Mark Hubley

Well, I know I have a gap in my exhaust system where the muffler joins to the cat. So, that's at the top of my to-do list.

I'm trying to remember off the top of my head whether I need to take both upper and lower front timing belt covers to check the balance shaft alignment. Either way, it's not that big a deal for me to expose the belts (I've done it plenty of times over the past year and a half).

The clutch has me a bit worried. Even if it's not the cause of my current issue, I'm actually considering a prophylactic clutch change--maybe as an off-season project. I probably am on the original rubber-centered clutch, which is probably a ticking bomb.

John_AZ

To check if you have a rubber center disc, you can unbolt the starter and poke with your fingers for small bits of rubber--1/16, 1/8" or larger.

You do need to remove both belt covers to check the BB rollers/pulleys.

The dark spots on the top of the BB shafts are the keyways in the picture.



John

Mark Hubley

I sooooo hope that Santa brings me a two-post lift this winter!

Mark Hubley

It appears that the winners of the "Identify that Vibration" contest are JoKa, Brett, Jim, and MAGK944, who suggested a balance shaft issue.

Yesterday I took off the front timing belt covers. In the process, I noticed some leaked oil (not what I wanted to see having changed the front seals a few weeks ago). With the covers off and the motor at TDC, both balance shafts lined up perfectly! So it wasn't a matter of the timing being off. However, I noticed that the three bolts holding the front of the upper balance shaft housing to the block were all loose. At this time, I am assuming that is the cause of both the bad vibration and the oil leak.

I tightened up the bolts, put everything back together, and started the car. Still the same bad vibrations, so just tightening the balance shaft housing back up didn't solve the problem. At this point I am guessing that the seal on that upper balance shaft is damaged/distorted. I've ordered all new seals for that upper shaft, and I'm crossing my fingers that resealing the shaft will finally solve the problem and get the 924S back on the road. I sure hope the shaft itself is not damaged. So, I get to remove and replace all the belts, sprockets, etc. again.

I'll update again after my next attempt at getting this sorted out.

I wonder if the muffler failure was caused by the balance shaft getting out of whack? Seeing how rusty the innards of my muffler were, and how violently the muffler shakes at 3200RPM, I'm thinking the balance shaft went bad, and then it quickly shook apart the corroded muffler.

Mark Hubley

Well, maybe not a balance shaft after all . . .

Yesterday evening and this afternoon I removed the timing belts and associated sprockets, rollers, etc. The upper balance shaft seal (and the lower one for that matter) looked fine, but I removed the front housing of the upper shaft and replaced the upper balance shaft seals anyway. Then I reinstalled the belts, sprockets, rollers, etc. and carefully checked all the timing marks and tensioned the belts.

After putting everything else back together I started up the car and it has the very same vibration (~3,200-3,500 RPM). No change.

While the motor was running I spent a few minutes looking at various things while I opened the throttle by hand. I can't say I found anything conclusive, but the headers look fine; nothing noticeably loose. I left the upper front engine cover off, and the balance shafts seem to be spinning just fine. With my hand on the throttle cam, adjusting the revs, I could feel when the car hit 3,200 RPM, but it wasn't all that distinct.

While I had the starter out, I felt around as best I could for any rubber clutch chunks, and I found none. I'm still thinking the fact that the symptoms are identical with or without the clutch pedal in indicates it is not a clutch/tranny issue.

So, I'm still open to advice, if anyone has any to offer. I'm also thinking about taking the car to a shop (maybe Tif's in Annapolis).

Scott924S

I am very interested to learn what may be the source of your troubles. My car (same as yours, '87 924S) started doing the same thing last weekend (strong vibration between 3k and 3500 rpm, most noticeable in the shifter, exists with and without clutch engaged). So far, I've checked and confirmed that the balance shafts are not the issue.

On my car, I have noticed it also seems like the transmission makes more noise shifting between gears though this could be unrelated. Thought it might be transmission mounts but I'm not sure how to check them accurately.

I've noticed other posts regarding this same vibration in other forums. Seems like a common problem for these cars. So far, no definitive answers. I'll be sure to post if I discover the solution.

Scott

Mark Hubley

Last week I brought the car to Tif's. Spoke with them today, and they want to replace the clutch. I did this once on a 944, and while it wasn't God-awful, right now I think I'd rather pay someone than give up all that time. Will update as I learn more.

Scott924S

I'm still in denial about the possibility it could be the clutch. Can't really justify paying all that labor but if I do the work myself, the car is not likely to see the road again until spring.

I can't recall if you checked the motor mounts on your car. I'll scroll back and check. That was the advice I got from another forum, but in my experience with broken motor mounts, the vibrations are more profound at lower rpms...

944hal

Similar vibration on an "89 S2. Rubber center in clutch disc came apart. Pieces lodged in the pressure plate causing it to be out of balance. Age deteriorates the rubber. No vibration with new clutch.

Mark Hubley

I put new motor mounts in the car (DIY) last year. I had the same issue with a 944 that I owned a while back. Totally different vibration. As you said, bad MM's give more vibration at idle.

Mark Hubley

Was confused by the fact that the vibration continues when I disengage the clutch, the clutch engages/disengages just fine, and I can shift OK.

A chunk of rubber in the pressure plate would account for all of that!

bonus12

I'm still thinking exhaust especially considering it's loose. same problem i had. a audio/video would help.

Scott924S

Hmmm, I just pulled the starter off and there is no evidence of deteriorating rubber at all. Is there a way to tell what clutch is in the car without pulling everything apart?

Motor mounts are within the 60mm spec cited in "Clark's Garage."

Exhaust is tight, no loose or deteriorated hangers and surprisingly very little rust on the system as a whole.

Mark Hubley

My current theory is that there is indeed a failure of the clutch. When I drove the car to the shop I did notice a slight clunking sound/feel most times when I engaged the clutch. I may not have noticed it earlier when I was focused all the other sensations. I'm thinking that this issue with the driveline caused the vibrations, shaking the muffler (Which is partially suspended from the torque tube), causing the corroded muffler to fall apart.

I will be sure to ask the shop to keep the clutch for me to view after the repair.

Mark Hubley

Scott,

How many miles on your car? I purchased mine last year with 52K miles and all the service records. Nothing showing a clutch replacement, so that pretty much means rubber-centered clutch for me.