When checking the flexplate runout with a dial indicator should the torque convertor be connected or disconnected? The problem I have is that I get a vibration most noticably between 12 and 1500rpm. When I disconnect the convertor and restart the engine, the vibration goes away. So what could it be? the flexplate or the convertor out of balance?

 

If I had to vote for either I would vote for the torque converter. The flex plate doesn't weigh much. I just got done dealing with the same thing on my car, except the vibration didn't become noticable until about 2400 RPM. It turned out to be the flywheel. Typically when something becomes that noticable at such a low rpm I would think it would be the heavier item. Rotate your converter and look for missing balancing weights.

 

Did the vibration just start? If so, what was changed?

 

45ACP, the vibration just now began after a tranny swap from the TH400 to a 200R. It is not a severe vibration yet very noticable. The trans and convertor are the new items. If I unbolt the convertor and push it away from the flexplate, I can run the engine with it disconnected. When I do this, the vibration goes away. Bolt the convertor back up and the vibration returns. I have still not driven the car since the swap. I wont untill I correct this problem. The flexplate being used is the same one that was used with the 400 trans. There was no vibration with this flexplate prior to the swap.


[Modified by Jvette73, 5:34 AM 9/17/2001]

 

The flex plate is very flimsy and distorts once bolted to the torque convertor. It also doesn;t weigh anything. If this is a 454 it needs the counter balance . I would say it is the convertor. They can be easily rebalance but it is a pain removing and re installing it.
Norval

 

Ok. You have pretty well got it isolated down to the converter as the source of the shake. There are still a couple of things to look at -

1. GM flexplates quite often fail with mileage/age. Sometimes when they crack out, because they are allowing the comverter (which, in this case, weighs 38lbs. dry) to run eccentrically, a vibe will be felt. Yes, sometimes the vibe comes and goes with rpm's. Look for cracks right around the bolt circle area where it bolts to the crank.

2. The pilot of the converter could be worn. No, I'm not kidding. The pilot of GM 298mm converters (sized at 1.703") has very little bearing area. As in works back and forth in the pilot hole that it sits in, it can become flat spotted on one side. If, when putting it back into service, the converter just happens to be placed into the pilot hole with the flat side down, you end up with the converter running eccentrically. This = vibes.

Sooo . . . unbolt the converter, then index it around so that the pads line up with the next set of bolt holes. Which is to say, give it 1/3rd of a turn, then bolt it back up.

With any luck, you are no longer centering the converter on the bad part of the pilot. If it runs true now, the vibe will be gone.

If the vibe is still there, do the index trick again. Be sure to do it in the same direction in order to make use of a " new" section of the pilot.

3. If you still have vibes, do a variation of #2 above.

It is possible (but not too likely) that the pilot hole itself in the crank is out of round. As the old converter worked back and forth, it could have worn the bore slightly on one side. Due to bad luck, you may have set the converter pilot into this bad spot.

Unbolt the converter. Now - without rotating the converter - index the flexplate so the next set of holes lines up. Yeah, it sucks because you need to turn the motor 1/3rd of a turn, but there is no avoiding it.

Now you may have a good section of the pilot hole to work with. If the vibe is still there, once again index it another 1/3rd in the same direction to get a "new" part of the bore to work with.


If 1, 2, and 3 above don't do the trick . . . take the coverter back and exchange it for another, it has been built in an asymetrical fashion and/or it is out of balance --> it is NFG.


[Modified by 45ACP, 9:48 PM 9/17/2001]

 

Didn't you get your 200-4r and converter from Steve Holmes at Bowtie Overdrives? If you did, you should give them a call and ask him what to do. It is possible that the torque converter is not balanced and needs to be.

 

Block is properly indexed, pilot in crank is in good shape, new convertor. I did get my trans and convertor from Bowtie. I spoke with Steve and he and I both believe its the unbalanced convertor. Another is on the way right now. I did try bolting the convertor up in all three posistions to no avail. My flywheel has miniscule amount of runout when unhooked. When hooked up it wobbles more. I think the unbalanced convertor is making the flywheel wobble a bit. Anyhow Steve at Bowtie is taking this convertor back for exchange whether its bad or not. Like me, he too wants this thing to be right. I have no problems with BTO. They've been with me all the time. So half a dozen bad convertors a year. Big Deal. I got one of them. im gonna throw a new, more beefy flexplate in there while im at it since they dont cost that much. Thanks for all the responses.