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Car Forum / Saab Cars / June 2006bad drivetrain sounds (c900)
Hi, I noticed a new sound today from my 1992 900S. It's a sort of rhythmic clicking noise. It occurs only when the car is in gear with the clutch out. The frequency changes with engine RPM (and therefore wheel speed), and is roughly 4 or 5 per second around 1200 RPM. I was unable to determine whether it is any slower in higher gears. No change when turning the wheels. It is most noticable when there is pressure on the drivetrain (especially engine braking in lower gears). The car has about 130k or 135k miles on it, and has had the right inner driver and clutch (and lots of other things too) replaced. The gearbox oil was switched to synthetic (BG Synchroshift) with the inner driver job. So, is this likely to be transmission or drive axle related? Also, I'd like to know if this sounds like an imminent failure item to anyone. All input welcome. Thanks, John  SignaturePosted via a free Usenet account from http://www.teranews.com > Hi, > [quoted text clipped - 3 lines] > or 5 per second around 1200 RPM. I was unable to determine whether it is any > slower in higher gears. No change when turning the wheels. Does it stay the same with road speed, or with engine speed? In other words, when you change from 1st to 2nd or whatever, does it change when your car is going the same speed? > So, is this likely to be transmission or drive axle related? Also, I'd like to > know if this sounds like an imminent failure item to anyone. All input welcome. CV maybe? Depends on if it's road speed or something else that changes it. If you start feeling the car "pulling back" in turns, especially in time with the clicking, get somewhere carefully without sharp turns. CV failures don't give much warning, and leave you sitting & spinning. Dave >> noise. It occurs only when the car is in gear with the clutch out. The >> frequency changes with engine RPM (and therefore wheel speed), and is roughly 4 [quoted text clipped - 4 lines] > words, when you change from 1st to 2nd or whatever, does it change when > your car is going the same speed? Dave, I tried to figure that out yesterday, but it was surprisingly difficult to determine. I think this is because at low speeds (which is when you can easily hear the relevant noise over the road noise and engine noise), the percent difference in road speed isn't very big between gears. Maybe I'll try to find a parking lot or something and try to test the difference between maybe 3rd gear and 1st. Hoping that it's a driveshaft and not the tranny (and that I don't get stranded somewhere today), John SignaturePosted via a free Usenet account from http://www.teranews.com > Does it stay the same with road speed, or with engine speed? In other > words, when you change from 1st to 2nd or whatever, does it change when > your car is going the same speed? Ok, I did some experimentation on the way to work today, and I think it goes with engine speed. But it only happens when the car is in gear-- letting the clutch out in neutral and reving the engine won't do it. What might this mean? John SignaturePosted via a free Usenet account from http://www.teranews.com The noise you describe sounds like throw-out bearing. mkw >> Does it stay the same with road speed, or with engine speed? In other >> words, when you change from 1st to 2nd or whatever, does it change when [quoted text clipped - 5 lines] > >John > The noise you describe sounds like throw-out bearing. How so, please? Only from personal experience. Had very similar noise, also at idle, self adjusting clutch cable was not self adjusting...local saab mechanic made adjustments and explained that noise was coming from "clutch riding on the throw-out bearing". He adjusted the cable, and noise was gone. mkw >> The noise you describe sounds like throw-out bearing. > >How so, please? >> Does it stay the same with road speed, or with engine speed? In other >> words, when you change from 1st to 2nd or whatever, does it change when >> your car is going the same speed? > Ok, I did some experimentation on the way to work today, and I think it goes > with engine speed. That's odd. > But it only happens when the car is in gear-- letting the > clutch out in neutral and reving the engine won't do it. If it's at engine speed, not road speed, it means it's more expensive to fix, I'm afraid, but I'm not getting a good instinct on this one. > What might this mean? You been out to Larry Gesch's place? About 20 minutes north of Oconomowoc, Neosho I think? >> Ok, I did some experimentation on the way to work today, and I think it goes >> with engine speed. > > That's odd. Yes, it is sort of odd. I'll continue to test things as I drive home today. But the most damning piece of evidence to me is that if the car is moving, clutch depressed, engine at idle, and in gear, and I then slowly release the clutch, as the engine comes up to speed the noise appears and speeds up accordingly. I suppose I should have a quick check of the tranny oil, just to make sure that's in order. > You been out to Larry Gesch's place? About 20 minutes north of > Oconomowoc, Neosho I think? Nope, I must confess that I have never set foot in the great state of Wisconsin. I'm on the east coast. If this were sounding like a drive shaft issue, I'd probably try to fix it myself. But if this is actually inside the tranny, I think I'll let my local indy Saab shop at least try to diagnose it. Ah well, I've had a very long run at avoiding the shop, I'm probably due anyway. John SignaturePosted via a free Usenet account from http://www.teranews.com >>> Ok, I did some experimentation on the way to work today, and I think it goes >>> with engine speed. >> >> That's odd. > Yes, it is sort of odd. I'll continue to test things as I drive home today. But > the most damning piece of evidence to me is that if the car is moving, clutch > depressed, engine at idle, and in gear, and I then slowly release the clutch, > as the engine comes up to speed the noise appears and speeds up accordingly. So it's on the engine side of the clutch then? Clutch disk itself or something? Has it been slipping lately? This isn't making sense yet. > I suppose I should have a quick check of the tranny oil, just to make sure > that's in order. Won't hurt but I think the above rules that out. Pilot bearing?!?!?! Actually, let's think about that. The pilot bearing, on the end of the clutch shaft, in the flywheel. Does that turn when you're hearing the noise and as you describe? >> You been out to Larry Gesch's place? About 20 minutes north of >> Oconomowoc, Neosho I think? > Nope, I must confess that I have never set foot in the great state of > Wisconsin. I'm on the east coast. Then you're also not the John B. that I've played guitar with, but that's OK - never met a John B. that I didn't get along with. > If this were sounding like a drive shaft issue, I'd probably try to fix it > myself. But if this is actually inside the tranny, I think I'll let my local > indy Saab shop at least try to diagnose it. Ah well, I've had a very long run > at avoiding the shop, I'm probably due anyway. Well my point about Gesch was that now may be the time to have the local independant specialist have a listen. One other thing I was thinkning - can you get the noise when the car is just sitting still with the parking brake on? Would help diagnose it a bunch, and eliminate the tranny/drivetrain side of things if so, and reduces the options significantly. Dave Hinz >> the most damning piece of evidence to me is that if the car is moving, clutch >> depressed, engine at idle, and in gear, and I then slowly release the clutch, >> as the engine comes up to speed the noise appears and speeds up accordingly. > > So it's on the engine side of the clutch then? Clutch disk itself or > something? Has it been slipping lately? This isn't making sense yet. I'm thinking not clutch, because, for one thing, I don't think I'd be able to hear it if it were all the way at the front of the car. Also, the clutch was replaced a mere 30k miles ago. I rebuilt the MC a year or two back, and the pedal is totally firm (except when it's really cold out- but I think that's another story). I was thinking that if it is inside the tranny, could it be something to do with the shaft that has the gears on it and goes into the diff (I'm sure it has a technical name that I don't know)? > Won't hurt but I think the above rules that out. Pilot bearing?!?!?! > Actually, let's think about that. The pilot bearing, on the end of the > clutch shaft, in the flywheel. Does that turn when you're hearing the > noise and as you describe? Not sure I know enough to answer that question. > One other thing I was thinkning - can you get the noise when the car is > just sitting still with the parking brake on? Would help diagnose it a > bunch, and eliminate the tranny/drivetrain side of things if so, and > reduces the options significantly. No, I haven't been able to do that. To hear it, the car must be (a) moving (b) in gear, and (c) clutch engaged. It's not distinctly audible much over 2000 rpm, because the frequency becomes too fast to hear individual 'clicks' or whatever. Can we derive anything from the frequency? It's roughly 4/5/6 per second around 1000-1500 RPM. This means that it's maybe once per every 4 revolutions of the engine, right? What is the ratio created by the drive chain? In other words, how many times does the transmission turn over for each revolution of the flywheel? John SignaturePosted via a free Usenet account from http://www.teranews.com > I was thinking that if it is inside the tranny, could it be something to do > with the shaft that has the gears on it and goes into the diff (I'm sure it has > a technical name that I don't know)? Output shaft but it's not that, because it'd be road speed dependant not engine speed dependant. >> Won't hurt but I think the above rules that out. Pilot bearing?!?!?! >> Actually, let's think about that. The pilot bearing, on the end of the >> clutch shaft, in the flywheel. Does that turn when you're hearing the >> noise and as you describe? > Not sure I know enough to answer that question. Agreed. Something still isn't adding up yet. We'll get there, hopefully before it announces itself to you. >> One other thing I was thinkning - can you get the noise when the car is >> just sitting still with the parking brake on? Would help diagnose it a [quoted text clipped - 3 lines] > No, I haven't been able to do that. To hear it, the car must be (a) moving (b) > in gear, and (c) clutch engaged. But it's engine speed dependant. So then on the input side of the tranny - drive chain to input shaft? Guys, jump in at any point here... > It's not distinctly audible much over 2000 rpm, because the frequency becomes > too fast to hear individual 'clicks' or whatever. Right, I don't think the RPM matters so much as the fact that it's engine speed specific. > Can we derive anything from the frequency? It's roughly 4/5/6 per second around > 1000-1500 RPM. This means that it's maybe once per every 4 revolutions of the > engine, right? What is the ratio created by the drive chain? In other > words, how many times does the transmission turn over for each revolution of > the flywheel? Depends. Which engine/tranny/Turbo did you say you have? And why can't we hear the noise when the car is in neutral, if it's at that point? Something still isn't adding up yet. >> engine, right? What is the ratio created by the drive chain? In other >> words, how many times does the transmission turn over for each revolution of [quoted text clipped - 3 lines] > we hear the noise when the car is in neutral, if it's at that point? > Something still isn't adding up yet. It's a 1992 2.1L NA 5-speed. I'm about to drive home, which will be another great opportunity to make observations and/or get stranded. John SignaturePosted via a free Usenet account from http://www.teranews.com Dave, Ok, I got some excellent data on the drive home, which I really hope will help rather confuse things more: If I drive along in 2nd gear, and then put the clutch in and shift into first, then slowly let the clutch out, I can hear the noise, starting at a high frequency and *slowing down* at the same time as the engine *speeds up*. So, doesn't this mean that the noise is linked to the speed of the shaft in the tranny that goes to the clutch? Also, I found that if I idle the car in neutral with the clutch out, and gently push the gear shift towards any gear, I hear a rhythmic noise very similar in sound and frequncy to the noise in question. Not sure if this is actually the same thing though... John SignaturePosted via a free Usenet account from http://www.teranews.com > Dave, > > Ok, I got some excellent data on the drive home, which I really hope will help > rather confuse things more: Excellent. (You're an engineer and/or technician, by the way, right?) > If I drive along in 2nd gear, and then put the clutch in and shift into first, > then slowly let the clutch out, I can hear the noise, starting at a high > frequency and *slowing down* at the same time as the engine *speeds up*. So when there is a differential in speeds between the engine and gearbox, the noise changes. Right? > So, doesn't this mean that the noise is linked to the speed of the shaft in the > tranny that goes to the clutch? Yes, I think so. Looks like you're visualizing the system well which always helps. > Also, I found that if I idle the car in neutral with the clutch out, and gently > push the gear shift towards any gear, I hear a rhythmic noise very similar in > sound and frequncy to the noise in question. Not sure if this is actually the > same thing though... Well, they synchro sleeves have springs, I've never had a problem in that area. Wouldn't hurt to change your gearbox oil and check for surprises, but I'm not going to get excited about that side just yet. Is the noise there when the clutch pedal is out and you're in gear, moving forward? If so then it's not the pilot bearing; the only thing moving relative to it's surroundings then, that's at engine speed, is that shaft itself, the drive chain and sprockets, and the input shaft of the tranny and the things attached to it. > Excellent. (You're an engineer and/or technician, by the way, right?) Close enough - biochemist/cell biologist. I do experiments in a lab all day. > Is the noise there when the clutch pedal is out and you're in gear, > moving forward? Yep, that's the only time it's audible. Most audible when the wheels are driving the engine, but this may be because the engine is quieter under this circumstance. > If so then it's not the pilot bearing; the only thing > moving relative to it's surroundings then, that's at engine speed, is > that shaft itself, the drive chain and sprockets, and the input shaft of > the tranny and the things attached to it. Ok, I guess we can rule out the pilot bearing then... John SignaturePosted via a free Usenet account from http://www.teranews.com >> Excellent. (You're an engineer and/or technician, by the way, right?) > Close enough - biochemist/cell biologist. I do experiments in a lab all day. Biomedical engineer by training, working IT as a designer/project guy. I like your approach. >> Is the noise there when the clutch pedal is out and you're in gear, >> moving forward? > Yep, that's the only time it's audible. Most audible when the wheels are > driving the engine, but this may be because the engine is quieter under this > circumstance. Sounds gearbox-ish at this point then, input shaft area. There are circular springs in the synchro hub area, if one of those were somewhat peeled out that could explain the noise. Time to look for swarf in the gearbox oil, I think. Should have a magnetic drain plug. You want to see if there's chunks - filings are, surprisingly enough, pretty common and not a huge deal. But any piece-parts or chunkies would be bad. >> If so then it's not the pilot bearing; the only thing >> moving relative to it's surroundings then, that's at engine speed, is >> that shaft itself, the drive chain and sprockets, and the input shaft of >> the tranny and the things attached to it. > Ok, I guess we can rule out the pilot bearing then... Right, which I think puts us into concerning territory. Just on a swag, though - is the speedometer doing any strange jumps or anyting? That shaft goes around at about that rate, but it'd be road-speed dependant rather than engine speed. But it sounds input shaft-ish from here. Are you comfortable pulling the side hatch off of the tranny to visualize the synchro hardare and shift forks? Dave Hinz > Sounds gearbox-ish at this point then, input shaft area. There are > circular springs in the synchro hub area, if one of those were somewhat > peeled out that could explain the noise. Time to look for swarf in the > gearbox oil, I think. Should have a magnetic drain plug. You want to > see if there's chunks - filings are, surprisingly enough, pretty common > and not a huge deal. But any piece-parts or chunkies would be bad. Ok, I'll have a look. Maybe today, if I get home early enough. I've never had the plug off before. It's a hex nut -looking thing on this model year. > rather than engine speed. But it sounds input shaft-ish from here. Are > you comfortable pulling the side hatch off of the tranny to visualize > the synchro hardare and shift forks? I think so. But will that require draining the transmission oil? If so, I'll have to take off the differential cover also, since this model year has no transmission drain plug. Also, will I need any new parts to put it back together? John SignaturePosted via a free Usenet account from http://www.teranews.com >> Sounds gearbox-ish at this point then, input shaft area. > Ok, I'll have a look. Maybe today, if I get home early enough. I've never had > the plug off before. It's a hex nut -looking thing on this model year. I know it when I see it by location but I'm not sure how to describe. Low on the gearbox, and the one that doesn't drain the engine oil. > I think so. But will that require draining the transmission oil? If so, I'll > have to take off the differential cover also, since this model year has no > transmission drain plug. Also, will I need any new parts to put it back > together? Hm, it's starting to sound like a hassle. It might be better to have that specialist take a listen. Either way, yeah, you probably want a new gasket for that cover. You can permatex it but getting it clean enough while it's in the car and your face is up against the exhaust system isn't fun. Please try not to drop the car on yourself either way, OK? Dave > I know it when I see it by location but I'm not sure how to describe. > Low on the gearbox, and the one that doesn't drain the engine oil. Ok, since I have no drain plug, I figured I could at least take off the dipstick and make sure there's actually oil inside. The dipstick was way harder to get off than I expected (screwed on tight with exhaust header pipe in the way), but I prevailed with only superficial injuries. The oil level is perfectly fine. I did however (earlier yesterday, before the dipstick project) notice liquid dripping a little bit from the bottom of the differential. It looked like clean oil, which would be consistent with transmission oil. But my car also leaks lots of PS fluid, so it's hard to be certain. > Hm, it's starting to sound like a hassle. It might be better to have > that specialist take a listen. Either way, yeah, you probably want a > new gasket for that cover. You can permatex it but getting it clean > enough while it's in the car and your face is up against the exhaust > system isn't fun. Well, I could order a gasket today and have it by the weekend. Is the side cover you're talking about the one that the dipstick comes out of? Or is it the one a bit further forward? Either way, they're relatively accessible (since this car is NA). > Please try not to drop the car on yourself either > way, OK? Don't worry, I'm totally paranoid about that. John SignaturePosted via a free Usenet account from http://www.teranews.com After driving around for awhile, I have observed that: A. the noise is not getting any worse, and B. the car still drives/shifts perfectly. So I have decided to ignore the noise for the time being, at least until it gets noticably worse or the gearbox explodes, whichever comes first. John SignaturePosted via a free Usenet account from http://www.teranews.com > After driving around for awhile, I have observed that: A. the noise is not > getting any worse, and B. the car still drives/shifts perfectly. So I have > decided to ignore the noise for the time being, at least until it gets > noticably worse or the gearbox explodes, whichever comes first. In summertime, that's a perfectly fine plan far as I'm concerned. Winter, not so much... Dave > After driving around for awhile, I have observed that: A. the noise is not > getting any worse, and B. the car still drives/shifts perfectly. So I have > decided to ignore the noise for the time being, at least until it gets > noticably worse or the gearbox explodes, whichever comes first. Hi John - If you're sure it's down to the gearbox now, try Honda MTF oil. You'll be amazed at the difference anyway ... It comes highly recommended by many C900 pilots. Paul 1989 900 Turbo S http://saab.go.dyndns.org/ > Hi John - If you're sure it's down to the gearbox now, try Honda MTF oil. > You'll be amazed at the difference anyway ... It comes highly recommended by > many C900 pilots. Thanks, noted. Already running synthetic MTF though- BG SynchroShift John SignaturePosted via a free Usenet account from http://www.teranews.com |
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