I have a rebuilt 400 sbc with a rebuilt 2004r that has a very noticeable vibration from 1200 to 1700 rpm. It has a 400 flex plate and I just replaced the harmonic balancer with a external balance type. What is the most logical process of elimination to find this vibration. Pull the pulleys off? If not a pulley then what?

I have a rebuilt 400 sbc with a rebuilt 2004r that has a very noticeable vibration from 1200 to 1700 rpm. It has a 400 flex plate and I just replaced the harmonic balancer with a external balance type. What is the most logical process of elimination to find this vibration. Pull the pulleys off? If not a pulley then what?


I have heard of people having torque converters that were not balanced properly.

Steve

Wrong flexplate? I had the same problem with a car I bought that had a 400sb in it and the previous owner put a 350 in it and used the flexplate from the 400 on it. After I swapped the flexplate out the vibes went away.

I wonder if 454 and 400 flexplates have the same weight? Anybody know for sure?

meanwhile, drop all the belts. try it. if that fixes it put the belts on one at a time.

if it doesn't fix it take the 3 bolts out of the converter, push it back into the tranny and try it.

My experience with balance problems is that they get worse with RPM, higher the RPM, worse buzzing.

#5 and #7 plug wires reversed? #4 and #6? easy to do.

Thanks...the best process to work through this was what I am looking for. If it isn't related to the pullys, can it be the torque convertor itself or is it generally how it is bolted to the flex plate that causes vibration?

You say this engine was rebuilt. Are you sure that it wasn't internally balanced during the rebuild. Did it get better or worse after you replaced the balancer?

I wonder if 454 and 400 flexplates have the same weight? Anybody know for sure?



I'm nearly positive no. I had a mcleod flywheel w/ 383/400 counter balance weight. I called mcleod and they said I needed a bigger weight for a 454. I took it to the balance shop and had my rotating assembly balanced and they also said I needed a bigger weight. Lucky they had one in stock and traded me my 383 weight.

loose trans bolts?

The machine shop sent the entire assembly out to be supposedly externally balanced. They furnished the new flexplate, I installed it and the torque convertor and transmission. Tonight I pulled the belts and checked the plug wires to ensure they were in proper order. I still have a vibration so I will start looking at the tranny later tonight. I will check the transmission bolts to make sure they are tight, then unbolt the torque convertor and see if the vibration persists.

kc,
Does the "vibration" get better above 1700 rpm ?? If so, I doubt that it is really a vibration related to somthing being out of balance. Normally, when an engine, flywheel, drive shaft etc are mechanically out of balance, the vibration will get worse as the rpm's go up. Just like an out of balance tire is worse as you go faster. Does the engine have a fairly radical cam in it ? If so, it just might be a characteristic of the cam that it does not run smooth in that rpm range. Could also be a carburetor or even ignition timing problem.

It might actually be something out of balance, but dont get too hung up on that being the cause. It might not be a bad idea to run it by your engine builder and let him "feel" it and give you his opinion.

By the way, did the crankshaft have a dowel pin in it so you could only install the flywheel in one position ?

could be the pinion angle. had the same type of vibration after the 2004r install. checked and moved convertor on flex plate. was driving me nuts. decided to lower the rear with those spring expanders/compressors that look like big U bolts and I noticed the vibration was less. pulled that junk out and cut the rear springs and now almost no vibration. I installed the adj upper control arms and less vibration with out even any adjustment.

Well I unbolted the torque convertor and left the belts off. With the torque convertor unbolted the vibration seems worse.

I do not remember if there was a dowel in the crank but it is a stock 400 sb crank.

The vibration smooths out but is still noticeable over 1900-2000 rpm. It is most noticeable between 1200 to 1700 rpm except when the torque convertor was unbolted it became noticable at 900 to 1000 rpm.

The info on the cam is .450 Int, 460 exh, duration .50 224, overlap 60. The engine builder referred to it as an RV cam, better than stock but not big enough to impact to reliability or vacuum.

I hadn't considered the vibration being characteristic of this cam, possibly it is??

kc,
That cam is not big enough to be causing a rough running situation. If you can see up through the dust cover, look at the flex plate where it is bolted to the crankshaft. There is an "extra" hole between two of the bolt holes and you should be able to see the dowel pin in that hole. The pin is long enough that it should be coming all the way through the hole. If its not there, then there is a good chance the flywheel is not positioned properly and can cause the vibration. Usually when this is the problem though, the vibration gets worse as the rpm's go up. But you never know ?

The 400 and NOT a 454 f/p/f/w has to line up by the dowel hole even if a dowel isn't there!!

That said, go back to a stock 400 damper and then see what happen's??

And to continue and I figure BillK will agree that whoever balanced it should NOT have removed anything off either the damper or f/w/f/p b/c to do so, make's them one engine specific and not stock for use w/ other stock engines later.

Imho, a rotating assembly need's to balance like stock if possible!!!!!!!!

pdq67

I checked this morning and did find the crank has the dowel pin through the flywheel. The flywheel was installed with the raised portion around the bolt holes towards the torque convertor. The pulley is still on the harmionic balancer but I'm beginning to believe this vibration must be related to something other than the balance of engine componets. After I get everthing underneath bolted back up and the car let back down I'm going to look at the ignition again.