75 chevy flywheel

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  #1  
Old 04-04-08, 07:25 AM
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Lightbulb 75 chevy flywheel

I have a 1975 chev pickup that developed a squeek/ slight knock that I determined was coming from the transmission area. I pulled the cover off of the flywheel and sure enough found a loose bolt. I tightened it and checked the rest to make sure they were tight, but the noise is still there. I've concluded that the flywheel must have warped while the bolt was loose. 2 questions for anyone: 1-Does my diagnosis sound right? And 2- I dont have the time to fix it and plan to sell it as is, can it be driven without causing damage?
 
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Old 04-04-08, 08:03 AM
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i'm assuming that you have an automatic trans? if so, it may well be cracked. they sound just like a rod knock to me...but the squeeking part, that I don't ever remember with loose flexplate bolts or a cracked one. could you maybe have spun a rod bearing? either way...cracked or otherwise it will continue to get worse and could possibly cause more damage as it progresses.
 
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Old 04-04-08, 08:13 AM
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Depending on the engine, the only bolts you would have access to with the inspection cover off would be bolts that attach the pressure plate to the flywheel. One of those loose wouldn't cause the flywheel to warp. A warped flywheel or one with too much run out would come with a good vibration.

When you say knock/squeek you are in two different areas. I would normally put the knock in a '75 engine as internal = rod/main bearing wear or piston slap. But you could have something striking in the bell housing = possibly the throwout fork/bearing. That would show up or disappear as you depress or release the clutch pedal. Also the pilot bearing/bushing for the input shaft on the transmission can be the source of noises as they wear out or get out of tolerances.

Work the clutch pedal and see if it makes any difference in the noise. If it does = clutch/tranny noise and you may have to pull the tranmission. If not, it could easily be in the lower end of the engine.

As for whether it would hurt to keep driving it, it would depend fully on what the noise is.

Hope this helps,

Bob
 
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Old 04-04-08, 08:29 AM
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Thanks for the input. I forgot to say that it has an automatic transmission. The knocking sound is definately coming from the area of the flywheel. I saw no missing teeth or visible cracks, but it could have a hairline crack. I'm almost (just almost) positive that it's not coming from the lower end of the engine. If I'm right, I'm wondering if it would be safe to drive it accross town, or if it needs to be towed. I don't want to tear it up, because other than that ,the old thing runs and drives perfect. Thanks again for the input.
 
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Old 04-04-08, 08:36 AM
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With an automatic you have probably cracked the flexplate. You could probably make it across town, but a lot of driving isn't advisable.
 
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Old 04-04-08, 09:03 AM
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Exclamation

Originally Posted by bertman21 View Post
Thanks for the input. I forgot to say that it has an automatic transmission. The knocking sound is definately coming from the area of the flywheel. I saw no missing teeth or visible cracks, but it could have a hairline crack. I'm almost (just almost) positive that it's not coming from the lower end of the engine. If I'm right, I'm wondering if it would be safe to drive it accross town, or if it needs to be towed. I don't want to tear it up, because other than that ,the old thing runs and drives perfect. Thanks again for the input.
they usually crack AROUND the bolt head and you can not see the crack. when it is pulled off, the section of the flexplate will probably come off looking like a ragged washer. fix it SOON!
 
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Old 04-04-08, 10:46 AM
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Very common issue on GM flexplates of this era. NAPA makes a H.D. one reasonably priced. One way to diagnose it is to see if the noise changes/gets lighter when you put the transmission in gear. It should make less to no noise in gear as compaired to in park or neutral.

Tips when changing yourself.

Remove driveline, crossmember (the bracket that has the trans. mount), disconnect shift detent cable (at carb - not trans). Transmission will then be tipped at an angle and supported by engine only. Watch the distributor cap....may have to remove it. Watch fan shroud as it may now be hitting fan blade....may have to unbolt /loosen shroud.
remove the two bolts on each side of transmission that are in about in the 3 & 9 o'clock position and replace with two bolts that are 4" long of same thread type.
remove the bolts that secure the flexplate to the torque converter and push the converter back into the transmission as far as you can. Try and secure the converter back into the transmission anyway you can (bungies, tape, making a bracket...whatever) as you do not want it to come out while you are messing with everything else. Then support transmission via trans. jack or makeshift jack and remove remaining transmission bolts. The transmission will now slide back on the long bolts installed earlier and you should now have enough room to gain access to the bolts that are holding the flexplate to the crankshaft. Hold the flywheel in place via a flywheel holding tool or large screwdriver placed between the flywheel teeth and the block as you use the proper socket and long handle ratchet to loosen/remove flexplate mounting bolts. Install new flexplate using locktite on bolts and reassemble.

Note:

1. Sometimes you can get by without removing the trans. cooler lines (they will make a dripping mess in your work area) as they can be slightly bent without kinking and stretch enough to be ok. If you have to remove them have a short piece of hose ready to loop cooler lines together to minimize mess.
2. Depending on your exhaust system. It may or may not have to be unbolted to gain access.
 
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