I've got a 1966 c-code, 4 speed man, convertible that's got a bad shake on takeoff.  It didn't have it when I bought the car in 2001 but it's had it now for a few years.  Here's what I've done so far to try to get rid of it.
- replaced clutch completely (including throwout and pilot bearing)
- replaced flywheel
- replaced transmission mount and all u-joints in the driveshaft.
- new front and rear shocks, springs and leafs.
There car runs and drives super well and there doesn't seem to be any play in the pedal or shift linkages, rear end, motor mounts, tranny etc...
Any and all suggestions welcome!!!!  

You have replaced the clutch so that seems to indicate you think its clutch chatter. Is that what this is? Clutch chatter is a common problem with mustangs and can be from several sources. You have already replaced the clutch and flywheel so lets assume they are ok now(even though that may not be the case). The next most reported problem is in my opinion the Z bar. Your clutch is controlled by a rotating (Z) bar that spans between your engine and the frame just in front of the bellhousing on the drivers side. This bar operates the throwout bearing fork. This Z bar is supported by bushings in each end which wear out. Even at its best it is prone to problems. You can try rebuilding the z bar or use a hydraulic clutch(good fix). I had this problem for years on my 68 and it was only solved when I rebuilt the z bar and installed a Centerforce clutch. To this day I revere those clutches as the best in the industry. They take less then half the pedal force to open which takes the stress off all other components. They are expensive but if you live with this problem for as long as I did ,,,when its fixed you are soooo relieved and the cost doesnt matter. Good luck  

Good advice from Mechguy48. I've also seen brand new & rebuilt clutch disks with loose hub springs. You might want to use a pilot bearing instead of a bushing also. I seem to recall reading somewhere that there was one version of the z bar that was better than the stock ones.  

@mechguy48-thanks for advice. Am I sure it's clutch chatter?..well no, but the whole car shakes if I release the clutch normally, with time you adapt but takeoff while loaded on a hill is tricky!! I've heard about the z-bar fix but there doesn't seem to be any play. Guess it's something I'll have to do just to eliminate that one before going for a CF.
@jlg2002 agreed that bearing is better than bushing, just doubt it would make a difference here, you never know though!
I've heard about too much end play in the crankshaft?  Anyone heard about that?
Will do the z-bar bushings and let you know.  

Yeah Alp your right to be a little skeptical because I suspect these things are generally a combination of several things. Wear in the clutch, the throwout bearing, the sleeve it rides on, the pilot bearing, the flywheel surface and runout, bellhousing alignment, Z-bar, end play, motor mounts, trans mounts, all these things play a small role and which one is giving you trouble is hard to just point at and say. Like doctors we tend to go with the most common solution and that isnt always it. It is good to listen to other peoples solutions because it gives ya a direction and sometimes it lights a light up there that says ,,,oh yeah,,, I was gonna replace that thing anyway, I bet that's it. One thing this forum is good for is that you often get conflicting or multiple shots of advice,,,, I see that as helpful because the first solution isnt always right.  

Definately on board here. As the saying goes, "it's the last thing you did". Regarding the pilot bearing vs. bushing comment. That was for your review if you decide to pull it down, in itself I don't think it's going to help the situation your facing.
JLG  

I've had this problem with various pressure plate/ clutch disc combos over the last 35 yrs. The best combo for clutch smoothness was the hipo 10.5" unit from Ford. But after building a 347 stroker for the 66 the Ford units begin slipping in third and forth gears. I went back to a heavy duty Hayes pressure plate still using the hipo Ford disc and it quit slipping. Several years back MM addressed this problem and recommended these two McLeod parts.

Pressure Plate, 360400
Clutch Disc, 260830

Haven't used these myself yet, but with the trouble comes back, I will.

cush  

Yeah in fact I use the McLeod clutch on my fastback and it has been trouble free so far. Nice smooth engagement. I converted it over with a late model bellhousing and T-5 for using the cable clutch from Ron Morris. The McLeod unit is beefy and a little hard on my left leg though. I wish I had spent the extra money and gotten the centerforce which uses a lot less leg power. I must be getting old!  

Yeah, the McLeod unit is tough to push in, and it grabs immediately, so you have to learn to drive with it, but man does it improve the launch.  

Thanks to everybody for advice and suggestions.
Did the z-bar rebuild and unfortunately there's no difference. I'm not surprised.  Maybe look into rear end and crankshaft end play next before reconsidering getting another clutch assembly.  

I'm on board with the Centerforce Dual-Friction clutch.  I've done a few of these and they never fail me.  Smooth, light pedal, very effective.  That, coupled with a pilot bearing (versus bushing) and a fresh linkage should do the trick.

Jim Smart
Senior Editor  

let me know if you figure it out my 68 with a 302 and 4 speed ,mine is doing extacly the same thing,if i let the car just idle when i let out the clutch it does fine but if i give it any gas it shakes bad,i was thinking it was the pressure plate ,but it feels like its coming from the rear end i didnt know if it had somthing to do with the limited slip  and if i drop the clutch hard both wheels spins and holds no problem  

I have a 1966 a-code GT convertable that has the same indentical problem w/ a four speed. This car has been
known to shake for the past 27 years. All clutches installed were three fingered style until recently. It has a diafram style with all new componants. STILL SHAKING!! I changed the pinion angle 2 degrees (lower) with the same results. All mounts are new. The bell housing is .004 T.I.R on the I.D. and .005 parallel on the faces. PLEASE HELP!!!  

Summit Racing offers this advice:

http://www.summitracing.com/streetandstrip/tech_content.asp?ID={AE711979-A6D0-4802-A262-500D9F59D71D}  

I have a truck that had the same type of problem. It was a bad driveshaft.