Getting ready for Lebanon Valley this weekend, did some work on weight transfer and hoping to break 14.5 in the 65 Gran Sport .. But I've got a slight vibration at about 70 mph, seemingly from the drive train or rear of the car..Could be anything from rear tires to driveshaft balance and I'll track it down. When I had the transmission done, they found the flex plate was cracked, so I had them throw one in (it came with the car). I have no idea if they installed it correctly though, and lined up the holes in the plate and the crank flange. I understand it could cause a vibration if installed in the wrong position. If I put the car in the air, is there any way to tell if they're lined up? I wouldnt think you could see between the converter and plate, or the block and the flange. Are there any external markings that should line up? PS - Doc, sorry I havent been able to call you back yet, I was on vacation when you called. I'll be in touch. Thanks,
If I remember right, there's an alignment hole in both the crank flange and flexplate/flywheel. Use the clock position that allows a pin to pass through both. Devon
I just went through this on another '65GS. I took the inspection pan/fleplate shield off & could see the weighted place on the flexplate was not aligned with the counter weighted crank flange. It IS possible to see this. Not very easily, but possible. Tom T.
Since flex mounting is engine speed related rather than drive shaft speed, you should be able to 'feel' the vib at the same engine rpm in other gears and neutral that you are finding at 70. If so, a possibility-I've run across a couple 'aftermarket/rebuilt' convertors that were not balanced or correctly. You may improve or learn something easily by rebolting your convertor to flex in the other 2 possble locations. If not engine speed related, I've sure run across plenty of tire/wheel 'issues' over the years-good luck with it
Thanks to everyone for your reponses. I'll pull the cover down and look, and with luck I can rule it out. As it's really semingly more related to road speed and not rpm, my bet is it's probably the rear wheels/tires. They balanced well, but one of the rims had a slight walk to it. Hadnt been a problem until now, but I'd bet it's time to get rid of that rim. Tom - will you be at Lebanon this weekend?
I found this shot of a 425 crank: Is the alignment hole on counter clockways side of the counterweight? Thanks,
Thanks Dan - Hard to see, but looks like somewhat inline with the bolt holes...(not way out on the weight where I first thought it was)?
i think we are all looking to deep into this... have you road forced the wheel and tire together? you can also do a rim runout on the tire balancer without the tire on it. balancing and roadforcing is two different things and most new tire machine have this feature available. it puts about 1500 hundred pounds of force per sq inch to check the tires integrity and will help you determined if you have a shifted or broken belt. when you feel this do you feel it in the back of your seat? in the floor pans? it does make a difference when chasing down vibrations. have you looked at the ujoints yet to see if thier is any play in them or if thier is any small dents in the driveshaft which would give you a similar feeling. gd luck and keep us updated... thanks Paul 66larkgs turbo401 nailhead
An externally balanced flex plate will only bolt to a Buick 455 or V6 crankshaft in only one position. The earlier Nailhead may not have that feature, but I bet it does. As stated earlier in this thread it sounds like the vibration is more road speed related than engine. Since the transmission was the last thing removed and replaced, consider a worn bushing in the tailshaft.
All the bolt holes are the same in a "Nail". The flexplate could bolt on in any one of six positions. Only ONE is CORRECT. I have to see how things go Rhett. IF I do go it will be Sunday. Tom T.
Paul - you are probably right...I just want to know what to look for when I get this car back in the air, because I KNOW the kid at the tranny shop was half my age, and had no idea it had to line up. I feel the vibration all through the car, not so much in the steering wheel or my butt, which is why I'm thinking about drivetrain. The driveshaft and U-Joints look good too, BTW. I know I have a runout issue in one rim, but it's minor (1/8 inch?) Roadforcing is a new one on me, can you explain? Babeola - great picture, now I totally get what I'm looking for. Tom - I'm going sunday too, if you're there come and track me down in the staging lanes. Red on red 65 GS with a white top. Thanks to all -
roadforce is when you put a tire and wheel on the balencer and another big wheel comes down and puts force on the tire and wheel simulating a tire on the road with the weight of a car on top of it. i have seen sooooo many wheel and tire issues at the dealer that is isent even funny..sometimes even brand new tires.. i we have a roadforce balancer @ the dealer, @ the trades school i teach @ and i know pretty much ever big tire shop like town fair tire also has roadforce. dont forget to make sure to check that driveshaft while it is up in the air for any dents too.. go luck and keep us posted.. paul 66larkgs turbo 401 nailhead 7psi boost 53 international chopped/channeled, 406ci .630 solid mech roller cam rpm ported heads, http://s917.photobucket.com/albums/ad19/66larkgs/66 skylark turbo nailhead/ http://s917.photobucket.com/albums/ad19/66larkgs/53 international hot rod/
This is gonna sound goofy, but..... More than once pulling the driveshaft and rotating 180 degrees has stopped a bad vibe. Can't hurt, might help and it sure is a crowd pleaser.
As an update: I think I found the issue with the vibration, it seems to be the rim with the excesive runout..funny becuase it balanced just fine. I played around on the way back from the track, and the car would set up the vibration from 70-80 mph, and if I let off the gas it would slow the car down like a bad shopping cart. It probably hurt my ETs some too.... So when I got home I switched out a pair of "known good" rims and tires on the rear, and the car ran as smooth as a sewing machine, with none of the throttle lift drag I had before. I found some new rims locally, so I'll switch them out and see if it cures it (and helps on the ET side this October) I put up a short post in the " Buick Events" section on how the day went..thanks to everybody who weighed in.
