Jerky start of roll.

[Manuel]

Good morning to all,

1971 Cuda 340.

When I start to drive taking the clutch out the car tends to jerk/vibrate.    Once it is out it accelerates smoothly.

Accelerating in neutral is smooth.

Transmission has light worn buzzing gears sound when stabilized at driving speed.

What can the cause of jerking be and were do I buy new pinion and crown if needed.
Can such a sound be only an adjustment thing?

Thanks

[jimynick]

I don't think I'd be looking at the crown and pinion regarding the jerking when starting out. I'd think it was a function of the clutch and/or your use of it. If you slip the clutch and engage it slowly while revving the engine, does it jerk then? Jerking is usually caused by either erratic engagement of the clutch via the pedal, or the compound making up the clutch friction plate. Some race oriented clutches have very hard material and their engagement is nothing like a street oriented friction plate. How's the flywheel? Heat coloured or cracked? The throw-out bearing and linkage? Just some thoughts. Good luck. 

[MoparLeo]

What is the rest of the story as people tend to only tell 10% of the story and not until much later to we find out the whole truth. If you want a good answer, we need good, complete information.
Broken mounts, contaminated/broken clutch disk??

[dodj]

Warped pressure plate.

[Manuel]

Thanks for the comments.

[Bullitt-]

  I'm remined of the fits my Duster gave me getting the clutch to release freely.
Ended up the problem was with missing Z-bar ball stud bearings, Had to replace a pivot as well.
https://www.rosevillemoparts.com/product/clutch-pivot-shaft-service-kit-66-74-b-e-body/

[MoparLeo]

I guess we don't get to hear the rest of the story...

[Manuel]

Jimynick,

I am not a mechanic, the clutch disc was "redone" I was told and don't have any details. 

If I accelerate the engine quite a bit and then start taking the clutch out vibration / jerking will be less.   Does that tell us something?

[MoparLeo]

OK Did you just get this car ? Or did you just have repairs done to it ?

[Manuel]

Have owned the car since 1974, it belonged to the dealership owner here in Guatemala and had only 1300 miles on it.  It was 100% like new, on display with new cars at the show room.
Car has always been well taken care of, has now 50K miles on it.

Stored the car some years back and this year decided to have a mechanic take a look at everything to get it in good mechanical condition and then repaint it.
My relationship with the mechanic did not end too well and I don't want to contact him for details on what he did to the clutch but do remember he send the disc to have it redone.

Have driven it only a few times since they finished the 9 months painting, geeee but it is gorgeous.

So, back to the jerking, I will take it to a shop but since I am not versed in the topic want to arrive with some knowledge as what the cause might be.
Any Q's you may have to provide further opinions are welcomed.

Thanks

[Filthy Filbert]

could be engine tune as well.   

Kind of like when you're learning to drive a clutch, and you don't give it quite enough gas at first, the car surges and bucks as you start rolling out.   If the tune is off, the RPM may be dropping too much as you release the clutch; and the symptom hidden as you use more revs when starting.

[70 Challenger Lover]

I'd pull the transmission and replace the clutch plate and pressure plate. They aren't that expensive. While it's open, remove the flywheel and have it surfaced. Also cheap. I've seen many cars like that and this always fixed them right up.

The guy who redid the clutch last time may not have resurfaced the flywheel or it could have been done poorly.

A buddy of mine has a 65 GTO which also did this. Every GTO guy out there said it was a common problem with that motor in 65. We replaced it with new, resurfaced the old flywheel and it's been smooth as silk ever since.

[Manuel]

Thanks, lets say the engine is not well tuned and that is the reason for the jerky start of roll.

Could the bad tuning be confirmed by any other means?   I checked acceleration in neutral and its OK, also let it at idle on first gear and then pushed the accelerator.   It accelerated also even.
So, any other checks to be done?

[70 Challenger Lover]

If it is clutch related, the whole car will shudder as you let the pedal out. It's very noticeable that it's clutch/flywheel. If it's bad enough, it can feel like the car is shaking itself apart. Especially if you're feathering the clutch going up a steep driveway or something like that. As the pedal fully engages, all vibration ceases immediately. It's mostly felt in first and reverse but not hardly at all going into second. It would have been present when you bought the car. Once the pedal is out most of the way, the clutch is engaged and the problem stops.

If it idles nicely in neutral and and you can rev it without sputtering or stumbling, then it may not be engine related. You also let the clutch out in first and drove it slowly just fine before acceleration. All this makes it seem that engine tune is not the source of your problem.

I doubt it has anything to do with the rear end. There might be a whine in the rear end but it's not related to this problem. Worry about the whine later.

You can have a mechanic drive it and give an opinion. You'll know for sure with the transmission out so you can inspect the parts.

[Bullitt-]

  Guys.... What would a broken motor mount do when pulling off?
I seem to remember that can be an issue.