal Engine Balance, 2-Piece Rear Main Seal, SFI 29.1, 6-Bolt, Mopar, 727, V8, Each
B&M flexplates are ideal for 6,000+ rpm usage. They have precision-stamped centers and a rust-resistant, gold iridited finish. Some units are SFI-approved and are NHRA/IHRA-legal for all classes.
When I got my 408 running last summer it also had a weird vibration in it. It felt like a miss. After going through all of the basic checks (most that are listed above) it turned out to be the clutch fan.
Ted
Ted
Electric fans....
forced 340
Well-Known Member
sounds to me like it is in the trans. possibly a worn converter hub bearing, or a broken converter... could also be the front pump of the trans. good luck!
txstang84
Well-Known Member
dammit...
MobileCustoms
Well-Known Member
I'm leaning towards tranny problem as well. You said you were running the wrong converter for a while, I'm thinking it took it's toll on something else in the tranny.
Maybe you can disconnect the tranny and try running it for a bit to see if the vibration goes away?
Maybe you can disconnect the tranny and try running it for a bit to see if the vibration goes away?
txstang84
Well-Known Member
Wasn't the tranny rebuilt too?
Yeah, complete rebuild, friction, bearing, all bushings and seals, servo, valve body etc. etc. ... Did it myself, checked and rechecked all tolerances.
forced 340
Well-Known Member
try running it without the accessory belts... could be harmonics from something in the front.
txstang84
Well-Known Member
OK, so far we've essentially eliminated:
engine balance
torque converter
trans parts
ignition misfire
You mentioned that the vibration is somewhat cyclic...comes and goes at RPM...I think a couple of these guys might be onto something with pulleys...
engine balance
torque converter
trans parts
ignition misfire
You mentioned that the vibration is somewhat cyclic...comes and goes at RPM...I think a couple of these guys might be onto something with pulleys...
txstang84
Well-Known Member
No, he's saying he's running electric fans...
Of course, I did have a problem once upon a time with the electric fans being out of balance and vibrating...but of course it didn't vary by engine RPM
cuda65vpt
cuda65vpt
:mumum:Big ole red flag:mumum:
MileHighDart
Well-Known Member
My 318 does the same thing. Had it out for a drive today and was annoyed by the vibration going down the road. Kicked it into neutral for a minute at 60 mph, vibration and associated noise went away.
It also does this sitting still, in neutral, or park, rev the engine up a little and you get that rhythmic vibration, comes and goes, same thing that I feel when driving down the road.
It also does this sitting still, in neutral, or park, rev the engine up a little and you get that rhythmic vibration, comes and goes, same thing that I feel when driving down the road.
Too bad it ain't a Chevy or Ford. You could disconnect the flex plate and bust the engine right off and tell for sure.
MileHighDart
Well-Known Member
Think I just figured out a little of mine.
Went to the garage and took the fan/alt belt off.
Fired the car up and let it warm up a bit. (was already warm from my drive at lunch time).'
So just sitting there in park, I revved it up to 2000, then 2500, then 3000rpm. (guessing since I don't have a tach). Sure enough, the engine is stumbling and missing at these steady rpms.
I thought the car was running good, starts easy, idles good, runs good under hard acceleration. But apparently when I'm at a steady cruise rpm, the engine is running like crap.
So now I have to figure out if this is a carburation problem, or bad wires / coil, plugs ?
Went to the garage and took the fan/alt belt off.
Fired the car up and let it warm up a bit. (was already warm from my drive at lunch time).'
So just sitting there in park, I revved it up to 2000, then 2500, then 3000rpm. (guessing since I don't have a tach). Sure enough, the engine is stumbling and missing at these steady rpms.
I thought the car was running good, starts easy, idles good, runs good under hard acceleration. But apparently when I'm at a steady cruise rpm, the engine is running like crap.
So now I have to figure out if this is a carburation problem, or bad wires / coil, plugs ?
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