flexplate wobble

[BigGun J]

I have a 85 6.2 that I pulled the turbo 400 off. Removed the flexplate and installed a NAPA flexplate to mate to the 700R4. I was under the truck checking for leaks, I hadn't installed the inspection cover yet.

The flexplate has a noticable wobble? No noise or rubbing, just not running true.

This is my second 6.2 that I am runnning in my 85 Toyota Landcruiser FJ60. The first was a military take out. The harmonic ballancer had a noticable wobble and that motor broke the crank. I purchased this motor in a running 85 p/u. The flexplate is off the motor that broke the crank behinde the #2 connecting rod. I left the harmonic ballancer that was on this engine as it runs very smooth, no noticable wobble.

The flexplate that was for the turbo 400 is much stouter looking and feel then the NAPA replacement.

Is a bit of wobble OK?

Thanks, Jim

[Robyn]

This is not all that uncommon to see, now here is the likely issue.

Try removing the bolts that hold the flex plate to the converter, then slide the converter back away from the engine.

Now start the engine and look at the flex plate, My guess is that it will run straight and true.

The likely cause of the wobble is a poorly rebuilt converter.
When converters are rebuilt, the weld on the periphery of the converter is cut, the halves split and the innards are worked over (thrust bearings replaced and the lockup clutch replaced.)

Depending on the condition of the HUB (goes into the tranny) it may be replaced to.

Now if the hub is not "Jigged" correctly with the pilot on the front of the converter and the entire assembly does not run concentric when the thing is welded back together it ends up wobbling.

This is not only BAD, its terrible and will not only ruin the tranny, it can potentially destroy the crankshaft in the engine.

The allowable runout in a converter is .002" max.

If your plate is WOBBLING, so is the converter.
Converters make the plate wobble, not the other way around.

Check this out and let us know.

If the plate runs true when unbolted, get the converter out of the truck and replace it with a good one.

If this is a rebuilt, take it back and demand a good one.

Back when I was doing trannies a lot, I would stick all rebuilt converters in the lathe and check them to be sure they ran true.

I have seen these things run out .025" at the hubs, and have the pilot and the hub running out even more. :eek:
A combination of the hub and pilots centerline on an angle as well as offset.

Allowing this wobble is a death sentence to your engine and tranny.

The Flex plate is just that FLEX and it will. The converter has to be true or the entire assembly will wobble, and it will shake too.

Good luck

Missy

[DmaxMaverick]

Are you using the same flexplate and/or TC from the previous engine that broke the crank? If so, that was probably the reason for the broken crank. These engines are externally balanced, and will destroy the engine with a bad flexplate/flywheel. As Robyn said, the problem is likely the torque converter, however, a flexplate that is bad or indexed incorrectly (counterweights wrong or missing) will eventually cause the TC to wobble, if the plate doesn't break first. Either way, I don't suggest reinstalling either of them, damage is done, and the flexplate is bad originally, or has been ruined by a bad TC. If you can "see" a wobble, it is a LOT. The allowable runout is so little, you can't see it on a running engine. If you are lucky, it hasn't destroyed the tranny bearing, or more.

[john8662]

Flexplate wobble.

So, I'm building a Balanced 6.2 for my folks an in the process I had to find a good flexplate.

I brought the machine shop with the balancer a new TH700 Pioneer branded flexplate. Lots of wobble on the balancer. I ended up getting two more from the parts house, some worse than the first. Got another from ATP, looked like the Pioneer, didn't run true either.

I ended up ordering a new GM Flexplate and hoping that it'd be true, because it'd be harder to return due to this pickyness.

It was much better than any of the others, but not perfect either. We ran with it, balanced the crank etc.

I'll bet that the Napa one isn't very true either. It's a problem, don't know what the fix is really and to what detrement it is on the engine/transmission when bolted to the converter...

J

[BigGun J]

Fall has arrived, winter is on my heels so my Landcruiser needs to be up for the task. The flex plate wobbled with the torque converter un-bolted. I went ahead and purchased a flexplate from summit and a torque converter from a local tranny shop. Bolted up the new flexplate, fired her up and just the slightist of wobble (nothing like before!) installed the tranny and all sundries. Fired her up and runs smooth, just the slightest of wobble. Prior to, I checked the tranny shaft for runout and nothing to note. Success for now so time to put some miles on her and see what comes next? Probably the heads off my old motor as I have some bubbles in my overflow tank. Oh well I should of perservered and rebuilt the block I bought from Robin. I all ways have that option for the next go round or two or three or four?

Jim

[john8662]

good to hear you got a true flexplate. What as the brand of the flexplate you got from Summit?

[BigGun J]

Not sure? It is stamped made in Mexico. Local tranny shop recommended a OER C57HD converter. 60 miles and all is well but there just short trips to and from work,. Going to take a drive up I-90 tomorrow. Run it down the interstate for a bit. locked converter turning 70 should be a good test. Sure like having it back on the road. Driving the little 40 mpg diesel jetta is ok, but it just not my Landcruiser!

Jim

[Robyn]

The issue was likely the converter.

The bolt bosses on the converter are machined true during manufacture, and oncw the flex plate is bolted up, things shound run true and smooth.

Far too many rebuilt converters are not indexed correctly and run out radially and others will see the crank pilot stub not on the same centerline as the drive hub.

I have seen these things soooooooo F'ED UP that the assembly would shake so bad, that at 1000 RPM the door mirrors would about fly off.

Had one that when checked between centers in the lathe, ran out .100"
on the diameter with the drive hub in the chuck, and the crank pilot was off center by nearly that much.

Had that unit been installed, it would have torn things apart in short order.

Sadly there are rebuilders out there that turn out this sort of $HIT and charge $$$$$$$ for it too :eek:

Normally the flex plate will run fine once its bolted to the converter, and if the assembly wobbles, 99% of the time it's due to a crappy converter rebuild.

When converters are rebuilt they are placed in a lathe and the weld thats just to the rear of the front end on the diameter is cut through.

The halves are then split and the internal parts removed.
The lockup clutch (if used) thrust bearings and stator one way clutch are replaced.

All the turbine and pump blades are examined for cracks and or loosness at this time too.

Some HD applications will have the blades tack welded to the torus to strengthen the unit.


If the drive hub is damaged where it rides in the front pump bushing area the hub will be cut off and a new one welded to the housing.

If the new hub is not indexed correctly, the unit is junk and no manner of excuses will save it.

Once the innards are ready, the front cover is reinstalled and rewelded.

The front pilot must run true radially and the drive bolt pads must be at right angles to the Center Line within .002"

This is not hard to do, it just has to be done right is all.

Sounds like you are ok now.

Missy