Ah, coincidence then.

 

Since I replied to this thread and because of speed mentioned, I jumped in direction of torque converter lock related. Yesterday mine started shuddering you could say at that speed. It felt very much like a very serious tire/wheel balance out of round issue. 20 more miles yielded check engine.

 

This is pretty much the problem my 4.2 has been having. New coils, wires, plugs, fuel filter TPS, Crank sensor, DPFE, etc. I've hit it with the parts cannon (several good broadsides) because no troubls codes, and when it goes into the shop, it's a perfectly well behaved little engine.

 

Just a quick update. I think the shuddering in neutral would eliminate the engine and transmission, right?

This leaves rotating parts and suspension components?

I have yet to do the live diagnostic.

 

Because it continued shuddering when you kicked in neutral while coasting itdoes sound like drive train related. Mine was the opposite but when shuddering it felt like I was about to throw a wheel. Eventually it got code for COP 7.

 

Yea, I don't think I'll ever get a code.

I may get the wheels balanced and go from there. The suspension in the front needs a little work, and I haven't touched the u-joints on the front either. I don't want to start pouring money into it but I know those items are wearing out, so I'll take care of those before I start poking around the ignition or transmission.

 

Right , if your not in motion anyway. Do you have an Android phone or know someone with one? If so, you can monitor real time M6 data, - at least picking up live monitor action. Many of those won't give you Mode 6 history, but they will monitor real time if anything else. That is one easy and cheap way to find the problem cylinder.

The app is like 4.75 initially for the app. -Torque pro supports an easy way to add extended PIDs. Depending upon what you want to monitor.

 

Yea, I can get access to an android phone no problem. I'll buy the app tonight I guess. Today was payday anyway...

edit: so I should focus on the ignition, then?

 

How many miles? Since it does it when coasting, I'd concentrate on drive train related. Most problems related to that should be located with visual or shake inspection. Is it 4X4? Did you get a goober of something splashed into wheel? A couple of months ago I picked up tar half way around a rear tire. None on front so either backed into or while cornering. I dug off enough to make a baseball. That created a shake.
How are tires? If they have a lot of life left, I'd spend the extra for a road force balance or equivalent. The benefit of that machine deciding your tire is bad before paying for tire is worth it when buying new. And good years have been having a very high rejection rate the last few years.

 

Coasting in neutral then , not stationary ? That's what I was trying to confirm anyway lol.

 

Ohh... yea. lol. I'll coast it in neutral at 45 mph. Also, the truck idles smoothly if I pop it in neutral from park, if that helps.

 

This is for the OP, -That's like a perfect description of a LS rear gear fluid problem. Feels exactly like that, I know lol. Also, when they get THAT bad, just throwing in friction modifier and/or changing the fluid out w/spec won't fix the problem right away. - It may take up to 80 miles before it begins to smooth out, after fresh.

Usually, 80 -100k miles is the norm, before requiring a service, -BUT, - if your breather is screwed up, - it can happen prematurely.

IMO, you can definitely tell the difference between Ignition and LS faults. You should be able to isolate that much. A rear problem like that can make it seem like the trans is bad, or causing the issues.

 

Yea, I've plowed through a construction site or two, but my rims and undercarriage are clean right now. My tires have 30,000 miles on them. I want to suspect them, but I've taken the truck up to top speed, and it's smooth up there.

Ah, so it may actually be the rear end? The fluid I have in there right now has only 1,000 miles on it, so just adding 4oz. of friction modifier will mitigate the shudder I'm feeling? Last time I checked, the breather is clear and still attached to everything.

Or will I need the clutches replaced? (please no)

If I was to better describe the shudder, I wouldn't say it was a perfect cyclical shudder, like when a cylinder misfires... that happened when I first bought the truck.

It's more of a shake with some variance in the severity.

 

If you didn't add modifier when you changed the gear lube, you need to do it anyway. Get it from Ford.

 

Was back to the beginning of this thread and don't see description of vehicle.
I was doing some checking on my 01 but figure I need to dig deeper for verification.
Supposedly, ford started using a permanent lube in rear differential that does not need additive added. A number of the aftermarket full synthetic have made that claim probably back to the early 90's.
So if you changed rear grease, what did you use?
On the other hand they did not do that for the front on 4X4 at that time. They hopefully have made that change as well.
Also I had a Bonneville with limited slip. It had over 100K when acquired and shortly I discovered the chattering when cornering. I suspect previous owners never had it serviced and by time I got into it there were lots of metal flakes in grease. I managed to salvage with new clutch pack and shims. I recall that when dumping all the fluid that one required a double dose of GM friction modifier, not just the maintenance dose.