Re: 1973 challenger vibration issue

[redneck 75]

ive built this car,put refurbed 383 motor and 727(both built by top UK mopar builder),its 19 67 10-1 cr,long tube headers,ive got this 73 running bloody great,starts,idles perfect,temp good,oil pressure good,new engine mounts(mancini)new trans mount,kickdown good,shifts good.Really great power and performance BUT she vibrates stood still when i rev her (centre console mainly)and when shes driving at 40-50 mph she vibrates again mainly centre console the goes smooth 50 + mph.Im made up by the car but the vibration issue really ruins the cruisin and fun!Im thinking harmonic balancer is fked or flexplate,or new mounts are crap.engine purrs at tickover,no missfires,no hessitation,goes like Bananarama! off a shovel,so engines good,Please give me youre advice n help.Thanks Jonny b

[Pete]

You just have to work the problem, but I guess I would start by checking Flex plate bolts, could be loose and maybe even thrown one. My car did after using Loctite and torquing down to 80 Ft/Lbs - be careful these were BIB bolts, but you get the idea..

Check motor mounts and also the Trans mount. A general nut and bolt check is always a good idea too.

[mygasser]

are the new mounts 'poly' ones or stock style rubber ones? poly mounts do tend to transmit more vibration so it could be as simple as fitting rubber mounts.
neil.

[redneck 75]

thanks for replies,new mounts are stock rubber from rockauto,im thinking to just change harmonic damper as it looks like the one fitted is probably original.Flexplate was in good order,got new bolts fitted and torqued.id love to get her on a car lift and check/see everything properly.Ill email real steel for advice.

[redneck 75]

The vibration is all coming through centre console/trans tunnel,i put new stock trans mount on also,the car in neutral or park sat on driveway when she vibrates ,bloody annoying as hell,everything else is ready but this makes driving noisy and annoying,i gotta get it right!

[Dave999]

if it was an engine balance problem you'd feel it at specific rpms always there but escalates considerably with rpm
if it was a harmonic damper problem much the same. the damper is set to deal with harmonic vibration in specific rpm range set by the twistyness of the crank, but its ability to do this changes as the rubber gets old and it doesn't damp at the rpm it should anymore. expect a miserable spot in the rpm range for normal driving. its not doing that much at idle. torque is low crank aint twisting, and if it was tuned to dmap at idle it would be utterly crap at doing it at any other rpm.
if it was a drive line problem like poor alignment of trans and axle you'd feel it under load all the time, but again with peaks at specific rpm. You are basically twisting the tail shaft equal amounts back and forth as you rotate the U-joints at different angles of operation, and the worst vibration is when the twists align with the tail shafts ability to spring back after each twist, add together two driving forces, for a nasty vibration. above and below that speed less vibration.

yours does it in park at idle and when driving, discounting most of that. when its going well you would still know if it was an rotating mass balancing problem, you would not say it was going well.... and the driveline stuff plays no part at idle and in neutral or park

too little advance at idle
Too much advance at 2500+?
mine doesn't seem to detonate with too much advance mine just gets noisy and vibrates
seems to have sweet spot where it just shuts up and does its job

28 total perfect for mine
34 total works fine, much the same seat of the pants performance, but my gear stick vibrates like hell, rattles in the housing and the daft hold down nylon nut comes un done, the stick comes out in your hand 70s cortina style....

you have made your engine more efficient, it may want more at idle to cater for cam carb compression and exhaust upgrades and not need as much advance at speed because the burn is quicker.

plug heat range, plug gap, and ignition type?
I don't know anything about 383s so can't really help, but all needed work when i built my motor with a longer duration cam and a hike in Static CR
and getting them all right made such a difference

more performance and smoother running at all rpms went hand in hand.
A new harmonic balancer certainly helped as well, mine was designed to counter a heavy twin plate clutch and cast iron flywheel and going to one that was lighter that matched the single plate light weight clutch and steel flywheel i used, made some difference to both smooth running and performance.

Dave

[redneck 75]

very interesting informative post,thank you!ill try some different settings on timing,ive tried ported and manifold vacuum but found no vac advance helped performance alot.the vibration gets worse at around 2500-4000 rpm,idle is ok ,on road its between 40-50mph,before and after that speed range i get no vibration??

[Dave999]

does it pull cleanly through the vibration or does it run rough mis cough etc

i guess what you are saying brings it back a bit to
driveline angles
or a balance problem

unless you specifically went and changed the counterweights on the crank, i.e serious crank lightening or knife edge, put in some wildly different heavy or light rods or are running some massively mis matched pistons. i can't see it being the general balance of the motor

who did the refurb? did they say what they did.



the other thing would be a flexplate converter or damper designed for an external balance engine in the mix, installed on one that is internally balanced like a 383.
counterweight on any of them? should be no counterweight

you need neutral balance versions on a 383 and you need the other type on a 360 small block or a 400 Big block
if you had a 400 big block part in the mix.... = problem

but i think you would feel that problem across the rpm range.

Dave

[Blue]

What does the top engine builder have to say about it? Please tell me he’s not on the isle of Sheppey….