Hi everyone,



about two months ago, I bought a 1978 C3. Before taking it on longer drives, I did some small maintenance work, like changing the exhaust and doing an oil change.



A few days ago, I went for my first longer ride (about 110 miles). The last 4 miles were downhill from a mountain. When I entered the village at the bottom, I noticed a strange noise coming from the engine bay. After some investigation, I discovered that the sound is coming from the clutch housing. the sound is only hearable when the clutch pedal is not pressed.



I checked the clutch area and found out that one of the anti-rattle springs is missing, as well as the clutch pedal return spring. I’ve already ordered replacements, and they are on the way.

To test things, I temporarily installed some other springs to see if the noise would go away. Then I drove about 30 miles, and the noise came back again — but this time, it was much quieter. I assume that’s because the car didn’t get as hot as on the first drive.



At this point, I hadn’t adjusted the clutch pedal properly yet (I didn’t know there’s an OEM adjustment procedure, but I’ll do that once I install the original springs).

I also noticed that the clutch fork has some unusual play — it moves not only left and right, but also up and down.



My suspicion is that it could be the throw-out bearing, the pivot ball, or maybe even the pilot bearing.


Do you think I’ll need to remove the transmission to get more information?



Has anyone here experienced something similar or has an idea what could be causing this?

Thanks in advance!

 

maybe the throw-out bearing..
can you verify with a stethoscope or hose and be sure what area it is coming from? you can also peak below while running to see fork and if its rattling around? if gently touching clutch pedal may indicate TO bearing..or not releasing allowing to spin?

 

Welcome to The Corvette Forum Milkman221!

I just wanted to welcome to to the Corvette Forum where any question about a C3 is fair game! This place has more Corvette experience than any other place on the internet. The best part is that we do it because we LOVE Corvettes like you do and want to see every Corvette on the roads.

That noise with your Clutch is troubling, I never tried to move my Clutch fork up and down let alone side to side. That noise in your engine bay sounded like a fan hitting or something of that nature. If that IS the clutch then you have a grave issue because it sounds like it is coming apart. I have heard bad bearings inside of belt tensioners and other accessories that fail and make a heck of a lot of noise. You might try taking off the belts and see if the noise is still there when the accessories are not spinning. I don't mean to be negative but I would probably not run it with that noise as it varies too much.

Do you have a set of the factory service manuals made especially for the year Corvette that you have? They are available in several formats. RockAuto has them under "Literature" tab and they sell a DVD with a complete manual for ~$35 and up. The Assembly Instruction Manual (AIM) is invaluable and you need to get one for your year Corvette.

Sometimes the local Corvette people will have ideas of any mechanic that is worthy to work on your Corvette. National Corvette Restoration Society (NCRS) is a group that perform verification of just How original is your car. They make their Corvettes look like they just rolled off the showroom and the competition is fierce. These guys are a great resource and check out their website. Corvette Clubs are very popular and they are all over the place. The Corvette life is really a Lifestyle, it is not just any car.

I know of older cars that when driving you would hear the clutch chattering and such. Newer cars in the last 30-40 years have pretty much done away with the noisy clutch assembly. I still use the older clutch in my 427 and it is glass smooth after I put the RodLinks conversion from Speed Direct and it has never made a sound since then. The Rodlinks system has Gleim Joints on the ends and is really smooth action.

I think that you are getting close to where the noise is coming from looking around down there. Remember the little bronze or brass pilot bushing in the flywheel, they likely make noise when they are getting worn. How old is the original clutch that came with the car? Is it time to replace the clutch and start fresh? When Pilot Bushings go bad they tend to make noise when the pedal is released and you are driving. I believe the squealing stops when the clutch is pushed but returns when the clutch is released again.

The newer Corvettes like your have a pretty busy engine bay. I am very lucky to have a 1968 C3 because of the simplicity of the systems. It is a simple and basic car made to go fast and handle well. My 427 has headers and I can still reach down and change the spark plugs when I need to. The car came with an air pump and a PCV valve and that was it for any emissions equipment. At Corvettes@Carlisle I was able to meet Zora Duntov and his gracious wife where he autographed a picture of my C3 and the 1968 sales Brochure showing a similar Corvette to mine.

I hope the guys will chime in here and suggest what they think is wrong with your clutch.

 

I'm really grateful for all the help so far!

To give you a quick update:
I’ve now installed the original springs and adjusted the two nuts on the clutch pedal rod according to the manual.

I’ve driven about 5–10 miles since then, and the noise is still there — but it’s much quieter now. Honestly, I probably wouldn’t even notice it if I didn’t already know what to listen for.

I’m not sure yet whether the noise will get louder again after driving more miles.

Unfortunately, I haven’t been able to try the stethoscope method yet because the car isn’t jacked up at the moment, and I don’t have anything long enough to reach my ear while lying underneath the car. Kind of stupid, I know 😅 — but I’ll prepare better and try again soon.

From what I can tell, the sound seems to come from somewhere between the end of the oil pan and the end of the clutch bell housing. If I fully depress the clutch pedal, the noise disappears completely. a few inches aren't enough to let the noise disappear.

I might try tightening the two rod nuts a bit more toward the driver’s side. The manual says to apply 5 pounds of pressure on the rod during adjustment, but that’s a bit hard to estimate — I may have applied too much force the first time.

One more thing I noticed: the clutch pedal now sits slightly higher than the other pedals, and you can still pull it slightly toward the driver. However, this doesn’t affect the noise at all, even when I manually pull the bottom of the rod near the clutch fork in the direction of travel.

 

My c4 vette started making a noise like marbles in a can, only when clutch was not depressed. The noise was also identifiable as coming from
the clutch housing. Push in the clutch and noise instantly would go away.
I suspected the throw out bearing was bad. Pulled clutch, replaced throwout bearing(the old one was toast) and the other wear components, put back together.
noise gone.

however, my noise was no where near as loud as yours, but maybe it’s how it was recorded it since you mention in your post that it’s not that loud.

 

Just Perhaps.
The photo below (lifted from RockAuto) shows Both sides of a Brand New friction disk (that's probably much like yours). See the Six coil springs? Those function as dampers. Most friction disks have damper springs. Occasionally, those can break or become dislodged; either way they can make a little noise or a helluva racket. Also, see other Ten, thin stamped steel pieces that're riveted ? Those also may become loose and noisy. AFAIK, the only solution to this failure mode it to replace clutch friction disk. If this disk has failed, I suggest R&R friction disk, pressure plate and ThrowOut bearing as a set. And, inspect clutch Pilot Bearing (actually a bushing) as well. Location: FIRMLY pressed into rear of crankshaft and can become noisy as well.

Just Perhaps.

 

Thanks a lot for your great input and support!

The tip about the clutch springs is really helpful.
I’ll be removing the gearbox soon to take a closer look and figure out where the problem actually is.
After that, I’ll decide whether to rebuild the entire clutch or just replace the release bearing.

I think the problem will be somewhere there

 

Something to consider if you need to replace your clutch.
https://www.corvetteforum.com/forums...vel-range.html

 

Thanks again for the helpful tip!

Now I’ve got a follow-up question:
Which clutch would you recommend that’s reliable and holds up well in the long run?

I’d prefer to order from RockAuto, since their delivery times to my country are excellent.

Has anyone here already replaced the clutch on a C3 and can share their experience or recommendations please?

 

Milkman221
Initially I was going to recommend other options but after listening to that video I suggest you quit driving it and just drop the tranny.

Let me see if I can find some tranny/clutch removal pointers on this forum.

A couple of things I have done that made a difference. 1. Put the pilot bearing in the freezer. 2. Press the pilot bushing into the hole instead of hammering it in.

I'll go look for a tranny removal thread.....

 

Milkman221
this is fairly clear.
Get the exhaust out of the way.
I would put the engine at top dead center. Mark where the distributor is and then REMOVE it. (put a rag in the distributor hole)
I would also disconnect the clutch outside the bellhousing since we're going to be tilting the engine and whatnot.


Take a look. Ask questions.

 

If ya prefer RA
RA has a good tool to remove clutch Pilot Bearing (Lisle P/N 55600) works with Your grease gun. Good price too.
Yes, there are many, many alternate methods to remove pilot bushing; but Lisle's grease tool is cheap & easy-peasy.

https://www.rockauto.com/en/moreinfo...0614&jsn=10715

 

Thanks a lot for your answers — I really appreciate the effort you guys are putting into helping me! Also, thanks for the video; I had already seen it before.

Threading out the transmission could be a bit tricky, and disassembling the shift linkage from the interior might be as well. I'll have to take a closer look first, but it should definitely be doable, and I’ve got plenty of time on the weekends.

I’ll most likely remove the transmission and then inspect the clutch. It would probably make sense to replace the pilot bearing at the same time — that tool looks great for the job!

However, I was actually more interested in the link to the other topic regarding the correct clearances the clutch needs to disengage properly, and, based on that, which RockAuto clutch I should go with. There seem to be several options available…

Of course, I’ll need to check first which one fits the crankshaft, the number of teeth, and so on.

i would love to give you an update as soon as the trans is dropped, would like to hear your opinions.

 

LuK makes a good quality replacement clutch package. If you expect regular visits to drag strip or autocross, suggest step up to one of the performance brands.

 

I would not get a stock replacement clutch. I had one put it because mine failed and I did not have to time to do it myself...... egad.... that things wouldn't even grab adequately...... I did have 4.11s and a L79 3237/350 but I was surprised how weak that thing was. I had taken it to shop that I knew did fine work but only did stock replacement stuff so i had nothing to complain about...... it worked adequately, a lot easier to use than the previous monster clutch I had in there.....just couldn't hammer it because it was blatantly obvious that it was slipping...so then after a while I put in a Centerforce Dual Friction..... I really liked it and it gripped and was easy to depress.

 

A lot of good comments here.
Country code "AT" is that Austria?
We love helping guys keep these running overseas, they must be extremely unique over there.

Three tips I have not seen mentioned:

• For a cheap and long listening device, use a piece of 1/2" PVC pipe
• I have never heard a clunking sound like that on a bad clutch before, I would not drive it, just pull the tranny. A bad release bearing is more of a grinding. That clunks.
• Pilot bushing in crank: please do not use the all too common solid steel ones available today. They gall. Even the common brass ones are too dry. The roller bearing ones die suddenly, they do not like the dirt there. The self-lubricating oilite bronze ones are still available, are what the factory used, and are drastically preferred. You just have to look hard to find them. PM me if necessary.

 

This helped me alot...

https://www.motortrend.com/how-to/17...rvettes-part-1
https://www.motortrend.com/how-to/17...rvettes-part-2

 

My old clutch was always fine until it wasn't so I pulled it out and got the exact same replacement part which happened to be a LUK. Easy installation and it works perfectly.

 

Thanks again to everyone!

I’ll be pulling the transmission soon, and then we’ll see exactly what’s broken.
I never drive the old lady faster than 60 mph — she deserves respect . Most of the time I just cruise around - if there wasn't the problem. We don’t really have drag strips here, and honestly for me the car feels too precious for that kind of use.
Unfortunately, I haven’t driven the car since the incident.

Thanks also for the tips on clutch manufacturers. I’ll dig deeper once the old clutch is visible. Hopefully it won’t turn out to be anything more dramatic.


And yes, AT stands for Austria. Cars like this are really rare here, which makes mine very special to me. I read somewhere that there are only about 70 C3s on the road in Austria.

Brooklynite — your linked description is absolutely first-class. That’s definitely something to work with!

I’ll keep you guys updated. Right now I’m still waiting on the delivery of something similar to Quickjacks.
Thanks so much for the interest and enthusiasm!

 

Well, unfortunately, the project has hit another snag. Things are definitely not going as planned, and I've run into a serious issue with the driveshaft to slip yoke connection.

The way the current driveshaft is attached to the slip yoke is incredibly poor—I honestly can't figure out how it was initially installed. My suspicion is that this mess happened when the differential was previously removed or worked on.

Now, I'm stuck with two main options for moving forward:

1. Attempt a Press-Out: I could use a proper tool and try to press out the bearings, hoping that the small pins currently visible on the side of the needle bearings (which are likely holding the universal joint in place) will give way. i cant burn them down, because the driveshaft is installed.
   
2. Cut and Replace: Cut the existing slip yoke off at the transmission (where the bearings sit) and install a new, screw-on type of slip yoke - i will probably do that anyways.
   

To be honest, the current setup is pathetic and I'm heavily leaning toward Option 2 just to replace the existing poor solution entirely with something reliable.

Has anyone dealt with a similar poor installation or this specific style of yoke connection? What would you recommend for the safest and most reliable fix?

Thanks in advance for the help!



I was able to remove the semicircular safety brackets