I just pulled my tranny out due to a clutch chatter problem (among other things). When I looked at the flywheel it had spots on it. See the pics here. The spots appear to have a different texture and color than the surrounding metal.

I just had the flywheel turned and replaced the clutch & pressure plate less than 3000 miles ago. Before it was turned, it had similar spots on it but they disappeared after it was turned so the guys at the shop said that it must not have been a problem. Well, the chatter is back.

Could these be the same as "hot spots" that I have heard about before? Is this a cause of the chatter?

Thanks!

Dale

 

Being the dumb@ss that I occassionally am, I installed my flywheel w/o having it turned and it looked exactly like yours. Maybe thats why it slips like a mother and becomes all mushy after taking off from a steep incline. To answer your question, yes technically speaking hot spots will warp a flywheel in the same way a brake rotor does fron excessively hard braking, and cause clutch chatter. Either get the flywheel turned again or get a new one. Every time you have it turned it gets thinner and your chances of warping it again get better.

 

It looks like it got too hot. If the flywheel turns all sorts of crazy colors, then it's toast.

It's almost the same process they use to make tool steel. You heat the crap out of it until it turn funky colors.

If that happens, don't bother getting it turned. Get a new one. You see, in order for it to be "turnable" it has to be softer than the bit they use to cut it. Now that it 's all shades of blue, it has hardened and the bit is just gonna chatter across it. They will prolly take in to turn it, but it's gonna be a crap job and ruin your clutch.

Get a new clutch, and try not to slip it so much.

 

Good places actually dont use a cutting bit (which are super hard and quite expensive) but rather a stone on a special machine, which leaves the surface marks (the circular ones) that are in the pics you posted. I never had a problem grinding away anything (like hard spots), nor did I ever have a problem with chatter or uneven surfaces. Something about using the right tool for the right job... Brake lathes and such should be left for cutting rotors.

The spots really dont look that bad, I have seen much worse than that before and reused the flywheel. Its hard to tell from the pics, but something tells me that flywheel has either been machined many times in the past, or alot at once. It could be its too thin and getting hot, or it could be the pressure plate. Are you getting new pressure plates or reman ones? The lesser quality and reman stuff really is hit+miss on the quality of the surface and the spring tension, and can cause problems.

 

I've always seen them use a bit for flywheels. Maybe I've been going to the wrong places!

 

A bit? Yuck. I'm not sure on the name, been a while... Accuturn brake lathe? I bet thats what they are using. Problem with using a bit is you can end up with a surface that is tapered from center to outside edge. Thats less of a problem with brake pads, they can wear in or adjust to that to some extent. Rotors dont like the opposite surfaces not being parallel though, and a brake lathe does a good job of keeping things parallel. A stone is a much better thing to grind a flywheel with, leaves a better surface that is for sure flat across the flywheel. The machines I have used are wet grinding machines, to prevent heating the flywheel up and to provide a smoother surface. Many many times when a flywheel comes in, its tapered from where the pressure plate bolts up to the center, just from the bolts pulling on the outside of the flywheel when you put the clutch in. IIRC the average was around .004-5 of taper. I think about the worst flywheel I had was worn away around .070 and wasnt parallel to the crank flange either, seemed to me it was bent. Customer wanted it cut anyway

 

Thanks all! I figured I should also add a few more things after reading the above.

1: I have no idea of the history of this flywheel. I am guessing that it was turned before because the parts from donor car included a spacer. Also, these spots were on it when I got it.

2: The spots cover about 1/2 of the surface of the flywheel. I could not get a usable picture of the entire flywheel to show this.

3:The first clutch/pressure plate set I put on the car was a no-name. The disc and pressure plate seem kinda weak/cheap compared to the RAM Stock Replacement set I bought to replace it.

If the spots are not bad enough to cause the chatter than I guess it could be the pressure plate. I wish I could be sure tho. I am getting tired of taking down the tranny to fix things.

Thanks again!

Dale

 

Well I guess I should add to this since I apparently didnt really answer your question.

Those spots could be causing some chatter. Its more how level the surface is rather than hard or soft spots until the flywheel gets pretty warm. If I had to guess, something in there isnt lining up right or the clutch is slipping (does the rear main or front tranny seal leak?) and its causing those marks. For some reason, the clutch is getting too hot. If you had a new pressure plate and disc, I'd be looking elsewhere like the flywheel or a leak somewhere.

 

The rear seal appears to be fine but the oil pan does leak back there. There does not appear to be any oil residue on the clutch, pressure plate or flywheel but I suppose it only takes a little bit.

It was chattering before we had the flywheel turned and the shop said that everything appeared straight and all they did was "clean it up." I asked but they never told me how much they took off.

Timeline of events:
1. 5000 miles ago - Put in unturned flywheel w/ new clutch and pressure plate. Car shook so bad starting from a light that it would almost jump across the intersection .

2. 3000 miles ago - Pulled tranny, turned flywheel and replaced disc only (dad's idea). Chatter came back but was mangeable. Would disappear if reved higher and slipped less.

I also noticed that this car has very little clutch pedal resistance. A strong wind could almost push the pedal down. Everyhing disengages fully but with no "feel" in the pedal. The hydraulics are new from GM as of 5K miles ago and seem to work fine. Could this be a problem with the pressure plate? I really do not want to spend $300 for a new flywheel if possible and I don't know if I can trust another used one.

Thanks for the help, all!

Dale