BlackPearl

Okay tech-wiz's; here's a challenge for you (Mr. Zimmerman, included):

After a fairly aggressive day at the AX here in San Diego, my '83 SC developed a low-pitched whirring/thrumming/clicking/flapping sound from the center tunnel behind the front seats. It happened after a road trip from SD to LA on SoCal fwy's.

1)The sound occurs when the wheels are rolling/spinning, without influence from engine rev's.
2)The sound occurs without influence of the clutch pedal in or out. When elevating one rear wheel, the sound can be heard when the car is in neutral and engine off... by spinning the wheel.
3)The sound occurs as two to three clicks/flaps per wheel revolution.
4)The sound appears to originate at the center of the trans housing, forward of the R&P area.

At speeds of 30-MPH or more it is a "buzzing/whirring/thrumming" sound, as speeds reduce, it become more of a "flapping/low-pitch-clicking" sound. It stops when the vehicle stops.

My first thought was CV joints/worn axles. The mechanics rebuilt/replaced what appeard to be worn CV joints on one side, repacked the other side, checked the wheel bearings (as best as they could) and went over the whole back-end to be sure nothing was missed. Trans seals were also checked for leaks. Trans fluid was drained, checked for clues (no chunks or bits of any kind) and fresh trans lube replaced. (note: the trans fluid was less than 1 year old Swepco.)

The car was returned ... only to develop the sound, again.

At the shop, the mechanic and I put the car on jackstands and took the trans speed up to 60mph in 4th (whoah! a little risky to be sure!!) ... meanwhile he listened to the trans with a stethoscope and said it was coming from the nose-cone at the front of the trans.

Trans/engine were pulled ... nosecone of the trans was pulled. Nothing obvious. the trans was separated from the engine and disassembled. With the supervising mechanic, the shop owner, and myself, (a combined experience time of about 45+ years between the three of us) we went through every part of the disassembled trans to try and find clues to the sound. Nothing. Bearings, races, rollers, gears, syncro's, shafts, spacers, etc., etc., all looked great. Intermediate plate area tight, clean, great shape. Housing looked great. No marks, filings, just clean fluid.

So, any ideas as to what could be the sound? One more thing: the trans was opened prior to my buying the car and 1st gear, and 1st/2nd gear syncro's were replaced.

Any ideas would be helpful prior to reassembling the trans with some new goodies next week.

Thanks all!!!

Peter Zimmermann

I would guess, that although your noise sounds like a tricky one, that it is not trans-related. Your numbers 1 & 2 above send me straight to your rear wheel bearings. I do not know what your #3 indicates, so for now I'll think about that one. The diagnosis for a rear wheel bearing is extremely difficult, because the noise will fill space, but it will also travel through conduits such as the rear axles/transmission. Unfortunately the car is now "down," but a surefire test can be done to check those bearings. Travel in a straight line until the noise is most pronounced, and when no cars or obstacles are near you, jerk the car in one direction (on the order of a quick lane change), straighten the car, then jerk it the other direction. If the noise intensifies slightly in one direction, and disappears in the other, you've got a bad rear wheel bearing. Deciding which, left or right, is so hard to do that my shop changed them in pairs, reasoning that if one was bad the other wasn't far behind.

BlackPearl

Excellent suggestion.

Actually, I did a variation on that theme: while rolling at ~ 30-MPH with engine off, turned sharply in both directions in a large parking lot. The sound neither diminished, nor intensified when turning sharply to one side or the other vs travelling in a straight line. (I guess I should have mentioned that earlier, during diagnosis). Also, the click/flap occurs at the same periodic episode regarless of if it is the right rear or the left rear wheel raised and spun. Again, no difference in intensity or 'rhythm' between left or right rear wheels.

Peter, should I take the further step of "while I'm in there" and just replace the rear wheel bearings anyway (yeah, I know ... more $$$)? I do plan on tracking this car a bit more. With no previous repair records from the PO, I know not the age of the wheel bearings currently in the rear of the car. (The front bearings were replaced with a recent brake job.) Your thoughts?

Peter Zimmermann

How many miles on your car? If you're on the high side of 150K miles, and you're going to track the car, yes, you should do the rear bearings.

A click/flap noise could be related to something broken in the handbrake assembly. Did you try to gently pull up on the e-brake handle to see if that had an effect on the noise? (If you do the rear bearings all of the handbrake system will be exposed for inspection) All I can think about besides the handbrake are the CV joints...

BlackPearl

170K miles on car. Just spoke to mechanic about r&r of rear bearings for 'tracking purposes' ... waiting for quote. They're leaning in my direction about re-doing the bearings anyway with the high-miles, future use, and lack of PO data.

Handbrake ...... DANG-IT! I didn't try pulling on it.

FWIW: the handbrake system works very well. When I replaced the rear rotors during last month's full brake-job, all looked good inside the vestigial assemblies (I checked to see if I needed the 'little shoes' for handbrake). Of course, that doesn't mean I didn't miss something....

Regarding CV's: not sure what else to do after replacing the worn ones, and repacking the side that looked newer...

Thanks for all your info, Peter. Keep those ideas coming.....

Peter Zimmermann

When you do the rear bearings just make sure that your technician checks out the handbrake system closely. If he can't find anything, I guess that you're going to have to take the CVs apart...let us know how it goes!

Droops83

Man sometimes those driveline noises can be tricky! Since it sounds like the noise happens w/ wheel rotation whether the engine is running or not , wheel bearings sound like a good possibility as Pete said, and of course he mentions check the parking brake mechanisms too, which I wasn't thinking of, great suggestion as usual!

The CV joints that weren't replaced are of course a possibility, but bad CV joints tend to make a clicking noise mainly on loading/unloading the drivetrain, and stay quiet at constant speeds. So your tech just repacked them without disassembly/inspection? It sounds like you're saying the noise is constant proportional w/ wheel speed, and independent of what you are doing w/ the clutch/throttle. Wheel bearings are tricky to diagnose just like Pete said, since unless they are real bad they sometimes won't make noise up on a lift, only when loaded while driving.

Another general tip which most likely doesn't apply to BlackPearl is that sometimes tires themselves can be the cause of a whirring/bad wheel bearing-type noise, always check those first (rotate/swap tires w/ a friend, etc).

Another funny one we had a few months ago is we had a customer w/ an '85 Carrera (915), complained of a drivetrain noise. It sounded exactly like a bad bearing in the trans (louder under load, etc). It turns out that the tranny mounts were sagging enough for the trans cross-mount to be resting on the sway bar. The normal whirring inside the trans resonated through the sway bar, and sounded like an expensive noise! Funny thing is the mounts weren't quite bad enough to be clunking/twisting noticeably under load. Pete, have you ever seen this?

So, sorry to add more confusion to anyone reading this trying to diagnose a noise like this, but I hope it helps!

Peter Zimmermann

Wow, Chris - good post! I never thought about the obvious - the tires. When I read your post I realized that the first thing that I would have done at the shop is put the car on a lift and hand spin each tire, looking for abnormalities.

On the trans mounts, no, I've never seen that. But, I have seen cars where the rear sway bar had been put on upside down, which allows the trans mount to touch it and produce, probably, the same noise that you heard.

BlackPearl

Chris; good points.

As for the tires: brand new and a good-quality Hankook tires for the street. Note: there was no noise prior to the Autocross (and I had done a whole year's autocross and DE on the car already). I had replaced brake pads, rotors, and brake lines last month ... and had driven the car for over 300 miles ... plus another autocross .... before the "new" noises started.

Also: the clicking sound will occur with the tire/wheel elevated off the ground, and turned by hand. so I don't think the tires are the culprit. When the click occurs, you can actually feel it in the trans housing as a 'tap' or light vibration effect.

Regarding the CV joints: both axles were dropped, and all 4 cv joints were pulled apart, cleaned, inspected. Two of the 4 were worn/damaged and those were replaced with new ones. The other two appeared "newer" and were re-packed with new lube and put back in. I personally saw all 4 CV joints apart, and inspected the parts one-by-one. So my confidence in the repacked/replaced/new CV joints is pretty high.

Trans mounts? Now ... you're on to something...

Our AX's here in SDR are pretty fast and hard-driving. Speeds of 80 on the straights and 30 to 40 in some turns is possible, and not unusual. I run oversized Toyo R888's that allow for a lot of lateral G's. So... yeah, I could have stressed the 26-year-old mounts beyond their limit. I'll definitely take a good look at those, and the sway bar ... and sway bar mounts ... and even the engine mounts.

Good one, Chris!! Thanks!

Droops83

Sorry to confuse, I highly doubt the tranny mounts are your problem, the problem I described is pretty rare, and I guess I posted about it just to make a point of how tricky it can be to track these pesky noises down sometimes. But I suppose it's worth checking to see if the swaybar is touching the tranny cross bar anyway. Your noise seems like it is directly correlated with the rotation of the wheels . . . . but does the noise occur when either wheel is turned by hand? How about when one wheel is on the ground?

Also, it seems like from your posts, the trans is apart right now? Maybe they'll find something in there. Anyway let us know what happens.

BTW I'm gonna have to make it down to San Diego for an auto-x sometime, I hear that SDR is pretty serious about driving events. Santa Barbara region is mainly the concours and social event crowd, not for me. Although my 951 is really nice and could be a show car, I prefer driving it. In the few months I've had it I've been to 4 track days but only 1 auto-x since they only have 2 a year up here!

BlackPearl

Okay: so the noise happens when you spin one wheel by hand, with the other one on the ground. It also makes a sound when you spin both wheels elevated.

We are planning on re-assembling the trans next week with as many new parts (bearings, syncro's, etc., etc.) as we can find to replace. the gears, ring&pinion, and base-materials are all good. The hope is ... with all new bearings, etc., we will have a quiet box. If not, I'll drive it till it pops!

Yes ... come down to San Diego for a really great time at an AX. You'll get anywhere from 12 to 15 laps on a course length from 3/4 of a mile to 1 mile in length. If it's the West Lot, you'll see some serious speeds for a parking-lot event (up to 80 MPH). If it's the East lot, it's a bit slower and tighter, but plenty of run.

Check the website for dates and locations: pcasdr.org. If you come down, look for a Black 911 with "Ballast Point Brewing Company" stickers ... #91, and say hello.

Thanks again!

BlackPearl

FIXED!

After tearing down the entire transmission to clean every moving part, replaced worn parts, and hope that the "noise" would be found, the culprit turned out to be a main bearing next to the pinion gear on the pinion shaft. This is one of the main bearings of the output shaft right next to the thrust-bearing, and is designed as two bearings in one: a large O-ring type inner bearing surrounded by a cage and roller-bearings. The outer surfacing of the large inner bearing ... where it contacts the roller bearings, was pitted. So with each revolution of the pinion shaft, the inner bearing would spin and the roller bearings would roll over the pitted surface ... making the rhythmic "worn bearing" sound.

The shop said this was a very unusual occurance, so it took a while for the parts to come in.

Now, I'll take it easy for the first 200 miles. Then, take it back to it's life on the street and track.

Thanks to all for your info. I hope my experience helps others with their cars.

Cheers!