The Stovebolt Site Forums The Shop Area Driveline Clutch chatter

I have a 37 gmc 1/2 ton with a pressure plate with coil springs. Gone through it several times and can't get the engagement into first gear to be smooth. It chatters when I start. No issues with second and third. Any recommendations?

Check the motor mounts. Most cases of clutch chatter from a stop are caused by the engine bouncing around on loose mounts. Oil on the clutch disc is another possibility, but if you've had things apart recently that should have been discovered already.
Jerry

Rubber mounts rot, and a guy can get in a hurry and totally forget to tighten up their own rear engine mount bolts because his wife interrupts him and yells at him about the smell and is envious that he has a passion for a hobby which she doesn't understand, while she doesn't have a hobby at all except shopping and yelling.
Carl

Been there, done that - different interruption

The "smell"?

Everything "smells' like grease to her. Grease is her nemesis apparently.

Well, I took my project around the block today for the very first time to see if it would shift, and to check the brakes.. I got some serious clutch chatter- just like the engine mounts were bad. But all mounts are brand new. Is it possible that I don't have the front mount set up properly (not torqued down enough?)? The truck was bucking like crazy. Engagement was smooth, but the drivetrain seems to be winding up like a rubber band. How tight are you guys running the bolts for the front engine mount?

Carb curb idle set too high? As mentioned earlier, oil on clutch disc? I've got the same issue with mine,with both symptoms I mentioned.I havent addressed either but I know it's most likely the problem.

If you get metal to metal contact within the front mount, it will transmit engine vibration to the chassis. It would not contribute to chatter.

Hmmm... My clutch installation was done very carefully- runout at the flywheel was checked and the clutch went in with everything very clean & dry. There is no evidence of oil leaking from anywhere n the vehicle. The idle is set slightly high right now. I forgot to mention that his is occurring on my '50 truck with the T5 transmission. It was the first time the truck has moved under it's own power since I bought it and pull it apart.

There is no metal to metal contact with the front mount as far as I can tell, but the bolts might be too loose. I can engage the clutch on level ground and make it engage without any driveline bucking if I am very careful, but if I'm on an incline, then it gets pretty bad. It feels to me just like bad engine mounts, except everything is new. I am going to add a little torque to the front engine mount bolts and then try to drive it again today.

How is your mount system set up, Dave? If there's not a mount at the tailshaft section of the trans, there might be enough torque on the transmission case to make it shake side to side. If that's the case and the transmission is only supported at the bellhousing, try attaching a couple of nylon ratchet straps around the tailshaft. Loop them over the frame rails at each side, and put some tension on both straps with the ratchet. Take a test drive. If the chatter goes away, or it's reduced noticeably, you might want to consider fabricating a rear crossmember with a rubber mount on it.
Jerry

Hi Jerry, my mount system is totally stock, with no rear crossmember added for the T5's trans mount. Your idea is excellent, and that will be my next course of action if it doesn't settle down after my next test.

I think there is more to this though- I must have had an episode similar to Carl's where I did not torque the front mount bolts (at all)- I could pretty much turn them by hand... So I I torqued the center two bolts down firmly and then tightened the outer two bolts a little beyond snug and put the cotter pins back in. I must have gotten three full turns on the center bolts to get them torqued..amazing.

It seemed to make a real difference when I took the truck around the neighborhood again today.

It's a bit comical, but I think that the real problem is between the seat and the steering wheel, so to speak- Because I added dual carbs, I had to fabricate a new throttle linkage, including a bell crank, because my stock bell crank was toast. At the moment, the gas pedal goes from idle to WOT with secondaries full open, and it does this with 1.25 inches of pedal travel. When I let the clutch out, I get forced back in the seat, and the spring seat bounces me forward a bit, and my foot moves off the throttle, clutch foot starts pulling away from the clutch, then I get thrown forward, and the clutch goes in and the throttle goes in as well...If I stabilize my feet and brace my body, everything seems to engage fine. I think I'm thrashing back-and-forth on the throttle causing a horrible reaction because the gas pedal arm on the bell crank isn't long enough to provide a decent amount of gas pedal travel- it's just waaayyy to sensitive. I simply cannot modulate it without hammering on it or having it go to idle. I look like a 12 year old girl trying to learn to drive a clutch!

I'm going to modify the bell crank and give myself a better ratio at the pedal and if that doesn't clear it up, then I'm going to strap the transmission and take it out for a drive. Wish I had left off the trans cover panel, because I could have someone put a hand on the trans while I'm engaging to see what if it's moving...but my floor mat is in and it'll take me 2 hours to unscrew and re-screw everything that is holding it down.

I'll let you know how changing the pedal geometry works.

Dave, can we have a video of that!😂

I used to tell pilots their planes had a dead short between the control column and the rudder pedals!
LOL!
Jerry

It scared the hell out of my girlfriend, who was riding shotgun at the time... if it had been a first date, I probably would not be having another.

Martin, I'm really glad that we both forgot our phones, so there was no video...

I welded up a new bell crank, have a little more than 2 inches of pedal travel now, I think- I will test drive tomorrow and report.

Jerry, I flew helicopters, and the mechanic used to say the problem was between the seat and the cyclic...!

It is called Pilot Induced Oscillation.

Ed

Yes, the Flight Manual for the EC135 specifically warned about it. But I see no mention of it in the 1950 Chevy 3600 Driver's Manual...lol

That's just one more item to add to the long list of why duals are "one carburetor too many!" It sounds like you really need even more pedal travel to accelerate smoothly, maybe with a second bellcrank somewhere in the linkage.
Jerry

I'll tell you what Jerry- if I had it to do all over again I would have left the entire truck stock. The only exception is the gearing that I've got right now, which is really nice (yes, I took it out on the road with no doors, fenders or electrical system and got it up to about 60 mph).

The Fenton dual exhaust and the dual carbs were way more trouble than they were worth (and they were expensive!), and they will continue to require additional work to keep them synched properly. It was a waste of money. The 261 has more power than this truck needs, and a stock 261 is a really nice engine. Live and learn. I was having hotrod fantasies when I bought the truck, and it wasn't until I was about half way through it that I realized that I would have enjoyed the truck far if I had left it stock. And saved my self a ton of time and money in the process.

The new linkage setup is working nicely now, so I think I'll leave it alone for the moment. My project will be slowing up now until next spring/summer as I head back into school soon.

Here's a quick video of engaging the clutch now: 1st gear on an incline

Now for a little bit of a confession- - - - -I'm actually considering building a multi-carb inline six! However, it's going to involve using three very small side draft carbs, one for each intake port on an early 1960's 230 engine. The carbs are originally designed for a Harley Davidson motorcycle, and they have vacuum-controlled venturi pistons like the old S-U carbs on British sports cars like the Austin-Healey or Jaguar. I'm planning on building the engine with some pretty sophisticated bottom end parts and some cylinder head porting, and possibly a roller cam, to perform in the 7K RPM range without coming unglued. The chassis it's intended to power will be a super lightweight Excalibur fiberglass roadster, maybe 2500-3K pounds gross weight. It should run like a molested monkey if I get everything built right!
Jerry

That sounds really cool Jerry. And the old SU's were great carbs, I always thought.