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engine vibration since 700r4 install


sd pacecar

When I start the car and rev the motor in park or neutral, there is a noticable vibration throughout the rpm range. I also had a new flex plate installed. Some one mentioned that the plate and converter may have to be balanced together. Is that true? Anyone have a similiar problem?

I have noticed a vibration in mine after I switched to a 700r4, mostly around 45mph or so, when driving I'll put the car in neutral and no vibration. I haven't been able to find the cause yet, not that I've looked all that hard for it though. I did have the half shafts powdercoated, and a new driveshaft made but I doubt those are the cause. I'd like to get some feedback as well, especially since I'm planning a high HP 383 install if all goes well in the next month or two.
I emailed with Steve at Bow Tie Overdrives and told him of the problem. He told me it may be the flexplate that was istalled and that
his shop hadn't come across that problem before. He also said it may be the converter.
I know what you mean about spending money, when I did my project I rebuilt everything behind the trans first with upgraded parts, spent 4 1/2 months doing that. Then I had a local shop build up a 700r4 for me, they came recommended by other hotrodders, I also used the Bow Tie Overdrives tubular crossmember. The convertor was brand new and the flexplate was already on the car. After the holidaze I'll go down to a couple local hotrod shops and ask some of the better mechanics what they think.

Hey Mike(stingray6974) are you out there? What do you think about this problem?
The first thing I would check is the drive shaft lentght. I know you said you had a new one made, but I would still check it again. I can't see the flex plate being the problem but, I might would suspect the tiorque converter. I have done many 700R4 conversions. They are not that hard and they should not be that expensive. The last one I did ran the cust about 600. plus the transmission. I have/sell a bracket for 45.00 that will work on your original crossmember. I then "adjust" the original shifter to go into 1st gear. Heck, even the 82's wouldn't do that. Then there is the final adjustment to the emer brake roller, and you're off. I have installed 700R4's in C-3's from 69 to 81. And, so far, they are all still rolling and enjoying 17 to 22 MPG.......Steve
If they changed the flywheel there is a real serious possibility that they installed a 1987 and newer flywheel on your pre 1987 engine. They are balanced different and will cause a very noticeable vibration.

I hope this is not the problem, but if you did swap the flywheel it won't take long to figure it out.
I dropped off the car last night and faxed them a description of the problem. I will definately mention what you have told me. The flexplate is starting to look like the culprit. At least I am getting more info from every post that I can apply to the solution. Thanks.
I printed a copy of this thread and faxed it to the shop. I think they are closed today, but I will be calling bright and early on Wensday morn.
you might want to have the torque converter lock-up switch check we had that problem in our 82 however it was more of a shuddering type of vibration, was especially noticeable when coming to a stop
This doesn't shudder. It is a vibration that is very noticable and causes rattles in the door and other places in the interior and the whole car. It comes in around 850 rpm and goes all the way to the redline. Annoying in the extreme.
if they used a used flywheel, the holes may have been out of round, this could have cuased the torque converted bolts to back off and cause this vibration also using used torque converted bolts without threadlock they tend to come loose
Since you've got a very significant vibration, the first thing to check is that flex-plate. Look for either the wrong flex-plate, a flex-plate that's lost a weight or a stock-balance flex plate fitted to an engine that was custom balanced.

When you remove the converter and flex-plate look for converter to flex plat fasteners that were left off. Enlarged flex-plate bolt holes are possible but I'd think that unlikely because of the severity of the vibration.
I apologize for not responding sooner. My email fouled up and I thought it was because of the Excite@home problems. I fixed the mail problem, so now on to the solution of my engine vibration. The shop installed the wrong flexplate. They got the right one and put it in and voila~ smoooooth running engine. Thanks to everyone who responded, especially 69MyWay, who nailed the problem. I appreciate the input. This forum is getting better every day. :)

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