That means both flywheels I've had are faulty. I'm leaning more to Jaysen's explanation.

as mentioned, hows the rear main? an oily or gummy plate will shudder and it will stop shuddering when riding it like you have been doing up a slight incline. no good for the clutch but heats it up and dries it out for a bit. i'm no mechanic but normally a clutch shudder is from hot spots, flywheel in need of machining or oily clutch plate.

Brand new when I converted it to manual - Its kinda pointless to remove the gearbox on an old motor without replacing a $15 seal. Now I have one of those rare ford 6's that doesn't leak any oil at all.

If I had a scanner I would stick up the docco out of the FR cat, Ill see if I can find it on FRP.com

Here we go, sorry I couldnt copy the pictures, Im a mechanic, and a computer retard at that
TECH TIPS
CLUTCH/TRANSMISSION
INSTALLATION TIPS
1986 and newer V-8 Mustangs
The flywheel to crankshaft bolts must be hand-torqued to 75-85 ft./lb. (302/351W) and 54-64 ft./lb. (4.6L) The 10.5" pressure plate bolts must be torqued to 12-24 ft./lbs. and 11" pressure plate bolts to 33 ft./lbs. + 1/4 turn. Be sure to use the alignment dowels in the flywheels. Pressure plate bolts and alignment dowels
for the 10.5" clutch can be purchased using PN M-6397-A302. Pressure plate bolts N808969-S100 and alignment dowels PN D1FZ-6397-B are for the 11" pressure plate. Evenly tighten bolts in a circular direction
one turn at a time. Bellhousing alignment is crucial for proper clutch and transmission function. Due to production tolerances of engine blocks and bellhousings, it is possible for the transmission centerline and crankshaft centerline to be misaligned. Misalignment can cause transmission gear wear, transmission
jumping out of gear, driveline vibration, clutch pedal vibration, pilot bearing noise, release bearing noise or excessive clutch spin time. It may also damage the pilot bearing, transmission mainshaft bearing and clutch hub. It will also cause harsh shifting. Before installing the bellhousing, check the block mounting surface and bellhousing surfaces for nicks, dents, paint debris, etc. These are some things that could affect the accuracy of your measurements.

HOW TO CHECK BELLHOUSING ALIGNMENT
The first step is to check bellhousing face runout. You are checking for parallelism of the back of the bellhousing to the back of the block. Install the dial indicator (as shown in Fig.1). Rotate the crankshaft and mark down the reading. Be sure to push the crankshaft against the thrust bearing for an accurate reading. Maximum runout is .010. The next step is checking bellhousing bore runout. You are checking to see if the bellhousing bore centerline is aligned with crankshaft centerline. Reposition the dial indicator in the bellhousing bore (as shown in Fig. 2). Rotate the crankshaft and mark down the readings. Maximum out of concentricity is .015. If the bore runout is out of spec. install appropriate offset dowels. Offset alignment dowels can be purchased from Lakewood.
.007 PN 15950
.014 PN 15960
.021 PN 15970

Compliments of the Ford Motor Company. This material is NOT my own and has been reproduced for the sole purpose of helping fordmods members with their cluch problems.

Source: Ford Racing Parts Catalog 2006 edition page 130

FINALLY SO I have been doing it the right way all these years as I read this in a ford technical bulletin in 1965 and have found quite a few OUT OF ALIGNMENT bellhousings over the years!

ive got the same problem as the thread starter. Just recently replaced the old 3 bolt flywheel and clutch with a machined 6 bolt flywheel and new heavy duty clutch, with new spigot and thrust bearings, and rear main seal.

Felt perfect for the first couple weeks, now this morning on a cold start, it shudders bad when taking off from first......... tried different ways to minimise it, but the only thing that helps is when you give it 1500rpms and ride the clutch until its got enough momentum before letting it out.

It only doing it when the motor is cold so far, but i assume its not normal and might get worse....

when the clutch was replaced did you put grease in the spigot hole?

if to much or the wrong type of grease is used on the spigot bearing the grease will melt and centrifical force will slowly work it outwards and end up on your clutch plate..
which will make it shudder and eventually destroy the clutch plate..

thanks, will keep an eye on it.

first thing i noticed the clutch is either in or out, in other words, the release point is not very gradual.

I LOL'd at this thread, because of the posts were Bozz mentioned cooking his clutch because it stopped it shuddering.
The reason this is funny, is because I was driving another members car, and was instructed to launch it hard, which I did, and the clutch did not
grip at all, and I kept into it thinking it would grip
Cue acrid clutch smell.
I blame s**t 4L clutches.

Anyway, I get a call from him the next day, saying thanks, because his clutch had stopped shuddering.
It did the same thing as Bozz's though, eventually came back.

You weren't instructed, you just did. And it was a s**t launch! Blame the driver, not the clutch.

And the shudder did come back, but to a lesser extent than previous.

You C*** told me to launch it you window licker.
It would have been a good launch if your hobo clutch had of actually gripped.
If you want to fix it again try 2nd gear burnouts out the front of my work, look for the lines that both kyle and I have left, try and add to them.
I expect to see them tomorrow morning.

I was drunk you f**k homo gnome, I don't remember much apart from telling you to beat the Excel - which you failed to to do!

My car don't do burn outs, its too grippy. I believe you have worked that out already.

No, your clutch is s**t. True story.

Same with your capabilities as a manual driver. True Story.