Some of you know I have a wicked vibration in the Duster at about 55+ and I get it in surges now and then at lower speeds. I've suspected Axles since thats the only thing I didn't touch in the cars going-through. the right rear seems to have a slight wobble to it.

But with the motor..

My set up is an early 360, with the Eagle Cast 4" crank. I have the Professional products balancer. I had a Boss Hogg TC that I am pretty sure of my memory has no added weights on it. I have the B&M flexplate with the offset as well.

I know i need to get with engine builder on how it was balanced exactly, but I noticed Eagle states their cast pieces are external balance.

With that in mind when I was setting at a light tonight, at idle, the car kinda shudders, you hear the steelwork of the body just buzzing. That and the bad vibration makes me curious about the balancer, etc the balancer has the weights you can add, depending on what you have. currently, this balancer has no weights in it. It's set for a neutral balance.

I'm just wondering, until I can talk to machine shop.

Proper balance is the most important part of a motor build.
You need to know what you have before you put it all together.

Wellll i didn't put it together. something tells me it's fine but some of this vibration is making me paranoid

What RPM do you have the idle set at? If my Charger is turned down to less than 950 it makes the whole car resonate. If you have a rotating assy balancing problem I'd imagine the engine would shake somewhat violently at an idle in or out of gear. As far as your vibration is concerned I'd be looking at replacing the rear with a 8.75 and if you have yet to install a heavier drive shaft/u-joints I'd be willing to bet the shaft is bent.

car was idling at about 750. and yes when it got below 900 is when it did it. I kicked the idle up a touch at the carb.

I had the driveshaft cut and balanced at a large truck shop, guy that does them ..thats his main job, all the time. I still won't count it out though, has new joints on it.

8 1/4 has all new bearings, inside the tubes and the carrier, pinion, etc.

I have Cragars and BFG's, when we had car up on stands, in drive with no gas applied, the passenger rear wheel down to the center cap you would notice a wobble. looking directly at the rim edge, you noticed it would move up and down about 1/16"-1/8"
I stuck a stock steel rim/tire on there and it wasn't as bad, but it was still there.
driver side was very minimal.

This is what made me think axles.

oh and at the transmission, I have a new Poly mount.

The vibration, when i hit the upper highway/Interstate speeds, gets a bit violent, I first feel it in my lower back against the bench seat, the lower, and I do mean lower part of the dash frame shakes, and besides that, everything else feels 'heavy' in the rear...it's a cycling, fluxuating pulse vibration...feels like something could come apart 'back there' and it seems to effect the speed too. Almost tried to slow you down. Other than that I tend to get it in stages...down a city street at about 25 it doesn't feel smooth, and sometimes i can accellerate out of it, but usually i can't unless i stop and start over.

If you have pounded on that thing at all you may have bent that drive shaft. Trust me, I have found out the hard way. If anything I'd have the wheels checked to see if they are true and also have the balance of the shaft verified. In my old 408 Valiant I could get the stock d-shaft/u-joints to last one solid day on the street with VHT enabled 205/75/14's. Once the air temp cooled down and the DA went down I'd break a u-joint or bend the shaft on the 1-2 shift.

If you have compromised an axle the car should be out of service until you get it fixed. Don't get me started on the stock axle with a stroker motor topic.

I really haven't beat on the car at all, I'm had it out for about 150 miles..if that, the axle came out of a slant six Duster with a towing package.

Something doesn't sound right with the balance setup. I admit I don't know stroker cranks, but a stock 360 external balance crank needs offset balance weights on both the front and rear at the same time. I can't imagine why a cast stroker advertised as being external balance would be any different in needing it on both ends.

I am assuming that the shop supplied the harmonic balancer? If they shipped the motor with no weights on it, it is possible that they internally balanced the cast crank using mallory metal. in which case you should not be using the offset weight flexplate you have on there now.

If you bought and installed the flexplate and balancer yourself, they need to be balanced to the rotating assembly, since it is extremely unlikely that it would match up with stock 360 offset weights.

My cast 4" eagle 360 style crank is balanced internally. My 318 stuff swapped right over. No weights bolted on the aftermarket damper and neutral balance flywheel. I did have the crank balanced to match the pistons n rods etc

My guess is you have something hitting in a tight spot like exhaust maybe, transferring vibration. Motor mounts are rubber? My car is no crazy beast but a low idle can have a serious drone. If there is a sympathetic vibration at a certain frequency that will always hum at that rpm...?

Good luck

Um, wait did you say slant six axle? Not the 7.25 I hope? I swapped one of those for a ford 7.5 in my 318 swinger because I have 225 tires on it and I didn't think it would last.

I even worry about my 8.75" dodge axle in my stroker car. I have a mild 408 with a stickshift.

its a built 8 1/4 axle, the slanty Duster had a tow package with 2.71;s i swapped it all out for a fresh 3.55 SG

Sounds like you have multiable issues. I'd check the trans tailshaft bushing, I bet it's shot. That don't explain why it shakes at idle. Good luck with it.

trans is brand new rebuild..already?

my point of view is this: if you have a bent axle in the differential, the brakes will show uneven and abnormal wear on that side. also, if the axles have been redrilled, that migth be a part of the vibration. hope this helps.

Hey buddy,
= If its any help , I build alot of strokers at my engine shop. The PP balancers for sbm use the same part#. The difference is they have changeable
weights that bolt to back of the balancer. You defenitley have to use the correct weight. It'll tell you in the paperwork wich part# to use. I think its 900something.
= The cast Eagle cranks are set up for ext. balance.
= I would think you should have a weight on your
converter aswell. Ive got several bad reviews on Bosshogs, but havent had 1st hand withem.
= 8 1/4s are pretty tuff. I have built and heavily
abused several of them. I would check axle runout,
and wheels for warpage or proper balance.(none of this concerns shake at idle though) So yeah you may have multiple issues. Maybye the carrier brg. preload has been set way to tight? hope this helps

Thats funny you asked.
About 10 years ago, I built a 68 V100, with a nasty sb, 833 4spd, 8 1/4 posi with richmond
4:10s, and 295/60 tires that hooked. It lasted
the duration. Of course there not a 8.75 but I think there under estimated. 8 1/4 are easier
to find, cheaper, and have common bolt pattern.
All a plus to me, for a sreet beater.
Hollis

Wow we have very similar problems. I have a external balance magnum 360 with the same balancer and torque converter as you except I have a weight installed on the balancer. Car shakes a little bit at idle but I'm using a solid motor mount on the drivers side and rubber mounts for the passenger side and trans mount, so I'm basically attributing the shaking at idle to the solid mount which Im fine with. I also noticed one of the ebrake cables was somehow touching between the muffler and body of the car so I need to do something about that.

As far as the pulsing vibrations go mine you could barely feel starting at around 40mph and getting stronger and faster pulses when accelerating around 60mph with them slowing down on deceleration. Had the drive shaft balanced, no help. Noticed the rear wheels were wobbling with the rear end on jackstands so I had the axles checked and bearings replaced (probably the original's from 68) and they were fine.

Then I took a look at my wheels. Turns out my Weld Draglites were actually the Cragar versions and for whatever reason the the center caps didn't quite sit flush with the face of the wheel so thats what was causing the wobble.

I checked the pinion angle on my not so level garage floor and looked like I needed to add 2* shims, which helped a lot! It hasn't quite gotten rid of the vibrations at speed but they seem to have been reduced. I'm waiting to find a shop that'll let me put the car on their drive on lift so I can get better readings.