Cracked flex plate?

[porkchop]

How can you tell if you have a cracked Flex Plate? When I punch it off the line at stop lights you can hear the torq conv bolts hitting the flex plate in a fast rattle sound. As soon as you get up to speed it stops. It will not do this if I take off normal (whatever normal is http://www.ifsja.org/ubb/biggrin.gif). Is there away to test for this.
Thanks,
Bryant

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'67/'79 Wagoneer mix
“Old Timer”
Check it out! (http://members.fortunecity.com/porkchopsfsj)

"I have a dream that one day FSJ's will be equal at every parts store."

[Dean]

Bryant, could it be your fan hitting the shroud or radiator? Also check your tranny to engine bolts. The TC is bolted to the flexplate so the bolts would have to be loose to be a source of noise and then I would think that they would be hitting your block or that thin plate sandwiched between the block and the tranny (if you have one). Could you have rocks in your bellhousing?

I'm just throwing out guesses here but I would check the fan first. Under hard accel the engine/tranny can flex the mounts pretty hard and start hitting things that have good clearance otherwise. Oh, also look to see it your drive shaft isn't rubbing on something.

Good luck, Dean.

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'78 Wagoneer Limited
401/Q-trac W/low range
Mods so far, carter 4 bbl., rancho 3" lift, rancho RS5000 & RS9000, stage one of the GB ign upgrade.

Donor rigs, '84 GW, '78 J20.

[nograin]

I think Dean is right.
Now this is from my car, not my jeep, but it also has a TF 727. When I was breaking flexplates (I broke two or three the first year) the rattle would also occur while driving at certain speeds. Now I don't have a dust shield on that vehicle. So when ever it sounded like it broke, I'd look underneath. It was always pretty obvious, sometimes had to turn the crank shaft a half turn. Usually the break would go across one of the ears, sometimes it would just shatter around a bolt (to the torque converter - never to the crank).

The other item I was thinking that may have broken was an engine or tranny mount. I broke both of mine (again) and just bought a more rigid torque strap. Thing is, that vibration is more general, but maybe under the gun, the left side lifts and the fan hits the shroud or something. Also maybe your engine is smoother than mine..

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360 auto select
body by beer (PO)
carries wood inside
no "wood" outside

[RudyC]

Sorry PC but if it sounds like bolts banging in your bell housing its the flex plate.
I replaced two within six months of each other. Crawl under, pull the inspection cover and with a good light the "wagon wheels" break on the thinnest part of the spoke at rhe crankshaft side. Replace the Torque converter if it is the flex plate. this is what was breaking mine. I dropped my tranny three maybe four times last year Two flex plates a Torque converter and the the tranny pump.

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"BULLSEYE"
1979 WAGONEER, 360,
Holley 600 CFM carb.
Stock 4bbl Intake,
TFI CONVERSION, TH400, Q-TRAC. 3" ADD A LEAFS, 31" MUD T/A'S (PEP BOYS CLONES).

http://home.earthlink.net/~zzjoecool/index.html

[jeepbob]

Also check the bellhousing (tranny)bolts for tightness. an old 78 I had would do the same thing when the bolts came loose. It also would shake the starter loose. When I finally pulled it down it had the wrong flex plate. If yours is broken, be sure to get the one for the proper size engine.

[porkchop]

Thanks Guys, I will check it out this weekend and let you know.

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'67/'79 Wagoneer mix
“Old Timer”
Check it out! (http://members.fortunecity.com/porkchopsfsj)

"I have a dream that one day FSJ's will be equal at every parts store."

[scotty]

and if it all looks OK then you have a little gremlin with a hammer hiding in there.like on the bugs bunny cartoon http://www.ifsja.org/ubb/biggrin.gif youll have to find a way to chase him out!

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scott
85 grand wagoneer
258 with motorcraft 2bbl/904/twin stick dana 300/dana 44/welded amc 20
38x15.5 gumbo mudders
snorkel/dual batteries/onboard air/"custom" convertable
3 inch body lift/mostly stock suspension/"modified" fender openings
custom front/rear bumpers and brushgaurd

T18/dana-spicer 18 with drum E brake and PTO,and offset dana 44 swap very soon
BIG tow truck PTO winch and full roll cage install shortly thereafter
searching for jeep 4.0 six engine

now we can do some 'wheelin!