Resonating sound at speed...wheel bearings? CV?

[DougB]

Hello all,

I have a '73 Fastback that has been on and off the road a bunch of times, mainly because people keep hitting me. It's solid, back in daily driver mode and runs great, though lately I've noticed a sound that didn't exist before.

At speed I'm noticing a resonating noise...kind of like a bad wheel bearing...that seems like it's coming from the rear. It becomes more noticeable than the engine at around 55MPH, especially when I back off the throttle (to around 5-10% of throttle). It sounds like a wheel bearing, but the fact that the throttle position affects it seems uncharacteristic for that. I've never really heard the sound symptoms of a bad CV so that's why I'm asking.

I also noticed this morning...that it seems more prominent when I'm veering left. Applying the brakes (via foot brake or hand brake) doesn't seem to have an impact on it.

Pretty much stock Fasty, around 82K original miles...CV boots all look decent though in the time I've owned the car (20 years and 40K miles of driving) I've never repacked them (embarrassed to say so).

Thoughts? Thanks!

- Doug
_________________
'75 Campmobile (tin-top to SpaceRoof)
'73 Fastback
'52 BMW R67/2
'41 Zundapp KS600
'55 Puch SGS250
A very, very understanding wife

[Donnie strickland]

If it's been that long, I'd take the driveshafts off and inspect/repack and/or replace the CV's. It's time. Then see if that stops the noise.
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71 Elm Green FI A/T Squareback

[KTPhil]

I'd also check the tranny fluid level.

[DougB]

Good tips, I'll do both. I have replaced the tranny fluid once in the past year and haven't noticed leakage on the pavement, but it's worth a check.

Anyone else? Thanks!
_________________
'75 Campmobile (tin-top to SpaceRoof)
'73 Fastback
'52 BMW R67/2
'41 Zundapp KS600
'55 Puch SGS250
A very, very understanding wife

[KTPhil]

Also eyeball the diagonal arm bushings. If worn, you may be getting harder contact (even metal to metal) which will transmit more noise, including an uptick in loudness when cornering. You'd probably notice the goofy handling already, though.

Could be a rear wheel bearing, too. I've never pulled them, just taken the axle out and repacked them and put in a new seal, IIRC.

Can you get the rear on jackstands and rev it up in gear, and then listen with a hose in your ear (redneck stethoscope) to locate the source?

[Bobnotch]

Also pull the cotter pin out of the big axle nut, and check that it's torqued up tight (like 262ftlbs tight). What you might be hearing id the drum/hub assembly fretting.
_________________
Bob 65 Notch S with Sunroof
71 Notch ...aka Krunchy; build pics here;
http://www.thesamba.com/vw/forum/viewtopic.php?t=249390 -been busy working
64 T-34 Ghia...aka Wolfie, under construction... http://www.thesamba.com/vw/forum/viewtopic.php?t=412120

[KTPhil]

[rockerarm]

Hello Doug.
Some diagnostic tips I've been taught and used are as follows.
While driving where the noise is noticeable if you can safely "swerve side to side" within your lane kinda like you would see race cars moving side to side (to warm up tires) may yield an answer. This technique may load and unload a bad rear (or even front) bearing and you might hear the "noise" change. The rear wheel bearings are one very neglected area on out cars and the job is relatively easy.
You could possibly have a bad tire and rotating front to rear may yield something here as the noise could change.
In my opinion, CV's would not cause a resonating/howl but more like a clacking/clicking noise.
And last, the trans. Since you mentioned by backing off the throttle the noise changes could be in the trans, possibly the differential's carrier bearings or ring/pinion. You could drain the gear oil into a clean container for inspection.
I assume you have the 4 speed trans and not the automatic?
Hope this helps, Bill.

[DougB]

Hello all,

Thanks for the awesome answers! It was a cold weekend in VA with two days of family activities so I didn't get to investigating the noise.

Bill, to your questions the noise does change if I swerve...when I swerve right it seems to go away, when I swerve left it becomes more noticeable.

Also, yes this is a 4-speed manual. I'm going to check/replace the gear oil first, just to make sure the level isn't low. But with the swerve info above, is there a rear wheel bearing I should check first? If I'm going to repack the CVs (even if it's not the problem they're certainly due) I might s well replace those rear bearings, too.

Thanks again, all!

- Doug
_________________
'75 Campmobile (tin-top to SpaceRoof)
'73 Fastback
'52 BMW R67/2
'41 Zundapp KS600
'55 Puch SGS250
A very, very understanding wife

[rockerarm]

Good job Doug. While gear oil change and CV joint service are supposed to be routine, we tend to overlook them. I highly doubt you will find your fault with the trans or CV's. Your diagnostic skills would pinpoint a rear wheel bearing.
For the neglect that we have imposed on the IRS rear wheel bearings it amazes me they aren't failing on a daily basis. That said your type 3 bearing components are the same as the type 1 cars, so original used could be an option for you vs some new 3rd world quality control issue. Also, most bearings, and seals, will have a universal part number identifier that could be used to obtain your parts from a bearing/seal house.
Bill.

[DougB]

Had a little time outside last night to crawl under the car. Checked the gear oil and it's right up at the proper level. None of the CV boots are torn, but I didn't have the time to get into them to repack. I did find that one of my rear brakes was adjusted quite a bit too tight, so I corrected that and will take it for a spin to see if that has any impact.
_________________
'75 Campmobile (tin-top to SpaceRoof)
'73 Fastback
'52 BMW R67/2
'41 Zundapp KS600
'55 Puch SGS250
A very, very understanding wife

[DougB]

Hello all,

Just an update...my disc rotors have been rust pitted for a while from periods of inactivity for the car (while I repaired it from it's various accidents - people love to hit this car), so while doing that I replaced by brake pads and more importantly for this resonating sound issue, all of the front bearings.

That said, there was no change in the sound, so I'm going to do the CVs and rear bearings (which I already had at home) next. Yay, what a fun job - not. Oh well...everything else about the car is great so why not just fix this, too, right?

Thanks!

- Doug
_________________
'75 Campmobile (tin-top to SpaceRoof)
'73 Fastback
'52 BMW R67/2
'41 Zundapp KS600
'55 Puch SGS250
A very, very understanding wife

[Bobnotch]

[DougB]

OK, will do...you mentioned that before but I'm glad you reminded me to check that. Would be awesome if it was something that easy...I don't love driving in rear wheel bearings. It was kind of a bear of a job when I did it on the bus a few months ago.

Thanks again,

- Doug
_________________
'75 Campmobile (tin-top to SpaceRoof)
'73 Fastback
'52 BMW R67/2
'41 Zundapp KS600
'55 Puch SGS250
A very, very understanding wife

[DougB]

WOW, no kidding...I made it home from work and popped off my center Caps and there is indeed a rear axle nut loose (passenger side). The cotter pin is still there so it wasn't spinning freely but it was definitely finger-loose. I'll tighten that right up and let you all know the result.

- Doug
_________________
'75 Campmobile (tin-top to SpaceRoof)
'73 Fastback
'52 BMW R67/2
'41 Zundapp KS600
'55 Puch SGS250
A very, very understanding wife

[Donnie strickland]

Good catch Bob!
_________________
71 Elm Green FI A/T Squareback

[DougB]

BOB! You are the man of the hour! Your suggestion just saved me $200+ in unneeded parts I'll still do the CV repack at some point but not having to do it now is a huge relief. After tightening that nut the noise is gone!

I hope you have one hell of a weekend because you (and everyone who gave suggestions) just started mine off right.

Thanks again!!

- Doug
_________________
'75 Campmobile (tin-top to SpaceRoof)
'73 Fastback
'52 BMW R67/2
'41 Zundapp KS600
'55 Puch SGS250
A very, very understanding wife

[Bobnotch]