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flex plate size for 6.5/4L80E?

F

Fysh Guide

Fysh Guide
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Location
Banff, Alberta
After grenading my transfer case a couple months ago and replacing it, and both driveshafts, I still have a vibration that has been slowly getting worse. Everything else seems fine on visual inspection, the vibration is speed related, although it seems to increase with RPM. The colder it is, the more noticeable. The last couple weeks I've occassionally noticed a metallic zinging sound at idle. I suspect that the flex plate has been flexxed a little too much and needs to be R&R'd. I figure a new HD torque converter at the same time would be worthwhile. Finding a quality converter is no problem but no-one seems to have a HD flexplate for this application nor do they even know what size it is.
Does anyone have an idea of what size of flex plate these rigs take?
 
I have a stock one. I can measure it for you and post tomarrow. If you want it we can work something out too.
 
Same size and teeth as the 6.2 'plate, butcept the bore for the crank hub is reduced slightly for tighter fit, so don't even use the 6.2 version, even if it's free
 
I measured mine this afternoon at just a hare over 14 inches from outer edge of teeth to outer edge of teeth.

It was between a 6.5 amd a 4L80e tranny.
 
So far what I've figured out is that the flexplate has an O.D. of 14.23 inches and seems to have 168 teeth. Would this be the same flexplate used on the 454/4L80E of possibly another combo? Is it internally or externally balanced, or maybe counterweighted? There seems to be a lot of options for HD flexplates but nobody mentions the 6.5....
 
MOTOR MOUNTS??????????

do me a favor please check the motor mounts on the truck all three driver side has a tendency to break and cause weird vibrations and the transfer case to lock up. and go blah and it causes weird noises and all sorts of other problems and only use gm mounts just my 2 cents worth Jerry
 
Was the tranny ever rebuilt along with a fresh converter???

If so remove the flywheel cover and run the engine, observe the converter and see if it is wobbling.

If its wobbling, therein lies the bad vibes and the flex plate is probably toast.

The other possibility (Very real) is the rubber dampened serp belt drive pulley.
These can break loose and make noise as well as cause bad vibes.

The center of the pulley has a bearing to stabilize it and the rubber is bonded to the inner ring to drive the setup and also dampen the power pulses so the accessories dont get beat up.

Both of these issues can and do cause crank failures in these engines.

Look it over carefully

MGW
 
IIRC, GM flexplates are exclusive to the engine for which it is attached - GM went to external balancing back in the '80's - tho most appear to be similar, at 168t, the spot-welded balance-weight tab is specific, as is the crank-hub diameter - again, the 6.2 bore is not as tight as the 6.5 bore, so they should not be interchanged on the 6.5 series
 
Fysh Guide said:
So far what I've figured out is that the flexplate has an O.D. of 14.23 inches and seems to have 168 teeth. Would this be the same flexplate used on the 454/4L80E of possibly another combo? Is it internally or externally balanced, or maybe counterweighted? There seems to be a lot of options for HD flexplates but nobody mentions the 6.5....
Click to expand...

The 6.5 is counterweighted, I wouldn't trust one from anything else. The 454 is also, but surely it is balanced different.
 
Does it vibrate in neutral when you rev it up? Do you have any transmission parts store around you, they should have a flex plate.
 
Yes it does vibrate as I rev it up. The vibration is more pronounced when under load. I put the truck up on ramps the other day to remove the cover, but I'll have to remove the x-over. When the exhaust was installed the muffler man forgot the driver side flange, had to cut off the connecting end of the pipe, slip the flange on and install it. So I ended up with a slightly shorter, lopsided x-over. I'm going to order a new x-overwith the new flexplate and torque converter on Monday but I may take the old one off to check the flex plate this weekend. The tranny has been running warmer than normal, even when it's cold.
Having said all that, I've been dying to put a Fluidampr on for awhile. The belt pulley is running nice and straight, but I just noticed that the dampener has suddenly got a slight wobble. This is new. (Thanks Missy) I'll have a fluidampr on it this week, I already have a new pulley on the shelf. I guess I should do the water pump and front seal while I'm at it. I'm tempted to install the phazer timing gears too, but have a bit of an aversion to DSG after being almost run down by an aggressive eurosedan with the plate DSG while flagging a workzone lane closure for a line painting crew, last fall. I found out after that it was an owners car, probably the teen son driving. Despite that I would love the gears in there....
 
Fysh Guide said:
Yes it does vibrate as I rev it up. The vibration is more pronounced when under load.
Having said all that, I've been dying to put a Fluidampr on for awhile. The belt pulley is running nice and straight, but I just noticed that the dampener has suddenly got a slight wobble. This is new. (Thanks Missy) I'll have a fluidampr on it this week, I already have a new pulley on the shelf.
Click to expand...

I'd replace the damper before pulling the trans. When my balancer went bad it caused a vibration as the rpm's went up.

Usually when a flex plate goes bad it cracks or it is loose causing it to knock. On a side not though your converter maybe coming apart inside, that will cause a vibration, I've had that happen before.
 
midniteplowboyy said:
I'd replace the damper before pulling the trans. When my balancer went bad it caused a vibration as the rpm's went up.

Usually when a flex plate goes bad it cracks or it is loose causing it to knock. On a side not though your converter maybe coming apart inside, that will cause a vibration, I've had that happen before.
Click to expand...

I agree. The nice thing is I'll be able to do the damper. The tranny was a little daunting and with work, not a chance. Even if it isn't the damper, I've been itching to get this on....
I'll be ordering it tomorrow!
 
The Fluidampr is in! It arrived this morning at work and I stayed after work and used the shop to install it. It didn't get rid of the vibration issue but it did make a difference. Green Thunder now has a noticeable deeper and softer rumble. It's a load off that I'm not vibrating the hell out of the crankshaft. Peace of mind!
Having said all that I was a little surprised at my misconception of a couple things. The balancer has no absorption qualities. Just a solid counterweight. For some reason I thought otherwise. My pulley didn't look too bad although the rubber was a little harder than the new one. I kept both old parts in case I need them down the road.
Next step is new tires (DuraGrapplers, maybe tomorrow) and then I'll look at dropping the cover and inspecting the flex plate, if need be.
 
Fysh Guide said:
The Fluidampr is in! It arrived this morning at work and I stayed after work and used the shop to install it. It didn't get rid of the vibration issue but it did make a difference. Green Thunder now has a noticeable deeper and softer rumble. It's a load off that I'm not vibrating the hell out of the crankshaft. Peace of mind!
Having said all that I was a little surprised at my misconception of a couple things. The balancer has no absorption qualities. Just a solid counterweight. For some reason I thought otherwise. My pulley didn't look too bad although the rubber was a little harder than the new one. I kept both old parts in case I need them down the road.
Next step is new tires (DuraGrapplers, maybe tomorrow) and then I'll look at dropping the cover and inspecting the flex plate, if need be.
Click to expand...

I think they have an internal viscous fluid that does the balancing. Leo
 
Correct - hence, the name FLUIDAMPR - also has an internal flyweight
 
Fysh I still have a flex plate that came out of a 94 "f" 6.5 with 4l80e if you find you need it let me know we can work something out.
 
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