'98 firebird transmission troubles
Hello yall, I've got a couple questions about my sisters firebird. First off its an '98 firebird with an 3.8L engine an auto transmission. Okay, well it all started when her pump in her old transmission broke, causing it to lock up and break the fly wheel. Well, we had a friend put a new pump in and I put a new flywheel on for her. Well, after that they car ran, but it had a ticking noise coming from the rear of the motor and it also started to shake the car while driving it. it eventually got to the point where she didn't want to drive it. Well, we had a couple of people tell us that the torque converter could be bad and that it messed up the whole transmission. so she went and bought another torque converter and as I was putting that one in i noticed that her fly wheel was broke again, and this was only maybe two weeks after i put the new one on. So i went and got another one for her and put that and the new torque converter on and it was still doing the same thing. So She ends up buying a rebuilt trans and I put it in for her and the car drives great for about a week. Then it started doing the same thing while she was sitting in line at a drive-thru. So, i finally gave up on it and made her take it to an trans shop, which said that there is a plate behind the fly-wheel which is rattling and causing the car to shake and break the fly-wheel, etc. Well, she called me wanting to know if i would do the work, and i told her that there was no plate behind the fly-wheel when i put the new ones on. So, my question is, is there really a plate that is suppose to be between the fly-wheel and the motor, and if there is, could it really break the fly-wheel and make the car do all those things. I personally don't believe that is the case. Any help or suggestion yall can give me will really help me out. Thanks
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First, a flywheel is used in a manual transmission car. It is what the clutch contacts to complete a coupling between the crankshaft and the input shaft of the transmission.
An automatic transmission uses what is called a flexplate. It is bolted to the crank just like a flywheel, but is of a different thickness and design. The torque converter acts like a fluid clutch to complete the coupling to the input shaft of the transmission and is physically bolted to the flexplate and it's hub engages the input shaft of the transmission.
If the flexplate keeps cracking, something is causing it. It could be anything from the crank walking back and forth within it's bearing caps, a bad torque converter, a worn input shaft to the transmission, improper installation of the torque converter, and the list goes on.
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Technically speaking, an automatic uses a flexplate and not a flywheel and no there is no plate between the flexplate and the crankshaft. On manual transmission cars, they sometimes use flywheel shims to compensate for the flywheel being ground or machined.
If the front pump locked up that abruptly and broke the flexplate, it is also likely that the crankshaft, rear main seal, and/or the main bearings and caps may have suffered some damage as well. This could be a likely cause of the 2nd broken flexplate as well.
It's a little difficult to diagnose something like this without being there in person, but just trying to give a few suggestions.
Does the "shaking" seem consistant with engine RPM's?Comment
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the shaking seems to lessen as the speed gets higher, but it never goes completely away. And thanks for the correction about the flexplate and fly-wheel, i knew there was a difference but around here we just always call either one a fly-wheel. Also, if the crank was walking back and forth that much, wouldn't oil be leaking pretty badly from the front and rear seals? I didn't think that there was any plate behind the flexplate, thats why i was asking yall. I think the shop was just trying to get one over on her since she a young woman. Also, is there anyway to tell if the torque converter is bad.Comment
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Joe snuck in his post before mine, sly devil!
It is fairly common for people to not seat the converter all the way onto the input shaft on the trans. They assume that when they tighten the 3 flexplate/converter bolts, that it will automatically pull everything "tight". This is not the case.
You also need to make sure that there is no debris or "gunk" on the crank/flexplate mounting surfaces. It doesn't take much to throw off the normal perpindicular relationship of the crankshaft centerline and the flexplate. You also should be "torquing" the flexplate/crankshaft bolts to the correct specs as well, and torque them in an opposing order.
It actually sounds like you might have wiped out one or both surfaces of the thrust bearing. It is most common for the front side of the thrust bearing to be hosed because of improper converter/flexplate installation, worn front pump bushing, or an out of balance converter causing undue pressure pushing the crankshaft forward.
I'm not exactly sure about the 3.8 V6's, but normal LT1's shouldn't show more than .005" crankshaft endplay. I would suspect that the V6's shouldn't vary too far from that.Comment
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well, she just called me and she's letting the shop pull her trans. and take off her flexplate and put a new "ring" in. Apparently they put the car on a lift and they saw it vibrating on the crank between the motor and flexplate. This makes no sense to me and she just wants her car fixed, then its getting traded in. I just don't see how that one "ring" is causing the whole car to shake like it is. Oh, and i didn't everything by the chiliton manual that we have for her car. Torqued everything it said to torque and I'm almost postive that we had the torque converter in all the way.Comment
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Well they can see the ring gear spinning around if they have the dust cover off, but it is likely the entire flexplate that is "wobbling". It could be the flexplate, it could be a hosed thrust bearing, it could be so many things........Originally posted by sicktight722
But, if they are going to attempt to alleviate the problem by removing the ring gear and then welding a new one on, they they must suspect that the starter drive gear is somehow making abnormal contact with the ring gear and trashing the flexplate and/or ring gear.
If this is the case, they need to be looking at the cause of this; possibly a bendix going bad in the starter, broken or deformed drive gear, bent armature, etc.Comment
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You may have also more then transmission problems that may cause the shake, since there in there already I would have them disconnect the transmission and the motor, turn the car on and see if it still shakes alot. (Thats what my old mechanic told me I should do with mine, but then again thats my old mechanic who charged me 40 bucks to hit the unlock button and tell me my door lock didnt work when I asked him to take a look at it.)
It makes sense though since there already there, takes another 5-10 mins and points you in the right direction.94 Formula Firebird, 355, heads port and polished, cc503 cam, 30# injectors, PCMforless Tune, B&M 2400 stall, K&N CAI, BBK Sorty Headers, Magnaflow Highflow Cat, Borla Catback exhaust with electronic cutout.Comment
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Well I know the LT1 is externally balanced and I was told that at GM the crankshaft is balanced with the flywheel/flex plate mounted to it. There is a spec to which the flywheel/flex plate is balanced to when new but they further balance the crank by adding or removing weight from the flywheel/flex plate. They then get assembled into the engine. So flywheel/flex plates are not interchangeable in the respects of how they are balanced. Yes they will bolt on but there is no guarantee they will balance the engine. So if you replaced the flex plate the engine is probably a little out of balance.2002 Electron Blue Vette, 1SC, FE3/Z51, G92 3.15 gears, 308.9 RWHP 321.7 RWTQ (before any mods), SLP headers, Z06 exhaust, MSD Ignition Wires, AC Delco Iridium Spark Plugs, 160 t-stat, lots of ECM tuning
1995 Z28, many mods, SOLD
A proud member of the "F-Body Dirty Dozen"Comment
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