Porsche 924S - bearing-like noise but.....help me diagnose

Finally took the 924S on a proper shakedown drive (i.e. with license plates and outside of my street at 10mph).. Everything feels great with the car, but I am getting a howling noise, and here are the details:

1. Definitely speed-related. The faster I go, the louder it gets, even if I kill the engine and coast.

2. It is a "solid" howl, not like most wheel bearngs I've had go bad which are more like a "whoo-whoo-whoo" with repetition. This one the tone does not change at all when driving straight.

3. Upon even the slightest jog of the steering wheel to the left, the sound is INSTANTLY silent, even if it is a very gentle jog that isn't transferring much if any weight.  However, if I maintain a mild turn to the left (like a neighborhood street where the street winds gently), the sound comes back. During any moderate or harder left-hand turn the sound is gone.

4. Since I have new 911 wheels and tires on it, I initially thought it might be rubbing, but I have spacers on the front for clearance and confirmed that the wheels/tires are defintely not rubbing anyplace.

5. I know that wheel sounds are notorioiusly hard to located, but it REALLY sounds like the sound is from the right side of the car (more right front than right rear). But that makes no sense that the sound would go away when loading that side, if it's a wheel bearing.

6. I triple-checked the front wheel bearing lock nut tightness in the front and it's perfect. Front bearings were repacked and they all felt good. There is minimal to no play in the front wheels when jacked up. They spin smoothly with minor resistance and no noise whatsoever.

7. Rear wheels when jacked up and transmission in neutral also spin fine, no grinding, no crunching, no vibrations, no nothing.

Thoughts:

- torque tube bearings (driveshaft) - but I don't see why these would change with minor steering movements only to one side

- diff bearings - again, don't see how a light turn only one way would cause ths

- tires - they are brand new BFG all-seasons, but I can't see why they'd make noise only when not turning left.

- brakes are not dragging, car coasts nicely in neutral

- steering-related? noise stays with engine (and PS pump) turned off and is not a steering groan, so that sounds iffy.

So that's all I can think of. Am I missing something obvious, or is the solution to start replacing wheel bearings, hoping I pick the right one first? Keeping in mind that all four of them feel good "by hand" diagnosis, spin nicely without any noise when jacked up, etc.

Bent backing plate rubbing against a rotor? (Assuming that model has backing plates)

hmm....will go check that now. Though not really a scraping or squeaking sound.

No evidence of that. Though one of the tie rod ends was loose. Tightened that up and I feel like the sound changed somehow, but is definitely still there. My daughter rode with me and thought it was from the front right of the car, which doesn't make much sense if it's a wheel bearing, because that's the side that would be loaded on a left turn :/

Sounds like a wheel bearing to me. They don't always go quiet when unloaded (turning), it can be the opposite. If the noise happens at 10mph driving, hopefully you can put the front of the car in the air and spin each front wheel as fast as possible while listening closely. I know you mentioned they spin quiet and smooth, but that's where I'd double check (how fast did you spin them?)

I will bet it is a rear wheel bearing. 

Oh and they suck to change. I would rather do a clutch. 

Can you use a stethoscope or hose to hold near the bearing while spinning by hand?Compare side to side. 

In reply to dean1484 :

Yeah, this is the fear. I want to rule out 110% everything else before I deal with doing a rear bearing. IDK though, the sound going away is so "instant" with any steering input, which woudln't have a big unloading effect on the rear left, so I'm leaning toward it just being a front. Those are easy, so I gues that'll be the first course of action.

Also changed to my other (old) wheels and tires and no change in the sound.

The noise changing as you go side to side with the load pretty much calls out a wheel bearing somewhere.  You may not be able to reproduce it with out weight on the wheel, so I always take a passenger to confirm front/rear and left/right.  It can be very tricky to tell from the drivers seat.

Yeah I took my daughter out and she said it was from the right side, but she couldn't tell front or rear for sure. But IDK, in my experience with wheel bearings it's usually the bearing on the inside of the turn when it goes quiet (in this case, it would be the left side that is unloaded).

I guess I'll do the front bearings on both sides frist since they're pretty easy to do, and hope it's one of those and not a rear

Reasonable plan.  Are the fronts a replacement hub, or an old timey tapered roller bearing setup?  That is about the time most of the Euro's were starting to think about hub assemblies.

Since the 924S is partly old 924 stuff and partly newer 944 stuff, The fronts are an inner and outer roller tapered bearing, and they're pretty easy to do - though on Porsches it's a bit of a dark art to get the hub nut preload right. The rear is a sealed bearing that is apparently hard as hell to get out without removing the entire trailing arm assembly and heating it. Plus the rear hub nut is something like 400ft-lbs....hence why I hope it's a front.

Could be a motor mount. But this would be load dependent. However I have seen bad ones to weird things in these cars. 

Yeah, motor mounts and all suspension bushings are brand new, literally, except for a couple rear suspension bushings that are NLA.

87 924s is a hog pog of early 944 and late 944. 88 924s is All post 85.5 944. 

irish44j said:

Since the 924S is partly old 924 stuff and partly newer 944 stuff, The fronts are an inner and outer roller tapered bearing, and they're pretty easy to do - though on Porsches it's a bit of a dark art to get the hub nut preload right. The rear is a sealed bearing that is apparently hard as hell to get out without removing the entire trailing arm assembly and heating it. Plus the rear hub nut is something like 400ft-lbs....hence why I hope it's a front.

All of the 924 and 944 used inner and outer tapered bearings on the front.

The Steel trailing arms use a Super Beetle style bearing with a huge torque spec.  I’ve not done them, so I can’t say how hard they are to do.

The aluminum trailing arms are a pressed in bearing with a much lower torque spec.  The trick with those is to pull the trailing arm and take it to the machine shop to have them heat the entire arm up while they push the old bearing out and then push the new bearing in.  

You CAN do this with them on the car with some home made pulling and pushing tools, a decent torch and a freezer for the new bearings.  It’s a huge PITA, but possible.

The only way to really tell if a rear bearing is bad is to disconnect the half shaft from the stub axle and the spin it. Also you put the tire back on and see if you can feel any play latterly.  The last couple I have done did not wiggle but you could here/feel the bearing with the half shaft disconnected. 

In reply to Stefan :

All 924s have the Alu rear trailing arms.

Thanks.  Couldn’t remember as they were built from leftover 924 bodies, so I wasn’t sure if Porsche used up some other parts while they were at it.

The offset is what I don’t remember. I think they all use the later offset but I really am not sure on that. I really should just go measure my set of dp’s In the barn.  

On a side note I have started a build with my 924s. The last piece I am looking for is a trans/dif with lsd. Otherwise I will be doing one wheel tire fires. 

dean1484 said:

87 924s is a hog pog of early 944 and late 944. 88 924s is All post 85.5 944. 

Not true, seeing as I had both: The red car is an '87 shell, the black car (which was the engine donor) was an '88. Literally the only difference I know of between the two is the extra 10hp in the engine (the '88 engine got the 944's increased compression vs. the '87's lower compression). The '88 still had the stamped (VW) front control arms and hubs (not aluminum 944 arms), for instance. The '88 still had the full early interior and dash. There may have been a few other little detail differences, but the '88 924S definitely is the same hodgepodge as the '87.

source: my garage

dean1484 said:

The offset is what I don’t remember. I think they all use the later offset but I really am not sure on that. I really should just go measure my set of dp’s In the barn.  

On a side note I have started a build with my 924s. The last piece I am looking for is a trans/dif with lsd. Otherwise I will be doing one wheel tire fires. 

I have to say, I was driving this one in the rain today (open diff) and though I wasn't pushing 100%, I had literally no wheel spin launching from stops, even around corners. I was actually quite amazed at the traction with the new 225s BFG A/S's on the back.

dean1484 said:

The offset is what I don’t remember. I think they all use the later offset but I really am not sure on that. I really should just go measure my set of dp’s In the barn.  

On a side note I have started a build with my 924s. The last piece I am looking for is a trans/dif with lsd. Otherwise I will be doing one wheel tire fires. 

924S is late 944 offset.

In reply to irish44j :

This proves my theory that They were using up old 924 sheet metal and the pre 85.5 driveline parts. My friends dad has an 88 and it has the alu front a arms. There must be a cut off date. 

Another theory I have is that some people change back to the stamped steel ones back in the day because the ball joints had to be replaced with the a arm. Then the aftermarket solved that problem and people stopped doing the swap.

This is all speculation on my part as I have never met anyone that has actually done the swap.